Discoid Meniscus

Objectives

Define discoid meniscus
Describe history and physical findings compatible with discoid meniscus in children
Describe a classification system for discoid meniscus
Describe treatment options for discoid meniscus
Describe results of treatment for discoid meniscus

Discussion point

What is the best surgical treatment of an unstable discoid meniscus: total menisectomy or meniscal/capsular stabilization? Which treatment offers the most definitive results and which treatment offers the best potential for joint preservation?
What lesion of the femoral condyle can accompany discoid meniscus, and how does it affect the outcome?

Discussion

Congenital discoid meniscus is a rather confusing entity. If a discoid meniscus is present at all, it is obviously present during childhood, yet it is often asymptomatic until adult life. When symptomatic during childhood, the symptoms are variable and inconsistent, including clunking, giving way, snapping, locking, or lack of mobility. If the child is hampered to the degree that the parents seek medical attention, there should be objective physical findings that indicate intra-articular pathology. Quadriceps atrophy, which appears after a few weeks of protecting the knee, lack of full extension, and joint line tenderness are helpful signs. Dickhaut noted a palpable snap near complete extension in all six children/ adolescents they treated for discoid meniscus. Effusion is less common. Routine radiography may reveal a widened lateral joint space, MR imaging reveals the lateral mensicus height to be greater than the medial, with a high intrameniscal signal.

Many present day writers use the classification system of Watanabe in describing the discoid meniscus; an incomplete meniscus, a complete discoid meniscus, and the Wrisberg type. The difference between the complete and incomplete is subjective and not of much clinical significance. The Wrisberg type is characterized by the presence of the ligament of Wrisberg passing from the posterior horn of the lateral meniscus to the posterior portion of the medial femoral condyle, and a lack of capsular attachment of the discoid meniscus. Such a meniscus is unstable and may displace medially, laterally, or anteriorly. There is considerable variation in the reported incidence of the Wrisberg type of discoid meniscus. Dickhaut reported all 6 children had a Wrisberg type of meniscus, Aichroth noted the majority of children had a Wrisberg type, Kocher recently reported that 28% of discoid menisci were unstable, and others such as Pellacci found a low incidence or none at all.

If a peripheral attachment of the meniscus is noted, saucerization may be performed, leaving a rim of about 6-8 mm. The evolution of meniscal repair techniques, has recently created controversy regarding the treatment of the unstable Wrisberg type of lateral discoid meniscus. In the past it was thought that these should be completely removed, because partial meniscectomy in this setting would leave an unstable posterior rim. Although long-term functional results of knees treated with open meniscectomy were generally acceptable, osteoarthritic changes were often noted. In an attempt to preserve the joint, current options include arthroscopically-aided stabilization of the unstable portion of the meniscus to the adjacent capsule using inside out technique (posterior horn) or outside in technique (anterior horn). Good has reported excellent short term (avg 3 year) follow-up results using this technique in all repairable menisci. The disadvantage to this approach is recurrence of the instability. All-inside techniques (darts and staples) are generally not appropriate for unstable discoid meniscal stabilization because there is no peripheral meniscal remnant to attach to. Newer all-inside devices using sutures may capture sufficient capsular tissue to be useful. Meniscal tears are associated with discoid menisci about 70% of the time, and the incidence increases with increasing patient age. Treatment is identical to that of non-discoid menisci, and an attempt should be made to repair unstable peripheral longitudinal tears.

Osteochondritis dissecans of the lateral femoral condyle is seen in a minority of knees with discoid menisci, but is associated with a poorer prognosis when present. Discoid meniscus appears to be more common in children of Asiatic descent.

References

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