Contribution of meniscal extrusion and cartilage loss to joint space narrowing in osteoarthritis

OBJECTIVE: This study was undertaken to determine the contribution of menis cal extrusion and cartilage loss to joint space narrowing on conventional r adiographs by correlation with magnetic resonance imaging (MRI), SUBJECTS AND METHODS: Sixty-two consecutive patients, 32 patients with oste oarthritis and 30 without osteoarthritis, over the age of 60 years that wer e referred for both radiographic and MRI of the knee were included in the s tudy. In each case, relative joint space narrowing on conventional AP radio graphs was assessed utilizing the Kellgren-Lawrence scoring system. Subsequ ently, the degree of meniscal extrusion and the integrity of articular cart ilage were evaluated from MR in the same patients. RESULTS: Each of 30 patients with normal joint space (Kellgren Grade 0) wer e noted to have normal articular cartilage, grade 1 meniscal extrusion was identified in only three of these patients. In comparison, meniscal extrusi on was identified in ail 32 patients with joint space narrowing (Kellgren G rades 1-4). Definite thinning or loss of articular cartilage was identified in only 15 of the 32 cases. In 17 patients with radiographic joint space n arrowing (Kellgren Grades 1-3) and meniscal extrusion, no loss of articular cartilage was observed. A statistically significant correlation (P<0.001) was observed between Kellgren Grade and degree of meniscal extrusion and ca rtilage thinning on MRI, CONCLUSION: Conventional radiographs are an unreliable method of evaluating for articular cartilage loss in patients with early osteoarthritis. Initia l joint space narrowing on conventional radiographs is secondary to menisca l extrusion rather than thinning of articular cartilage in most cases.