MRI of intermittent meniscal dislocation in the knee.

The aim of this work was to demonstrate meniscal dislocation on magnetic resonance (MR) imaging, in cases with no meniscal tear but a strongly suggestive clinical history of reproducible intermittent locking of the knee. Three patients with a strong history of intermittent knee locking had negative initial MR scans but were able to reproduce locking of their knee voluntarily. A further MR study involving T(2) weighted sagittal and coronal imaging of the knee was performed in the "locked" position using either a standard knee coil if the joint was straight or a flexible coil if flexed. MR demonstrated meniscal dislocation in all three patients when they intentionally adopted the "locked" knee position. On review of the initially negative scans, the menisci were confirmed to be normal in appearance. All three were confirmed arthroscopically to have deficiency of the corresponding meniscocapsular ligaments with instability of the meniscus to direct probing, but no meniscal tear. A normal conventional MR may not detect the cause of intermittent locking, particularly in the absence of a meniscal tear. When patients are able to intentionally adopt the "locked" position at will, a further study in the "locked" position can be diagnostic.