Some knee pains are notoriously difficult to diagnose.
It is even more baffling when the expensive MRI scan of the painful knee is reported as being normal!
I occasionally encounter such patients. They come into my clinic with a problem of pain in the inner side (medial joint line) of the knee. There may be a history of twisting injury to the knee but sometimes there is no antecedent trauma to that knee.
Physical examination may be normal except for point tenderness (pain) in the posteromedial joint line. A clinical diagnosis of a medial meniscus tear is usually made. An MRI scan would usually be done to confirm the diagnosis.
However, in medial menisco-capsular separations, the MRI scan can often look perfectly normal.
A high index of suspicion is needed to come to a diagnosis and the treatment is surgery via arthroscopic repair of the tear.
What is Medial Menisco-Capsular Separation?
The menisci are C -shaped fibro-cartilaginous structures attached to the shin bone and their main functions are to enhance the contact between the two articular surfaces of the knee: thigh bone and shin bone. The thick outline of menisci allows for a firm attachment to the joint capsule.
In a medial menisco-capsular separation, the attachment of the medial meniscus to the joint capsule is disrupted. These fibres are called menisco-tibial ligaments (attaching the meniscus to the shin bone) and menisco-femoral ligaments (attaching the meniscus to the thigh bone of the knee joint).
It may be associated with an anterior cruciate ligament tear in some patients.
The separation causes the medial meniscus to move excessively during physical activities such as running, walking, squatting and pivoting. This causes medial sided joint line pain.
During arthroscopy, the meniscus will appear to be lifted off the tibial bone.
What Can MRI Show?
True menisco-capsular separation can be seen on MRI scan if it is done soon after the injury. There will be fluid signal extending from the superior to the inferior aspect of the menisco-capsular junction medially.
However, in the chronic cases, MRI scans are usually reported as being normal.
How to Treat?
A trial of conservative treatment through the use of pain medications and physiotherapy can initially be tried.
If the pain persists, key-hole surgery to the knee may be needed.
Key-hole surgery to the injured knee via knee arthroscopy can allow the surgeon to visualize the tear directly and to repair it.