Collateral Ligaments Tears
Medial collateral ligament tear
It constitutes the intermediate portion of the three layers of the medial supporting structures, composed of the fascial planes most superficially, and followed by the so-called medial collateral ligament as the intermediate and the joint capsule as the deepest layer.
The ligament originates from the medial femoral condyle and inserts on the medial aspect of the tibia approximately 7-cm distal to the tibial joint surface.
Damage to the MCL results from excessive valgus stress in the flexed knee. Usually the deepest layer (capsule) is ruptured first, as it is the weakest of the medial supporting structures. Mostly, lesions are located in the femoral portions of the ligament (Fig. 8.7.16).
There are three grades of ligament affection, which correlate with specific findings on MRI.
Grade I is microscopic fiber disruption with some internal hemorrhage in the ligament, local pain at palpation, and no instability.
Grade II corresponds to partial macroscopic tears of the ligament, local pain, and increased knee mobility with valgus stress.
Grade III is the complete disruption of the ligament and clear instability.
MRI findings are obtuse margins of the ligament, focal signal intensity increase (edema, hemorrhage); disruption of ligament continuity, wavy contours, and eventually separation from the bony insertion site. There may be increased signal intensity in the periligamentous tissue, with loss of a clear delineation of the subcutaneous fat.
Lateral collateral ligament tear
In contrast to the MCL, the LCL does not blend with the joint capsule. It has a more oval, cross-sectional shape running from the lateral aspect of the fibular head to the lateral femoral condyle. Slight angulation of the coronal plane may help to visualize the LCL in its entire length within one section. Similar to the MCL, three grades of injury can be diagnosed for the LCL with corresponding MRI findings. However, whereas more and more often there is conservative treatment for MCL tears, complete LCL disruption constitutes a serious injury to the posterolateral corner of the knee, which if left untreated, results in continued posterolateral instability and a high rate of ACL or PCL repair failure and premature osteoarthritis OA.