Effect of Medialization of the Trochlear Groove and Lateralization of the Tibial Tubercle on TT-TG Distance: A Cross-sectional Study of Dysplastic and Nondysplastic Knees

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.

Increased tibial tuberosity torsion has the greatest predictive value in patients with patellofemoral instability compared to other commonly assessed parameters

PURPOSE

The multifactorial nature of patellofemoral instability requires a comprehensive assessment of the affected patients. While an association between tibial tuberosity (TT) torsion and patellofemoral instability is known, its specific effect has not yet been investigated. This study investigated the effect of TT torsion on patellofemoral instability.

METHODS

This retrospective cohort study compared patients who underwent surgical intervention for patellofemoral instability and asymptomatic controls. TT torsion was measured in addition to other commonly assessed risk factors for patellofemoral instability using standardised computed tomography (CT) data of the lower extremities. The diagnostic performances of the assessed parameters were evaluated using receiver operating characteristic curve analysis and odds ratios (ORs) were calculated.

RESULTS

The patellofemoral instability group consisted of 79 knees, compared to 72 knees in the asymptomatic control group. Both groups differed significantly in all assessed parameters (p < 0.001), except for tibial torsion (n.s.). Among all parameters, TT torsion presented the best diagnostic performance for predicting patellar instability with an area under the curve of 0.95 (95% confidence interval [CI], 0.91-0.98; p < 0.001). A cut-off value of 17.7° yielded a 0.87 sensitivity and 0.89 specificity to predict patellar instability (OR, 55.2; 95% CI, 20.5-148.6; p < 0.001).

CONCLUSION

Among the evaluated risk factors, TT torsion had the highest predictive value for patellofemoral instability. Patients with TT torsions ≥ 17.7° showed a 55-fold increased probability of patellofemoral instability. Therefore, TT torsion should be included in the assessment of patients with patellofemoral instability.

LEVEL OF EVIDENCE

Level III.

Reliability of Tibial Tubercle-Trochlear Groove Distance for Assessing Tibial Tubercle Lateralization: A Study Comparing Different Anatomic References

Background

The tibial tubercle-trochlear groove (TT-TG) distance is a measurement used to quantitatively assess tibial tubercle lateralization (TTL), and it has important reference value for the treatment of patellar dislocation (PD). However, TT-TG distance accuracy has been questioned, so many new parameters have been proposed.

Purpose

To compare which of the TT-TG, tibial tubercle-midepicondyle (TT-ME), tibial tubercle-Roman arch (TT-RA), tibial tubercle-tibial intercondylar midpoint (TT-TIM), and tibial tubercle-mid inter-epicondyle trochlea intersection (TT-MIELTI) distances better reflect TTL in patients with PD.

Study Design

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

Methods

A total of 96 patients who had undergone surgery for PD and 96 patients without PD (controls) were included in the study. The patients had all undergone computed tomography examination. The TT-TG, TT-ME, TT-RA, TT-TIM, TT-MIELTI distances and the TTL distance were measured independently by 2 surgeons in a blinded and randomized fashion. The t test was used to detect whether the parameters were significantly different between the 2 groups. The TTL distance was used as a reference value for lateralization of tibial tubercle. Pearson correlation coefficients were calculated to determine correlations between the defined measurements.

Results

The intra- and interobserver reliability of the defined measurements was excellent. All parameters except for TT-TIM distance were significantly larger in the PD group than the control group (P < .01 for all). There was a moderate correlation (r = 0.601) between the TT-TG distance and TTL, and other parameters were less correlated with TTL.

Conclusion

Among 5 the parameters tested, the TT-TG distance still had the highest correlation with TTL and was able to reflect TTL better in patients with PD. The role of TT-TIM distance in the assessment of PD needs further study.

Addition of Tibial Tubercle Osteotomy to Combined MPFL Reconstruction and Lateral Retinacular Release not Recommended for Recurrent Patellar Dislocation in Patients with 15 to 20 mm TT-TG

Surgery is the primary treatment for recurrent patellar dislocation. However, there is still a lack of consensus regarding the choice of combined surgical methods due to the complexity of the anatomical factors. This study aimed to investigate the efficacy and radiological changes in medial patellofemoral ligament reconstruction (MPFLR) and lateral retinacular release (LRR) with and without tibial tubercle osteotomy (TTO) for recurrent patellar dislocation in patients with a tibial tubercle-trochlear groove (TT-TG) distance of 15 to 20 mm. Fifty-four patients were enrolled in this retrospective study between 2010 and 2014. The average patient age was 21.6 ± 5.0 years. All patients underwent MPFLR and LRR, and in 18 patients, these procedures were combined with TTO. Patients were evaluated preoperatively and postoperatively for patellar lateral shift, patellar tilt angle, TT-TG distance, Q-angle, Caton-Deschamps index (CDI), Kujala, and Lysholm scores. The minimally clinical important difference was used to compare clinical outcomes between two groups. In the mean follow-up of 82.6 ± 15.9 months, functional scores improved significantly in both groups (p < 0.01). There were no significant differences in postoperative function scores between the two groups (Kujala, p = 0.25, mean difference = 1.5, 95% confidence interval [CI]: -1.4-4.4; Lysholm, p = 0.76, mean difference = -0.6, 95% CI: -5.9-4.7). Additionally, TTO significantly decreased Q-angle (23.6 ± 2.4 vs. 17.4 ± 2.9, p < 0.01), TT-TG (17.1 ± 1.5 vs. 10.4 ± 1.8, p < 0.01), and CDI (1.18 ± 0.12 vs. 1.08 ± 0.07, p < 0.01). Combined MPFLR and LRR with and without TTO are both effective techniques for recurrent patellar dislocation. Additional osteotomy can correct patellar alta and tibial tubercle lateralization. However, given that there were no significant differences in postoperative functional scores or recurrence rate between groups, we may not recommend TTO in addition to MPFLR and LRR in patients with TT-TG of 15 to 20 mm. Long-term and prospective cohort studies are required to assess further outcomes.

Trochlear Shape and Patient-Reported Outcomes After Arthroscopic Deepening Trochleoplasty and Medial Patellofemoral Ligament Reconstruction: A Retrospective Cohort Study Including MRI Assessments of the Trochlear Groove

Background

Sparse objective data are available documenting changes of trochlear shape after trochleoplasty.

Purpose/Hypothesis

The purpose was to investigate whether standardized magnetic resonance imaging (MRI) measurements that characterize trochlear dysplasia (TD) change significantly after arthroscopic deepening trochleoplasty (ADT) combined with medial patellofemoral ligament (MPFL) reconstruction. It was hypothesized that MRI measurements would approximate normal values.

Study Design

Case series; Level of evidence, 4.

Methods

Patients who underwent ADT between October 2014 and December 2017 were considered for this study. The preoperative inclusion criteria for ADT surgery were patellar instability, a dynamic patellar apprehension sign at 45° of flexion, a lateral trochlear inclination (LTI) angle of <11°, and failed physical therapy. MRI was performed pre- and postoperatively, and standardized MRI measurements were calculated: LTI angle, trochlear depth, trochlear facet asymmetry, cartilage thickness, and trochlear height. The Banff Patella Instability Instrument 2.0 (BPII) score, Knee injury and Osteoarthritis Outcome Score (KOOS), and Kujala score were obtained pre- and postoperatively.

Results

A total of 16 knees in 15 patients (12 female and 3 male; median age, 20.9 years; range, 14.1-51.3 years) were evaluated. The mean follow-up time was 63.6 months (range, 23-97 months). The median LTI angle improved from 1.25° (range, -25.1° to 10.6°) preoperatively to 10.7° (range, -17.7° to 25.8°) postoperatively (P < .001), trochlear depth increased from 0.0 mm (range, -4.2 to 1.8 mm) to 3.23 mm (range, 0.25-5.3 mm) (P < .001), and trochlear facet asymmetry improved from 4.55% (range, 0.0%-28.6%) to 17.8% (range, 0.0%-55.6%) (P < .003). Cartilage thickness was unchanged: 4.5 mm (range, 1.9-7.4 mm) preoperatively and 4.9 mm (range, 0.6-8.3 mm) postoperatively (P = .796). BPII, KOOS, and Kujala scores improved significantly (P < .0034 for all).

Conclusion

Combined ADT and MPFL reconstruction led to statistically significant and clinically relevant improvements in patient-reported outcomes and standardized MRI measurements that characterize TD. The improvements corresponded to those obtained by open trochleoplasty. No significant reduction in cartilage thickness was seen.

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.

The Tibial Tuberosity-Rotational Angle as a Novel Predisposing Parameter for Patellar Dislocation

Background

The tibial tuberosity (TT) in the axial plane is located on a curved line along the anterior cortex of the proximal tibia. Therefore, the linear measurement of TT position may not fully reflect TT malposition.

Purpose

To introduce TT-rotational angle (TT-RA) as a new anatomical parameter, which means the rotation of the TT relative to the dorsal condylar line of the tibia, and to validate its predictive value for patellar dislocation.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

Included were 46 patients with a history of patellar dislocation and 46 age- and sex-matched controls who underwent axial magnetic resonance imaging. Seven radiological parameters were measured and compared between the 2 groups, including TT-trochlear groove (TT-TG) distance, tibial tubercle-posterior cruciate ligament (TT-PCL) distance, TT-PCL ratio, TT lateralization (TTL), trochlear groove medialization (TGM), TT-RA, trochlear groove-posterior condylar axis angle (TG-PCA), and knee rotation. The predictive values of parameters for patellar dislocation were assessed using multiple logistic regression analysis.

Results

The intra- and interobserver correlation coefficients for measuring the radiographic parameters showed good to excellent values., respectively. There were significant differences in the TT-TG distance (13.9 vs 6.8 mm; P < .001), TT-RA (16.0° vs 9.1°; P < .001), TG-PCA (93.7° vs 95.4°; P = .017), and knee rotation (0.9° vs 5.3°; P < .001) between the 2 groups. However, there was no significant difference in TT-PCL distance (20.7 vs 19.4 mm; P = .075), TT-PCL ratio (28.0% vs 26.6%; P = .136), TTL (65.7% vs 64.9%; P = .270), or TGM (54.9% vs 55.0%; P = .923). Multivariable analysis showed that 3 parameters were significantly associated with patellar dislocation: TT-RA (OR, 1.57; P < .001), TT-TG distance (OR, 1.52; P = .002), and knee rotation (OR, 0.75; P = .022).

Conclusion

The TT-RA was a reliable predisposing parameter of patellar instability. It can be an alternative method of measurement when the TT-TG distance is not clearly defined.

Change of the cross-sectional area of vastus medialis oblique in patients with recurrent patellar dislocation treated by tibial tubercle transfer combined with medial patellofemoral ligament reconstruction on axial CT

PURPOSE

To investigate the change of the cross-sectional area (CSA) of vastus medialis oblique (VMO) in patients with recurrent patellar dislocation (RPD) treated by tibial tubercle transfer combined with medial patellofemoral ligament (MPFL) reconstruction by imaging methods, and to guide clinical treatment and rehabilitation.

METHODS

From October 2015 to March 2022, 23 patients with RPD who underwent tibial tubercle transfer combined with MPFL reconstruction were retrospectively enrolled. All patients were assessed by CT in the supine position with the knee fully extended and the quadriceps relaxed. The CSA of VMO and the ratio of CSA of VMO to body weight (CSA/BW) were measured at the upper pole of the patella, 5 mm above the upper pole of the patella and 5 mm below the upper pole of patella. The differences of measured parameters were compared before surgery and at follow-up, including CSA of VMO and CSA/BW. Test level α = 0.05.

RESULTS

The tibial tubercle-trochlear groove (TT-TG) distance was significantly reduced at follow-up compared with that before surgery (27.91 ± 1.95 mm vs 12.33 ± 1.07 mm, P < 0.001). The CSA of VMO was significantly increased at follow-up compared with that before surgery at 5 mm below the upper pole of the patella (473.06 ± 106.32 mm² vs 562.97 ± 157.90 mm², P < 0.001), at the upper pole of the patella (641.23 ± 188.45 mm² vs 700.23 ± 177.55 mm², P = 0.029), and at 5 mm above the upper pole of the patella (788.25 ± 238.62 mm² vs 849.79 ± 180.84 mm², P = 0.018). The CSA/BW was significantly increased at follow-up compared with that before surgery at 5 mm below the upper pole of the patella (7.83 ± 2.52 mm²/kg vs 9.22 ± 3.54 mm²/kg, P < 0.001), at the upper pole of the patella (10.48 ± 3.62 mm²/kg vs 11.42 ± 4.14 mm²/kg, P = 0.020), and at 5 mm above the upper pole of the patella (12.86 ± 4.65 mm²/kg vs 13.68 ± 3.86 mm²/kg, P = 0.017).

CONCLUSION

After tibial tubercle transfer combined with MPFL reconstruction, CSA of VMO increased in patients with RPD, which will help to enhance patellar stability and reduce recurrence.

The tibial tubercle-posterior cruciate ligament (TT-PCL) distance does not truly reflect the lateralization of the tibial tubercle

PURPOSE

The role of the tibial tubercle-posterior cruciate ligament (TT-PCL) and tibial tubercle-trochlear groove (TT-TG) in recurrent patellar instability (RPI) remains unclear. This study aims to confirm the validity of the TT-TG and TT-PCL in predicting RPI and to verify whether the TT-PCL can truly reflect the lateralization of the tibial tubercle.

METHODS

A total of 50 patients with RPI and 50 controls were recruited and underwent magnetic resonance imaging examinations. The TT-TG, TT-PCL, and tibial tubercle lateralization (TTL) were measured independently by two authors in a blinded and randomized fashion. T-test was used for parametric variances and the Mann-Whitney U and Chi-square tests were used for non-parametric variances. Pearson's product moment correlation coefficients were calculated to determine correlations between the defined measurements. The intraclass correlation coefficient was used to assess the reliability of the measurements.

RESULTS

All defined measurements showed excellent intra- and inter-observer reliability. The TT-TG distance, TT-PCL distance, and TTL were significantly greater in the PI group than in the control group. The AUC was highest for the TT-TG distance compared with that for the TT-PCL distance, and TTL were 0.798, 0.764, and 0.769, with the calculated cut-off value of 12.5 mm, 16.5 mm, and 66.1 percentages. There was a moderate correlation (r = 0.595) between the TT-TG distance and TTL, and a weak correlation (r = 0.430) between the TT-PCL distance and TTL.

CONCLUSION

Both the TT-TG distance and TT-PCL distance can be measured with excellent reliability on magnetic resonance imaging. The TT-TG distance, rather than the TT-PCL distance, has a better performance in predicting RPI. Most interestingly, the TT-PCL distance cannot reflect the real lateralization of TT. This study provides new information to evaluate TTL in patients with RPI.

LEVEL OF EVIDENCE

III.

Reliability of the Tibial Tubercle-Roman Arch Distance for Evaluating Tibial Tubercle Malposition and Predicting Patellar Dislocation via Magnetic Resonance Imaging

Background:

The tibial tubercle (TT)–trochlear groove (TT-TG) distance has low reproducibility in patients with a dysplastic trochlea, whereas the clinical value of the TT–posterior cruciate ligament (TT-PCL) distance remains controversial.

Purposes:

To establish a method to assess the position of the TT on magnetic resonance imaging (MRI) scans using the TT–Roman arch (TT-RA) distance, compare this method with the TT-TG and TT-PCL distance, and provide the pathological threshold value of the TT-RA distance in patients with patellar dislocation.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

The TT-RA distance, TT-TG distance, and TT-PCL distance were measured on MRI scans in 70 patients with a history of patellar dislocation and 70 healthy individuals. Inter- and intraobserver reliability of each measurement parameter were evaluated. The discriminatory capacity and the interrelationship of the 3 measurement parameters were investigated using Pearson correlation and the receiver operating characteristic curve. The pathological threshold values of these measurements were calculated according to the data of healthy individuals. Finally, logistic regression analysis was performed using these values.

Results:

Patients with patellar dislocation had a greater TT-RA distance compared with healthy individuals (18.05 ± 4.16 vs 13.86 ± 2.90 mm; P < .001). The TT-RA distance had a stronger diagnostic capacity, with an area under the curve of 0.802 compared with 0.625 for TT-PCL distance. Excellent reproducibility was seen for TT-RA distance measurement at any degree of trochlear dysplasia (all intraclass correlation coefficients [ICCs] >0.90). The inter- and intraobserver ICCs of the TT-TG distance measurements were extremely low for Dejour type D dysplasia (ICC, 0.509 and 0.616, respectively). The pathological TT-RA distance threshold was calculated as 19.5 mm. Logistic regression showed that patients with a TT-RA distance >19.5 mm were 11.7 times more likely to sustain patellar dislocation than were those with TT-RA distance less than this value.

Conclusion:

The TT-RA distance was a more reliable parameter with which to evaluate TT position than was TT-TG distance in patients with trochlear dysplasia. The TT-PCL distance was the least reliable among the 3 parameters studied.

Sports Medicine Image Modeling for Injury Prevention in Basketball Training

In order to solve the problem of sports medical image in basketball training, a sports medical image modeling research method based on injury prevention in basketball training was proposed. By the method, the current situation of sports injury in university basketball was investigated. At the same time, the injury factors were analyzed on four occasions, including basketball class, extracurricular activities, competition, and training. In order to reduce the occurrence of injury and enhance the security of basketball sports for nonbasketball students of physical education, combined with the problems and reasons, the corresponding suggestions were put forward. Through the experiment, it was found that the incidence of basketball injury for nonbasketball male university students was as high as 90.7%. The results of the experiment showed that it was necessary to enhance the awareness of self-protection, control emotions and exhibitionism, strengthen physical training, attach importance to basic skills training, do warm-up activities, stay focused, pay attention to exercise load, and prevent excessive fatigue.

Medialization of trochlear groove was correlated with extended lateral trochlear in trochlear dysplasia: a transverse CT analysis

Purpose

To investigate the difference of trochlear width between normal and dysplastic trochlear and to analyze whether the medialization of trochlear groove was correlated with abnormal width of trochlear facets in trochlear dysplasia.

Methods

This study involved CT scans of fifty knees with trochlear dysplasia (TD group) and fifty knees without obvious trochlear dysplasia (Normal group). The linear distance from the medial femoral epicondyle to the various reference points was measured on axial CT images which included the medial edge of medial trochlear facet (dMTE), trochlear groove (dTG), and the lateral edge of lateral trochlear facets (dLTE). The medial and lateral trochlear width was calculated and standardized by the width of the anatomical epicondylar axis. Pearson’s correlation analysis was performed between the dTG and the width of the medial and lateral trochlear.

Results

The reliability of the results was good. Intraclass correlation coefficient (ICC) ranged from 0.89 to 0.97. The dMTE was significantly greater in the TD group than the normal group (32.7 ± 5.1% vs. 29.6 ± 3.5%, p = 0.009). There was no significant difference in the dLTE between groups. The dTG was reduced in the TD group compared with the normal group (45.2 ± 4.1% vs. 49.1 ± 3.9%, p = 0.019). In the TD group, there was a significant reduction in the medial trochlear width (13.9 ± 4.1% vs. 19.4 ± 2.9%, p < 0.001) and a significant increase in the lateral trochlear width (31.3 ± 4.0% vs. 26.9 ± 3.6%, p < 0.001) compared with the normal group. The dTG was significantly correlated with the lateral trochlear width (r value = − 0.693, p < 0.001) and not correlated with the medial trochlear width (r value = 0.044, p = 0.766) in trochlear dysplasia.

Conclusions

This study demonstrated that dysplasia of trochlear morphology was related to the reduction of medial trochlear width and increase in lateral trochlear width. The medialization of trochlear groove was significantly correlated with the increased lateral trochlear width.

Tibial Tuberosity-Trochlear Groove Distance and Its Components in Patients with and without Episodic Patellar Dislocation: A Study of 781 Knees

BACKGROUND

The purposes of the present study were (1) to measure the tibial tuberosity-trochlear groove distance and its components with the knee in extension, (2) to determine their diagnostic performance in distinguishing between patients with and without episodic patellar dislocation, and (3) to investigate the relationship of each component to the total tibial tuberosity-trochlear groove distance.

METHODS

We retrospectively reviewed computed tomography (CT) images of the knee joint in a group of patients with episodic patellar dislocation and a group of control subjects who were treated for another type of knee disorder in our institution between 2015 and 2021. Tibial tuberosity-trochlear groove distance, tibial tubercle lateralization, trochlear groove medialization, and knee rotation were measured on axial images. Partial correlation analysis of the measured parameters was performed after adjusting for remaining variables. Receiver operating characteristic (ROC) curves and the areas under the ROC curves (AUCs) were assessed to assess the diagnostic accuracy. A subgroup analysis based on femoral trochlear dysplasia classification was also performed.

RESULTS

After screening of 653 patients (947 knees) in our hospital's patient registry, a total of 521 patients (781 knees) were analyzed, including 541 knees (69.3%) with episodic patellar dislocation and 240 knees (30.7%) without episodic patellar dislocation (control group). The tibial tuberosity-trochlear groove distance demonstrated the best diagnostic performance, with the AUC being significantly better than that for other parameters (p < 0.001). The tibial tuberosity-trochlear groove distance was moderately to strongly correlated with knee rotation and trochlear groove medialization in the control and episodic patellar dislocation groups (p < 0.001). However, tibial tubercle lateralization showed a weak correlation with the tibial tuberosity-trochlear groove distance in the control group and moderate correlation in the episodic patellar dislocation group (p < 0.001). Knees with a type-D femoral trochlea had a significantly greater tibial tuberosity-trochlear groove distance than those with a type-A, B, or C femoral trochlea (p ≤ 0.011).

CONCLUSIONS

Tibial tuberosity-trochlear groove distance, a reliable predictor of episodic patellar dislocation, was affected more by knee rotation and trochlear groove medialization and was less affected by tibial tubercle lateralization, and it increased with an increasing grade of femoral trochlear dysplasia. The correlation of the tibial tuberosity-trochlear groove distance and its components as noted in the current study will help to achieve a better understanding of the tibial tuberosity-trochlear groove distance.

LEVEL OF EVIDENCE

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

The Patellar Instability Probability Calculator: A Multivariate-Based Model to Predict the Individual Risk of Recurrent Lateral Patellar Dislocation

BACKGROUND

Predicting the risk of recurrence is of great interest when counseling patients after primary lateral patellar dislocation (LPD).

PURPOSE

To investigate a multivariate model to predict the individual risk of recurrent LPD.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

The study population included patients with primary LPD, knee imaging, and a minimum 2-year follow-up after nonoperative treatment. Data including patient characteristics and anatomic patellar instability risk factors were collected retrospectively from 7 national study centers. Bivariate and multivariate regression analyses were carried out to identify risk factors for recurrent LPD and to generate an accuracy-optimized model for out-of-sample prediction.

RESULTS

In total, 115 of 201 patients (57%) experienced recurrent LPD within 2 years after primary LPD. Age ≤16 years at primary LPD (odds ratio [OR], 5.0), history of contralateral instability (OR, 2.4), and trochlear dysplasia (Dejour type B-D: OR, 2.5; lateral trochlear inclination ≤12°: OR, 2.7) were significant risk factors for recurrent LPD (P < .05). The prediction accuracy including these 3 risk factors was 79%. Patella alta, an increased tibial tubercle to trochlear groove distance, and patellar tilt had neither an association with increased recurrence rates nor an influence on prediction accuracy of recurrent LPD.

CONCLUSION

Young age and trochlear dysplasia are major risk factors for early recurrent LPD. A multivariate model including age at primary LPD, lateral trochlear inclination, and history of contralateral LPD achieved the highest prediction accuracy. Based on these findings, the patellar instability probability calculator is proposed to estimate the individual risk of early recurrence when counseling patients after primary LPD.

Ability of Medial Patellofemoral Ligament Reconstruction to Overcome Lateral Patellar Motion in the Presence of Trochlear Flattening: A Cadaveric Biomechanical Study

BACKGROUND

Medial patellofemoral ligament (MPFL) reconstruction is an established operative procedure to restore medial restraining force in patients with patellar instability. In the setting of a shallow sulcus, it is unclear whether an isolated MPFL reconstruction is sufficient to restore patellofemoral stability.

HYPOTHESIS

Progressively increasing the sulcus angle would have an adverse effect on the ability of an MPFL reconstruction to restrain lateral patellar motion.

STUDY DESIGN

Controlled laboratory study.

METHODS

Seven fresh-frozen human cadaveric knees were harvested and prepared for experimentation. Each specimen was run through the following test conditions: native, lateral retinacular release, lateral retinacular repair, MPFL release, MPFL reconstruction, and MPFL reconstruction with trochlear flattening. Four 3-dimensional printed wedges (10°, 20°, 30°, and 40°) were created to insert beneath the native trochlea to raise the sulcus angle incrementally and simulate progressive trochlear flattening. For each test condition, the knee was positioned at 0°, 15°, 30°, and 45° of flexion, and the force required to displace the patella 1 cm laterally at 10 mm/s was measured. Group comparisons were made with repeated measures analysis of variance.

RESULTS

In the setting of an MPFL reconstruction, as the trochlear groove was incrementally flattened, the force required to laterally displace the patella progressively decreased. A 10° increase in the sulcus angle significantly reduced the force at 15° (P = .01) and 30° (P = .03) of knee flexion. The force required to laterally displace the patella was also significantly lower at all knee flexion angles after the addition of the 20°, 30°, and 40° wedges (P≤ .05). Specifically, a 20° increase in the sulcus angle reduced the force by 29% to 36%; a 30° increase, by 35% to 43%; and a 40° increase, by 40% to 47%.

CONCLUSION

Despite an MPFL reconstruction, the force required to laterally displace the patella decreased as the sulcus angle was increased in our cadaveric model.

CLINICAL RELEVANCE

An isolated MPFL reconstruction may not be sufficient to restore patellar stability in the setting of a shallow or flat trochlea. Patients with an abnormal sulcus angle may have recurrent instability postoperatively if treated with an isolated MPFL reconstruction.

Conservative versus tailored surgical treatment in patients with first time lateral patella dislocation: a randomized-controlled trial

Background

Patellar instability has a high incidence and occurs particularly in young and female patients. If the patella dislocates for the first time, treatment is usually conservative. However, this cautious approach carries the risk of recurrence and of secondary pathologies such as osteochondral fractures. Moreover, there is also risk of continuous symptoms apparent, as recurrent patella dislocation is related to patellofemoral osteoarthritis as well. An initial surgical treatment could possibly avoid these consequences of recurrent patella dislocation.

Methods

A prospective, randomized-controlled trial design is applied. Patients with unilateral first-time patella dislocation will be considered for participation. Study participants will be randomized to either conservative treatment or to a tailored patella stabilizing treatment. In the conservative group, patients will use a knee brace and will be prescribed outpatient physical therapy. The surgical treatment will be performed in a tailored manner, addressing the pathologic anatomy that predisposes to patella dislocation.

The Banff Patellofemoral Instability-Instrument 2.0, recurrence rate, apprehension test, joint degeneration, and the Patella Instability Severity Score will serve as outcome parameters. The main analysis will focus on the difference in change of the scores between the two groups within a 2-year follow-up.

Statistical analysis will use linear mixed models. Power analysis was done for the comparison of the two study arms at 2-year follow-up with regard to the BPII Score. A sample size of N = 64 per study arm (128 overall) provides 80% power (alpha = 0.05, two-tailed) to detect a difference of 0.5 standard deviations in a t-test for independent samples.

Discussion

Although several studies have already dealt with this issue, there is still no consensus on the ideal treatment concept for primary patellar dislocation. Moreover, most of these studies show a unified surgical group, which means that all patients were treated with the same surgical procedure. This is regarded as a major limitation as surgical treatment of patella dislocation should depend on the patient’s anatomic pathologies leading to patellar instability. To our knowledge, this is the first study investigating whether patients with primary patella dislocation are better treated conservatively or operatively with tailored surgery to stabilize the patella.

Trial registration

The study will be prospectively registered in the publicly accessible database www.ClinicalTrials.gov.