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.