A recurrence of objectively measured knee laxity after anterior cruciate ligament (ACL) reconstruction has previously been reported in various papers; the purpose of this study was to accurately measure in vivo knee laxity after both bone-tendon-bone (BTB) and hamstring reconstruction using radiostereometric analysis (RSA), and to differentiate between graft fixation slippage and graft stretching and their relative contributions to any increase in laxity.

Twenty patients were studied prospectively after ACL reconstruction. Ten had been operated on using BTB grafts, and ten using hamstring (four-stranded semitendinosus/gracilis) grafts. Tantalum markers were inserted in the distal femur, proximal tibia and into the graft itself. (RSA) was used to measure sagittal laxity, graft stretching and fixation slippage early post-operatively, and then at intervals up to 1 year.

A steady increase in total anteroposterior laxity was found in both groups over the year. For the BTB group, total mean slippage of the bone plugs increased to 1.28 mm at 1 year. For the hamstring group, the tunnel attachments had slipped by a total of 6.82 mm. More stretching was found for the hamstrings grafts than for the BTB grafts and the amount of stretching increased significantly with time post-surgery. The hamstring grafts stretched by a mean of 4.18%, the BTB grafts by 1.18%.

This is believed to be the most detailed application of RSA in analysing the performance of the two commonly used grafts in ACL reconstruction. Details such as graft stretching and fixation slippage have not been available previously; the data obtained in this study may have implications for clinical practice.