Meniscal Injury

A meniscal injury is a tear of the fibrocartilage menisci of the knee, either traumatic in younger people after a twist on a loaded, flexed knee or degenerative in older adults.

The distinction drives management. A locked knee or a possibly repairable traumatic tear needs MRI and orthopaedic referral. A degenerative tear, often found with knee osteoarthritis, is managed with exercise first: arthroscopic partial meniscectomy has not outperformed exercise or sham surgery in randomised trials.

The medial and lateral menisci sit on the tibial plateau. They spread load across the joint, absorb shock, and add to stability, congruity and proprioception. The medial meniscus is C-shaped and tethered to the deep MCL and capsule, so it is less mobile and more often injured. The lateral meniscus is more O-shaped and mobile, has no LCL attachment, and is often torn with an ACL injury.

Blood supply decides healing:

• •Red-red zone (outer third): well vascularised; tears here are candidates for repair
• •Red-white zone (middle third): intermediate vascularity and variable healing
• •White-white zone (inner third): avascular and does not heal

Tear patterns:

• •Vertical longitudinal, including bucket-handle: the typical traumatic tear. A displaced bucket-handle fragment in the notch causes true locking
• •Horizontal cleavage: the typical degenerative tear, and the usual cause of a meniscal cyst at the joint line, most often laterally
• •Radial: runs from the free edge outward and disrupts the circumferential hoop fibres
• •Root tear: biomechanically similar to losing the whole meniscus. A medial posterior root tear shows meniscal extrusion of 3 mm or more and a ghost sign on MRI