Patella alta and elevated tibial tubercle-trochlear groove (TT-TG) distance are known to predispose patients to lateral patellar dislocations and recurrent instability. The purpose of this study was to evaluate the influence of these risk factors on patient-reported outcomes following isolated medial patellofemoral ligament (MPFL) reconstruction.
A all patients who underwent isolated MPFL reconstruction at a single institution between 2008 and 2016 were identified. Performance of an isolated MPFL reconstruction was at the discretion of the operating surgeon with the primary indication for tubercle osteotomy being a large j-sign with patella alta or elevated TT-TG distance. Patient demographics and surgical details were collected via chart review, and patients were contacted to collect patient-reported outcomes including the Norwich Patellar Instability Score (NPI), the Knee Injury and Osteoarthritis Outcome Score (KOOS), and Marx Activity Score. Preoperative imaging was reviewed, and patellar height (Caton-Deschamps Index [CDI]) and TT-TG distance were measured. Patient-reported outcomes were compared based on CDI > 1.20 versus CDI < 1.20 and TT-TG > 20mm versus TT-TG < 20mm.
During the study period, 165 patients underwent isolated MPFL reconstruction. 125 patients (76%) with minimum one year follow-up were contacted at a mean of 5.2 years. following surgery. Mean CDI was 1.13, and 35% had a CDI > 1.20. Mean TT-TG distance was 17.5mm, and 26% had a TT-TG distance greater than 20mm. No significant differences in patient-reported outcomes were noted based on patella alta or elevated TT-TG distance. Recurrent dislocation occurred in 5 patients (4%).
In patients without a large j-sign, neither moderately elevated TT-TG distance nor patellar alta are associated with poorer patient-reported outcomes following isolated MPFL reconstruction for patellar instability.