Prospective randomised controlled trial comparing PLLA and PLDLA/HA/β-TCP interference screws in anterior cruciate ligament reconstruction: CT scans, MRI and clinical outcomes.

PURPOSE: Modifying interference screw composition may ensure better osteoconductive properties in order to reduce tunnel enlargement after anterior cruciate ligament (ACL) reconstruction. The primary and secondary purposes were to evaluate tunnel and screw volume changes in poly-L-lactide acid (PLLA) and poly-D-lactic acid + hydroxyapatite + β-tricalcium phosphate (PLDLA+) screws. The tertiary purpose was to compare patient reported- and functional outcomes between PLLA and PLDLA+ group. It was hypothesised that PLLA group would show more tunnel enlargement and a lower rate of resorption than PLDLA+ group with similar clinical results.

METHODS

Patients were treated with ACL reconstruction using hamstring autograft with femoral and tibial interference screw fixation (PLLA or PLDLA+). Tunnel volume changes were assessed after 0, 24 and 36 months on computed tomography (CT) scans. Screw volume changes were analysed after 0, 3, 6, 12, 24 and 36 months on magnetic resonance imaging (MRI). Patient reported outcome scores (PROMS) and knee laxity were analysed after 12 and 36 months. Data were evaluated using analysis of variance (ANOVA) with Bonferroni correction. Significance was set at <0.05.

RESULTS

Femoral/tibial tunnel volume enlarged 10.7 ± 46.6%/3.8 ± 14.4% (PLLA, n = 9) and 2.6 ± 30.8%/19.0 ± 20.5% (PLDLA +, n = 13) after 36 months on CT scans (p = 0.063/p = 0.070). Using MRI scans, femoral/tibial screw volume decreased -53.8 ± 6.9%/-48.8 ± 9% (PLLA) and -88.2 ± 8.9%/-80.6 ± 3.4% (PLDLA+) (p ≤ 0.001/p ≤ 0.001). No difference was found between the two groups (PLLA, n = 17; PLDLA+, n = 19) in PROMS and knee laxity (n.s. and/or minimal clinically important difference (MCID) not reached).

CONCLUSIONS

Tunnel volumes remained slightly enlarged, screw degradation was significantly higher in the PLDLA+ group while clinical outcomes led to good short-term results. Comparable tunnel enlargement for both screws can be expected in revision ACL reconstruction.

LEVEL OF EVIDENCE: Level I randomised controlled trial.