In vivo degradation characteristics of bioabsorbable cross-pins in anterior cruciate ligament reconstruction

BackgroundWe evaluated degradation of bioabsorbable femoral cross-pins following anterior cruciate ligament (ACL) reconstruction.MethodsFour patients underwent ACL reconstruction using hamstring autograft with femoral fixation provided by a polylactic acid/polyglycolic acid copolymer (LactoSorb L15) cross-pin. Serial computed tomography (CT) scans were performed of the reconstructed knees at approximately 6 weeks, 4 months, 1 year and 2 years, postoperatively. A radiologist evaluated the scans for density of pins and surrounding bone and pin morphology.ResultsThe cross-pins demonstrated a relative reduction in density of 7.7%, 49.1%, and 75.0% at 4 months, 1 year and 2 years, respectively. Bone density values adjacent to the pin decreased by an mean of 8.6% between 6 weeks and 4 months. At one year an additional 14.2% reduction in bone density was seen but at 2 years the relative reduction in bone density had decreased to 7.4%. Evaluation of pin morphology revealed that minimal change had occurred after 6 weeks. At 4 months all of the pins were showing some morphologic changes on the surface, but none had fractured. After 1 year, two of the pins had fractured. By 2 years all of the pins had fractured. None of the pins had completely reabsorbed at 2 years postoperatively.ConclusionsLactoSorb L15 cross-pins for femoral fixation in ACL reconstruction remain largely unchanged 4 months postoperatively, suggesting that this device maintains the necessary structural integrity to allow early integration of soft tissue grafts within bone tunnels.Level of evidenceIV, case series.