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 cruciate ligament were prospectively correlated with the clinical and arthroscopic findings. The variable MR features of the neo-ligament depend on the integrity of the prosthesis, the degree and extent of tissue ingrowth, and the time delay between surgical placement and MRI. The ABC ligament gives a uniform low signal when freshly placed, which is slowly lost by the incorporation of tissue ingrowth and therefore the loss of MR visualization of the ABC ligament is not synonymous with failure. Analysis of the imaging features suggests that a neo-ligament emerging through the tibial tunnel either at or posterior to the mid point of the AP diameter of the tibia is likely to be intact ( P=0.008) compared with one placed anteriorly. The presence of an effusion (64%) indicates that symptoms are more likely to be due to other internal mechanical derangement rather than failure of the neoligament. 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 neoligaments in 16 replacements. MRI in the post-operative period detects rectifiable problems before the development of irreversible mechanical damage and re-rupture of the neo-ligament, but a thorough MRI technique needs to be utilized in examining the entire knee.