Accuracy of tibial tuberosity-trochlear groove distance and tibial tuberosity-posterior cruciate ligament distance in terms of the severity of trochlear dysplasia

The Morphologic Patella Entry Point Into the Proximal Trochlea Is More Lateral in Recurrent Dislocators Than Controls as Measured by Entry Point-Trochlear Groove Angle

PURPOSE

To create a metric for evaluating the degree of laterality of the patella's entry into the trochlea, the entry point-trochlear groove (EP-TG) angle, and to evaluate if this laterality is associated with recurrent patella instability.

METHODS

The time frame of the study was January 2020 to February 2023. The inclusion criteria were patients treated by the senior author (J.P.F.) (with the exception of 2 patients who were treated by another provider at the institution who was aware of the study) who have been diagnosed with recurrent atraumatic patellar dislocations. Controls without knee pathology were selected from the New Mexico Decedent Imaging Database (NMDID). Simpleware ScanIP was used to create 3-dimensional (3D) models of the distal femurs from computed tomography scans. Anteroposterior images of these 3D models were uploaded to a custom EP-TG angle measuring tool. Three measurers used the tool to measure the EP-TG angle of the distal femurs.

RESULTS

Twenty-eight patients were included for the recurrent dislocator group. Twenty-four decedents from the NMDID were selected for the control group, each with a left or right knee chosen randomly for measurement. A 1-sided Mann-Whitney U test, used to evaluate whether the recurrent dislocators had higher EP-TG angle values, yielded a P value <.001, demonstrating a high level of significance. A Bayesian mixed-effect model, used to determine how different the EP-TG angles are between the 2 groups, gave a posterior predictive interval of [11.93°, 19.12°] for the EP-TG angle shift of dislocators. The intraclass correlation coefficient was 0.648.

CONCLUSIONS

The morphologic entry point of the patella into the proximal trochlea is more lateral in recurrent patella dislocators than in controls. This increased laterality can be measured by the EP-TG angle, which may be useful information for optimizing treatment of recurrent patella instability.

LEVEL OF EVIDENCE

Level III, case control study.

Patellofemoral Instability: Preoperative Considerations and Postoperative Imaging

Patellofemoral instability is common, often affecting young female patients. It contributes to significant morbidity, such as pain and premature osteoarthritis. Patient presentation varies, from acute instability events to chronic/recurrent instability. This article provides a detailed description of the anatomy and biomechanics of the patellofemoral joint and relates it to the pathology of patellofemoral instability. There are well-recognized predisposing anatomical factors, such as trochlear morphology, patella height, excessive lateralization of the tibial tubercle, excessive valgus alignment, and femoral or tibial torsion.Diagnosis of patellofemoral instability requires a thorough clinical history and physical examination, combined with a multimodality imaging approach. Imaging is useful in surgical planning to define the severity of predisposing anatomical factors and to detect postoperative complications. The operative management of patellofemoral instability targets predisposing anatomical factors, such as medial stabilizing ligament reconstruction or repair, tibial tubercle osteotomy, femoral trochleoplasty, coronal plane realignment osteotomy, and torsional osteotomy.

Patellar tendon lateral deviation angle: a new computed tomography scan measurement for evaluation of patellar instability

BACKGROUND

The tibial tuberosity-trochlear groove (TT-TG) distance is an important reference for the evaluation of patellar instability. However, measurement of the TT-TG distance has disadvantages with relatively low reproducibility. This study aimed to investigate the reliability of patellar tendon lateral deviation angle (PTLD-A) measured on a single computed tomography (CT) slice and the clinical significance for predicting patellar instability.

METHODS

Seventy-eight knees with recurrent patellar dislocation were included as the study group, and 76 normal knees in the control group. The PTLD-A and the TT-TG distance were measured on CT images, inter- and intra-observer reproducibility were assessed, and correlation was analyzed, and compared between the groups. The predictive value of both measurements for patellar instability was examined using the receiver operating characteristic curve, and the cut-off value was predicted using the Youden index.

RESULTS

Inter- and intra-observer reproducibility of PTLD-A was better than TT-TG distance in both groups as well as across all extents of trochlear types. The correlation between the two measurements was strong (r = 0.756, P < 0.001). Notably, both measurements were significantly higher in the study group than in the control group (P < 0.05). PTLD-A showed high predictive value for patellar instability, whereas TT-TG distance showed medium predictive value. A PTLD-A value of ≥ 13.7° was the threshold for diagnosis of patellar instability.

CONCLUSION

PTLD-A measured on a single computed tomography slice of the distal femoral trochlear groove is more reliable than TT-TG distance for prediction of patellar instability. A PTLD-A ≥ 13.7° predicts patellar instability.

Tibial Tubercle Osteotomy: Indications, Outcomes, and Complications

PURPOSE OF REVIEW

The tibial tubercle osteotomy (TTO) is a versatile surgical technique used to treat a range of patellofemoral disorders, including patellar instability, painful malalignment, focal chondral defects, and patellar maltracking that have failed conservative therapies. TTO is a personalized procedure that can be tailored to the pathoanatomy of the patient based on physical examination and imaging. The complication rate associated with TTO strongly depends on the indication for surgery, the severity of the patient's condition, and the surgical approach. Despite the literature on TTO, to our knowledge, no single source has addressed the indications, techniques, outcomes, and complications of this procedure. The purpose of this article is to serve as such a valuable resource.

RECENT FINDINGS

Highlights from recent studies we would like to emphasize are two-fold. First, maintaining a distal cortical hinge yields lower complication rates than osteotomies involving complete tubercle detachment with classic or standard techniques. Second, based on current evidence, TTO consistently provides symptomatic relief, and most patients can return to work or sport at their pre-operative level within 3 and 6 months, respectively. TTO is a personalizable surgical technique that may be utilized for multiple patellofemoral disorders and is associated with good outcomes.

The diagnostic value of TT-TG and TT-ME distances in the assessment of patellofemoral instability

PURPOSE

This study aims to evaluate the application value of the tibial tubercle-trochlear groove distance (TT-TG distance) and tibial tubercle-midepicondyle distance (TT-ME distance) on CT images in patellofemoral instability, and further investigate the association between knee joint rotation angles and patellofemoral instability.

METHODS

We retrospectively analyzed CT image data of 59 patients with patellar dislocation (case group) and 39 normal knee joints (control group). We measured the TT-TG distance, TT-ME distance, and knee joint rotation angle (KJRA) of both groups, and the related indicators were analyzed using single-factor/multi-factor binary logistic stepwise regression analysis. Two senior radiologists were assigned to assess the inter-rater reliability. Interclass correlation coefficients (ICC) were calculated. Finally, we used receiver operating characteristic (ROC) curves to compare the diagnostic efficiency of these indicators in patellofemoral instability.

RESULTS

The results found significant differences between both groups in terms of TT-TG distance, TT-ME distance, KJRA angle, age, location, and gender (P < 0.05). In terms of inter-rater reliability, TT-TG distance and TT-ME distance ratios showed an excellent correlation between observers (TT-TG inter-rater ICC 0.969, TT-ME inter-rater ICC 0.955). Univariate logistic regression analysis indicated that except for location and gender, all other factors significantly affected patellofemoral instability (P < 0.05). The multivariate logistic regression analysis revealed that the TT-ME distance, age, and KJRA angle were statistically significant factors related to patellofemoral instability, with TT-ME distance being a risk factor for patellofemoral instability (OR value 1.572, P value 0.000). Moreover, the ROC curve analysis demonstrated that the diagnostic capability of the TT-ME distance for detecting patellofemoral instability was higher than that of the TT-TG distance and KJRA (AUC were 0.912, 0.851, and 0.735, respectively).

CONCLUSION

The TT-ME distance, age, and knee joint rotation angle are factors that affect patellofemoral instability. The TT-ME distance has better diagnostic efficiency for patellofemoral instability compared to the TT-TG distance and knee joint rotation angle.

Femoral anteversion angle is more advantageous than TT-TG distance in evaluating patellar dislocation: A retrospective cohort study

PURPOSE

The purpose of this study is to report the parameter characteristics of the femoral anteversion angle (FAA) and tibial tubercle-trochlear groove (TT-TG) distance in patients with patellar instability compared to healthy individuals and to evaluate their reliability in predicting patellar dislocation, providing potential indications for osteotomy.

METHODS

A retrospective collection of consecutive patients with patellar instability constituted the study group, while individuals without patellofemoral disorder served as the control group. Measurement of the FAA and TT-TG distance were conducted by lower extremity computed tomography scans and knees with true patellar dislocation were recorded. The diagnostic capability of the FAA and TT-TG distance was assessed using receiver operating characteristic curves and area under the curve (AUC), determining the pathological values by sensitivity and specificity.

RESULTS

The FAA (21.6 ± 9.0°) and TT-TG distance (20.1 ± 4.8 mm) in the study group were significantly greater than the control group (10.6 ± 7.9° and 15.6 ± 4.6 mm, respectively) (p < 0.001). The AUCs for patellar dislocation were 0.869 for FAA and 0.712 for TT-TG distance, with pathological cut-off values of 18.2° and 18.2 mm, respectively. The odds ratios for FAA and TT-TG distance were 1.185 and 1.125, respectively (p < 0.05).

CONCLUSIONS

Patients with patellar instability exhibited significantly greater FAA and TT-TG distance compared to healthy individuals. The FAA demonstrated superior predictive capability for patellar dislocation compared to the TT-TG distance. The FAA (>18.2°) measured by surgical transepicondylar axis and TT-TG distance (>18.2 mm) were the potential pathological thresholds. Additionally, an increase of 1° in FAA and 1 mm in TT-TG distance was associated with a 18.5% and 12.5% increased risk of patellar dislocation, respectively. Surgeons should be aware of the risk of patellar dislocation associated with rotational malalignment.

LEVEL OF EVIDENCE

Level III.

Medial orientation of the trochlear groove is a strong indicator of high-grade trochlear dysplasia

PURPOSE

The objective is to evaluate the orientation of the trochlear groove in patients with objective patellar instability (OPI) compared to a control group. The hypothesis is that the trochlear groove angle (TGA) is correlated with the severity of the trochlear dysplasia.

METHODS

From 2019 to 2023, magnetic resonance imaging of 82 knees with OPI were compared with 82 control knees. TGA quantified the angle between the femoral anatomical axis and the trochlear groove. The intraclass correlation coefficient for TGA was evaluated. Central spur in the sagittal plane (CSSP) and cranial trochlear orientation (CTO) angle were also measured. TGA, CSSP and CTO were compared between the two groups. A TGA subgroup analysis separating the OPI group into low-grade (CSSP < 5 mm or negative CTO) and high-grade dysplasia (CSSP ≥ 5 mm or positive CTO) was also performed.

RESULTS

A significant difference (p < 0.001) was found between the TGA of the OPI group (mean [SD], 11.3 [3.7]°) and the control group (4.2 [2.5]°). TGA for patients with high-grade dysplasia (11.9 [3.8]°) was significantly higher than patients with low-grade dysplasia (9.6 [3.9]°).

CONCLUSION

Patients with OPI have a TGA of 11°, compared to the control group, which exhibits a TGA of 4°. The femoral mechanical axis can be considered an appropriate threshold for separating these two groups. Furthermore, TGA is correlated with the severity of dysplasia.

STUDY DESIGN

Case-control study.

LEVEL OF EVIDENCE

Level III.

Isolated Medial Patellofemoral Ligament Reconstruction Results in Lower Failure and Complication Rates Than Isolated Trochleoplasty and Tibial Tubercle Osteotomy: A Systematic Review

PURPOSE

To evaluate outcomes and complications of isolated medial patellofemoral ligament reconstruction (MPFLR), tibial tubercle osteotomy (TTO), and trochleoplasty for management of patellar instability.

METHODS

A query of Scopus, PubMed, Google Scholar, Cochrane CENTRAL Register of Controlled Trials, and the Cochrane Database of Systematic Reviews was performed in accordance with 2020 Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Included studies reported clinical outcome data after isolated MPFLR, TTO, or trochleoplasty for patellar instability with a minimum 12-month follow-up. Meta-analysis and data aggregation was not performed.

RESULTS

Thirty-six studies (5 trochleoplasty, 14 TTO, and 18 MPFLR) consisting of 1,389 patients (114 trochleoplasty, 374 TTO, and 1,001 MPFLR) were included. Risk of bias was assessed with the Methodological Index for Non-Randomized Studies score, which ranged from 11 to 12 in trochleoplasty, 10 to 18 in TTO, and 8 to 18 in MPFLR studies. Patient-reported outcome measures, including Lysholm score (trochleoplasty: 51.1-71 to 71-95; TTO: 57-63.3 to 84-98; MPFLR: 37.4-59.1 to 74-92.5), Kujala score (trochleoplasty: 56-71 to 78-92; TTO: 48.6-68 to 78-92; MPFLR: 53.3-60 to 81.5-92), visual analog scale for pain (trochleoplasty: 52-25; TTO: 54-76 to 14-27; MPFLR: 29 to 17, out of 100), and Tegner score (TTO: 3-4 to 3-4; MPFLR: 2.5-6 to 4.9-5), improved after all surgeries. Failure rates ranged from 0% to 33.3% after MPFLR, 0% to 30.8% after TTO, and 5.3% to 40% after trochleoplasty. Complication rates ranged from 0% to 14.7% after MPFLR, 1.6% to 58.3% after TTO, and 8% to 26.3% after trochleoplasty.

CONCLUSIONS

Isolated MPFLR, TTO, or trochleoplasty may be effective treatment options for patellar stabilization. Although failure rates were highest after isolated trochleoplasty and complication rates were highest after TTO, these procedures are not interchangeable as each addresses a specific pathology.

LEVEL OF EVIDENCE

Level IV, systematic review of Level II to IV studies.

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.

Increased TT-TG distance caused by excessive tibiofemoral rotation predicts poor clinical outcomes after tibial tubercle osteotomy in recurrent patellar dislocation

PURPOSE

To compare clinical outcome between recurrent patellar dislocation (RPD) with or without actual tibial tubercle lateralisation (TTL) after medial patellofemoral ligament reconstruction (MPFL-R) combined with tibial tubercle transfer.

METHODS

From 2015 to 2018, a total of 172 knees with RPD and a tibial tubercle-trochlear groove (TT-TG) distance of > 20 mm were treated with MPFL-R combined with tibial tubercle transfer. Patients were divided into the lateralisation group (TT-PCL > 24 mm, n = 74) and the nonlateralisation group (TT-PCL ≤ 24 mm, n = 60) based on the presence or absence of actual TTL (TT-PCL > 24 mm). Clinical outcomes were assessed postoperatively at a minimum of 2 years. Second-look arthroscopic evaluations were available for 84 knees to assess cartilage damage.

RESULTS

A total of 134 knees with a median follow-up time of 32 months were included. Tibiofemoral rotation (TFR) was significantly higher in the nonlateralisation group than in the lateralisation group (15.4° vs. 9.4°, P < 0.001). At the final follow-up, the nonlateralisation group had significantly lower Kujala (78.2 vs. 86.4, P = 0.001) and Lysholm (80.3 vs. 88.2, P = 0.003) scores than the lateralisation group. At the time of the second-look arthroscopic assessment, 38.9% of the patients in the nonlateralisation group showed cartilage worsening in the medial patellar facet that was significantly higher than that in the lateralisation group (38.9% vs. 12.5%, P = 0.015).

CONCLUSION

Patients with RPD and an increased TT-TG distance of > 20 mm but without actual tibial tubercle lateralisation benefit less from tibial tubercle transfer than patients with actual tibial tubercle lateralisation, which may be related to the significantly higher tibiofemoral rotation angle of the former.

LEVEL OF EVIDENCE

III.

Tibial Tubercle-Trochlear Groove Distance Has Better Diagnostic Reliability Than Tubercle-Posterior Cruciate Ligament Distance For Predicting Patellar Instability: A Systematic Review

OBJECTIVE

The tibial tubercle-trochlear groove (TT-TG) distance is now routinely utilized to help determine whether a realignment procedure is necessary for patients with patellar instability. The tibial tubercle-posterior cruciate ligament (TT-PCL) distance has been explored as an alternative measurement. The aim of this study is to compare the reliability of TT-TG and TT-PCL; to explore whether there is a relationship between the TT-PCL and the TT-TG distance; to determine whether there is a relationship between the TT-TG and TT-PCL distances and knee rotation; and to compare the abilities of the TT-PCL distance and the TT-TG distance with predicted patellar instability.

METHOD

This systematic review was performed in accordance with PRISMA guidelines. Three databases, PubMed, EMBASE, and Cochrane Central Register of Controlled Trials, were searched from inception to September 2021 to identify clinical studies comparing TT-TG and TT-PCL distances to patellar instability. Data on patient baseline characteristics, TT-TG and TT-PCL distances, inter-observer reliability, and area under the receiver-operating characteristic curve (AUC) were recorded. The methodological quality of the studies was assessed using the quality assessment form recommended by the Agency for Healthcare Research and Quality (AHRQ).

RESULT

Twenty studies were included in the final analysis, comprising 2330 knees from 2260 patients. The current study showed that TT-TG and TT-PCL have similar observer reliability. The inter- and intra-observer reliability of TT-TG ranged from 0.807 to 0.98 and 0.553 to 0.99, respectively. The inter- and intra-observer reliability of TT-PCL ranged from 0.553 to 0.99 and 0.88 to 0.981, respectively. Six studies compared the AUC for predicting patellar instability and showed that TT-TG had better predictive performance than TT-PCL. Three studies reported a correlation between TT-TG and knee rotation, but no such relationship was found for TT-PCL. Eight studies reported a weak or moderate correlation between TT-TG and TT-PCL.

CONCLUSION

TT-TG and TT-PCL have similar inter- and intra-rater reliability (as measured by ICC), but TT-TG has greater discriminatory power to predict patellar instability than TT-PCL (as measured by AUC values and odds ratio). However, considering trochlear dysplasia and individual variations, future studies need to find more accurate and individualized methods to predict patellar instability.

Medial patellofemoral ligament reconstruction and tibial tuberosity transfer can be used to successfully manage patellofemoral instability in the setting of trochlea dysplasia

BACKGROUND

Management of patella instability remains a challenge particularly in the presence of trochlea dysplasia. The aim of this study is to assess the recurrence rates of those with patellar instability who have undergone a combined tibial tuberosity transfer (TTT) and medial patellofemoral ligament reconstruction (MPFLR) in the setting of trochlea dysplasia.

METHODS

All skeletally mature patients who underwent combined TTT and MPFLR for recurrent patella instability were identified between January 2009 and December 2019. A retrospective review was conducted, with information regarding re-dislocation/subluxation and complications collected.

RESULTS

Seventy patients with a mean age 25.3 years were identified and evaluated. Thirteen patients were found to have low-grade dysplasia (Dejour A), with 57 patients having high-grade dysplasia (Dejour B/C/D). No patients in the low,grade dysplasia group suffered a recurrence of their symptoms, with four in the high-grade group suffering episodes of re-dislocation/subluxation. Three patients subsequently underwent a trochleoplasty, with the other patient managed successfully non-operatively. There were a total of 13 complications in 11 patients.

CONCLUSIONS

A combined procedure of MPFLR and TTT can be used to manage patellofemoral instability even in the setting of trochlea dysplasia with a low rate of recurrence. Trochlea dysplasia, however, remains an anatomical risk factor for recurrence and patients should be counselled accordingly. The anatomical risk factors should be assessed in all patients to allow for the development of the most appropriate management plan, of which this combined procedure represents a potentially successful option.

LEVEL OF EVIDENCE

IV (Case Series).

Tibial tubercle to trochlear groove distance versus tibial tubercle to posterior cruciate ligament distance for predicting patellar instability: a systematic review

PURPOSE

To determine the reliability and diagnostic accuracy of tibial tubercle-trochlear groove (TT-TG) distance versus tibial tubercle-posterior cruciate ligament (TT-PCL) distance, and to determine cutoff values of these measurements for pathological diagnosis in the context of patellar instability.

METHODS

Three databases MEDLINE, PubMed and EMBASE were searched from inception to October 5, 2022 for literature outlining comparisons between TT-TG and TT-PCL in patellar instability patients. The authors adhered to the PRISMA and R-AMSTAR guidelines as well as the Cochrane Handbook for Systematic Reviews of Interventions. Data on inter-rater and intra-rater reliability, receiver-operating characteristic (ROC) curve parameters such as area under the curve (AUC), sensitivity and specificity, as well as odds ratios, cutoff values for pathological diagnosis and correlations between TT-TG and TT-PCL were recorded. The MINORS score was used for all studies in order to perform a quality assessment of included studies.

RESULTS

A total of 23 studies comprising 2839 patients (2922 knees) were included in this review. Inter-rater reliability ranged from 0.71 to 0.98 and 0.55 to 0.99 for TT-TG and TT-PCL, respectively. Intra-rater reliability ranged from 0.74 to 0.99 and 0.88 to 0.98 for TT-TG and TT-PCL, respectively. AUC measuring diagnostic accuracy of patellar instability for TT-TG ranged from 0.80 to 0.84 and 0.58 to 0.76 for TT-PCL. Five studies found TT-TG to have more discriminatory power than TT-PCL at distinguishing patients with patellar instability from patients who do not. Sensitivity and specificity ranged from 21 to 85% and 62 to 100%, respectively, for TT-TG. Sensitivity and specificity ranged from 30 to 76% and 46 to 86%, respectively, for TT-PCL. Odds ratio values ranged from 1.06 to 14.02 for TT-TG and 0.98 to 6.47 for TT-PCL. Proposed cutoff TT-TG and TT-PCL values for predicting patellar instability ranged from 15.0 to 21.4 mm and 19.8 to 28.0 mm, respectively. Eight studies reported significant positive correlations between TT-TG and TT-PCL.

CONCLUSION

TT-TG resulted in overall similar reliability, sensitivity and specificity as TT-PCL; however, TT-TG has better diagnostic accuracy than TT-PCL in the context of patellar instability as per AUC and odds ratio values.

LEVEL OF EVIDENCE

Level IV.

Lateral Patellar Instability

➤

Patellar instability represents a common problem with an evolving understanding and multifactorial pathoetiology. Treatment plans should be based on the identification of contributing anatomical factors and tailored to each individual patient.

➤

Risks for recurrent instability are dependent on several patient-specific factors including patella alta, increased tibial tubercle-to-trochlear groove (TT-TG) distance, trochlear dysplasia, younger skeletal age, and ligamentous laxity.

➤

Cartilage or osteochondral lesions and/or fractures are commonly observed in first-time patellar dislocation, and magnetic resonance imaging (MRI) should be strongly considered. Advanced imaging modalities, such as computed tomography (CT) or MRI, should also be obtained preoperatively to identify predisposing factors and guide surgical treatment.

➤

Medial patellofemoral ligament (MPFL) reconstruction with anatomical femoral tunnel positioning is associated with lower recurrence rates compared with MPFL repair and has become a common and successful reconstructive surgical option in cases of instability.

➤

Lateral retinacular tightness can be addressed with lateral retinacular release or lengthening, but these procedures should not be performed in isolation.

➤

Tibial tubercle osteotomy is a powerful reconstructive tool in the setting of underlying skeletal risk factors for instability and can be of particular benefit in the presence of increased TT-TG distance (>20 mm), and/or in the setting of patella alta.

➤

The indications for trochleoplasty are still developing along with the clinical evidence, but trochleoplasty may be indicated in some cases of severe trochlear dysplasia. Several surgical techniques have indications in specific clinical scenarios and populations, and indications, risks, and benefits to each are progressing with our understanding.

➤

Combined femoral derotational osteotomy and MPFL reconstruction can be considered for patients with a femoral anteversion angle of >30° to improve patient outcomes and reduce recurrence rates.

Factors That Affect the Magnitude of Tibial Tubercle-Trochlear Groove Distance in Patients With Patellar Instability

BACKGROUND

Tibial tubercle-trochlear groove (TT-TG) distance is a risk factor for recurrent patellar dislocation and is often included in algorithmic treatment of instability. The underlying factors that determine TT-TG have yet to be clearly described in orthopaedic literature.

PURPOSE/HYPOTHESIS

The purpose of our study was to determine the underlying anatomic factors contributing to TT-TG distance. We hypothesized that degree of tubercle lateralization and knee rotation angle may substantially predict TT-TG.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

All patients evaluated for patellar instability at a single institution between 2013 and 2021 were included. Patients with previous knee osseous procedures were excluded. TT-TG and its anatomic relationship to patellofemoral measures, including dysplasia, femoral anteversion, tibial tubercle lateralization, knee rotation angle, and tibial torsion, were measured and subsequently quantified using univariate and multivariable analysis.

RESULTS

In total, 76 patients met the inclusion criteria (46 female, 30 male; mean ± SD age, 20.6 ± 8.6 years) and were evaluated. Mean TT-TG was 16.2 ± 5.4 mm. On univariate analysis, increasing knee rotation angle (P < .01), tibial tubercle lateralization (P = .02), and tibial torsion (P = .01) were associated with increased TT-TG. In dysplastic cases, patients without medial hypoplasia (Dejour A or B) demonstrated significantly increased TT-TG (18.1 ± 5.4 mm) as compared with those with medial hypoplasia (Dejour C or D; TT-TG: 14.9 ± 5.2 mm; P = .02). Multivariable analysis revealed that increased knee rotation angle (+0.43-mm TT-TG per degree; P < .01) and tubercle lateralization (+0.19-mm TT-TG per percentage lateralization; P < .01) were statistically significant determinants of increased TT-TG distance. Upon accounting for these factors, tibial torsion, trochlear width, and medial hypoplasia were no longer significant components in predicting TT-TG (P≥ .54). Of note, all patients with TT-TG ≥20 mm had tibial tubercle lateralization ≥68%, a knee rotation angle ≥5.8°, or both factors concurrently.

CONCLUSION

TT-TG distance is most influenced by knee rotation angle and tibial tubercle lateralization.

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.

Patellar Tendon-Trochlear Groove Angle Measured on a Single Computed Tomography Slice of the Distal Femoral Trochlear Groove Is a Reliable Measurement for the Evaluation of Patellar Instability

PURPOSE

To verify the reliability of patellar tendon-trochlear groove angle (PTTG-A) measured by computed tomography (CT) and the clinical significance in evaluation of patellar instability.

METHODS

A retrospective study of hospitalized patients with knee pain or injury and had knee CT from January 2017 to June 2021 was performed. PTTG-A and tibial tuberosity-trochlear groove (TT-TG) distance were measured on CT. Spearman correlation analysis was analyzed between the 2 measurements. The intraclass correlation coefficient was determined for inter- and intraobserver reproducibility. The capacity of PTTG-A and TT-TG to predict patellar instability was evaluated by the receiver operating characteristic curve. Data from the control group were used to determine the pathologic thresholds and logistic regression analysis.

RESULTS

Included were 113 patients. There were 60 patients with the history of at least 2 episodes of patellar dislocation (study group) and 53 patients without a history of patellar dislocation (control group). The respective PTTG-A and TT-TG distances in the study group (35.2 ± 8.4° and 19.6 ± 4.6 mm) were significantly greater than those of the controls (20.8 ± 5.8° and 13.3 ± 4.5 mm) (P < .001). The correlation between the 2 measurements was strong (r = 0.730, P < .001). The inter- and intraobserver reliability of the PTTG-A were better than TT-TG distance in both groups. The AUC of PTTG-A was greater than that of the TT-TG distance (0.895 vs 0.769, respectively). With the cutoff value of PTTG-A and TT-TG being 26.3° and 16.3 mm, the value of the pathologic threshold of PTTG-A was 30.0°, with a dominance ratio of 16.88 (95% confidence interval 2.88-98.89, P = .002).

CONCLUSIONS

The PTTG-A measured on a single CT slice of the distal femoral trochlear groove is a more reliable measurement than TT-TG distance for the prediction of patellar instability.

LEVEL OF EVIDENCE

III; A retrospective cohort study.

Assessment of the reliability and validity of imaging measurements for patellofemoral instability: an updated systematic review

OBJECTIVE

To provide an update on the reliability and validity of all radiological measures used to assess patients presenting with patellofemoral instability.

METHODS

A search of the CINHAL, EMBASE, MEDLINE, and SCOPUS databases and the Cochrane library was conducted. All studies assessing the validity, reliability, sensitivity, and specificity of radiological measures of the patellofemoral joints of patients with patellofemoral instability from 2010 onwards were considered for inclusion. Discrimination validity, inter- and intra-observer reliability, and the sensitivity and specificity of specific imaging measures were evaluated.

RESULTS

Seventy-three studies met the selection criteria and were included for analysis. We identified eight radiological measures in four categories with good reliability and validity: the tibial tubercle to trochlear groove distance, specific measures of patellar height (Blackburne-Peel index, Caton-Deschamps index and Insall-Salvati ratios), three measures of trochlear dysplasia (sulcus angle, trochlear depth, and lateral trochlear inclination), and the tibial tubercle to posterior cruciate ligament distance. No included studies examined the reliability and validity of patellofemoral instability ultrasound measures.

CONCLUSION

Our updated review demonstrated good inter- and intra-observer reliability and discrimination validity for the tibial tubercle-trochlear groove distance, specific patellar height, and trochlear dysplasia measures on MRI. The tibial tubercle to posterior cruciate ligament distance, an indirect measure of rotational asymmetry, was a valid and reliable measure on MRI. Due to a lack of assessments across more than one study, there are a variety of proposed measures with insufficient evidence to determine their validity, reliability, sensitivity, and specificity.

Application of CT-MRI Fusion-Based Three-Dimensional Reconstruction Technique in the Anatomic Study of Posterior Cruciate Ligament

Objective

During PCL reconstruction surgery, precise and personalized positioning of the graft tunnel is very important. In order to obtain patient‐specific anatomical data, we established a three‐dimensional knee joint fusion model to provide a unified imaging strategy, as well as anatomical information, for individualized and accurate posterior cruciate ligament (PCL) reconstruction.

Methods

This is an exploration study. From January 2019 to January 2020, 20 healthy adults randomly were enrolled and assessed via CT and MRI imaging. A three‐dimensional fusion model of the knee joint was generated using the modified MIMIMICS and image fusion software. On the fused image, the areas of the femoral and tibial PCL footprint of both knees were measured. The anatomical center of the PCL footprint was measured at the femoral and tibial ends. The relevant bony landmarks surrounding the PCL femoral and tibial attachment were also measured. Paired t‐tests were employed for all statistical analyzes, and p < 0.05 was considered as statistically significant.

Results

All 20 subjects achieved successful image fusion modeling and measurement, with an average duration of 12 h. The lengths of the LF1‐LF3 were 32.1 ± 1.8, 6.8 ± 2.5, and 23.3 ± 2.1 mm, respectively. The lengths of the LT1‐LT3 were 37.3 ± 3.3, 45.6 ± 5.3, and 6.0 ± 1.2 mm, respectively. The distances between the tibial PCL center of the left knee to the medial groove, champagne‐glass drop‐off, and the apex of the medial intercondylar were 8.4 ± 2.4, 9.2 ± 1.8, and 15.3 ± 1.4 mm, respectively, and the corresponding distances from the right knee were 8.0 ± 2.0, 9.4 ± 2.2, and 16.1 ± 1.8 mm, respectively. We observed no difference between the bilateral sides, in terms of the distance from the PCL center to the PCL attachment‐related landmark, under arthroscopic guidance. The area of the femoral and tibial PCL footprints on the left knee were 115.3 ± 33.5 and 146.6 ± 24.4 mm², respectively, and the corresponding areas on the right knee were 121.8 ± 35.6 and 142.8 ± 19.5 mm², respectively. There was no difference between the bilateral sides in terms of the PCL footprint areas.

Conclusion

In the fusion image, the PCL attachment center and relevant bony landmarks which can be easily identified under arthroscopy can be accurately measured. The model can also obtain personalized anatomical data of the PCL on the unaffected side of the patient, which can guide clinical PCL reconstruction.

Tibial Tubercle to Trochlear Groove Distance Measured by Posterior Condylar Reference Line on MRI Can Over-Evaluate Lateralization Deformity of Tibial Tubercle in Patients with Recurrent Patellar Dislocation

Background: The tibial tubercle to trochlear groove (TT-TG) distance is currently considered as an indication for tibial tubercle osteotomy. While the influence of femoral condylar morphology on such measurement remains unclear. Methods: A total of 86 patients with patellar dislocation (PD) and 86 healthy individuals were enrolled. Femoral condylar morphology and the TT-TG distance measured by anatomical transepicondylar axis (TT-TGa), by surgical transepicondylar axis (TT-TGs), and by posterior condylar reference line (TT-TGp) were assessed by MRI. Unpaired t-test, Spearman, and Pearson correlation analysis were conducted. We determined the pathological value of the parameters and established a binary regression model. Results: The interclass correlation coefficients of all the TT-TG distances were greater than 0.75 in all types of trochlear dysplasia. The lateral/posterior femoral condyle was shorter and the medial/posterior condyle was longer in the study group (28.5 ± 3.3 and 35.2 ± 2.8, respectively) than in the control group (30.9 ± 2.7 and 33.5 ± 2.3, respectively). In the study group, the TT-TGp distance was greater than TT-TGs and TT-TGa distance (p < 0.001). The pathological value of the TT-TG distance was 13.0 mm. Each TT-TG distance revealed a significant OR with regard to PD. Conclusion: The TT-TGa, TT-TGs, and TT-TGp distance can be reliably measured by MRI even in patients with trochlear dysplasia. While the TT-TGp distance may overestimate the lateralization deformity of the tibial tubercle. Posterior femoral condylar dysplasia may be a reason for such overestimating. These findings have not been correlated to clinical outcomes and further studies are required.

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.