INTEGRITY OF ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION: A ROENTGEN STEREOPHOTOGRAMMETRIC ANALYSIS

Introduction Roentgen stereophotogrammetric analysis (RSA) is the most accurate radiographic technique for measuring three-dimensional micromotion in joints, and is now being developed for the study of anterior cruciate ligament (ACL) injury and outcome after surgical reconstruction. Using RSA a prospective study of ACL reconstruction is being undertaken. The aim is to obtain accurate information on the performance of both bone-patellar tendon-bone (BPTB) and hamstring grafts post-operatively. Materials and methods 14 patients with a unilateral ACL tear who underwent ACL reconstruction have been studied prospectively. Seven had BPTB grafts, and seven had four-stranded semitendinosus/gracilis. Tantalum markers were inserted at the time of surgery, 4 each into the femur and tibia, and 8 into the graft, at regular intervals along the length. Stress stereo radiographs (90N anterior and posterior draw forces) were taken at 1, 6, 12 and 24 weeks post-operatively. They were analysed using Medis RSA software. Results Initial results suggest that in addition to measuring total anteroposterior knee laxity, detailed analysis of the graft itself is possible. Beads placed in the bone blocks of the BPTB grafts, and in the intraosseous ends of the hamstrings, enable calculation of slippage of the fixation. The BPTB bone plugs moved 0.6 to 1.2mm by 12 weeks, the Hamstrings fixation was more variable. Beads placed in the intraarticular graft may enable measurement of any post-operative stretching, but are also somewhat erratic. Identification of the site of stretching – around the tunnel entrances, or intraarticularly, should be possible. Conclusions We believe that this detailed application of RSA in analysing the performance of the two commonly used grafts in ACL reconstruction has not been previously described. We hope to gain valuable insight into the behaviour of both graft types and reasons for graft failure. This presentation will demonstrate the methods developed and include the technical difficulties encountered in this on-going study.