RSA can measure ACL graft stretching and migration: development of a new method.

UNLABELLED: We describe the development of a method using radiostereometric analysis to measure fixation slippage and graft stretching after anterior cruciate ligament reconstruction. Initial development used a glass phantom object, then a series of laxity measurements of cadaveric knees. After this, we prospectively studied 14 patients after anterior cruciate ligament reconstruction using bone-patellar tendon-bone and hamstrings grafts. Tantalum markers were inserted into the femur, the tibia, and the graft. Radiostereometric analysis was used to measure sagittal laxity, graft stretching, and fixation slippage postoperatively and at intervals up to 1 year after surgery. The cadaveric knee laxity measured by RSA correlated with clinically-accepted KT2000 measurements. A steady increase in total anteroposterior laxity was found in both clinical groups during the year of followup. Migration of the bony fixations and stretching of the grafts tended to be higher in the hamstrings group. This method of anterior cruciate ligament graft analysis provides a new way to ascertain laxity changes in the reconstruction after surgery. LEVEL OF EVIDENCE: Diagnostic Level II. See Guidelines for Authors for a complete description of levels of evidence.