Title:
Analysis of failure and clinical outcome after unsuccessful medial patellofemoral ligament reconstruction in young patients.

Abstract:
Reconstruction of the medial patellofemoral ligament (MPFL) has become a popular procedure for patients with patellofemoral instability. Nevertheless, complication rates of up to 26 % have been reported. This study presents the analysis of failure and clinical outcome of subsequent revision surgery in young patients following unsuccessful medial patellofemoral ligament reconstruction.
Nineteen consecutive patients with unsuccessful MPFL reconstruction underwent revision surgery. Pre-operative assessment included physical examination, radiographs and magnetic resonance imaging to assess the MPFL graft, trochlear dysplasia, tibial tubercle-trochlear groove (TT-TG) distance, patella alta and femoral tunnel positioning. Evaluation also included the detection of cartilage injuries as well as visual analog scale (VAS), knee function scores and patient satisfaction. Each complication was analysed and an appropriate revision procedure was performed according to the identified technical or untreated anatomical risk factor.
The average age at the time of the index operation was 20.2 years (range, 16-27 years). The average age at the time of the primary MPFL reconstruction was 18.4 years (range, 15-25). Three main reasons for failure after MPFL reconstruction could be identified: failure to consider additional risk factors, intra-operative technical errors and inappropriate patient selection. In five patients severe trochlear dysplasia and in two patients concomitant excessive femoral anteversion as additional risk factors were detected. Seven patients experienced medial retinacular pain with limited flexion due to technical errors caused in three patients by anterior placement of the femoral tunnel and in four others by overtensioning of the MPFL graft. Four patients with patellofemoral pain were found to have ICRS grade III or IV cartilage injuries. The median postoperative Kujala scores improved from 57 (34 - 73) pre-operatively to 83 (49 - 94), the median knee function improved from 5 (range, 2 - 6) pre-operatively to 8 (range, 3 - 10). Median VAS scores improved from 4 (2 - 7) to 2 (0 - 5). A total of 78.9% of patients were satisfied or very satisfied, 15.8% were partially satisfied and one patient (5.3%) was not satisfied with the result after revision surgery.
Failure to consider additional risk factors, technical intra-operative errors and inappropriate patient selection were identified as reasons for revision surgery after MPFL reconstruction. Identifying the potential causes of failure can help to treat and possibly prevent future complications.