 Specifically the study has the following objectives: 1 To quantify the extent of tibial tunnel enlargement at 3-, 6- and 12-months post ACL reconstruction with autogenous quadrupled hamstring graft; 2 To determine if the incorporation of beta tricalcium phosphate to the bioabsorbable interference screw alters the observed magnitude of tunnel widening; 3 To hypothesize mechanisms for any observed differences between tibial fixation devices; and 4 To correlate tibial tunnel widening with clinical outcome status. It is hypothesized that the PLLATCP bioabsorbable interference screw will not be associated with a reduction in tibial tunnel widening around the implant but rather between the implant and articular surface, compared to the PLLA alone screw. It is also hypothesized that there will be no effect of observed tunnel widening on clinical outcomes or graft failure rates. 