Long-Term Degradation of Self-Reinforced Poly–Levo (96%)/Dextro (4%)–Lactide/β-Tricalcium Phosphate Biocomposite Interference Screws

PurposeTo evaluate the long-term in vivo degradation of biocomposite interference screws made with self-reinforced poly–levo (96%)/dextro (4%)–lactide/β-tricalcium phosphate [SR-PL(96)/D(4)LA/β-TCP].MethodsA study of the in vivo biologic behavior of an SR-PL(96)/D(4)LA/β-TCP biocomposite interference screw was initiated in 2011 using an anterior cruciate ligament (ACL) reconstruction model. Eight patients undergoing a bone–patellar tendon–bone ACL reconstruction fixed at both the femur and tibia with an SR-PL(96)/D(4)LA/β-TCP screw at least 36 months earlier were evaluated by physical, radiographic, and computed tomography (CT) evaluations. Lysholm, Tegner, Cincinnati, and International Knee Documentation Committee scores were obtained. After incomplete degradation was observed in these 8 patients, a subsequent series of 17 patients were evaluated at a minimum of 48 months after surgery. By use of CT scans, Hounsfield unit (HU) data were obtained at the femoral and tibial screw and other bone sites. An ossification quality score (range, 1 to 4) was used to determine osteoconductivity at the screw sites.ResultsEleven male and 6 female patients evaluated by CT scan and radiographs at a mean of 50 months (range, 48 to 61 months) after surgery showed bone plug healing to the tunnel wall and the SR-PL(96)/D(4)LA/β-TCP screws were replaced with material that was calcified and non-trabecular. Osteoconductivity was present in 24 of 34 tunnels (70.58%) and nearly complete or complete (type 3 or 4 ossification) in 11 of 34 (32.35%). Mean screw site densities (femoral, 242 HU; tibial, 240 HU) were consistent with cancellous bone density. One positive pivot-shift test was found. Lysholm, Cincinnati, Tegner, and International Knee Documentation Committee activity scores improved from 44.5, 40.7, 2.3, and 1.4, respectively, preoperatively to 92, 92.4, 5.7, and 3.3, respectively, at follow-up (P < .0001). The average postoperative Single Assessment Numeric Evaluation score was 92. The mean KT arthrometer (MEDmetric, San Diego, CA) difference was 1.25 mm.ConclusionsThe SR-PL(96)/D(4)LA/β-TCP interference screw was replaced with calcified, non-trabecular material 4 years after implantation in a bone–patellar tendon–bone ACL reconstruction model. Osteoconductivity was confirmed in 24 of 34 screw sites (71%), with nearly complete or complete filling in 11 of 34 (33%). The SR-PL(96)/D(4)LA/β-TCP biocomposite interference screw is osteoconductive.Level of EvidenceLevel IV, therapeutic case series.