Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients.

Background: Due to open femoral physis the therapy of patellar instability in skeletally immature patients is challenging. We developed a modified surgical technique of the 'Adductor-Sling-Approach' by Sillanpää. The purpose of this study was to evaluate the clinical outcome of the operative technique and to analyse the reasons for failure.

Methods: Thirty 'modified adductor sling' reconstructions in 28 patients were included in the study. From 2010 to 2016 modified adductor sling reconstruction was performed by looping the gracilis or semitendinosus tendon around the adductor magnus tendon and attaching it at the medial facet of the patella. Clinical outcome was retrospectively evaluated at a mean follow up of 25.6months (range 12-43). The evaluation also included subjective International Knee Documentation Committee (IKDC), Lysholm Score, Kujala Score and Tegner Activity Score.

Results: The average age at the time of operation was 15.10years (range 11-17). Eighty-seven percent of the patients, who underwent the modified adductor sling technique, gained a stable patella and excellent results in postoperative scores. Recurrent dislocation occurred in four of 30 cases (13%). Analysis showed that possible reasons for failure of the tendon graft could be maltracking of the patella due to patella alta, trochlear dysplasia or an elevated tibial tuberosity to trochlear groove distance.

Conclusion: The modified adductor sling technique for MPFL reconstruction in children and adolescents showed elevated redislocation rates. Only in absence of additional patellofemoral maltracking, caused by elevated tibial tubercle to trochlear groove distance (>15mm), patella alta or especially severe trochlear dysplasia, the modified adductor sling technique could be recommended.