Randomized controlled trial of osteoconductive fixation screws for anterior cruciate ligament reconstruction: a comparison of the Calaxo and Milagro screws.

PURPOSE To compare the outcome of 2 bioabsorbable screws for tibial interference fixation in anterior cruciate ligament reconstruction with reference to rate of absorption, osteoconductive properties, and clinical outcome. METHODS Patients undergoing primary anterior cruciate ligament reconstruction with hamstring autograft in a single unit were invited to participate in this study. Patients were randomized to receive either the Calaxo screw (Smith & Nephew, Andover, MA) or Milagro screw (DePuy Mitek, Raynham, MA) for tibial fixation. Patients were reviewed with subjective and objective evaluation by use of the International Knee Documentation Committee form, Lysholm score, KT-1000 arthrometry (MEDmetric, San Diego, CA), and clinical examination. Magnetic resonance imaging was performed at 1 year and computed tomography scanning at 1 week and at 6, 12, and 24 months. RESULTS Sixty patients agreed to participate in the study, with 32 patients randomized to the Calaxo screw and 28 to the Milagro screw for tibial fixation. There was no significant difference in subjective or objective clinical outcome between the 2 groups. At 24 months, 88% of Calaxo screws showed complete screw resorption compared with 0% of Milagro screws (P < .001). Tibial cysts were present in 88% of the Calaxo group and 7% of the Milagro group (P = .001). At 24 months, the mean volume of new bone formation for the Calaxo group was 21% of original screw volume. Ossification of the Milagro screw was unable to be accurately assessed as a result of incomplete screw resorption. CONCLUSIONS Both screws showed similar favorable objective and subjective outcomes at 2 years. The Calaxo screw resorbed completely over a period of 6 months and was associated with a high incidence of intra-tunnel cyst formation. The Milagro screw increased in volume over a period of 6 months, followed by a gradual resorption, which was still ongoing at 2 years. Both screws were associated with tunnel widening, and neither showed evidence of significant tunnel ossification. We conclude that, despite satisfactory clinical outcomes, the addition of "osteoconductive" materials to bioabsorbable screws is not associated with bone formation at the screw site at 2 years. LEVEL OF EVIDENCE Level I, randomized controlled trial.