Introduction

Recurrent patellar instability is a complex problem that affects primarily adolescent patients. Current recommendations regarding the optimal timing and scope of surgical intervention are evolving. It is essential to identify whether a patient is experiencing pain, instability or a combination of both, as the best treatment for these pathologies varies significantly. It is not currently understood which subgroup of first time dislocators should be managed operatively as well as which subset of recurrent dislocators require concomitant bony realignment procedures, tibial tubercle osteotomies (TTO), in addition to a soft tissue stabilization, medial patellofemoral ligament (MPFL) reconstruction. If the patient’s complete pathology is not addressed at their index procedure, there is a high risk of recurrent instability necessitating revision surgery. This study assesses a series of patients who presented with recurrent instability after failed patellofemoral instability surgery.

Methods

Patients who underwent any prior procedure for patellar instability that experienced recurrent patellar instability requiring additional surgical intervention from March 2014 to July 2019 were identified from an institutional patellofemoral registry. Prior procedures included MPFL reconstructions, tibial tubercle transfer, lateral release, imbrication/reefing/plication, and loose body removal. Baseline demographic, radiographic, and knee-specific PROMs were collected prior to surgery. Follow-up data included the KOOS QOL, Pedi-Fabs, IKDC, KOOS-PS, and Kujala patient reported outcome measures (PROMs) which were collected at 1- and >/= 2-years postoperatively. Additionally, return to sport (RTS) rates and recurrent instability events were collected.

Results

This study cohort included 71 knees (67 patients) of which 79% were female. The average patient age was 25.0 years +/-8.4 and the average BMI was 25.9+/-5.9. Previous surgical procedures included 29 (41% of patients) MPFL reconstructions, 16 (23%) tibial tubercle transfers, 25 (35%) lateral releases, 21 (30%) imbrication/reefing/plication procedures, and 13 (18%) loose body removals. Revision procedures consisted of 39 MPFL+TTOs, one MPFL+TTO+distal femoral osteotomy, 23 isolated MPFL reconstructions, and eight isolated TTOs.

After their revision procedure, 81% of patients were able to return to sport. Of those that returned to sport, 92% returned at the same or a higher level. One patient (2%) reported a recurrent subluxation event and no patients (0%) reported a recurrent dislocation event following their revision procedure. Significant improvement from baseline scores at 2-year follow-up were found in the KOOS-QOL (19.0 vs 54.1, p<0.001), IKDC (38.4 vs 69.2, p<0.001), KOOS-PS (40.1 vs 18.7, p<0.001), and Kujala (50.8 vs 80.0, p<0.001). No differences were observed for Pedi-FABS. Additionally, no statistically significant differences were observed between 1- and 2-year follow-up for all PROMs.

The mean TT-TG was 17.0 +/- 5.1 with 31% (n=21) of patients having a TT-TG greater than 20 mm. The mean CDI was 1.11 +/- 0.19, 14% (n=10) patients had a CDI >=1.3 and 8% (n=6) had CDI <= 0.8. The mean PTI was 48.2% +/- 18.3%. Trochlear dysplasia, defined as a TDI < 3 mm, was present in 73% (n=52) of patients. The measure of extensor mechanism containment, TT-LTR within 1 mm, found to be predictive of recurrent instability, was found in 11% of patients (n=8). PT-LTR, a measurement of lateral patellar tracking, was mean 6.2 +/- 7.3.

Discussion And Conclusion

Recurrent patellofemoral instability is a complex problem and the ideal surgical intervention as well as optimal surgical timing is not yet well defined. This study demonstrates that patients who underwent revision surgical stabilization procedures for failed patellofemoral instability surgery were both able to return to sport and benefit from improved subjective outcomes with low recurrent instability at short term follow-up. Continued data collection is currently underway to determine if these results will be sustained long term.