All-Suture Anchor Onlay Fixation for Medial Patellofemoral Ligament Reconstruction: A Biomechanical Comparison of Fixation Constructs.

Abstract

Background: The use of all-suture anchors (ASAs) for onlay patellar and femoral fixation of medial patellofemoral ligament (MPFL) grafts may provide clinical benefit, particularly in the small or pediatric knee; however, biomechanical data supporting the use of ASAs are lacking.

Purpose/hypothesis: The purpose of this study was to compare ASAs to larger interference implants for MPFL reconstruction in a time-zero biomechanical model. It was hypothesized that ASAs would have comparable cyclic elongation to interference fixation and would exceed published biomechanical values for the native human MPFL.

Study design: Controlled laboratory study.

Methods: Eighteen fresh-frozen porcine patellas and femurs were divided into equal groups (n = 9 per group) for MPFL reconstructions. Patellar fixation utilized two 3.9-mm interference suture anchors (ISAs) or two 2.6-mm ASAs, while femoral fixation utilized one 6×20-mm interference screw (IS) or one 2.6-mm ASA. Human gracilis tendon grafts were used. Specimens were dynamically loaded for 100 cycles each in sequential 5- to 30-N (phase 1) and 5- to 50-N (phase 2) blocks at 1 Hz followed by load-to-failure testing at 305 mm/min.

Results: No differences were found in cyclic elongation after phase 1 and phase 2 loading between ASA and interference implants on either the femoral or patellar side. On the femur, IS had significantly greater ultimate stiffness (54.2 vs 46.1 N/mm; P < .001) and ultimate load (366 vs 278 N; P = .019) compared to ASA. On the patella, ISAs had significantly greater ultimate stiffness (70.5 vs 53.1 N/mm; P < .001) but a significantly lower ultimate load (244 vs 307 N; P = .014) compared to ASAs. All groups significantly exceeded the published physiological values for native human MPFL stiffness and failure load.

Conclusion: ASA onlay fixation had comparable cyclic elongation to that of interference fixation for femoral and patellar MPFL reconstruction. Although differences in ultimate stiffness and ultimate load were noted between implants, all of the values exceeded published values for the human MPFL.

Clinical relevance: This biomechanical study presents ASA cortical onlay fixation as a viable option for MPFL reconstruction. ASAs require less bone removal, potentially reducing the risk of patellar fracture and minimizing fixation complexity in the setting of open femoral growth plates. Future clinical studies will provide insight into successful tendon-to-bone healing, failure rates, and near- and long-term patient-reported outcomes.