Containment of the extensor mechanism within the trochlea may predict patellar instability
Assessing containment measures of the extensor mechanism within the trochlea could predict recurrent patellar instability and aid in treatment decision-making, according to recently presented study results.
“In other non-stable joints, containment and tracking are heavily discussed. Maybe for [the patellofemoral joint], we should discuss it as well,” said Daniel Weltsch, MD, a sports and translational medicine specialist at The Chaim Sheba Medical Center in Tel HaShomer, Israel, who presented findings of his retrospective review on patellar containment at the American Orthopaedic Society for Sports Medicine Annual Meeting. The meeting was held as a virtual meeting.
“We included 165 patients (median age of 14 [years]) with a first-time traumatic dislocation,” Weltsch said in the presentation. “Before collecting the data, we divided our cohort into two groups: one-time dislocators (67 patients) and recurrent dislocators (98 patients). Then, we assessed the MRIs of every patient in the cohort, looking for classic measurements and some novel measurements.”
Classic measurements included tibial tubercle to trochlear groove (TT-TG) and tibia tuberosity to the PCL(TT-PCL), while novel measurements included axial distance of patellar tendon beyond lateral trochlear ridge (PT-LTR), lateral trochlear ridge to trochlear groove (LTR-TG) and trochlear tuberosity to lateral trochlear ridge (TT-LTR).
“So, we did intra-class correlation for all measurements. The most reliable measurements were added to our univariable analysis,” Weltsch said.
After multiple regression analysis, Weltsch and colleagues found TT-LTR as in the only independent predictor of recurrent dislocation, as patients with a TT-LTR value greater than 1 mm had a recurrent dislocation rate of 72%.
“A positive TT-LTR actually means that the tuberosity is outside of the LTR, and it is associated with significantly increased odds of recurrent instability,” Weltsch said. “Using the TT-LTR as a potential clinical implication, it represents the containment and tracking of the extensor mechanism within or outside of the trochlear structure. It is not surprising that it can predict the affinity for recurrent dislocation,” he added.
“Understanding the relative interplay between the tibial tubercle and the lateral trochlear ridge is a crucial milestone,” he said. “Dislocation recurrence is higher when the attachment point of the extensor mechanism is outside of the lateral trochlear ridge or the area of the containment of the trochlea. This may help us direct our treatment.” Weltsch added.
“Decision-making for patellofemoral instability patients should ensure that patients have an overall alignment that is well contained within the limits of the trochlea. Further comprehensive multiplanar investigations are needed to better understand the structural variants and their effect on patellar containment,” Weltsch concluded.
Perspective
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Risk factors for recurrent patellofemoral instability have been studied often over the last 10 years. The ability to predict who is at high risk for recurrent instability guides office discussions and treatment algorithms. Younger age, activity level, trochlear dysplasia and patella alta all play a role in determining recurrence. Clearly, this is a multifactorial issue with many confounding variables.
Weltsch and colleagues presented research at the recent virtual AOSSM Annual Meeting looking at MRI measurements after initial patellofemoral dislocation. They concluded that the tibial tubercle-lateral trochlear ridge measurement greater than 1 mm predicted recurrent instability. They postulated that a lateral tracking vector limits joint containment and predisposes young patients to recurrent instability. While this makes sense intuitively, it is important to remember that there are multiple factors in these cases.
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Weltsch D, et al. Presentation 13. Presented at: American Orthopaedic Society for Sports Medicine Annual Meeting; July 8-9, 2020 (virtual meeting).
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