Clinical outcomes of a minimally invasive isolated medial patellofemoral ligament (MPFL) reconstruction technique without considering bone anatomical factors in patients with patellar instability

Objective: The aim of this study was to demonstrate the clinical results of a minimally invasive anatomic reconstruction technique for isolated MPFL in cases of recurrent patellar instability, without consideration of Patella alta, TT-TG distance, and trochlear dysplasia. Methods: Retrospective analysis was conducted on prospectively collected data from patients who underwent minimally invasive isolated MPFL reconstructive surgery at Norinco General Hospital between 2014 and 2019. Preoperative evaluation included assessment of the J-sign, trochlear dysplasia according to Dejour classification, patellar height using the Caton-Deschamps index (CDI), and tibial tubercle–trochlear groove (TT-TG) distance. Postoperatively, Kujala score, International Knee Documentation Committee (IKDC) score, and Tegner score were assessed. Complications such as re-dislocation of the patella, patellar fracture, hematoma formation, and knee stiffness were recorded as failure if they severely affected knee function after MPFL reconstruction. Results: A total of 106 patients (Average age, 21.5 ±5.9 years; 68% females; mean follow-up, 7.2±1.6 years) were included. 28 individuals (26%) presented with a preoperative positive J-sign, trochlear dysplasia was observed in 102 cases (A,48%; B,22%; C,18%; D,8%). The mean CDI value was 1.18±0.16 (range,0.9-1.5); average TT-TG distance, 21.0±3.8 mm (range,10-26 mm). The final follow-up mean Kujala score was 83.2 ± 14.6 (range 40-100); mean IKDC score, 77.8 ± 12.6 (range 24 - 93); mean Tegner score, 4.0 ± 1.8 (range 1-9). Postoperative patellar instability and re-dislocation were observed in 5 patients (5%). Knee pain emerged as the most prevalent postoperative complication (17%). Joint release surgery was required for two patients experiencing postoperative knee stiffness. The Kujala score of 70 patients was ≥80, and the clinical excellent rate reached 66%. Patients with positive J-sign and severe trochlear dysplasia before surgery are more likely to have unsatisfactory results（Kujala score＜80）, and both have significant differences. However, the two anatomical factors, CDI and TT-TG value, had no statistical significance on the satisfied and unsatisfied results of Kujala scores. Conclusion: The reconstruction of the isolated medial patellofemoral ligament has shown positive clinical results in treating patellar instability. Especially for young female patients, a minimally invasive MPFL reconstruction technique with minimal scarring leads to increased patient satisfaction. However, in cases where preoperative assessment shows a positive J-Sign and severe trochlear dysplasia, it may be necessary to consider incorporating bony procedures such as tibial tubercle osteotomy or trochleoplasty.