Bisect offset ratio and cartilaginous sulcus angle are good combined predictors of recurrent patellar dislocation in children and adolescents

Application of a machine learning and optimization method to predict patellofemoral instability risk factors in children and adolescents

PURPOSE

Conservative treatment remains the standard approach for first-time patellar dislocations. While risk factors for patellofemoral instability, a common paediatric injury, are well-established in adults, data concerning the progression of paediatric recurrent patellar dislocation remain scarce. A reproducible method was developed to quantitatively assess the patellofemoral morphology and anatomic risk factors in paediatric patients using magnetic resonance imaging (MRI) and machine learning analysis.

METHODS

Data were analyzed from a retrospective review (2005-2022) of paediatric patients diagnosed with acute lateral patellar dislocation (54 patients) who underwent MRI and were compared with an age-based control group (54 patients). Patellofemoral, tibial, tibiofemoral and patellar height parameters were measured. Differences between groups were analyzed with respect to MRI parameters. The potential diagnostic utility of the parameters was assessed via machine learning and genetic algorithm analyses.

RESULTS

Significant differences were observed between the two groups in six patellofemoral morphological parameters. Regarding patellar height morphological parameters, all methods exhibited significant between-group differences. Among the tibia and tibiofemoral morphological parameters, only the tibial tubercle-trochlear groove distance exhibited significant differences between the two groups. No sex-related differences were present. Significant variations were observed in patellar height parameters, particularly in the Koshino-Sugimoto (KS) index, which had the highest area under the curve (AUC: 0.87). Using genetic algorithms and logistic regression, our model excelled with seven key independent variables.

CONCLUSION

KS index and Wiberg index had the strongest association with lateral patellar dislocation. An optimized logistic regression model achieved an AUC of 0.934. Such performance is considered clinically relevant, indicating the model's effectiveness for the intended application.

LEVEL OF EVIDENCE

Level Ⅲ.

Patho-morphology of patellar instability in children and adolescents: A systematic review and meta-analysis

BACKGROUND

Children and adolescents have the highest incidence of patellar instability among the population. We aimed to identify patho-morphological and epidemiological factors associated with patellar instability, and to identify factors predisposing to recurrence in children and adolescents.

METHODS

Published and unpublished literature databases, conference proceedings and the reference lists of included studies were searched to the 14th of March 2024. Studies were eligible if they compared history characteristics, examination features and radiological parameters between patients with and without instability, or evaluated risk factors for instability recurrence. A random-effects meta-analysis was performed. Included studies were appraised using tools respective of study design.

RESULTS

The evidence was moderate to low in quality. Forty-five studies (including 9000 patients) were eligible. Tibial tubercle - tibial groove (TT-TG) distance (weighted mean difference [WMD] 5.96 mm, 95% Confidence Interval [CI]: 4.94 to 6.99 mm), sulcus angle (WMD: 13.93˚, 95% CI: 9.1˚ to 18.8˚), and Insall-Salvati index (WMD: 0.2, 95% CI: 0.16 to 0.23) were greater in patients with patellar instability. Risk factors for recurrent dislocation included age less than 18 years (Odds ratio [OR]: 2.56, 95% CI: 1.63 to 4.0), skeletal immaturity (OR: 1.79, 95% CI: 1.21 to 2.64) and presence of trochlear dysplasia (OR: 3.37, 95% CI: 1.85 to 6.15).

CONCLUSION

Knowledge of patho-morphological factors associated with patellar instability could help explain its pathophysiological processes, allowing for the design of treatment approaches and the identification of patients at risk.

The Trochlear Paradox in Native Knees and Its Potential Impact on Total Knee Arthroplasty: An MRI-Based Correlation Study Investigating the Effect of Varying Posterior Femoral Condyle Angles on the Patellofemoral Joint

BACKGROUND

Since the beginning of total knee arthroplasty, implant alignment has been a central point of discussion. As diverse as the discussed alignment theories are, as uniform is the implant design, which is supposed to be based on the "average knee." Steady upgrades in prosthesis design and modern alignment theories have achieved improvements. However, knee arthroplasty continues to be burdened by a significant percentage of dissatisfied patients. In current knee arthroplasty, femoral implant alignment is referenced by the dorsal and distal condylar axes. The patellofemoral joint variance is not sufficiently considered. Predominantly dorsal and distal referencing at the femoral condyle determines the postoperative shape of the anterior knee joint. The present study investigated a possible relationship between dorsal and distal joint parameters and the patellofemoral joint.

METHODS

In this explorative retrospective monocentric study, MRI cross-sectional images of 100 native knee joints were evaluated. By determining parametric correlations according to Pearson, the study investigates whether the independent variables "posterior femoral condyle angle" and "lateral distal femoral angle" are related to "lateral trochlear inclination", "patella tilt", and "bisect offset".

RESULTS

The posterior condylar angle significantly correlates with lateral trochlear inclination, patella tilt, and bisect offset. There is a positive correlation with patella tilt and bisect offset but a negative correlation with lateral trochlear inclination. The lateral distal femoral angle did not correlate with the studied parameters.

CONCLUSION

The lateral trochlear inclination decreases with an increased posterior femoral condylar angle. The posterior referencing of the femoral component in total knee arthroplasty simultaneously establishes the shape of the anterior knee joint. Our results indicate that increasing posterior condyle angles significantly correlate with flattened lateral trochlear inclinations in native knees and suggest a systematic biomechanical conflict in total knee arthroplasty.

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.

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.

Sulcus depth, congruence angle, Wiberg index, TT-TG distance, and CDI are strong predictors of recurrent patellar dislocation

PURPOSE

To characterize patellofemoral morphology, determine radiological cutoff values based on computed tomography (CT) images, and clarify predominant anatomic risk factors in young patients with recurrent patellar dislocation (RPD).

METHODS

A total of 212 knees (age 23.0 ± 5.3 years, female: male = 110:102) with CT-confirmed RPD were enrolled for analysis. The control group was matched by age and sex (2:1). Patellofemoral and trochlear morphology, patellofemoral alignment, and other parameters were assessed by CT. Standardized methods were used for measurements. Receiver operating characteristic (ROC) curves and the areas under the ROC curve (AUCs) were used to assess accuracy in diagnosing RPD. The index of union (IU) was employed to identify a cutoff value for risk. A binary logistic regression model (Forward, LR) was constructed, and standardized coefficients were calculated to compare the relative strength of different predictors. Factors included in the model were employed to calculate distributions in the studied population.

RESULTS

The majority of measurements showed a significant difference between the RPD and control groups when comparing mean values. The AUC value was favorable for sulcus depth and significantly better than that for other trochlear morphology parameters (P < 0.0001). Cutoff values were 0.58 for the Wiberg index, 153.3° for the sulcus angle, 3.6 mm for the sulcus depth, 1.94 for the trochlear width ratio, 16.2° for the lateral trochlear inclination, 17.2° for the patellar lateral tilt, 25.5° for the congruence angle, 1.2 for the patellar height [Caton-Deschamps index (CDI)], 6.1° for the knee rotation, and 16.4 mm for the tibial tubercle-trochlear groove (TT-TG) distance. A binary logistic regression model (χ² = 20.826, P = 0.008) including the Wiberg index, sulcus depth, congruence angle, patellar height (CDI), and TT-TG distance was constructed for RPD (P ≤ 0.015), which showed excellent diagnostic performance, as indicated by an AUC of 0.989 (95% CI, 0.979 to 0.998). Sulcus depth showed the strongest relationship with RPD, followed by the congruence angle and Wiberg index, as indicated by the standardized coefficients - 1.43, 1.02, and 0.97, respectively. Eighty-seven percent of the RPD population had sulcus depth ≤ 3.6 mm.

CONCLUSIONS

This study provides a systematic reference of cutoff values based on CT data. The combination of five anatomic risk factors (sulcus depth, congruence angle, Wiberg index, TT-TG distance, and CDI) may be an excellent predictor of RPD as initial risk assessment. Sulcus depth, as the most frequently observed anatomic risk factor, showed the best diagnostic performance among trochlear morphological parameters and the strongest relationship with RPD, followed by the congruence angle and Wiberg index. In clinical practice, the sulcus depth, congruence angle, Wiberg index, TT-TG distance, and CDI with the proposed cutoff values can be used in combination to evaluate RPD. When assessing trochlear morphology, sulcus depth is recommended as the best radiological parameter.

LEVEL OF EVIDENCE

Level III.