Bony Erosion with Mucoid Degeneration of the Anterior Cruciate Ligament

The first reported case of mucoid degeneration of the anterior cruciate ligament (MDACL) was provided by Kumar et al in 1999.1 The pathogenesis is still unclear, but this condition is thought to be secondary to ACL degeneration. A 2004 study reported theprevalence ofMDACL as 0.043%,2 but a 2008 study found a prevalence of 5.3%.3 Although MDACL is not as rare as previously thought, it is not still well known by physicians and is probably underdiagnosed or misdiagnosed as an ACL tear. More accurate data on MDACL are needed. MDACL with erosion of adjacent bone is extremely rare; only a few cases have been reported to date.1,4,5 We treated two patients with MDACL, one with an eroded lesion in the lateral femoral condyle and one with tibial insertion of the ACL. We report these two cases and discuss their clinical features with reference to previous MDACL reports, focusing on bone erosion.