Purpose: To investigate factors predicting patient-reported outcomes and revision interventions after surgical treatment of patients with patellofemoral instability.
Methods: From a prospective database of a university orthopaedic department, 138 knees of 116 patients who had undergone surgery for patellofemoral instability between 2012 and 2019 were included in the analysis: 34 cases of isolated MPFL reconstruction, 92 cases of MPFL reconstruction plus tibial tuberosity transfer, and 12 cases of MPFL reconstruction plus trochleoplasty. Patient-reported outcome measures (PROMs) were recorded for knee-specific function (KOOS), general quality of life (EQ-5D) and activity level (Tegner scale). Postoperative revision procedures were also recorded. Preoperative and postoperative PROMs values were compared using paired statistical tests. Potential predictive factors included patient demographics (sex, age, BMI), radiological data (preoperative: patella height and inclination, tuberosity-trochlear groove distance, trochlear dysplasia, knee osteoarthritis; postoperative: MPFL insertion point) and intraoperative parameters (isolated vs. combined procedures, macroscopic cartilage condition of the knee using Chondropenia Severity Score - CSS) were analysed using multivariate linear regression models.
Results: After a median follow-up of 4.4 (1.0-8.9) years, all patient-reported outcome measures had significantly increased from preoperative to postoperative values: KOOS cumulative, from 71 (15) to 78 (16); EQ -5D-3L-TTO, from 0.68 (0.20) to 0.78 (0.21); and Tegner activity scale, from 3 (0-10) to 4 (0-10). No revision surgery was performed for patellofemoral instability. Patients who required postoperative knee manipulation under anaesthesia or arthroscopic debridement showed lower postoperative improvement in KOOS cumulative and EQ -5D-3L-TTO. Age, BMI, patellofemoral knee osteoarthritis and shorter follow-up time showed significant negative correlations with some of the postoperative KOOS subscales. Age was negatively correlated with postoperative EQ-5D-3L-TTO, while postoperative Tegner activity scale was negatively correlated with female sex and patellofemoral CSS. The femoral MPFL insertion point, tibial tuberosity transfer or trochleoplasty showed no association with any outcome measures. There were no differences in patellar height before surgery, immediately after surgery, and at last follow-up, except in patients who underwent intentional TT distalisation.
Conclusion: Surgical treatment of patellofemoral instability using isolated or combined (with tibial tuberosity transfer or trochleoplasty) MPFL reconstruction was safe and significantly improved patients' subjective knee function, overall quality of life and activity level. Older age, higher BMI, poorer preoperative patellofemoral cartilage status and female gender had negative effects on outcome. Patients who required postoperative knee manipulation or arthroscopic debridement had less postoperative improvement in subjective measures, whereas the femoral MPFL insertion point was not associated with any of these factors. Serious adverse events were rare, with no recurrence of patellofemoral dislocation or changes in patellar height.
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