MRI OF THE KNEE FOLLOWING PROSTHETIC ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

The MRI appearances of the knee in 30 patients with residual symptoms following active biocomposite (ABC) reconstruction of the anterior cru ciate ligament were prospectively correlated with the clinical and art hroscopic findings. The variable MR features of the neo-ligament depen d on the integrity of the prosthesis, the degree and extent of tissue ingrowth, and the time delay between surgical placement and MRI. The A BC ligament gives a uniform low signal when freshly placed, which is s lowly lost by the incorporation of tissue ingrowth and therefore the l oss of MR visualization of the ABC ligament is not synonymous with fai lure. Analysis of the imaging features suggests that a neo-ligament em erging through the tibial tunnel either at or posterior to the mid poi nt of the AP diameter of the tibia is likely to be intact (P=0.008) co mpared with one placed anteriorly. The presence of an effusion (64%) i ndicates that symptoms are more likely to be due to other internal mec hanical derangement rather than failure of the neo-ligament. Meniscal tears were seen in 67% while osteo-chondral defects were noted in 30% of all patients. Excellent correlation with arthroscopic findings was established confirming intact neo-ligaments in 16 replacements. MRI in the post-operative period detects rectifiable problems before the dev elopment of irreversible mechanical damage and re-rupture of the neo-l igament, but a thorough MRI technique needs to be utilized in examinin g the entire knee.