The knee after partial meniscectomy: MR imaging features

The magnetic resonance (MR) examinations of 51 menisci treated by means of partial meniscectomy were reviewed. Menisci were divided into three groups: group 1, near normal length without osteoarthritis; 2, substantially shortened without osteoarthritis; and 3, any length with osteoarthritis. Group 1 menisci resembled normal menisci except for mild shortening and frequent signal inhomogeneity (56%). Group 2 menisci varied in appearance, with marked contour irregularity simulating fragmentation in 40% of segments despite a normal postoperative appearance at follow-up arthroscopy. Group 3 menisci appeared similar to menisci of the same length without osteoarthritis. Arthroscopic correlation, available for 23 menisci (45%), confirmed the MR diagnosis of a tear in 11 and no tear in 49 and revealed an unsuspected tear in three meniscal segments. There is a spectrum of normal MR appearances after partial meniscectomy. Standard MR criteria can be used to diagnose tears in the absence of marked contour irregularity; however, the diagnosis of tears of segments with marked contour irregularity must be made cautiously, since this irregularity can mimic a tear and was not predictive of an arthroscopically visible tear.