1. To be able to distinguish normal from pathological postoperative MR features in ACL reconstruction.
2. To understand the clinical relevance of postoperative ACL reconstruction imaging.
The ruptured anterior cruciate ligament (ACL) is regularly reconstructed. Preoperative radiographs provide valuable information about intercondylar slope and extension in the knee joint. In the past, reconstruction techniques focused on isometric grafts, though recently there is a clear turn towards “anatomic” reconstruction. This has led to a marked increase in early postoperative imaging to assess tunnel placements. Femoral tunnel placements are evaluated in a grid and tibial tunnel placements are evaluated in the lateral view. Graft impingement is evaluated in the lateral view with the knee in full extension. Early imaging also detects hardware failure and may serve as a baseline for later examinations. Radiographs and CT are usually used for early assessment. MRI is excellent for assessing soft tissue complications, such as localized arthrofibrosis (Cyclops lesion), re-rupture of the graft, concomitant meniscal or missed injuries to lateral stabilizing structures. The graft may have high signal intensity for as long as two years post-operatively. Anterior translation of the tibia is a useful indicator of partial rupture and consequent instability, rather than graft signal in this period. Further useful signs are uncovering of the posterior horn of the lateral meniscus and buckled posterior cruciate ligament, although MRI is not sufficiently accurate to differentiate between unstable and stable knee ligament injuries.