Biomechanical Evaluation of Classic Solid and All-Soft Suture Anchors for Medial Patellofemoral Ligament Reconstruction

Abstract

Background: Multiple techniques for patellar fixation with classic solid suture anchors (SAs) in medial patellofemoral ligament (MPFL) reconstruction have been described. Fixation of the graft to the patella with all-soft suture anchors (ASAs) has not been studied. Purpose/Hypothesis: To evaluate the biomechanical performance of 2 different MPFL patellar fixation techniques: ASA fixation and SA fixation. We hypothesized that the ASA group would show no statistical difference in the ultimate failure load and stiffness compared with the SA group. Study Design: Controlled laboratory study. Methods: Reconstruction of the MPFL with gracilis autografts was performed in 16 fresh-frozen cadaveric knees (mean age, 52.6 ± 9.0 years). The specimens were randomly assigned to 2 groups of 8 specimens each based on the method used to fix the graft to the medial patella: ASA or SA fixation. Patellar fixation with ASAs was completed with 2 parallel 1.8-mm anchors (Q-Fix, Smith & Nephew). Fixation with SAs was completed with 2 parallel 2.9-mm anchors (Osteoraptor, Smith & Nephew). The reconstructions were cyclically loaded for 10 cycles to 25 N and then loaded in tension at 6 mm/s until failure. Ultimate failure load (N), displacement (mm), stiffness (N/mm), and mode of failure were recorded for each specimen. Results: Load to failure testing showed an ultimate failure load of 228.5 ± 53.1 N in the ASA group. In the SA group, the ultimate failure load was 156.2 ± 84.9 N. The difference between the 2 groups was not statistically significant ( P = .064). Stiffness values between the ASA and SA groups were not significantly different (21.3 ± 4.1 N/mm vs 20.9 ± 9.3 N/mm, respectively, P = .905). The most common mode of failure in both groups was anchor pullout (8 of 8 in the ASA group; 6 of 8 in the SA group). Conclusion: This experimental study showed no statistically significant differences in biomechanical performance between 1.8-mm ASAs and 2.9-mm SAs. Clinical Relevance: Patellar fixation with 2 parallel ASAs may provide adequate patellar fixation for MPFL reconstruction, while their smaller diameter could potentially decrease the risks for patella fracture and violation of the articular surface in the cadaver model.