Review Question - QID 217521

Figure A demonstrates squaring of the lateral condyle with increased joint space, indicative of a discoid lateral meniscus. Discoid menisci are the result of disorganized type 1 collagen.

A discoid meniscus is the result of abnormal development, which results in a hypertrophic and discoid-shaped meniscus. This patient is demonstrating signs of a torn discoid meniscus, which may not always be present. The diagnosis can be made on MRI by 3 or more 5 mm sagittal images with meniscal continuity. Because of the inferior tissue quality, these discoid menisci are prone to tears. Treatment for asymptomatic discoid menisci is observation. Surgical treatment usually includes saucerization and repair of any unstable tears.

Kocher et al. published a review in JAAOS on discoid lateral meniscus in children. They state that they are predisposed to tears due to their lack of peripheral attachments, increased thickness, and poor tissue quality. When surgery is necessary, they recommend saucerization with repair of any unstable tears.

Atay et al. performed meniscal biopsies on 12 patients with discoid meniscus tears and 6 patients with non-discoid-related tears. They performed transmission electron microscopy to compare the ultrastructure. They found that discoid menisci had a decrease in the collagen fibers with a more heterogeneous course than the controls.

Papadopoulos et al. performed a similar histomorphologic study on discoid menisci compared to lateral menisci excised during total knee arthroplasty. They found that discoid menisci lacked the continuity and homogeneity of collagen fibers when compared to normal menisci.

Figure A is a radiograph of the knee showing squaring of the lateral femoral condyle, suggestive of a discoid lateral meniscus.

Incorrect Answers:
Answer 1: A tibial eminence fracture is the result of the ACL avulsing from the tibial insertion, but is not seen in Figure A.
Answer 2: A bipartite patella results from abnormal patella ossification, but is not seen in this patient.
Answer 4: Blount’s disease is a dyschondrosis of the proximal tibia that leads to genu varum.
Answer 5: A patellar sleeve avulsion is the separation of the cartilage sleeve from the ossific nucleus of the patella, but is not seen in this radiograph.