57 patients scheduled for double-bundle anterior cruciate ligament (ACL) reconstruction were randomized to tibial fixation with either the use of pure poly-L-lactic acid interference screws or screws containing beta (B)-tricalcium phosphate (TCP). Patients were assessed on CT at 12 months for tibial tunnel enlargement at four tunnel depths: at the joint line, mid-tunnel, mid-screw, and at the tunnel aperture. Both groups demonstrated significant increases in tunnel cross-sectional area after 12 months. At the mid-screw level, the B-TCP group demonstrated a significantly lesser increase in CSA when compared to the PLLA group. In contrast, at the mid-tunnel level, the B-TCP group demonstrated a significantly greater increase in CSA when compared to the PLLA group.