Predicting Risk of Recurrent Patellar Dislocation

Abnormal lateral meniscal signal in MRI after patellar dislocation does not indicate a meniscal tear: MR findings with surgical correlation

Background

Combined injuries observed with first-time lateral patellar dislocation (LPD) of the knee, particularly significant soft tissue injury, can inform surgical intervention criteria.

Purpose

The purpose of this study was to compare MRI findings in LPD to surgical correlation concerning meniscal pathology as a guide for surgical management.

Study design

Retrospective case series, Level of evidence, 4.

Methods

A retrospective review was conducted of 355 cases of patients with lateral patellar dislocation from 2012 to 2022. Imaging was reviewed by musculoskeletal radiologists blinded to surgical results for evidence of soft tissue injury, and associated arthroscopic data and operative reports were reviewed.

Results

Out of 44 cases of LPD in 42 patients who underwent MPFL reconstructive surgery, 27 (61%) cases had grade 2a or higher signal changes in the anterior horn of the lateral meniscus, of which 10 (23%) had grade 3 signal changes. There were zero cases of meniscal tear in these cases upon review of operative reports and arthroscopic images.

Conclusion

MRI findings of signal alterations in the lateral meniscus post-LPD may not indicate an actual tear. This could aid in surgical decision-making in primary LPD management.

Femorotibial rotation is linearly associated with tibial tubercle-trochlear groove distance: A cadaveric study

OBJECTIVES

A tibial tubercle-trochlear groove (TT-TG) distance of 20 millimeters (mm) is typically used when determining whether tibial tubercle medialization is performed for the surgical treatment of patellar instability. Without knowledge of how the variability of an individual's TT-TG distance is influenced by through-the-knee femorotibial rotation, the use of a specific TT-TG distance during preoperative planning for patellar instability may lead to incorrect decisions on the use of tibial tubercle medialization. We hypothesized that knee joint internal/external (IE) rotation is related to the TT-TG distance.

METHODS

Eight independent human cadaveric knee specimens (age: 32 ​± ​6 years; 4 males, 4 females) were utilized. A robotic manipulator (ZX165U, Kawasaki Robotics, Wixom, MI, USA) instrumented with a universal force/moment sensor was used to determine knee joint IE rotation under applied moments of ±5 newton-meters (Nm) at full extension. Two independent reviewers selected the trochlear groove and tibial tuberosity points on computerized tomography (CT) images of each specimen to define TT-TG. To determine the influence of knee joint IE rotation on TT-TG distance, three-dimensional (3D) models generated from CT scans were registered to tibiofemoral kinematics. Linear regression was performed to determine the relationship between knee joint IE rotation and TT-TG distance. The regression coefficient, standard error of measurement (α ​= ​0.05), and coefficient of determination (r2) were reported.

RESULTS

At 0° of rotation, the mean TT-TG distance was 14.2 ​± ​5.0 ​mm. Knee joint IE rotation averaged 23.0 ​± ​4.2°. For every degree of knee joint IE rotation, TT-TG distance changed by 0.52 ​mm.

CONCLUSION

TT-TG distance was linearly dependent on knee joint IE rotation, changing by 0.52 ​mm for every degree of knee joint IE rotation. Thus, an offset of IE rotation of 10° would lead to a change in TT-TG distance of 5.2 ​mm, enough to alter the surgical decision-making for/or against tibial tubercle medialization.

LEVEL OF EVIDENCE

IV: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

No significant difference in thick versus thin osteochondral flap trochleoplasty in the treatment of trochlear dysplasia: A systematic review

PURPOSE

Trochleoplasty has become increasingly utilised to address patellar instability in the setting of severe trochlear dysplasia. There remains a paucity of literature on the outcomes of 'thick'- versus 'thin'-osteochondral flap trochleoplasty. The purpose of this study is to compare clinical and radiographic outcomes between patients with patellar instability with symptomatic trochlear dysplasia treated using a 'thick' versus 'thin' osteochondral flap trochleoplasty.

METHODS

A systematic review and meta-analysis were conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines using a PRISMA checklist. Quality assessment of final articles was conducted by two blinded reviewers. Articles were separated based on the use of a 'thick' versus 'thin' flap trochleoplasty. Data collection consisted of recording the following variables: patient demographics, indications for trochleoplasty, mean follow-up time, additional procedures performed during trochleoplasty, patient-reported outcome measures (PROMs), radiographic outcomes (tibial tubercle-trochlear groove [TT-TG] distance, Caton-Deschamps Index [CDI] and sulcus angle [SA]) and the incidence of any postoperative complications and patellar redislocation rates.

RESULTS

A total of 24 studies, consisting of 927 patients, were identified as meeting inclusion criteria. A total of five papers described a 'thick' flap technique, while 19 papers described the use of a 'thin' flap technique. No significant difference in the mean improvement of Kujala scores was appreciated when comparing 'thick' versus 'thin' techniques (p > 0.05). Improvements in mean radiographic outcomes based on TT-TG, CDI and SA were observed in both 'thick' and 'thin' flap trochleoplasty groups. The overall redislocation rate was 0.35%.

CONCLUSION

No significant difference in Kujala scores was observed in patients undergoing trochleoplasty utilising 'thick' versus 'thin' technique, while improvements in mean TT-TG, CDI and SA were noted in both technique groups, with an overall redislocation rate of 0.35%.

LEVEL OF EVIDENCE

Level IV.

Patellar height: an important parameter in knee MRI associated with tendinopathy, quadriceps fat pad edema (QFPE), anterior cruciate ligament mucoid degeneration (ACL-MD), and lateral cartilage damage

BACKGROUND

Some pathologies associated with abnormal patellar height have been reported in the literature. However, its relationship with some pathologies, such as anterior cruciate ligament mucoid degeneration (ACL-MD) and focal cartilage defect, has not been investigated.

PURPOSE

To investigate the relationship between patellar height with patellar-quadriceps tendinopathy, quadriceps fat pad edema, ACL-MD, and focal cartilage defect.

MATERIAL AND METHODS

Magnetic resonance imaging of the knees of 261 patients were classified into three groups as normal, patella alta, and patella baja, and evaluated in terms of patellar-quadriceps tendinopathy, quadriceps fat pad edema, ACL-MD, and focal cartilage defect.

RESULTS

There were 261 patients (140 men, 121 women; age range = 18-60 years; mean age = 30 ± 4.7 years). Of the 261 patients, 181 (69.3%) were normal, 56 (21.4%) were patella alta, and 24 were patella baja (9.1%). Patellar-quadriceps tendinopathy, quadriceps fat pad edema, and ACL-MD rates were significantly higher compared to the normal group (P <0.05). While a moderate positive correlation was found between patellar height shift and patellar-quadriceps tendinopathy and ACL-MD, there was a small correlation between patellar height shift and quadriceps fat pad edema. The rate of focal cartilage defect was significantly higher in the middle part of the lateral femoral condyle and lateral knee joint only in patella alta.

CONCLUSION

The risk of patellar-quadriceps tendinopathy, quadriceps fat pad edema, ACL-MD, and lateral focal cartilage defect is higher in patients with alta-baja. The radiologist should evaluate these pathologies more carefully, especially subtle ones, in patients with abnormal patellar height.

Editorial Commentary: Regression Modeling and Nomograms in Biomedical Research Are Valuable Decision-Making Tools When Externally Validated and Well Maintained

The mathematical formulas underpinning biostatistical modeling in medical research can be complicated. Nomograms are pictoral tools showing a graphical solution of a formula in which all variables in the formula can be read off the diagram. Nomograms can be used to simplify the calculation of risk of recurrence of injuries or disease. Although nomograms can be valuable, external validation is required (of all models) to ensure accuracy outside of the original population, because variation in patient populations, activities, and risk behaviors outside of the patient data used in the original analysis may deteriorate model performance (external validity). A model also needs to be maintained over time to ensure continued accuracy as populations and activities change. A model that fails to keep up will eventually have its accuracy and clinical utility fade. An externally validated, well-maintained model can be a valuable tool for patient counseling and decision-making.

Development of patellofemoral osteoarthritis with knee joint malalignment and lateral patellar dislocation after hindlimb suspension in growing rats

Knee malalignment is a risk factor for patellar instability and patellofemoral osteoarthritis (PFOA), but etiologies remain unknown. We investigated the potential effects of decreased weight loading during growth on knee alignments and patellofemoral (PF) joint pathology. Hindlimb suspension (HS) was performed in 4-week-old female rats for 2, 4, and 8 weeks (HS groups). Age-matched rats were used as controls. Three-dimensional reconstructed images of the knee were obtained using X-ray computed tomography. Tibial tubercle-trochlear groove (TT-TG) distance, patellar tilt angle, and bisect offset were measured as indices of knee alignment. Histological analysis was also performed to evaluate the changes in cartilage and synovium in the PF joints. At Week 8, TT-TG distance, patella tilt angle, and bisect offset were significantly larger in the HS group than in the control group, respectively, indicating tibial external rotation, outward patellar tilt, and external displacement of the patella. Lateral patellar dislocation was frequently found in the HS group at Week 8 (five of eight knee joints, p < 0.05). Degenerative changes in the cartilage of the trochlear groove were observed at Week 8, and synovial changes such as hypertrophy and synovitis were observed at Weeks 4 and 8. Correlation analyses revealed significant relationships between the Mankin score and bisect offset, and between the OARSI synovitis score and all knee alignments indices. These results suggest that decreased weight loading on the lower extremities in growing rats resulted in knee malalignments characterized by external rotation of tibia and high incidence of lateral patellar dislocation with concomitant PFOA.

The Adductor Sling Technique for Pediatric Medial Patellofemoral Ligament Reconstruction Better Resists Dislocation Loads When Compared With Adductor Transfer at Time Zero in a Cadaveric Model

Purpose

To characterize the ability of the intact medial patellofemoral ligament (MPFL) and the adductor transfer and adductor sling MPFL reconstruction techniques to resist subluxation and dislocation in a cadaveric model.

Methods

Nine fresh-frozen cadaveric knees were placed on a custom testing fixture with the femur fixed parallel to the floor, the tibia placed in 20° of flexion, and the patella attached to a load cell. The patella was displaced laterally, and subluxation load (in newtons), dislocation load (in newtons), maximum failure load (in newtons), patellar displacement at failure, and mode of failure were recorded. Testing was conducted with the MPFL intact and after the adductor sling and adductor transfer reconstruction techniques. Statistical analysis was completed using 1-way repeated-measures analysis of variance with the Holm-Šidák post hoc test.

Results

The subluxation load was not significantly different between groups. The native MPFL dislocation load was significantly higher than the dislocation loads of both reconstruction techniques, but no significant difference between the dislocation loads of the 2 reconstruction techniques occurred. The native MPFL failure load was significantly higher than the failure loads of both reconstruction techniques. The adductor sling failure load was significantly higher than the adductor transfer failure load. The mode of failure varied across groups. The native MPFL failed by femoral avulsion, patellar avulsion, and midsubstance tear. The main mode of failure for adductor transfer was pullout, whereas failure for the adductor sling technique most often occurred at the sutures. Most of the native MPFLs and all adductor sling reconstructions failed after dislocation. The adductor transfer reconstructions were much more variable, with failures spanning from before subluxation through dislocation.

Conclusions

Our cadaveric model showed that neither the adductor transfer technique nor the adductor sling technique restored failure load to that of the native condition. There was no significant difference in the subluxation or dislocation loads between the 2 MPFL reconstructions, but the adductor sling technique resulted in a higher load to failure. The adductor transfer technique frequently failed before subluxation or dislocation when compared with the adductor sling technique and the native MPFL.

Clinical Relevance

The best technique for MPFL reconstruction in patients with open physes is a topic of debate. Given the long-term consequences of MPFL injury and potential for growth plate disturbance, it is important to study MPFL reconstruction techniques thoroughly, including in the laboratory setting.

Comparison of Failure Rates at Long-term Follow-up Between MPFL Repair and Reconstruction for Recurrent Lateral Patellar Instability

Background

The medial patellofemoral ligament (MPFL) is the primary soft tissue restraint to lateral patellar translation and is often disrupted by lateral patellar dislocation. Surgical management for recurrent patellar instability focuses on restoring the MPFL function with repair or reconstruction techniques. Recent studies have favored reconstruction over repair; however, long-term comparative studies are limited.

Purpose

To compare long-term clinical outcomes, complications, and recurrence rates of isolated MPFL reconstruction and MPFL repair for recurrent lateral patellar instability.

Study Design

Cohort study; Level of evidence, 3.

Methods

A total of 55 patients (n = 58 knees) with recurrent lateral patellar instability were treated between 2005 and 2012 with either MPFL repair or MPFL reconstruction. The exclusion criteria were previous or concomitant tibial tubercle osteotomy or trochleoplasty and follow-up of <8 years. Pre- and postoperative descriptive, surgical, imaging, and clinical data were recorded for each patient.

Results

MPFL repair was performed on 26 patients (n = 29 knees; 14 women, 15 men), with a mean age of 18.4 years. MPFL reconstruction was performed on 29 patients (n = 29 knees; 18 women, 11 men), with a mean age of 18.2 years. At a mean follow-up of 12 years (range, 8.3-18.9 years), the reconstruction group had a significantly lower rate of recurrent dislocation compared with the repair group (14% vs 41%; P = .019). There were no differences in the number of preoperative dislocations or tibial tubercle-trochlear groove distance. The reconstruction group had significantly more time from initial injury to surgery compared with the repair group (median, 1460 days vs 627 days; P = .007). There were no differences in postoperative Tegner, Lysholm, or Kujala scores at the final follow-up. In addition, no statistically significant differences were detected in return to sport (RTS) rates (repair [81%] vs reconstruction [75%]; P = .610) or reoperation rates for recurrent instability (repair [21%] vs reconstruction [7%]; P = .13).

Conclusion

MPFL repair resulted in a nearly 3-fold higher rate of recurrent patellar dislocation (41% vs 14%) at the long-term follow-up compared with MPFL reconstruction. Given this disparate rate, the authors recommend MPFL reconstruction over repair because of the lower failure rate and similar, if not superior, clinical outcomes and RTS.

The accuracy of multiple regression models for predicting the individual risk of recurrent lateral patellar dislocation

BACKGROUND

Recurrent lateral patellar dislocation (RLPD) poses a significant threat to patients' quality of life due to knee pain, patellofemoral cartilage damage, and potential traumatic arthritis. Predictive scoring systems have been developed to assess the risk of RLPD; however, their relative accuracy remains uncertain.

PURPOSE

To investigate the accuracy of the multiple regression models to predict the individual risk of recurrent LPD.

METHODS

The Patellar Instability probability calculator (PIP), Recurrent Instability of the Patella Score (RIP), and Patellar Instability Severity Score (PIS) scoring rules were measured in 171 patients with a history of patellar dislocation and 171 healthy individuals. Three prediction models were calculated based on the data to predict the risk of recurrent lateral patellar dislocation. The inter-observer and intra-observer reliability of each measurement parameter was evaluated. The predictive capacity of the three-prediction model was investigated using the receiver operating characteristic curve.

RESULTS

In the case group of 171 patients, PIS accurately predicted recurrent lateral Patella dislocation in 143 patients. RIP was 96, and PIP was 83. The positive predictive values were 92.9%, 64%, and 68% respectively. In the control group of 171 patients, the PIS was validated in 160 patients who would not experience dislocations. RIP was 117, and PIP was 50. The negative predictive values were 85.1%, 60.9%, and 36.2%, respectively. The area under the curve score for the PIS was 0.866, and the RIP was 0.673. the PIP was 0.678.

CONCLUSION

RIP and PIP did not work to predict LPD. PIS can accurately predict recurrent lateral patellar dislocation. It can aid doctors in making treatment decisions.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Comparison of Bone Bruise Pattern Epidemiology between Anterior Cruciate Ligament Rupture and Patellar Dislocation Patients-Implications of Injury Mechanism

Different bone bruise patterns observed using magnetic resonance imaging (MRI) after non-contact anterior cruciate ligament (ACL) rupture and lateral patellar dislocation may indicate different knee injury mechanisms. In this study, 77 ACL ruptures and 77 patellar dislocations in knee MR images taken from patients with bone bruises at our institution between August 2020 and March 2022 were selected and analyzed. In order to determine typical bone bruising patterns following by ACL rupture and patellar dislocation, sagittal- and transverse-plane images were used to determine bone bruise locations in the directions of medial-lateral and superior-inferior with MR images. The presence, intensity, and location of the bone bruises in specific areas of the femur and tibial after ACL rupture and patellar dislocation were recorded. Relative bone bruise patterns after ACL rupture and patellar dislocation were classified. The results showed that there were four kinds of bone bruise patterns (1-, 2-, 3-, and 4- bone bruises) after ACL rupture. The most common two patterns after ACL rupture were 3- bone bruises (including the lateral femoral condyle and both the lateral-medial tibial plateau, LF + BT; both the lateral-medial femoral condyle and the lateral tibial plateau, BF + LT; and the medial femoral condyle and both the medial and lateral tibial plateau, MF + BT) followed by 4- bone bruises (both the lateral-medial femoral condyle and the tibial plateau, BF + BT), 2- bone bruises (the lateral femoral condyle and tibial plateau, LF + LT; the medial femoral condyle and the lateral tibial plateau, MF + LT; the lateral femoral condyle and the medial tibial plateau, LF + MT; the medial femoral condyle and the tibial plateau, MF + MT; both the lateral-medial tibial plateau, 0 + BT), and 1- bone bruise (only the lateral tibial plateau, 0 + LT). There was only a 1- bone bruise (the latera femoral condyle and medial patella bone bruise) for patellar dislocation, and the most common pattern of patellar dislocation was in the inferior medial patella and the lateral anterior inferior femur. The results suggested that bone bruise patterns after ACL rupture and patellar dislocation are completely different. There were four kinds of bone bruise patterns after non-contact ACL rupture, while there was only one kind of bone bruise pattern after patellar dislocation in patients, which was in the inferior medial patella and lateral anterior inferior femur.

Tibial Tuberosity Rotation in Patients With Patellar Instability Versus Age- and Sex-Matched Controls

Background

Several methods have been described to measure external rotation of the tibial tuberosity; all use femoral landmarks.

Purpose

To develop reproducible tibial-based methods to measure external rotation of the tibial tuberosity in patients with patellar instability.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

Included were magnetic resonance images of 61 patients with patellar instability and 61 age- and sex-matched healthy controls. Three novel methods using tibial landmarks to measure the rotation of the tibial tuberosity (plateau axis-tuberosity axis [PA-TA] angle, tibial geometric center-tuberosity axis [GC-TA] angle, and plateau axis-midtuberosity point [PA-MT] angle) as well as a femoral-based rotational measurement (surgical transepicondylar axis-tuberosity axis [sTEA-TA] angle) and the tibial tuberosity-trochlear groove (TT-TG) distance were measured and compared in instability patients and controls using unpaired t tests, and the cutoff values for predicting instability were calculated using receiver operating characteristic curves. The correlations between the angle measurements and the TT-TG distance were analyzed.

Results

Instability patients had significantly higher external rotation of the tibial tuberosity compared with controls with regard to the PA-TA angle (18.2° ± 9.6° versus 13.1° ± 6.8°; P = .001), GC-TA angle (8.4° ± 4.5° versus 11.5° ± 3.9°; P = .0001) and sTEA-TA angle (122° ± 8.5° versus 113.6° ± 6.3°; P = .0001). The mean TT-TG distance was also significantly higher in the instability group (18.2 ± 5.4 versus 11.5 ± 2.7 mm; P = .001). The cutoff values were 17.5° (area under the receiver operating characteristic curve [AUC] = 0.66) for PA-TA angle, 8.5° (AUC = 0.705) for GC-TA angle, 118.8° (AUC = 0.79) for sTEA-TA angle, and 15.2 mm for TT-TG distance (AUC = 0.863). PA-TA angle was significantly correlated with all other measurements (r = 0.35-0.71; P ≤ .006 for all), whereas sTEA-TA angle had the strongest correlation with TT-TG distance (r = 0.78; P = .001).

Conclusion

The tibial tuberosity was externally rotated in patellar instability patients compared with age- and sex-matched controls, and this intrinsic malalignment of the proximal tibia was demonstrated in the tibial-based measurements.

Reconstruction of medial patellofemoral ligament with adductor magnus tendon for recurrent patellar dislocation in children: a retrospective comparative cohort study

BACKGROUND

The purpose of current retrospective study was to explore the outcomes of using the adductor magnus tendon to reconstruct the medial patellofemoral ligament in the treatment of recurrent patellar dislocation in children.

METHOD

Thirty-two children with recurrent patellar dislocation were selected. Sixteen cases in the conservative group, seven males and nine females, with an average age of 11.81 ± 1.28 years; sixteen cases in the surgical group, eight males and eight females, with an average age of 11.56 ± 1.15 years. All patients had no surgery history. The IS index (> 1.2), Q angle (> 20°) and tibial tubercle-femoral trochlear groove (TT-TG) distance (> 20 mm) were measured by X-ray and MRI. The conservative group was treated with closed reduction and a brace, and the surgical group received surgical treatment. Two years after surgery, congruence angle (CA) (- 6° to 6°) and lateral patellofemoral angle (LPFA) (7.7°-18.7°) were measured by X-ray image and all children were evaluated based on Kujala and Lysholm scores. The re-dislocation rate was recorded. Analysis was performed by t test and chi-square with the statistical SPSS software. P < 0.05 was considered a statistically significant difference. Furthermore, we measured the length (mm) of the adductor tendon and MPFL in three knee cadaveric specimens, and also observed the positional relationship between the two structures.

RESULT

There were no significant differences in sex, age, injury site between groups (P > 0.05). Patients in the two groups were followed up for 2 years in average. Among the 16 cases in the conservative group, 7 cases (43.75%) had recurrence of patellar dislocation, while none of recurrence in the surgical group (P < 0.05). The Lysholm score of the surgical group (94.63 ± 8.99) was significantly better than that of the conservative group (79.31 ± 18.90), and the Kujala score of the surgery group (95.25 ± 10.32) was also significantly better than that of the conservative group (77.06° ± 14.34°) (P < 0.05). The CA and LPFA of the two groups of patients after treatment were significantly recovered. The CA (- 5.81° ± 7.90°) in the surgical group was significantly better than that in the conservative group (20.94° ± 8.21°), and the LPFA (6.44° ± 3.22°) was also significantly better than that in the conservative group (- 9.18 ± 11.08), and the difference is statistically significant (P < 0.05). We found it through autopsy that adductor magnus tendon was 124.33 ± 1.53 mm long, MPFL was 48.67 ± 2.08 mm, and the femoral insertion of the adductor magnus tendon was adjacent to the MPFL femoral insertion.

CONCLUSION

Reconstruction of Medial patellofemoral ligament with the adductor magnus tendon, fixing with PEEK suture anchors on the patellar side, can achieve satisfactory results in the treatment of children with recurrent patellar dislocation. Compared with conservative treatment, the rate of recurrence is lower and the stability of the patella is better.

Recurrence and return to duty following patellar instability events in military personnel

INTRODUCTION

Military service members experience patellar dislocations at a rate 10 times that of civilians. The purpose of this study was to determine the return to duty rate of active duty military personnel following first-time or recurrent patellar dislocation. Secondary goals were to identify patient variables and radiographic parameters associated with recurrent instability and requiring medical separation from military service.

METHODS

The Military Health System Data Repository was used to identify all active-duty military personnel who sustained a patellar dislocation between 2013 and 2018. Medical records were searched for patient variables including demographics, clinical findings, radiographic findings, treatment, adverse outcomes and military disposition. Patient variables associated with recurrent instability and undergoing medical separation were determined using univariate analysis and multivariate logistic regression. A total of 207 patients met inclusion and exclusion criteria.

RESULTS

Following patellar instability event, 30% of the cohort underwent surgical treatment. Fourteen per cent (29 of 207) underwent medical separation from military service. Regardless of treatment, 9% (18 of 207) experienced recurrent dislocation and 3% (6 of 207) experienced recurrent instability without dislocation. On multivariate analysis, none of the studied patient variables were associated with recurrent instability or medical separation.

CONCLUSIONS

Among military personnel, return to duty rates are similar to return to sport rates in civilians. This study demonstrates no difference in risk of recurrent instability or medical separation based on anatomical factors, which is useful during shared decision-making regarding treatment options and goals.

Trochlea dysplasia, increased TT-TG distance and patella alta are risk factors for developing first-time and recurrent patella dislocation: a systematic review

PURPOSE

The aim of the study was to perform a systematic review and best knowledge synthesis of the present literature concerning biomechanical risk factors for developing first-time and recurrent patella dislocation.

METHODS

The study was performed as a systematic review following PRISMA guidelines. PubMed and EMBASE were systematically searched. Studies investigating participants with risk factors for first-time as well as recurrent patella dislocation were included. The records were screened, and data extracted independently by two researchers supervised by a third independent assessor. The study was registered in PROSPERO.

RESULTS

A total of 6233 records were screened, and 50 studies met the inclusion criteria. The biomechanical risk factors: trochlear dysplasia, increased tibial tuberosity-trochlear groove distance (TT-TG), and patella alta were found to be statistically significantly associated with patella dislocation in several publications and were thus recognized as risk factors for patella dislocation. The soft-tissue stabilizers: longer and thinner MPFL ligament, increased number of type 2C and decreased number of type 1 muscle fibers, and joint laxity were found to be statistically significantly associated with patella dislocation in a few publications, but due to limited evidence, no conclusion was made on this matter.

CONCLUSION

There is strong evidence in the literature that abnormalities of bony stabilizers, trochlear dysplasia, increased TT-TG distance, and patella alta are risk factors for patella dislocation. There is less evidence that soft-tissue stabilizers are risk factors. The study emphasizes the importance of a thorough investigation of bony stabilizers in clinical decision-making.

LEVEL OF EVIDENCE

Level IV.

Familial association and epidemilogical factors as risk factors for developing first time and recurrent patella dislocation: a systematic review and best knowledge synthesis of present literature

PURPOSE

The aim of our study was to perform a systematic review and best knowledge synthesis of the present literature concerning the familial association and epidemiological factors as risk factors for developing first-time and recurrent patella dislocation.

METHODS

The study was conducted according to the PRISMA guidelines and registered in PROSPERO. EMBASE and PubMed were systematically searched on the 5th of May 2022. Studies investigating participants with genetic and epidemiological risk factors for the first time as well as recurrent patella dislocation were included. The records were screened, and data were extracted independently by two researchers supervised by a third independent assessor.

RESULTS

A total of 6,649 records were screened, and 67 studies were included. Familial association was described as a risk factor for patella dislocation in 17 studies. One study found that participants with a family history of patella dislocation had a 3.7 higher risk for patella dislocation in the contralateral asymptomatic knee, and another study found a family history of PD in 9% of 74 participants. Eleven studies found an accumulation of patella dislocation across generations in specific families. Additionally, a range of genetic syndromes was associated with patella dislocation. Young age is a well-investigated risk factor for patella dislocation, but the results are inconsistent. Only five and eight studies investigated skeletal immaturity and gender as risk factors for patella dislocation, respectively.

CONCLUSION

There may be a familial association with patella dislocation, but further investigation is necessary to determine the strength and etiology of the association. There is weak evidence that epidemiological risk factors, such as age, skeletal immaturity, gender, and BMI are risk factors for patella dislocation.

LEVEL OF EVIDENCE

IV.

Concomitant Tibial Tubercle Osteotomy Reduces the Risk of Revision Surgery After Medial Patellofemoral Ligament Reconstruction for the Treatment of Patellar Instability

PURPOSE

To compare postoperative complication rates between patients who underwent medial patellofemoral ligament reconstruction (MPFLR) and those who underwent MPFLR with tibial tubercle osteotomy (TTO) in a large-scale study. A secondary goal was to investigate demographic associations with outcomes.

METHODS

Patients who underwent MPFLR (n = 3,480) or MPFLR-TTO (n = 615) for patellar instability were identified in the PearlDiver database. Rates of surgery for infection, procedures for knee stiffness, patellar fracture, and revision MPFLR within 2 years postoperatively were compared using multivariable logistic regression. Demographic associations with outcomes were also investigated.

RESULTS

The MPFLR-TTO cohort exhibited a significantly lower rate of revision surgery at 2 years (0.8% vs 1.9%; odds ratio [OR], 0.33; 95% confidence interval [CI], 0.10-0.80; P = .036) when compared with the MPFLR group. Independent of index procedure, patients younger than 21 years had significantly lower rates of requiring procedures for knee stiffness (OR, 0.35; 95% CI, 0.22-0.54; P < .001) and any complication at 2 years (OR, 0.59; 95% CI, 0.45-0.78; P < .001) when compared with older patients. Male patients displayed a significantly lower rate of requiring procedures for knee stiffness at 2 years than female patients (OR, 0.46; 95% CI, 0.25-0.78; P = .007). Tobacco use was associated with a significantly higher rate of postoperative infection at 2 years (OR, 2.35; 95% CI, 1.00-5.38; P = .046).

CONCLUSIONS

The MPFLR cohort exhibited higher rates of revision surgery at 2 years compared with the MPFLR-TTO cohort. Patient age under 21 years was associated with lower rates of any complication and requiring procedures for knee stiffness, male sex was associated with a lower rate of requiring procedures for knee stiffness, and tobacco use was associated with a higher rate of surgery for postoperative infection. This information can assist surgeons when counseling patients before these procedures are performed.

LEVEL OF EVIDENCE

Level III, retrospective, comparative prognostic trial.

Framing Patellar Instability: From Diagnosis to the Treatment of the First Episode

The patellofemoral joint (PFJ) is a complex articulation between the patella and the femur which is involved in the extensor mechanism of the knee. Patellofemoral disorders can be classified into objective patellar instability, potential patellar instability, and patellofemoral pain syndrome. Anatomical factors such as trochlear dysplasia, patella alta, and the tibial tuberosity-trochlear groove (TT-TG) distance contribute to instability. Patellofemoral instability can result in various types of dislocations, and the frequency of dislocation can be categorized as recurrent, habitual, or permanent. Primary patellar dislocation requires diagnostic framing, including physical examination and imaging. Magnetic resonance imaging (MRI) is essential for assessing the extent of damage, such as bone bruises, osteochondral fractures, and medial patellofemoral ligament (MPFL) rupture. Treatment options for primary dislocation include urgent surgery for osteochondral fragments or conservative treatment for cases without lesions. Follow-up after treatment involves imaging screening and assessing principal and secondary factors of instability. Detecting and addressing these factors is crucial for preventing recurrent dislocations and optimizing patient outcomes.

Concomitant anterior medializing osteotomy and MPFL reconstruction improves patellar tilt when compared to MPFL reconstruction alone

PURPOSE

Understanding how surgical procedures influence anatomic factors associated with patellofemoral instability can help guide surgeons when planning treatments for individual patients. This study sought to understand how patellar tilt is affected in adolescent patients with elevated pre-operative tibial tuberosity to trochlear groove (TT-TG) values undergoing medial patellofemoral ligament reconstruction (MPFLR) with or without an anterior medializing osteotomy (AMZ).

METHODS

Utilizing a prospective database of 274 patellofemoral instability patients who underwent MPFLR ± AMZ by one of two orthopedic surgeons at a single institution, those who underwent MPFLR + AMZ were identified. Pre-operative and post-operative magnetic resonance imaging (MRI) were used to measure TT-TG distance, while radiographs were used to measure patellar tilt (tilt). Patients were matched based on age at surgery (within 2 years) and pre-operative TT-TG distance (within 2 mm) to a comparison cohort of patients who underwent isolated MPFLR (iMPFLR) without osseous procedures.

RESULTS

A total of 56 patients were analyzed (28 per group). The mean age of the cohort was 15.5 ± 2.0 years and was similar between both groups (15.9 ± 1.9 versus 15.1 ± 2.0 years [n.s]). When comparing the two cohorts, significant pre- to post-operative decreases in patellar tilt for both MPFLR + AMZ (6.6 degrees, p < 0.001) and iMPFLR (3.9 degrees, p = 0.013) were noted. While there were no differences in pre-operative patellar tilt (21.2 ± 3.5 versus 21.1 ± 3.4 [n.s]), post-operatively, MPFLR + AMZ had significantly less patellar tilt than iMPFLR (13.2 ± 5.5 versus 16.5 ± 4.4, p = 0.017).

CONCLUSIONS

This study found that patellar tilt significantly improved in participants undergoing either MPFLR + AMZ or iMPFLR. In addition, those undergoing MPFLR + AMZ were found to have significantly lower post-operative tilt than those undergoing iMPFLR. If patellar tilt is found pre-operatively to be significantly elevated and a risk for future dislocations, these findings suggest that surgeons might strongly consider MPFLR with AMZ to further address the increased tilt.

LEVEL OF EVIDENCE

III.

Patellofemoral Arthroplasty Is an Efficient Strategy for Isolated Patellofemoral Osteoarthritis with or without Robotic-Assisted System

There is relative paucity in the literature concerning outcomes after robotic-assisted Patellofemoral Arthroplasty (PFA). The aims were (1) to evaluate outcomes in patients undergoing PFA with inlay or onlay components, with or without robotic arm assistance and (2) to identify risk factors of poor outcomes after PFA. This retrospective study included 77 PFA for isolated patellofemoral joint osteoarthritis, assigned to three groups (18 conventional technique, 17 image-free robotic-assisted system and 42 image-based robotic-assisted system). The demographic data were comparable between the three groups. The clinical outcomes assessed were: Visual Analogue Scale, Knee Society Score, Kujala score and satisfaction rate. The radiological measures were: Caton Deschamps index, patellar tilt and frontal alignment of the trochlea. Functional outcomes, satisfaction rate and residual pain were comparable between the three groups. Patellar tilt improvement was superior when a robotic device was used (either image-based or image-free) compared to the conventional technique. There were three revisions (3.9%) at the last follow-up related to femorotibial osteoarthritis progression. Multivariate analysis found no significant risk factors for poor outcomes, with respect to the surgical technique or implant design. Functional outcomes and revisions rate after PFA were comparable between the surgical techniques and implants. Robotic-assisted systems were associated with a superior improvement of the patellar tilt compared to the conventional technique.

Redefining Trochlear Dysplasia: Normal Thresholds Vary by Measurement Technique, Landmarks, and Sex

BACKGROUND

Trochlear dysplasia is a known risk factor for patellar instability. Multiple radiographic measurements exist to assess trochlear morphology, but the optimal measurement technique and threshold for instability are unknown.

PURPOSE

To describe the optimal measurements and thresholds for trochlear dysplasia on magnetic resonance imaging (MRI) that can identify knees with patellar instability in male and female patients.

STUDY DESIGN

Cohort study (diagnosis); Level of evidence, 3.

METHODS

Knee MRI scans of patients with patellar instability were compared with those of age- and sex-matched controls. Measurements of the sulcus angle, lateral trochlear inclination (LTI), and trochlear depth were performed on axial images using bony and cartilaginous landmarks. Receiver operating characteristic curve analysis was performed, with the area under the curve (AUC) describing the accuracy of each diagnostic test. Optimal cutoff values were calculated to distinguish between knees with and without patellar instability. AUC and cutoff values were reported for each measurement as well as for male and female subgroups.

RESULTS

A total of 238 knee MRI scans were included in this study (138 female, 100 male; age range, 18-39 years). Trochlear depth measurements had the greatest diagnostic value, with AUCs of 0.79 and 0.82 on bone and cartilage, respectively. All measurements (sulcus angle, LTI, trochlear depth) on bone and cartilage had an AUC ≥0.7 (range, 0.70-0.86), with optimal cutoff values of 145° (bone) and 154° (cartilage) for the sulcus angle, 17° (bone) and 13° (cartilage) for LTI, and 4 mm (bone) and 3 mm (cartilage) for trochlear depth. Optimal cutoff values in female patients varied from those in male patients for all measurements except for cartilaginous trochlear depth.

CONCLUSION

Normal thresholds for trochlear dysplasia varied based on the use of bony versus cartilaginous landmarks. Cartilaginous trochlear depth measurements had the greatest ability to identify knees with patellar instability. Furthermore, optimal cutoff values for all measurements except for cartilaginous trochlear depth differed between female and male patients. These findings suggest that sex-specific parameters of normal values may be needed in the assessment of risk factors for patellofemoral instability.

Preoperative Patella Alta on Caton-Deschamps Index Is a Predictor of Outcome Following Isolated Medial Patellofemoral Ligament Reconstruction

Purpose

The purpose of this study was to determine whether a preoperative Caton-Deschamps index (CDI) ≥ 1.30, as measured by magnetic resonance imaging, is associated with rates of postoperative instability, revision knee surgery, and patient-reported outcomes in patients undergoing isolated medial patellofemoral ligament (MPFL) reconstruction.

Methods

Patients who underwent primary medial patellofemoral ligament reconstruction (MPFLR) between 2015 and 2019 at a single institution were assessed. Only those with at least 2 year follow up were included. Patients who had undergone a previous ipsilateral knee surgery, concomitant tibial tubercle osteotomy and/or ligamentous repair/reconstruction at the time of MPFL reconstruction were excluded from the study. CDIs were evaluated by three investigators based on magnetic resonance imaging measurement. Patients with a CDI ≥ 1.30 were included in the patella alta group, while those with a CDI between 0.70 and 1.29 served as controls. A retrospective review of clinical notes was used to evaluate the number of postoperative instability episodes and revisions. Functional outcomes were measured by the International Knee Documentation Committee (IKDC) and 12-Item Short Form Health Survey (SF-12) physical and mental scores.

Results

Overall, 49 patients (50 knees, 29 males, 59.2%) underwent isolated MPFLR. Nineteen (38.8%) patients had a CDI ≥ 1.30 (mean: 1.41, range: 1.30-1.66). The patella alta group was significantly more likely to experience a postoperative instability episode (36.8% vs 10.0%; P = .023) and was more likely to return to the operating room for any reason (26.3% vs 3.0%; P = .022) compared to those with normal patellar height. Despite this, the patella alta group had significantly greater postoperative IKDC (86.5 vs 72.4; P = .035) and SF-12 physical (54.2 vs 46.5; P = .006) scores. Pearson's correlation showed a significant association between CDI and postoperative IKDC (R ² = 0.157; P = .022) and SF-12P (R ² = .246; P = .002) scores. There was no difference in postoperative Lysholm (87.9 vs 85.1; P = .531). and SF-12M (48.9 vs 52.5; P = .425) scores between the groups.

Conclusion

Patients with preoperative patella alta, as measured by CDI had higher rates of postoperative instability and return to the OR with isolated MPFL reconstruction for patellar instability. Despite this, higher preoperative CDI was associated with greater postoperative IKDC scores and SF-12 physical scores in these patients.

Level of Evidence

Retrospective cohort study, Level IV.

Effects of hindlimb suspension on development of proximal and distal femur morphological abnormalities in growing rats

Although morphological abnormalities of the femur are known predisposing factors for numerous musculoskeletal disorders, the etiology of these abnormalities is poorly understood. This study aimed to investigate whether femoral morphogenesis is affected by hindlimb suspension (HS) in growing rats. We used 41 four-week-old female rats in this study. In the HS groups, rats were suspended from their tails for 2, 4, and 8 weeks. Age-matched animals were used as controls. We examined morphological indices of the femur using three-dimensional reconstructed images from X-ray computed tomography. The femoral neck anteversion angle (AVA) was higher with growth in the experimental groups and did not differ in control groups. The AVAs in the HS groups were larger than controls at any time point. In the control groups, the trochlear angle (TA) was higher, rotating inward with growth, but did not differ in the HS groups. The TAs in the HS groups were smaller and rotated more outward compared with the control groups at any time point. The height ratios of the medial and lateral condyles (MC/LC), an asymmetry index, were larger in the HS groups compared to controls at any time point. There were strong relationships between proximal (AVA) and distal morphologies, such as the TA (Spearman's coefficient [r_s ] = -0.80, p < 0.001) and MC/LC (r_s  = 0.79, p < 0.001). Our data suggest that sufficient physical activity in early life may protect against morphological femur abnormalities associated with hip and knee joint diseases.

Influence of medial and lateral imaging plane inclination on assessment of trochlear depth, sulcus angle, and facet asymmetry in the setting of trochlear anatomy: a cadaveric study

PURPOSE

(1) to assess the influence of medial or lateral imaging plane inclination on the measurement of sulcus angle, trochlear depth, and facet asymmetry on transverse cross-sectional images. (2) to assess the effect of measurement level (height) on these respective parameters.

MATERIALS AND METHODS

Twenty dry femurs (9 left, 11 right) were imaged with CT. A 3D dataset was obtained from which axial images were reconstructed in the ideal plane without inclination as well as with 8° of medial and lateral inclination. Sulcus angle, trochlear depth, and facet asymmetry were measured on the 3 image sets. In addition, the measurements were performed at 5 mm and 10 mm from the superior margin of the medial trochlear facet. Statistical analysis consisted of the Wilcoxon test and calculation of measurement variation.

RESULTS

There were no statistically significant differences between the indicated measurements on the reference set compared to medial or lateral inclination. All measurements were significantly different depending on measurement height.

CONCLUSION

Medial or lateral inclination in the transverse imaging plane of 8° does not influence the values of typical parameters used for the assessment of trochlear dysplasia. The measurement height has a significant influence, and a consensus should be found as to which is the optimal measurement height.

Unpacking the Tibial Tubercle-Trochlear Groove Distance: Evaluation of Rotational Factors, Trochlear Groove and Tibial Tubercle Position, and Role of Trochlear Dysplasia

BACKGROUND

The tibial tubercle to trochlear groove (TT-TG) distance is often utilized for determining the surgical treatment for patients with patellar instability (PI). It is thought to directly represent the position of the TT on the tibia. Recent work has shown that the measurement of the TT-TG distance is multifactorial.

PURPOSE

To investigate the relationship between relative tibial external rotation (rTER) and trochlear dysplasia (TD), as well as the location of the TG and TT in patients with and without PI, and to correlate these and other anatomic measurements with the TT-TG distance.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

A total of 89 patients with PI who underwent magnetic resonance imaging were identified with 92 matched control patients. A standardized measurement protocol on axial magnetic resonance imaging determined rTER, the proximal and distal TG lateralization (pTGL and dTGL, respectively) ratios, and the TT lateralization (TTL) ratio. Other measures of interest included the lateral trochlear inclination angle, sulcus angle, and lateral patellar inclination angle. Univariate regression was used to determine the associations of TD (lateral trochlear inclination angle, sulcus angle) with rTER and the TG position, and multivariate regression was used to model associations among all the variables with the proximal and distal TT-TG distances.

RESULTS

rTER was significantly higher in the study group (P < .001), and univariate regression showed a significant association between dysplasia measures and rTER (P < .001). The pTGL ratio was lower in the study group (P = .025), but there was no difference in the dTGL ratio (P = .090) or the TTL ratio (P = .098) between the groups. There were no associations between dysplasia measures and the pTGL and dTGL ratios (P > .05). Multivariate regression showed that the proximal TT-TG distance is predicted by the sulcus angle, pTGL ratio, rTER, and TTL ratio (P < .05) and that the distal TT-TG distance is predicted by the lateral patellar inclination angle, dTGL ratio, sulcus angle, rTER, and TTL ratio (P < .05).

CONCLUSION

rTER had a significant association with TD. The position of the proximal TG was more medial in patients with PI. There was no significant difference in the TTL ratio between patients with and without PI. The TT-TG distance was associated with multiple anatomic measures and was not solely predicated on the position of the TT.

Prediction of Subsequent Contralateral Patellar Dislocation after First-Time Dislocation Based on Patellofemoral Morphologies

The subsequent dislocation of a contralateral patellofemoral joint sometimes occurs after a first-time lateral patellar dislocation (LPD). However, the anatomic risk factors for subsequent contralateral LPD remain elusive. This study included 17 patients with contralateral LPD and 34 unilateral patellar dislocators. The anatomic parameters of the contralateral patellofemoral joints were measured using CT images and radiographs that were obtained at the time of the first dislocation. The Wilcoxon rank-sum test was performed, and a binary regression model was established to identify the risk factors. The receiver operating characteristic curves and the area under the curve (AUC) were analyzed. The tibial tubercle-Roman arch (TT-RA) distance was significantly different between patients with and without contralateral LPD (24.1 vs. 19.5 mm, p < 0.001). The hip−knee−ankle (HKA) angle, patellar tilt, congruence angle, and patellar displacement were greater in the study group than in the control group (p < 0.05). The TT-RA distance revealed an OR of 1.35 (95% CI (1.26−1.44]), p < 0.001) and an AUC of 0.727 for predicting contralateral LPD. The HKA angle revealed an OR of 1.74 (95% CI (1.51−2.00), p < 0.001) and an AUC of 0.797. The Patellar tilt, congruence angle, and patellar displacement had AUC values of 0.703, 0.725, and 0.817 for predicting contralateral LPD, respectively. In conclusion, the contralateral patellofemoral anatomic parameters were significantly different between patients with and without subsequent contralateral LPD. Increased TT-RA distance and excessive valgus deformity were risk factors and could serve as predictors for contralateral LPD. At first-time dislocation, the abnormal position of the patella relative to the trochlea may also be an important cause of subsequent LPD.

Outcomes, Return to Sport, and Failures of MPFL Reconstruction Using Autografts in Children and Adolescents with Recurrent Patellofemoral Instability: A Systematic Review

INTRODUCTION

This study systematically reviews and updates the current evidence on the outcomes of medial patellofemoral ligament (MPFL) reconstruction using autografts in children and adolescents with recurrent patellofemoral instability. The outcomes of interest were improvements in patient reported outcomes measures (PROMs), return to sport rates, and the rates of surgical failure.

METHODS

This systematic review was performed according to the 2020 PRISMA guidelines. The following electronic databases were accessed in October 2022: PubMed, Scopus, Web of Science. All the clinical studies which investigated the outcomes of MPFL reconstruction using autografts in children and adolescents with recurrent patellofemoral instability were accessed. Only studies which included patients younger than 18 years were considered. Techniques, case reports, guidelines, comments, editorials, letters, protocols, reviews, and meta-analyses were excluded. Studies which included patients with congenital or acute patellofemoral instability were not eligible, nor were those which focused exclusively on hyperlaxity.

RESULTS

Data from 477 patients (510 procedures) were retrieved. Of the patients, 41% (196 of 477) were women. The mean length of follow-up was 33.7 ± 28.8 months. The mean age of the patients was 14.6 ± 1.6 years. At the last follow-up, all PROMs of interest were statistically improved. The mean time to return to sport was 6.1 ± 1.1 months. Of the patients, 27% reduced their level of activity after surgical stabilization. A total of 87% of patients returned to practice sport. A total of 5% (26 of 477) and 2% (9 of 363) of patients experienced further dislocations and subluxations, respectively, during the follow-up period. Moreover, 4% (16 of 403) of patients underwent a further surgical procedure for patellofemoral instability within the follow-up period.

CONCLUSION

MPFL reconstruction using autografts is effective in children and adolescents with recurrent patellofemoral instability.

Gait Pathology in Subjects with Patellofemoral Instability: A Systematic Review

Identifying potential gait deviations in patellofemoral instability (PI) can help with the development of effective rehabilitation strategies. The purpose of this systematic review was to examine whether there are specific gait alterations in subjects with PI. The present review followed the PRISMA guidelines and was initially registered at PROSPERO (CRD42021236765). The literature search was carried out in the databases of PubMed, the Cochrane library, Web of Science, ClinicalTrials.gov, and Medline. The search strategy resulted in the identification of seven relevant publications. Subjects with PI show decreased walking speed, stride length, and cadence. Some studies reported changes not only in knee kinematics and kinetics but also in hip and ankle kinematics and kinetics. There is evidence that most subjects with PI walk with a quadriceps avoidance gait and show increased genu valgum posture, but there is still great variability in the coping responses within individuals with PI. The discrepancy among the study results might underpin the fact that PI is a multifactorial problem, and subjects cope with the different underlying morphological as well as functional deficits using a variety of gait strategies, which makes the interpretation and understanding of the gait of subjects with PI a clinically challenging task.

Changes in Anatomic Risk Factors for Patellar Instability During Skeletal Growth and Maturation

BACKGROUND

Several anatomic risk factors have been identified in the pathogenesis of patellofemoral instability. The literature is sparce regarding how these anatomic risk factors change during skeletal growth and development.

HYPOTHESIS

The anatomic risk factors associated with patellar instability change significantly during skeletal growth and maturation with different patterns in male versus female patients.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Magnetic resonance imaging data from 240 unique, asymptomatic knees (7-18 years of age; 50% female) were used to measure patellar height (Caton-Deschamps index), lateral patellar tilt angle, trochlear height, trochlear groove depth, trochlear sulcus angle, and tibial tubercle-trochlear groove (TT-TG) distance. Linear regression was used to test the associations between age and anatomic findings. Two-way analysis of variance with Holm-Šídák post hoc test was used to compare anatomic characteristics between sexes in 3 age groups: prepubertal school-aged children (7-10 years old), early adolescents (11-14 years old), and late adolescents (15-18 years old).

RESULTS

Patellar height (female sex), lateral patellar tilt angle (male sex), and trochlear sulcus angle (both sexes) decreased with age (P < .001). Trochlear height, depth, and TT-TG distance increased with age in both male and female participants (P < .02). Male participants had a larger sulcus angle (by 5.3°± 1.6° at age 11-14 years) and greater trochlear height (by >5 mm across medial, central, and lateral regions at age 15-18 years) than age-matched female participants (P < .01). We found no other sex-related differences in quantified anatomic features (P > .1).

CONCLUSION

The findings partially support our hypothesis indicating significant age-related changes in all quantified features, which were not different between male and female participants except for trochlear sulcus angle in early adolescence and trochlear height in late adolescence. In general, the majority of anatomic risk factors for patellar instability change with maturity in a direction that assists in reducing the risk of patellar instability and/or dislocation. The only outlier is the TT-TG distance, which increased by age, and in our oldest cohort of patients, the mean fell below the normal adult range. The current observations highlight the importance of age in the interpretation of risk for injury as well as the need for further studies to identify intrinsic and extrinsic factors that may result in abnormal development of these anatomic features during skeletal growth and maturation.

Management of Patellar Instability: A Network Meta-analysis of Randomized Control Trials

BACKGROUND

Multiple surgical options exist for the treatment of patellar instability; however, the most common procedures involve either a reconstruction of the medial patellofemoral ligament (MPFL) or a repair/plication of the MPFL and medial soft tissues.

PURPOSE

To perform a network meta-analysis of the randomized controlled trials (RCTs) in the literature to compare MPFL reconstruction, MPFL repair, and nonoperative management for patellar instability.

STUDY DESIGN

Systematic review and network meta-analysis; Level of evidence, 1.

METHODS

The literature search was performed based on the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. RCTs comparing MPFL reconstruction, MPFL repair, and nonoperative management for patellar instability were included. Clinical outcomes included recurrent instability (including both dislocations and subluxations), redislocation, and Kujala score. Clinical outcomes were compared using a frequentist approach to network meta-analysis, with statistical analysis performed using the statistical software R. The treatment options were ranked using P scores.

RESULTS

There were 13 RCTs with a total of 789 patients, all with a minimum follow-up of 24 months. There were 150 patients treated using MPFL reconstruction, 353 treated using MPFL repair, and 286 treated nonoperatively. Overall, MPFL reconstruction had the highest P score (0.9967) and resulted in a significantly lower recurrence rate than did MPFL repair (odds ratio [OR], 0.42; 95% CI, 0.07-0.72) and nonoperative management (OR, 0.09; 95% CI, 0.03-0.32). In addition, MPFL repair resulted in a significantly lower recurrence rate than did nonoperative management (OR, 0.42; 95% CI, 0.25-0.70). MPFL reconstruction had the highest P score (0.9651) and resulted in a significantly higher Kujala score than did nonoperative management (mean difference, 10.45; 95% CI, 0.41-20.49) but not MPFL repair (mean difference, 0.15; 95% CI, 0.03-0.68). Subgroup analysis revealed that MPFL reconstruction had the highest P score for all outcomes in those with first-time dislocation.

CONCLUSION

The current study demonstrated that MPFL reconstruction results in the lowest rate of recurrent patellar instability and best functional outcomes as measured using the Kujala score.

Patellar Height Correlates Modestly With Trochlear Dysplasia: A Magnetic Resonance Imaging Analysis

Purpose

To evaluate whether there is a correlation between the position of the patella and trochlear morphology in patients with and without patellar instability using exclusively MRI measurements.

Methods

MRI scans of knees in patients with patellofemoral instability and knees of patients with an ACL (anterior cruciate ligament) tear as a control group were reviewed. Measurements of patellar position (Canton-Deschamps ratio, Patellar Trochlear Index, and lateral patellar inclination) and trochlear morphology (lateral trochlear inclination and sulcus angle) were obtained from each scan. Bivariate and multivariate analysis was performed to identify correlations between study group, demographics, and patellofemoral joint measurements.

Results

There were 70 knees in the patellofemoral instability group and 60 knees in the control group. Bivariate analysis showed a significant difference in all measurements between the patellar instability group and the control group. Multivariate analysis showed modest correlations between patellar position and trochlear morphology. The Caton-Deschamps (CD) ratio correlated with patellar trochlear index (P < .001) and lateral trochlear inclination (P < .001). The respective R-square goodness of fit was 41.1%. Patellar trochlear index correlated with CD ratio (P < .001), lateral trochlear inclination (P < .001), lateral patellar inclination (P < .001), and patellar instability group (P = .011). The R-sq goodness of fit was 37.3%. Lateral patellar inclination correlated with patellar trochlear index (P < .001), Lateral trochlear inclination (P < .001), and age at first dislocation or injury (P = .02). The R-sq goodness of fit was 68.56%.

Conclusions

Using MRI-based measurements of the patellofemoral joint, we identified modest, but significant, correlations between measures of patellar height (patellar trochlear index, CD ratio, and lateral patellar inclination) and trochlear dysplasia. This correlation is unclear and is likely multifactorial, but on the basis of this work, a causal relationship between trochlear dysplasia and patella alta cannot be established.

Clinical Relevance

Radiographic evaluation of the patella and how it relates to the surrounding boney anatomy provides important information regarding our understanding of patella instability and its treatment.

Articular Cartilage Damage Worsens from First-time to Recurrent Patellar Dislocation—A Longitudinal Magnetic Resonance Imaging Study

Purpose

To compare the frequency and severity of articular cartilage injury on longitudinal magnetic resonance imaging (MRI) in patients after their initial dislocation and subsequent recurrent dislocations for those undergoing patellar stabilization surgery.

Methods

Between January 2012 and December 2017, patients undergoing patellar stabilization surgery were retrospectively reviewed. Only patients with an MRI after both the initial dislocation and subsequent dislocation events were included. The MRI scans were blindly examined to assess the Outerbridge classification grade of articular cartilage injury following each dislocation. Comparison was performed of each MRI for grade of articular cartilage damage and location.

Results

Thirty-five patients undergoing patellar stabilization surgery with recurrent instability were eligible. The incidence of articular cartilage injury following initial dislocation was 45.7%. Following a second dislocation, the incidence of articular cartilage injury increased to 62.9%, a statistically significant increase of 17.2% (P = .031). Furthermore, of the 16 patients with articular cartilage injury following their initial dislocation, 56.2% of patients (9) had an increase in grade of articular cartilage injury following the second dislocation, whereas 43.8% (7) of patients had no progression in their articular cartilage injury. Six (17.1%) patients had no articular cartilage injury following their initial dislocation but did have articular cartilage injury following their second dislocation.

Conclusions

Articular cartilage injury following patellar dislocation is common, and delayed surgical treatment may lead to an increase in articular cartilage damage. The incidence of articular cartilage injury following recurrent patellar dislocation was high (62.9%), and the majority of patients experienced an increase in their articular cartilage injury grade between their initial and recurrent dislocation on MRI evaluation.

Level of Evidence

Level IV, retrospective case series.

Patellar instability: will my patella dislocate again?

PURPOSE OF REVIEW

The incidence of patellar instability in pediatric patients ranges is 50-100 in 100,000 patients per year. Risk of recurrent dislocations however has been cited from 8.6% to 88% depending on individual patient factors. This manuscript highlights the demographical, historical, and anatomic factors associated with recurrent patellar instability following a first-time patella dislocation in the pediatric population.

RECENT FINDINGS

In recent years, various studies have focused on identifying risk factors for recurrent patellar instability following a primary patellar dislocation. A mix of patient factors, including age of first dislocation, patella alta, elevated tibial tubercle to trochlear groove and trochlear dysplasia have all been noted in the literature, which have helped to develop various scoring tools to predict recurrent dislocation following nonoperative treatment.

SUMMARY

Risk of recurrent patellar instability in patients who have previously suffered a patellar dislocation can be due to many factors. These risk factors should be used and applied to a variety of risk scores in order to provide physicians and healthcare providers with a tool to counsel patients and families on their patellar redislocation risk and help guide further management.

Alteration of patellar tendon morphology in patellofemoral instability (trochlear dysplasia)

INTRODUCTION

Trochlear Dysplasia (TD) is a condition that is characterized by the presence of an abnormally shaped trochlear groove, which hinders the patellofemoral joint (PFJ) stability. PFJ stability is determined by static and dynamic structures around the knee joint. We analysed whether the patellar tendon morphology is altered in patients with patellofemoral instability in Trochlear Dysplasia (TD).

MATERIAL AND METHODS

Magnetic Resonance Imaging (MRI) studies for 50 consecutive knees with TD and 50 consecutive knees with normal PFJ morphology were obtained for evaluation. For each MRI study, the cross-sectional area (CSA) of the medial and lateral components of the patellar tendon was measured and used to calculate the cross-sectional area ratio (CSAR) by two readers.

RESULTS

There was a statistically significant difference in the CSAR of the lateral-to-medial components of the patellar tendon between knees with normal PFJ morphology and knees with TD (one way ANOVA, F (4,95) = 7.743, p < 0.001). Pairwise comparisons amongst the Dejour subtypes of TD, revealed a statistically significance difference (p < 0.05) in the CSAR ratio between patients with normal PFJ morphology, and patients with type A (p = 0.007) and type C, TD. There was moderate correlation between the readers on Intraclass Correlation Coefficient (ICC) analysis (ICC- 0.7).

CONCLUSION

Our findings reveals hypertrophy of the medial part of the patellar tendon in patients with PFJ instability and TD. These differences could reflect the dynamic compensatory changes occurring at the PFJ to counteract the laterally directed instability vectors found in this condition.

Lateral Patellar Inclination Angle Measured via a Two-Image Technique on Axial Magnetic Resonance Imaging

Lateral patellar inclination (LPI) measures patellar tilt and is historically described on axial X-ray or a single magnetic resonance image (MRI). Given the variability in patellar height, LPI may be better represented by performing this measurement on two separate axial MRI images. We hypothesized that a two-image LPI measurement would be different from the current single-image LPI and have similar, if not superior reliability. Sixty-five patients treated for patellar instability (PI) between 2014 and 2017 were identified. Single image and two-image LPI were measured on axial MRI images. All measurements were performed by two independent observers. Reliability analysis was based on three observers' measurements of 30 randomly selected patients. Both the one image and two image LPI showed good inter-rater reliability (intraclass correlation coefficient [ICC] = 0.71 and 0.89, respectively), although the two image LPI had less variability. Both single image and two image LPI had near perfect intra-rater reliability (ICC = 0.98 and 0.98, respectively). Average single image LPI (14.6 ± 9.9 degrees) was 6.1 ± 3.4 degrees less than the average two image LPI (19.6 ± 9.4 degrees) (p = 0.037). Referencing a previously described 13.5 degrees maximum threshold, 54% of the patients had excessive patellar tilt based on single image LPI, while 73% had pathologic patellar tilt based on two image LPI. Two image LPI has similar reliability with less inter-rater variability compared with the historical single image LPI measurement. Significantly greater patellar tilt was identified with two image LPI that was found with single image LPI. A larger percentage of patients were classified as having pathologic patellar tilt based on two image LPI than single image LPI. The two image LPI provides more consistent and representative measurements of patellar tilt. Previously described threshold values for patellar tilt should be re-examined using this new measurement technique to appropriately risk stratify patients with PI and patellofemoral pain.

The risk of osteochondral fracture after patellar dislocation is related to patellofemoral anatomy

PURPOSE

Despite the comprehensive literature on the anatomical risk factors for patellar dislocation, knowledge on the risk factors for subsequent osteochondral fracture (OCF) remains limited.

METHODS

Magnetic resonance imaging was used to compare measures of patellofemoral anatomy in patients with OCF after patellar dislocation and propensity score matched patients without OCF. For differing measures, limit values showing a 50% probability for the occurrence of OCF were calculated using predictive logistic regression modelling. Proportions of abnormal measures in the groups were compared using Chi-square test. The association of anatomical measures with OCF location was examined by comparing subgroup mean values in the different OCF locations.

RESULTS

Propensity score matching provided a total of 111 matched pairs of patients with OCF and patients without OCF. The patients with and without OCF differed in patellotrochlear index (PTI; 0.54 [95% CI 0.52-0.57] vs. 0.47 [95% CI 0.45-0.49]; p < 0.001), tibial tubercle-posterior cruciate ligament distance (TT-PCL; 21.6 mm [95% CI 21.0-22.3 mm] vs. 20.5 mm [95% CI 20.0-21.1 mm]; p = 0.013), trochlear depth (2.5 mm [95% CI 2.3-2.7 mm] vs. 3.0 mm [95% CI 2.8-3.2 mm]; p < 0.001) trochlear facet asymmetry ratio (0.54 [95% CI 0.51-0.57] vs. 0.43 [95% CI 0.42-0.45]; p < 0.001) and trochlear condyle asymmetry ratio (1.04 [95% CI 1.03-1.04] vs. 1.05 [95% CI 1.04-1.05]; 0.013. Thresholds for increased OCF risk were > 0.51 for PTI  > 21.1 mm for TT-PCL < 2.8 mm for trochlear depth > 0.48 for trochlear facet asymmetry ratio and < 1.04 for trochlear condyle asymmetry ratio.

CONCLUSION

In patients with OCF after patellar dislocation, trochlear configuration and patella vertical location were closer to normal anatomy, whereas patella lateralization was more severe when compared to patients without OCF. These anatomical factors contribute to the risk of OCF during patellar dislocation.

LEVEL OF EVIDENCE

III.

Biomechanical evaluation of three patellar fixation techniques for MPFL reconstruction: Load to failure did not differ but interference screw stabilization was stiffer than suture anchor and suture-knot fixation

PURPOSE

The purpose of this study was to compare the maximum load to failure and stiffness of three medial patella-femoral ligament (MPFL) reconstruction techniques: (i) suture anchor fixation (SA), (ii) interference screw fixation (SF), and (iii) suture knot (SK) patellar fixation. The null hypothesis was that the comparison between these three different patella fixation techniques would show no difference in the ultimate failure load and stiffness.

METHODS

Reconstruction of the MPFL with gracilis tendon autograft was performed in 12 pairs of fresh-frozen cadaveric knees (24 knees total; mean age, 63.6 [Formula: see text] 8.0 years). The specimens were randomly distributed into 3 groups of 8 specimens; SA reconstruction was completed with two 3.0-mm metal suture anchors; (SF) fixation was accomplished by two 6-mm bio-composite interference screws; SK fixation at the lateral side of the patella was accomplished after drilling two semi-patellar tunnels with a diameter of 4.5 mm. The reconstructions were subjected to cyclic loading for 10 cycles to 30 N and tested to failure at a constant displacement rate of 15 mm/min using a materials-testing machine (MTS 810 Universal Testing System). The final load of failure (N), stiffness (N / mm) and failure mode was recorded in each specimen and followed by statistical analysis.

RESULTS

There was no significant difference in mean ultimate failure load among the three groups. The SK group failed at a mean ([Formula: see text] SD) ultimate load of 253.5 [Formula: see text] 38.2 N, the SA group failed at 243 [Formula: see text] 41.9 N and the SF group at 263.2 [Formula: see text] 9.06 N. The SF group had a mean stiffness of 37.8 [Formula: see text] 5.7 N/mm. This was significantly higher (p < 0.05) than the mean stiffness value achieved for the SK group 21.4 [Formula: see text] 9.5 N/mm and the SA group 18.7 [Formula: see text] 3.4 N/mm. The most common mode of failure in the SA group was anchor pullout, and in the SK group was failure at the graft-suture interface. All the reconstructions in the SF group failed due to tendon graft slippage from the tunnel.

CONCLUSION

Load to failure was not significantly different between the 3 techniques. However, screw fixation was found to be significantly stronger than the anchor and the suture knot fixation in terms of rigidity of the reconstruction. From a clinical point of view, all methods of fixation can be used reliably for MPFL reconstruction, since they were found to be stronger than the native MPFL.

Abnormal femur rotation in patients with recurrent patellar dislocation: A study on upright standing three-dimensionally reconstructed EOS images

BACKGROUND

The measurements of lower extremity rotational deformities in patients with recurrent patellar dislocation (RPD) in the standing position are available with the application of the EOS imaging system. The aim of our case-control study was to identify the differences on the femur rotation between the supine and standing positions, and to investigate the differences of anatomical and functional femur rotation between RPD patients and controls.

METHODS

Thirty-five lower extremities affected by RPD from 30 patients and 27 intact lower extremities from 27 controls with acute meniscus tear or anterior cruciate ligament injury were recruited. Anatomical femoral anteversion (AFA), functional femoral anteversion (FFA), femorotibial rotation (FTR) and distal femoral torsion (DFT) of all subjects were measured with the EOS imaging system. Computed tomography scans were carried out to analyze the AFA and FFA in the supine position in PRD patients. The differences in FFA between supine and standing position and in AFA, FTR and DFT between RPD and controls were analyzed. The predictor importance of each variable on RPD was observed after cluster analysis.

RESULTS

The EOS images were available in all subjects. The FFA was significantly smaller in the standing position than in the supine position (P < 0.05) in RPD patients. When comparing with the controls, RPD patients showed higher AFA, FTR and DFT (P < 0.05) but comparable FFA (P < 0.05). The cluster model prompted that FTR and DFT had higher predictor importance than AFA.

CONCLUSION

Larger AFA but comparable FFA in patients with RPD than the controls in an upright standing position suggested more internally rotated distal femur in the RPD patients. AFA may be inadequate and FFA should also be considered while planning the treatment for RPD. DFT and FTR should be taken into consideration when evaluating the abnormalities in femur rotation in RPD patients.

Elongation and orientation pattern of the medial patellofemoral ligament during lunging

Unfavorable clinical outcomes after medial patellofemoral ligament (MPFL) reconstruction, such as early osteoarthritis of the patellofemoral joint, were considered to be associate with tunnel malpositioning. Length change studies have found that small changes in the femoral position can cause great changes in elongation trends. Further studying the MPFL kinematics may help us to understand the consequences of tunnel malpositioning and optimize the reconstruction techniques. Fifteen healthy subjects were studied with a combined computed tomography and biplane fluoroscopic imaging technique during a lunge motion. Five femoral and three patellar attachments were used to simulate different MPFL bundles. Kinematics of MPFL was defined as elongation and orientation changes (i.e., deviation angle and elevation angle). The mean deviation angle was 28.7° (95% confidence interval, 28.0°-29.4°) at full extension and remained nearly unchanged up to 60° of flexion, and increased to 56.5° (54.1°-58.9°) at 110°. The elevation angle decreased linearly from 12.6° (9.3°-15.9°) at full extension to -86.2° (-92.7-79.7°) at 110° of flexion. The MPFL was most stretched anteriorly and laterally relative to femur from full extension to 30° of flexion and remained near isometric beyond 30°. The current study found that proximal and anterior femoral attachments caused excessive lateral stretching of the MPFL at deeper flexion angles. Such abnormal MPFL kinematics may subsequently cause overconstraint and increased cartilage pressures of the medial patellofemoral joint.

Ipsilateral patellofemoral morphological abnormalities are more severe than those of contralateral joints in patients with unilateral patellar dislocation

PURPOSE

To determine the differences in anatomic parameters between ipsilateral dislocated knees and contralateral non-dislocated knees in patients with unilateral patellar dislocation and to identify any variations in ipsilateral knees contributing to contralateral anatomic abnormalities.

METHODS

A total of 82 patients with unilateral patellar dislocation from 2016 to 2019 were retrospectively evaluated. Bilateral anatomic factors, including the tibial tubercle to trochlear groove (TT-TG) distance, lower limb rotational deformities, trochlear dysplasia, patella tilt, and patellar height, were assessed by CT.

RESULTS

The study included 46 patients (32 females and 14 males, mean age ± SD 20.5 ± 6.8). The interobserver reliability of each parameter showed excellent agreement. The ipsilateral TT-TG distance (P = 0.004), patella tilt (P = 0.001), and patellar height (P = 0.01) were greater in the ipsilateral knees than in the contralateral knees. The lateral trochlea inclination (LTI) in the contralateral knees was larger than that in the ipsilateral knees (P = 0.022). There was a significant difference in the distribution of trochlear dysplasia of Dejour between the ipsilateral knees (dislocated side) and the contralateral knees (P = 0.036). However, bilateral femoral and/or tibial torsion, and bilateral knee joint rotation did not differ significantly. Binary logistic regression showed that only ipsilateral LTI revealed significant ORs of 8.83 (P = 0.016) and 7.64 (P = 0.018) with regard to contralateral abnormal tibial torsion and LTI, respectively.

CONCLUSION

In patients with unilateral patellar dislocation, the ipsilateral TT-TG distance, patella tilt, and patellar height values were larger in the ipsilateral knees than in the contralateral knees, and trochlear dysplasia was more severe in the ipsilateral joints. The risks of contralateral pathological tibial torsion and LTI were 8.8- and 7.6-fold higher, respectively, in patients with abnormal ipsilateral LTI.

LEVEL OF EVIDENCE

Level IV.

Prevalence of lateral patellofemoral maltracking and associated complications in patients with Osgood Schlatter disease

OBJECTIVE

To evaluate adults with history of Osgood Schlatter disease (OSD) for imaging features of lateral patellofemoral maltracking.

METHODS

In a span of four years, 10,181 unique non-contrast knee MRIs were performed on patients aged 20-50. Patients with acute trauma, prior surgery, and synovial pathologies were excluded. 171 exams had imaging findings of OSD, and an age-matched control group of 342 patients without OSD was randomly selected. Two radiologists retrospectively reviewed MRIs for features of lateral patellofemoral maltracking. Maltracking was defined as edema in superolateral Hoffa's fat or a tibial tuberosity-trochlear groove (TT-TG) distance ≥20 mm with either patellar tilt/translation. Binomial logistic regression identified predictors of maltracking in OSD. Optimal TT-TG distance to indicate maltracking was determined by receiver operating characteristic curve.

RESULTS

59% (101/171) of the knees with OSD showed findings of maltracking, with patella alta, trochlear dysplasia, and quadriceps tendinosis as significant predictors of maltracking (p < 0.001). Patellofemoral chondrosis was present in 63% (107/171), with maltracking contributing to higher grade chondrosis more so than increasing age (OR 8.4 versus 1.07). 13 mm was the optimal cut-off TT-TG distance to indicate maltracking (sensitivity 83%, specificity 80%). The prevalence of maltracking in the control group was 15% (p < 0.001 compared with the OSD group).

CONCLUSION

Adults with sequelae of OSD are at high risk of maltracking and are likely to develop patellofemoral chondrosis. A lower threshold for identifying maltracking patients, including a lower cut-off TT-TG distance can help identify those at risk. Radiologists should maintain a high index of suspicion for maltracking in adults with OSD to guide clinical intervention.

Objectively quantified lower limb strength recovery in people treated surgically or non-surgically after patellar dislocation: A systematic review

OBJECTIVE

Synthesize evidence on objectively quantified lower limb strength recovery in people treated surgically or non-surgically after patellar dislocation.

METHODS

MEDLINE, EMBASE, Cochrane Library, SPORTDiscus, PEDro, AMED and CINAHL databases were last searched on July 30th, 2020 for randomized controlled trials and observational studies that objectively quantified lower limb strength in people (any age or sex) treated surgically or non-surgically after patellar dislocation.

RESULTS

24 studies were included (877 participants, median age 20.7). All assessed knee extension strength, 11 knee flexion strength, three hip abduction strength, two hip external rotation strength, and one hip flexion, extension, adduction, and internal rotation strength. One randomized controlled trial judged at high risk of bias and two cohort studies with methodological limitations compared lower limb strength recovery between surgically and non-surgically treated people, with conflicting findings. After surgery, median long-term (>8 months) knee extension strength was 82.5% (IQR 78.5-88.2; 13 studies) of the unaffected leg and knee flexion strength was 91.5% (IQR 90.7-96.9; five studies). After non-surgical treatment, median long-term knee extension strength was 86% (IQR 79.3-87.4; four studies) and mean flexion strength ranged from 95.2 to 96.7% (two studies). Mean hip strength was always >90% (two studies). Two redislocations during eccentric isokinetic knee testing and knee pain during isokinetic knee extension testing were reported as adverse events.

CONCLUSIONS

Available evidence indicates that after patellar dislocation, knee extension strength deficits in the affected limb are frequently observed and can persist long term, but this remains uncertain due to the limitations of relevant included studies. Whether lower limb strength recovery differs between people treated surgically and those treated non-surgically after patellar dislocation also remains uncertain.

TRIAL REGISTRATION

(PROSPERO CRD42019139533).

Primary Medial Patellofemoral Ligament Reconstruction in Military Servicemembers: Can We Reliably Restore Preinjury Function and Stability?

Background:

Medial patellofemoral ligament (MPFL) reconstruction for patellar instability is a commonly performed procedure with a reported high rate of return to preinjury activity. However, no previous study has assessed the functional outcomes of military servicemembers undergoing MPFL reconstruction.

Hypothesis:

Primary MPFL reconstruction confers patellar stability, but with limited return to preinjury function and ability to maintain unrestricted military active duty status.

Study Design:

Case series; Level of evidence, 4.

Methods:

Using the Management Analysis and Reporting Tool database, we conducted a retrospective review of active duty servicemembers throughout the US Department of Defense Health System who underwent primary MPFL reconstruction between 2012 and 2015. Demographic variables were recorded as well as ability to return to impact activities—defined as running, jumping, rucking with a load >40 pounds (18 kg), and returning to airborne operations—and to remain on active duty status. The rates of recurrent instability and the need for subsequent surgeries were identified and assessed for statistical significance using uni- and multivariate analyses. Patients were evaluated for a minimum of 2 years postoperatively.

Results:

Of the 213 patients who underwent primary MPFL reconstruction, including 34 with concomitant tibial tubercle osteotomy, 19 (8.9%) patients developed recurrent instability. The presence of bilateral patellar instability was associated with higher recurrence rate. Patients with bilateral instability comprised 47.3% of those with recurrence but only 24.9% of patients without recurrence (P = .019). Impact activity restrictions were present in 57.6% of patients (n = 121), with 86 patients (52.1%) undergoing medical separation from the military. Patients who were prescribed activity restriction before surgery were significantly more likely to have postoperative activity restrictions (64.5%; P = .019), and junior enlisted servicemembers were more likely to be medically separated from service postoperatively than higher ranking senior enlisted members or officers.

Conclusion:

Only 42.4% of US military servicemembers undergoing primary MPFL reconstruction were able to return to unrestricted impact activity after surgery. Bilateral instability negatively affected return to impact activities. Military servicemembers, particularly junior enlisted members, should be counseled on this poor prognosis for a full return to unrestricted activity postoperatively.

Evaluation of recurrent dislocation of the patella in children with MRI: Goldthwait technique combined with lateral release, and VMO advancement-a retrospective study of 85 knees

PURPOSE

There are certain risk factors responsible for patella instability that should be identified before choosing the most appropriate treatment.

METHODS

We evaluated 83 skeletally immature patients who, after two or more patellar dislocation episodes, underwent surgical treatment to address the condition of patellar instability. Each patient was evaluated for patellar instability risk factors using the Balcarek patellar instability severity score. Evaluation of patellar instability included knee MRI to systematically identify anatomical risk factors. The preoperative and postoperative clinical evaluation included the modified Cincinnati score and the Kujala score. The Roux-Goldthwait technique combined with lateral retinaculum release and the advancement of the vastus medialis oblique (VMO) was performed on all knees.

RESULTS

The mean patient age at the time of surgery was 12.2 ± 1.59 years (range 8-14 years). The average follow-up was 4.72 ± 1.37 (range 3-8) years. Trochlear dysplasia (decreased trochlear depth), the most common anatomical risk factor, was identified in 71 knees (83.5%). The modified Cincinnati score increased from 58.46 ± 8.75 (range 49-76) points to 94.07 ± 2.88 (range 88-98) postoperatively. The mean Kujala scores increased from 58.51 ± 8.94 (range 49-76) points to 93.66 ± 2.65 (range 87-98) postoperatively. The two-tailed P value was less than 0.0001. The patients were followed until their skeletal maturation, without reporting any incidents of patella dislocation, except one.

CONCLUSION

The Roux-Goldthwait technique combined with lateral retinaculum release, and the advancement of VMO, can restore patellar tracking and can decrease the probability of another dislocation. It was an effective treatment in skeletally immature patients who had two or more episodes of patellar dislocation.

LEVEL OF EVIDENCE

IV.

A computed tomography cadaveric study of the radiological anatomy of the patella: the size of the patella correlates with bone bridge between tunnels and R angles are introduced for safe tunnel drilling during MPFL reconstruction

PURPOSE

To measure the safe range of angles during tunnel drilling and map ideal patella tunnel placement with the use of preoperative computed tomography (CT) scan and compare results after medial patellofemoral ligament (MPFL) reconstruction using a hardware-free patellar fixation technique with two semi-patellar tunnels between a) a free-hand technique, and b) its modification with the use of an anterior cruciate ligament (ACL) tibia aiming device.

METHODS

CT scan was performed on 30 fresh-frozen cadaveric knees a) prior to any intervention and b) after MPFL reconstruction. For MPFL reconstruction, specimens were randomly allocated to 1) Group A, which consisted of knees operated with free-hand, hardware-free patellar fixation technique with two semi-patellar tunnels and 2) Group B, which consisted of knees operated on with a technique modification with the ACL tibia device.

PATELLAR MEASUREMENTS

L1 was the maximal patellar length. L2 was the minimum possible distance of placement for the upper tunnel from the proximal pole of the patella. The maximum bone bridge between tunnels was calculated as half of L1 minus the L2 distance (L1/2-L2). We also measured R1 and R2 angles at the proximal and distal tunnel that represent safe angles at the entry point during tunnel drilling (without breaching the anterior cortex or articular cartilage).

RESULTS

Preoperatively, mean L1 was 3.45 cm (range 3.05-4.52). Mean L2 was 0.62 cm (range 0.49-0.89). The mean maximum possible bone bridge between tunnels (L1/2-L2) was 1.1 cm (range 0.77-1.58). R1 was 6.05⁰ (range 4.78-7.44), R2 was 6.64⁰ (range 4.57-9.03), and their difference reached statistical significance (p = 0.03). Postoperatively, in group A, in 4 out of 15 patellas, multiple attempts were made during tunnel drilling in order to avoid anterior cortex or cartilage breaching. In group B, all tunnels were correctly drilled with the first attempt. Bone bridge between tunnels was significantly shorter postoperatively (0.93 cm, p < 0.01).

CONCLUSION

Small-size patellae correlate with short maximum bone bridge between tunnels, which makes anatomic, double-bundle, hardware-free patella fixation, with two semi-patellar tunnels MPFL reconstruction challenging. Furthermore, R angles create a narrow window to avoid intraoperative breaching, rendering the use of the ACL tibia device an extremely useful instrument.

LEVEL OF EVIDENCE

II.

Predicting Risk of Recurrent Patellofemoral Instability With Measurements of Extensor Mechanism Containment

BACKGROUND

Identifying risk factors for recurrent patellar dislocation after a primary dislocation may help guide initial treatment. Magnetic resonance imaging (MRI) measurements relating the alignment of the extensor mechanism to trochlear morphology have been shown to distinguish patients with dislocations from controls, but their usefulness in predicting the risk of a second dislocation is not known.

PURPOSE

To identify the association of novel MRI measures of patellar containment with recurrent instability in pediatric patients presenting with a first-time patellar dislocation.

STUDY DESIGN

Cohort study (Prognosis); Level of evidence, 3.

METHODS

The study was conducted at a tertiary care children's hospital (2005-2014) on patients (age, 8-19 years) with a first-time patellar dislocation. MRI measurements were made by 2 independent raters. Interobserver reliability was assessed for all measurements via an intraclass correlation coefficient (ICC). Only measurements with an ICC >0.8 were included. Univariable and multivariable logistic regression analyses were used to evaluate variables associated with recurrence.

RESULTS

A total of 165 patients with a median age of 14 years and a slight (57.6%) female predominance was identified. The median follow-up length of the whole cohort was 12.2 months (interquartile range, 1.6-37.1 months). Subsequent instability was documented in 98 patients (59.4%). MRI measurements with excellent correlation (ICC > 0.8) were the tibial tubercle to trochlear groove distance (TT-TG), the tangential axial width of the patella, the tangential axial trochlear width, the axial width of the patellar tendon beyond the lateral trochlear ridge (LTR), and the tibial tubercle to LTR distance. In univariate analysis, all mentioned MRI measurements had significant association with recurrent instability. However, after both backward and forward stepwise regression analyses, the tibial tubercle to LTR distance was the only independent predictor of recurrent instability (P = .003 in both). Patients with a tibial tubercle to LTR distance value greater than -1 mm had a significantly higher rate of recurrent patellar dislocation (72%).

CONCLUSION

Of numerous axial view MRI parameters, only the tibial tubercle to LTR distance demonstrated a statistically significant association with recurrent patellar instability upon multivariable logistic regression analysis during short-term follow-up of a pediatric population presenting with initial lateral patellar dislocation. Interobserver correlation of the tibial tubercle to LTR distance was good (ICC > 0.8) and similar to that of TT-TG.

Reconstruction of the medial patellofemoral ligament using two blind transverse semi-patella tunnels and an implant-free technique for patellar fixation: a technical note

Background

The double-bundle technique with two points of patellar fixation in the upper half of the patella replicating the broad attachment site of the native medial patellofemoral ligament (MPFL) is the most commonly performed procedure for MPFL reconstruction. Complete transverse patella tunnels pose a threat to the integrity of the patella. We present an implant-free, double-bundle technique for MPFL reconstruction with gracilis autograft, overcoming the problem of complete patella bone tunnels and over-drilling.

Methods

After standard gracilis graft harvesting, the anteromedial side of the patella is exposed. With the guidance of an anterior-cruciate-ligament (ACL) tibia-aiming device, two 2-mm parallel guide pins are inserted from medial to lateral at the upper half of the patella. The two guide pins are over-drilled with a cannulated 4.5-mm drill bit 2-cm deep, to create two transverse blind semi-patellar tunnels. For the femoral fixation, a 2.4-mm guide pin with an eyelet is drilled at the Schöttle point and over-reamed with a 6-mm cannulated reamer to a depth of 30 mm. The two free ends of the graft (with two running Krakow sutures placed) are pulled into the two patella tunnels and the graft sutures are tied together with tension for stable graft fixation at the lateral patella rim. With the help of a femoral suture loop (which is inserted in the femoral bone tunnel), the graft-loop is advanced into the femoral bone tunnel and the graft is finally fixed with a 7-mm interference screw at 30° of knee flexion.

Results

The utilization of blind transverse tunnels (not trans-patellar tunnels) offers the advantage of avoiding stress risers at the patella. Thanks to the ACL tibia aiming device, multiple drilling, and breaching of the anterior patellar cortex or articular surface of the patella is avoided.

Conclusions

This implant-free, and consequently affordable technique, isolated or combined with bony procedures, minimizes possibilities for perioperative bony complications at the patella fixation site.

Lateral Trochlear Inclination Angle: Measurement via a 2-Image Technique to Reliably Characterize and Quantify Trochlear Dysplasia

Background:

Trochlear dysplasia (TD) is a risk factor for patellar instability (PI). The Dejour classification categorizes TD but has suboptimal reliability. Lateral trochlear inclination (LTI) is a quantitative measurement of trochlear dysplasia on a single axial magnetic resonance imaging (MRI) scan.

Hypothesis:

A modified LTI measurement technique using 2 different axial MRI scans that reference the most proximal aspect of the trochlear cartilage on 1 image and the fully formed posterior condyles on the second image would be as reliable as and significantly different from the single-image measurement technique for LTI. Further, the 2-image LTI would adequately represent overall proximal trochlear morphologic characteristics.

Study Design:

Cohort study (diagnosis); Level of evidence, 2.

Methods:

Patients aged 9 to 18 years treated for PI between 2014 and 2017 were identified. The Dejour classification was radiographically determined. Single-image LTI was measured on a single axial MRI scan at the most proximal aspect of visible trochlear cartilage. A 2-image LTI was measured from 2 separate MRI scans: 1 at the most proximal aspect of trochlear cartilage and the second at the fully formed posterior condyles. This 2-image LTI was repeated at 3 subsequent levels (the first measurement is referred to as LTI-1; repeated measurements are LTI-2, LTI-3, and LTI-4, moving distally). In total, 65 patients met the inclusion criteria, and 30 were randomly selected for reliability analysis.

Results:

Inter- and intrarater reliability trended toward more variability for single-image LTI (intraclass correlation coefficient [ICC], 0.86 and 0.88, respectively) than for 2-image LTI (ICC, 0.97 and 0.96, respectively). The Dejour classification had lower intra- and interrater reliability (ICC, 0.31 and 0.73, respectively). Average single-image LTI (9.2° ± 12.6°) was greater than average 2-image LTI-1 (4.2° SD ± 11.9°) (P = .0125). Single-image LTI classified 60% of patients with PI as having TD, whereas the 2-image LTI classified 71% as having TD. The 2-image LTI was able to capture 91% of overall proximal trochlear morphologic characteristics.

Conclusion:

LTI has higher reliability when performed using a 2-image measurement technique compared with single-image LTI and Dejour classification. The strong correlation between 2-image LTI and average LTI shows that 91% of TD is represented on the most proximal axial image. Because the single-image measurement appears to underestimate dysplasia, previously described thresholds should be reexamined using this 2-image technique to appropriately characterize TD.

Evaluation of risk correlation between recurrence of patellar dislocation and damage to the medial patellofemoral ligament in different sites caused by primary patellar dislocation by MRI: a meta-analysis

Purpose

Non-surgical treatment of primary patellar dislocation has a high risk of recurrent dislocation; thus, we tried to identify injuries in which sites of the medial patellofemoral ligament (MPFL) were most associated with recurrent dislocation by analyzing relevant original literature in order to provide improved suggestions on early surgical treatment.

Methods

According to the preset retrieval strategy, the original studies were retrieved until January 2020 using MEDLINE, Embase and Cochrane Library. Review Manager 5.3 software was used to summarize and compare the differences of recurrent dislocation of MPFL injuries at different attachments.

Results

Although the incidence of recurrent patellar dislocation at the femoral attachment of MPFL was higher overall (femoral only vs. patellar only vs. combined: 37.6% vs. 32.3% vs. 35.8%), no statistical difference was found among the three groups (femoral only vs. patellar only, RR = 1.32 [95% CI 0.89–1.95]; P = 0.17) (femoral only vs. combined, RR = 1.15 [95% CI 0.59–2.22]; P = 0.68) (patellar only vs. combined, RR = 0.94 [95% CI 0.69–1.29]; P = 0.72). In addition, the sulcus angle of recurrent dislocation group is significantly greater than that in the non-recurrent dislocation group (MD = 3.06 [95% CI 0.42–5.70]; P = 0.02).

Conclusions

Based on the pooled data collected from the original studies available, the risk of recurrent patellar dislocation due to damage to the MPFL at different sites did not differ. Additionally, the sulcus angle in the group with recurrent dislocation was considerably higher when comparing with the group without recurrent dislocation, that is, the shallower and flatter of the trochlear groove, the higher the risk of recurrent patellar dislocation.