Introduction

It is not currently understood which subset of patients with recurrent patellofemoral instability require concomitant bony realignment procedures in addition to a soft tissue stabilization. Additionally, the optimal timing of surgical intervention is not well defined by current literature and can be dictated by the skeletal maturity of a patient. If the patient’s complete pathology is not addressed at their primary procedure, there can be a high risk of recurrent instability necessitating revision surgery. It is not known if the outcomes of medial patellofemoral reconstruction with concomitant tibial tubercle osteotomy (MPFL+TTO) performed as a revision procedure equate the outcomes of MPFL+TTO performed in the primary setting. This study compares patients who underwent primary MPFL+TTO versus those who underwent the same procedure in the revision setting.

Methods

Patients who underwent a MPFL+TTO from March 2014 to December 2018 were identified from an institutional patellofemoral registry. Patients were separated into two groups, those undergoing a primary MPFL+TTO and those undergoing a MPFL+TTO after a previously failed surgical attempt for patellar stabilization. Baseline demographic, radiographic, and knee-specific patient reported outcome measures (PROMs) including KOOS QOL, Pedi-Fabs, IKDC, KOOS-PS, and Kujala were collected prior to surgery and at 1- and 2-years following surgical intervention. Return to sport (RTS) rates and recurrent instability events were also collected. Radiographic measurements included the Caton-Dechamps Index (CDI), Patellar Trochlear Index (PTI)1, Tibial Tubercle-Trochlear Groove (TT-TG), Tibial Tubercle-Lateral Trochlear Ridge (TT-LTR)2, Patellar Tendon-Lateral Trochlear Ridge (PT-LTR)3 and the Trochlear Depth Index (TDI)

Results

92 knees (84 patients) were included; 59 in the primary group and 33 in the revision group. No differences were identified between the groups with respect to sex (85% vs. 82%, p=0.715), age (23.7 vs. 22.5, p=0.468), BMI (26.3 vs 24.5, p=0.144), TT-TG (20.3 vs 19.3, p=0.238), or patella alta (33% vs 19%, p=0.354). Previous procedures in the revision cohort included 12 MPFL reconstructions, 3 tibial tubercle transfers, 16 lateral releases, 9 imbrications/reefings/plications, 7 loose body removals and 9 chondroplasties.

53 (90%) patients in the primary group and 29 (88%) patients in the revision group had a minimum of 2-year follow-up. There was no difference between the groups for recurrent dislocation (4% vs 0%, p=0.547), recurrent subluxation (9% vs 0%, p=0.162) and RTS (88% vs 83%, p=0.713). In regard to RTS, 79% of the primary surgery group and 71% of the revision group returned at an equal or higher level (p=0.461). At baseline, the primary group had a higher IKDC (42.0 vs 34.7, p=0.049).

At 2-year follow-up both groups had significant improvements from baseline in all PROMs, except Pedi-FABS which had no change. There was no difference between groups at 2-year follow-up in KOOS-QoL (60.8 vs 51.1, p=0.186), Pedi-FABS (8.0 vs 7.3, p=0.796), IKDC (75.2 vs 67.7, p=0.206), KOOS-PS (15.8 vs 20.9, p=0.379), and Kujala (86.5 vs 77.9, p=0.143).

The mean TT-TG, CDI, PTI and presence of patella alta was similar between groups. Trochlear dysplasia, defined as a TDI < 3 mm, was present in 77% of patients in both groups. The measure of extensor mechanism containment, TT-LTR, was similar between groups and the rate of TT-LTR within 1 mm, found to be predictive of recurrent instability, was 18% in the primary group and 26% in the revision group. PT-LTR, a measurement of lateral patellar tracking, was statistically significantly higher in the primary group (11.9 vs 8.7, p=0.045).

Discussion And Conclusion

Management of patellofemoral instability is complex. The optimal timing of surgical intervention and whether a concomitant bony realignment procedure is indicated has yet to be elucidated. This study demonstrates that primary MPFL+TTO versus revision MPFL+TTO have comparable objective and subjective outcomes at short term follow-up. Ongoing data collection for this patient cohort will determine whether these results are sustained at long term follow-up.