Subchondral bone marrow edema in patients with degeneration of the articular cartilage of the knee joint.
PURPOSE: To retrospectively determine at magnetic resonance (MR) imaging the prevalence of subchondral bone marrow edema beneath arthroscopically proved articular cartilage defects. MATERIALS AND METHODS: The study was performed in compliance with HIPAA regulations, and a waiver of informed consent was obtained from the institutional review board before the study was performed. The study consisted of 132 patients (70 men, 62 women; average age, 53 years) with articular cartilage defects of the knee joint who underwent MR imaging of the knee and subsequent arthroscopic knee surgery. At the time of arthroscopy, each articular cartilage lesion was graded by using the Noyes classification system. MR examinations were retrospectively reviewed to determine the size, depth, and location of subchondral bone marrow edema without knowledge of the arthroscopic findings. Pairwise Fisher exact tests and two-sample t tests were used to correlate MR imaging findings of subchondral bone marrow edema with the arthroscopic grade of articular cartilage degeneration. RESULTS: Subchondral bone marrow edema was seen beneath 105 (19%) of 554 articular cartilage defects identified at arthroscopy. It was not observed beneath any of the six grade 1 cartilage defects but was observed beneath eight (4.9%) of 163 grade 2A defects, 40 (14.4%) of 278 grade 2B defects, 54 (55.1%) of 98 grade 3A defects, and three (33.3%) of nine grade 3B defects. Subchondral bone marrow edema was also seen beneath four (1.4%) of 238 articular surfaces that appeared normal at arthroscopy. The mean depth and cross-sectional area of subchondral bone marrow edema increased with increasing grade of the articular cartilage lesion. CONCLUSION: Higher grades of articular cartilage defects are associated with higher prevalence and greater depth and cross-sectional area of subchondral bone marrow edema.