Patellofemoral morphology may predict risk of recurrent instability in pediatric patients
Tibial tubercle to lateral trochlear ridge distance may accurately predict recurrent patellar instability in a pediatric population with first-time lateral patellar dislocation, according to published results.
From 2005 to 2014, Daniel Weltsch, MD, and colleagues from the Children’s Hospital of Philadelphia used serial axial MRI to analyze 165 patients aged 8 to 19 years with first-time lateral patellar dislocations. The median follow-up was 12.2 months.
According to the study, the researchers assessed all measurements with the intraclass correlation coefficient (ICC), including only measurements with an ICC greater than 0.8. Additionally, they performed univariable and multivariable logistic regression analyses to evaluate variables associated with recurrent instability and dislocation.
Overall, Weltsch and colleagues documented 98 cases (59.4%) of subsequent instability among the cohort. After regression analysis, they determined tibial tubercle to lateral trochlear ridge (LTR) distance was an independent risk factor for recurrent instability, as “patients with a tibial tubercle to LTR distance value greater than 1 mm had a significantly higher rate of recurrent patellar dislocation (72%),” the researchers wrote in the study.
“The main finding in this study was that a new measure relating the center of pull distally to the lateral edge of the trochlear groove, the tibial tubercle to LTR distance, was a significant independent predictor of recurrent patellar instability in an adolescent population,” they concluded. “While further comparative studies are certainly needed, in the assessment of patients with first-time patellar dislocation, the tibial tubercle to LTR distance may aid surgeons and patients in understanding the relevant pathoanatomy and thus help direct treatment,” they wrote.
Perspective
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A conundrum that many orthopedists encounter in their treatment of first-time patella dislocations is predicting which patient will subsequently have recurrent instability or dislocations and require surgical interventions vs. those who will do well with nonoperative treatment of their acute dislocations.
Weltsch and colleagues in their study present additional data to previously noted risk factors for recurrent patellofemoral instability following acute dislocation such as age, trochlear dysplasia and TT-TG distance, etc., noted on imaging studies.
In their retrospective study, MRI imaging of 165 young (8- to 19-year-old) patients with acute patella dislocations, the authors correlate that the tangential measurement between the lateral trochlear ridge (LTR) and the tibial tubercle (TT) in serial axial MRI images identify patients at risk for future recurrent patellofemoral instability.
Those individuals in which the LTR/TT measurements showing lateral or “off-track“ alignment of greater than 0.8 mm gave a high correlation predictability of incurring recurrent problems of patellofemoral instability or dislocation. The elegance of their measurement would be applicable to patellofemoral anatomic variants, such trochlear dysplasia.
This is a timely study to further identify those patients who are at risk for having recurrent patellofemoral instability occurrences following an acute patella dislocation using well delineated anatomical landmarks in MRI imaging of patellofemoral joint. Applying these science-based findings in our clinical practices will enable the clinician to counsel patients on which treatment options for their acute patellofemoral dislocation will predict a favorable outcome of their injury.
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Understanding the pathoanatomic features that drive patellar instability is multifaceted and considerably complex, especially to the early career surgeon. Traditional measurements, including TT-TG and dysplasia, attempt to localize dysfunctional anatomical elements that contribute to increased lateral patellar force vectors, but typically fall short in explaining the whole picture. Rather, more novel measurements, such as tested here by Weltsch and colleagues, emphasize measurements that provide more reliable insight into alignment. They specifically found that the distance between the tibial tubercle and the lateral trochlear ridge was not only a reliable measurement, but was also independently relevant to risk of recurrent instability even after controlling for TT-TG.
I commend the authors for going a step beyond the presentation of their findings to further illustrate how trochlear morphology in isolation may not lead to an “off-track” alignment, which offers valuable guidance when formulating a final surgical plan.
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