Summary

In this prospective study for patients undergoing isolated MPFL reconstruction for recurrent patellofemoral instability, patients with post-operative J-signs showed worse PROMs at 2-years, a higher percentage of patients who had preoperative knee hyperextension and post-operative apprehension did not RTS and patients who had post-operative apprehension did not experience recurrent instability.

Abstract

Objectives:

A multicenter prospective trial is currently underway to identify which subset of patients with recurrent patellofemoral instability would benefit from a concomitant bony realignment procedure in addition to a medial patellofemoral ligament (MPFL) reconstruction. The aim of this study is to investigate if post-operative apprehension is measure of sub-optimal outcomes to determine if this may be an additional indicator of patients who may need bony realignment in addition to an isolated soft tissue procedure. Post-operative J-sign, a clinical exam finding that may indicate patellar maltracking was also investigated. Recurrent instability, return to sport (RTS), and patient reported outcome measures (PROMs) were used as outcomes for this study.

Methods

Patients with recurrent patellar instability were prospectively enrolled in an institutional registry beginning March 2014. All patients underwent primary, unilateral, isolated MPFL reconstruction regardless of their bony anatomy. Radiographic measurements including TT-TG, Caton-Deschamps Index (CDI), Patellar Trochlear Index (PTI), Trochlear Depth Index (TDI), Patellar Tendon to Lateral Trochlear Ridge (PT-LTR) and Tibial Tubercle to Lateral Trochlear Ridge (TT-LTR) were obtained at baseline. Recurrent instability, patient outcomes including PROMs, and return to sport (RTS) were obtained annually. Presence of post-operative apprehension, post-operative J-sign, and knee hyper-extension were also collected. Independent samples t-tests and chi-square analyses were used to compare continuous and discrete variables, respectively, between groups.

Results

138 patients (72% female; mean age 20.1 ± 6.1 years) underwent isolated MPFL reconstruction between March 2014 and December 2019. Mean Beighton Score was 5.3 ± 3.0 and knee hyperextension was 5.4 deg ± 2.8 deg. Eighty-nine patients (65%) had pre-operative knee hyper-extension.

At 2-year follow up, six patients (5%) reported an episode of recurrent instability, nine patients (8%) reported post-operative apprehension, and 44 patients had a post-operative J-sign (37%). No patients with post-operative apprehension reported recurrent instability.

By 2-year follow-up, 89% of patients were able to return to sport (RTS). 50% of patients who had pre-operative knee hyper-extension and post-operative apprehension did not RTS (p=0.034). While not statistically significant, a higher percentage of patients who had recurrent instability or apprehension did not RTS (40%) compared to those who did not (11%).

Patients with post-operative J-signs had significantly worse IKDC (P=0.022), KOOS-PS (P=0.011), and Kujala (P=0.035) at 2-years. For patients with recurrent instability or post-operative apprehension, Kujala was statistically significantly lower at 1-year compared to those without (84.9 vs. 91.7, P=0.019). At 2-year follow-up the difference was still maintained between the two groups (83.6 vs. 91.6).

Conclusion

Patients with post-operative J-signs showed worse PROMs at 2-years post-operatively. A higher percentage of patients who had pre-operative knee hyper-extension and post-operative apprehension did not RTS. Patients who had post-operative apprehension did not report a recurrent instability event at most recent follow up. These findings support the need to further investigate if post-operative J-sign and apprehension may be important markers of sub-optimal outcomes after isolated MPFL reconstruction for recurrent instability, which in turn, may help identify patients that may benefit from concomitant bony realignment procedures at the time of their index procedure.