Comparison of a Novel Modified PLA/HA Bioabsorbable Interference Screw With Conventional PLGA/β-TCP Screw: Effect on 1-Year Postoperative Tibial Tunnel Widening in a Canine ACLR Model

Background: Tibial bone tunnel widening (TW) is a common postoperative phenomenon after anterior cruciate ligament reconstruction (ACLR). Purpose: To compare the physical, biomechanical, osteoinductive, and histological characteristics of 2 fabricated bioabsorbable interference screws: (1) a modified poly(l-lactide- co-d, l-lactide) and hydroxyapatite (mPLA/HA) screw and (2) a poly(l-lactide- co-glycolide) and β-tricalcium phosphate (PLGA/β-TCP) screw; and to evaluate the effect of the PLA/HA screw on ameliorating postoperative TW in a canine ACLR model. Study Design: Controlled laboratory study. Methods: In vitro, the physical and biomechanical properties of the mPLA/HA and PLGA/β-TCP screws were tested. The osteoinductive activity of the screws was studied by cell experiments. In vivo, ACLR was performed on 48 beagle dogs, divided into the mPLA/HA group and the PLGA/β-TCP group. The femoral and tibial ends of the graft were both fixed with screws. Six animals in each group were sacrificed after live computed tomography (CT) scanning at 1, 3, 6, and 12 months postoperatively. For six knee samples of each group, three knee samples underwent biomechanical testing, and 1 of them, along with the other 3 samples, underwent micro-CT and histological examination to evaluate tibial TW. Results: The mPLA/HA screw exhibited better particle dispersion, bending strength, desirable self-locking effect, and optimized degradation behavior both in vivo and in vitro. Histologically, the mPLA/HA screw had comparative osteoinductive activity. There was good screw-bone integration using the mPLA/HA screw, while most fibrous scar healing was in the PLGA/β-TCP group. There were significant differences between the mPLA/HA and PLGA/β-TCP groups in tibial bone tunnel diameter at the screw body (6 months postoperatively: 5.09 ± 0.44 vs 7.12 ± 0.67; 12 months postoperatively: 4.83 ± 0.27 vs 6.23 ± 0.56; P < .01 for both) and the screw tail (6 months postoperatively: 4.84 ± 0.28 vs 5.97 ± 0.73; 12 months postoperatively: 4.77 ± 0.29 vs 5.92 ± 0.56; P < .01 for both). Conclusion: Compared with the PLGA/β-TCP screw commonly used in clinics at present, the mPLA/HA screw had comparative biosafety and mechanical properties, satisfactory biomechanical properties, and osteoinductive activity in vivo and in vitro. It effectively ameliorated the postoperative tibial TW in a canine ACLR model and increased the quality of screw-bone integration. Clinical Relevance: The good mechanical and biological properties of the mPLA/HA screws may provide an option to reduce the incidence of complications after ACLR.