Comparison of resorption and remodeling of bioabsorbable interference screws in anterior cruciate ligament reconstruction.

PURPOSE: The purpose of the study was to evaluate the influence of β-tricalcium phosphate (β-TCP) content on absorption rate and osteoconductive behavior of β-TCP/poly-L-lactic acid (PLLA) interference screws for anterior cruciate ligament (ACL) reconstruction. The authors compared two biocomposite β-TCP/PLLA screws containing 30 % (30TCP) and 60 % (60TCP) β-TCP (Ligafix®, SBM), respectively, used in ACL reconstruction with patellar tendon (BPTB) and hamstrings (HS) autografts.

METHODS

Twenty-eight knees with a 30TCP screw and 25 knees with a 60TCP screw were retrospectively included. Mean follow-up period was 37.5 months (range, 29-45 months). Post-operatively, all patients were examined clinically, had stress X-rays to measure anterior tibial translation and computed tomography (CT) to determine screw tract density, osteoconductivity and completed functional scores.

RESULTS

Clinical evaluation and functional scores were similar for both groups. There was no case of tunnel widening, cyst formation, increased inflammatory process or osteolysis. Both types of screws evidenced a decrease of Hounsfield units (HU) density over time (p < 0.001). The 60TCP screw resorbed more rapidly than the 30TCP (-62 vs -52 % of initial HU density respectively, p < 0.01) at latest follow-up. At three years, 97 % of the 30TCP and 96 % of the 60TCP screws showed osteoconductivity according to the Barber-Dockery's architectural score.

CONCLUSIONS

Both types of screws showed considerable osteoconductivity at the site of the screw tract. The majority of the 30 % β-TCP screws were fully resorbed and osteointegrated during the fourth postoperative year. The clinical results are good-to-excellent for both groups. The addition of 30 % or 60 % β-TCP in the biocomposite screw did not adversely affect clinical outcome and it minimized the inflammatory process. The material with the highest β-TCP content was absorbed more rapidly, supporting the hypothesis that increased β-TCP content in β-TCP/PLLA biocomposite material resulted in enhanced absorption rate of interference screws used in ACL reconstruction without affecting fixation strength.

LEVEL OF EVIDENCE: Level IV, Therapeutic case series.