A Long-Term, Prospective, Randomized Study Comparing Biodegradable and Metal Interference Screws in Anterior Cruciate Ligament Reconstruction Surgery Radiographic Results and Clinical Outcome

Background: During the past decade, the use of biodegradable implants in anterior cruciate ligament surgery has increased. Hypothesis: Poly-L-lactide acid (PLLA) interference screws would render the same clinical results but greater tunnel enlargement than metal screws 8 years after anterior cruciate ligament reconstruction using hamstring tendon (semitendinosus/gracilis) autografts. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: A randomized series of 77 patients, all with a unilateral anterior cruciate ligament rupture, were divided into 2 groups (PLLA and metal). In both groups, hamstring tendon autografts were used with interference screw fixation at both ends and the patients were examined with standard radiographs, Tegner activity level, Lysholm knee score, single-legged hop test, early C-reactive protein response, and KT-1000 arthrometer knee laxity measurements. Results: The preoperative assessments in both groups were similar in terms of gender, clinical tests, and the time from injury to surgery. The patients returned for a radiographic and clinical examination a mean of 96 months (range, 78-120 months) after the index operation. The PLLA group displayed significantly larger bone tunnels on the radiographs than the metal group on the femoral side (mean, 11.4 mm [range, 0-17.8 mm] vs 8.0 mm [range, 0-16.3 mm]; P < .005) but not on the tibial side (mean, 10.7 mm [range, 7.8-14.1 mm] vs 10.5 mm [range, 0-20.3 mm]; difference not significant). At follow-up, no significant differences were found between the PLLA and metal groups in terms of knee laxity measurements (median, 1.0 mm [range, -2.0-4.0 mm] vs 1.0 mm [range, -3.0-6.5 mm]), Tegner activity level (median, 7 [range, 3-9] vs 6 [range, 2-9]), or the Lysholm knee score (median, 90 points [range, 51-100] vs 89 points [range, 53-100]). The C-reactive protein values did not differ significantly between the 2 groups except for an increase in the PLLA group compared with the metal group at day 1 postoperatively -23 mg/L (range, <6-55) vs 9 mg/L (range,<6-55) (P < .001). Conclusion: There were significantly larger radiographically visible bone tunnels on the femoral side but not on the tibial side in the PLLA group compared with the metal group 8 years after anterior cruciate ligament reconstruction using hamstring tendon autografts. This finding did not correlate with inferior clinical results. Because of the results in the present study, the authors have discontinued the use of PLLA interference screws.