The mere presence of a disc-shaped cartilage does not cause any problem. Rather, the condition condition is often asymptomatic in infancy and early childhood.
By the sixth or eighth year of life the child may complain of following in the affected knee.
- Snapping
- Click
- Giving way
- Catching
Symptoms may be precipitated by a recent injury, especially in the adolescent.
On examination
- Fullness may be detected in the lateral parapatellar area at the joint line.
- Loud “clunk” is audible during the last 15 to 20 degrees of extension of the flexed knee.
The clunk is produced by the lateromedial movement of the semilunar cartilage.
On extension of the knee joint, the lateral meniscus does not remain in place under the lateral femoral condyle because it is not fixed posteriorly to the tibia, but is dislocated medially onto the intercondylar space by the pull of the short meniscofemoral ligament.
During flexion the ligament relaxes, and the lateral meniscus is replaced in its usual position by the contracting popliteus and coronary ligaments.
- Atrophy of the thigh, joint effusion, and synovial thickening are significantly absent.
- Unless connected with an injury, there is no functional disability.
Forced hyperextension of the knee may elicit pain on the lateral aspect of the joint.
Differential Diagnosis
Other causes of snapping of knee can be
- Meniscall cyst
- Congenital subluxation of the tibiofemoral joint
- Abnormal movement of the popliteus tendon
- Snapping of the tendons about the knee
- Subluxation or dislocation of the proximal tibiofibular joint or of the patellofemoral joint.
Radiographic Imaging
Xrays
Increase in lateral joint space may be found on plain xray if discoid meniscus is thick. Flattening of the lateral femoral condyleand cupping of the lateral aspect of the tibial plateau are other features
Magnetic resonance imaging
It will clearly depict the configuration of the menisci and is the ivestigation of choice.
Contrast arthrography
About 10 ml of a water soluble contrast agent is injected into the infra-patellar synovial space through a lateral approach and anteroposterior, lateral oblique, medial oblique, poseroanterior, and lateral views are taken.
The diagnosis of discoid meniscus is made when the meniscus can be demonstrated extending to the intercondylar notch separating the cartilages of the lateral femoral condyle and lateral tibial plateau.
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