Bone tunnel enlargement following anterior cruciate ligament (ACL) reconstruction can complicate revision surgery. This study compared postoperative tibial tunnel widening in patients who underwent arthroscopically assisted, single-incision, four-strand hamstring ACL reconstruction using a poly-L-lactic acid/hydroxyapatite blend (PLLA+HA) bioabsorbable interference screw for tibial fixation, with those in whom a plain poly-L-lactic acid (PLLA) screw was used. Thirty-four patients (13 with PLLA+HA tibial interference screw fixation and 21 with plain PLLA tibial interference screws) underwent a spiral CT scan to assess maximum tibial tunnel cross-sectional area at an average of 28.7 months follow-up. An assessment of tunnel wall sclerosis adjacent to the screw (cortication) was also made. The two groups were well matched for age, sex and graft diameters. Mean tibial tunnel enlargement in patients with PLLA+HA screws was 29.9% at average 30.9 months follow-up compared with 46% in patients with plain PLLA screw at an average 26.5 months follow-up (p=0.03). The tunnel wall adjacent to the screw appeared corticated in only 21% of patients with PLLA+HA screws (p=0.02) compared with 73% of patients with PLLA screws. The blending of HA with PLLA appears to reduce postoperative tunnel widening, and the reduced tunnel wall sclerosis seen postoperatively may indicate improved screw incorporation.