Before surgery, 277 menisci in 144 knees were examined with magnetic resonance (MR) imaging. They were then examined directly with arthroscopy or arthrotomy. Menisci were graded on a scale of 1-3 according to the character of the intrameniscal MR imaging signal. At surgery, 137 of 154 (89%) menisci exhibiting only grade 1 or grade 2 signal were found to be normal. One hundred sixteen of 123 (94%) menisci exhibiting intrameniscal signal communicating with a meniscal articular surface (grade 3 signal) had tears. If only a grade 3 signal is considered consistent with meniscal tears, then MR findings and surgical findings agreed in 91.3% of menisci. MR imaging can separate surgically significant from nonsignificant meniscal lesions and is useful in the noninvasive preoperative screening of suspected meniscal tears.

Scant attention has been paid to the role of magnetic resonance (MR) imaging in the assessment of posttraumatic disorders of bone and cartilage at the knee. The authors reviewed 66 cases and identified four types of injuries that were not clearly evident on plain radiographs. A bone bruise was the most common lesion, having a high association with anterior cruciate ligament tears. Osteochondral fractures, stress fractures, and supracondylar femoral and tibial plateau fractures were also identified. MR imaging appears extremely useful in the detection and assessment of bone and cartilage disorders around the knee.

Menisci from 12 autopsies and above-knee amputations were imaged with magnetic resonance (MR) at 1.5 T and then sectioned for gross and histologic examination. A histologic staging system was developed and showed a one-to-one correlation with corresponding grades of MR signal intensities. Histologic stages 1 and 2 represented a continuum of degeneration culminating in stage 3 fibrocartilaginous tears, seen most frequently in posterior-horn segments of the medial meniscus. Correlation of histologic stages with MR signal intensity allows for an improved diagnostic reading of MR images.

Eccentric muscular actions involve the forced lengthening or stretching of muscles and tend to produce exertional injuries. This study used magnetic resonance (MR) imaging to serially evaluate muscles in five healthy, untrained subjects who performed exhaustive biceps exercise by doing isolated eccentric and concentric actions with a dumbbell. Symptoms were assessed, and T2-weighted images of the arms were obtained before exercise and 1, 3, 5, 10, 25, 40, 50, 60, and 80 days after exercise. Statistically significant increases in T2 relaxation times indicative of muscle injury occurred on each day of MR imaging evaluation in muscles performing eccentric actions, peaking on day 3 in two subjects; day 5, two subjects; and day 10, one subject. The pattern and extent of the abnormalities on MR images were variable. Pain, soreness, and joint stiffness were present on days 1, 3, and 5 in muscles that performed eccentric actions. MR imaging showed subclinical abnormalities that lasted as long as 75 days after the disappearance of symptoms (two subjects). Muscles that performed concentric actions had no changes in T2 relaxation times and were asymptomatic throughout the study.

Discoid menisci of the knee are not uncommon, and the criteria for arthrographic diagnosis and the clinical symptoms are well known. Although enlarged menisci have been recognized at magnetic resonance (MR) imaging, there are no criteria for the MR imaging diagnosis. The authors describe 29 discoid menisci imaged by means of MR. A discoid meniscus was said to be present if three or more 5-mm-thick contiguous sagittal images demonstrated continuity of the meniscus between the anterior and posterior horns. High-resolution coronal images allowed more graphic depiction of the abnormally wide meniscus. In approximately one-third of the cases in which coronal images were obtained, the measurable height difference between the discoid and the opposite meniscus was greater than or equal to 2 mm. Arthroscopic correlation (obtained in 10 cases) revealed that six cases of discoid meniscus were diagnosed correctly with MR imaging, although one meniscus was considered discoid at MR imaging but was not considered discoid at arthroscopy. Of three discoid menisci seen to be torn at arthroscopy, two were seen to be torn at MR imaging.