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.

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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.

Coronal T1-weighted magnetic resonance (MR) images were obtained on a 1.5-T system in 23 patients in whom there was a high clinical suspicion of hip fracture although initial radiographs were normal. MR imaging correctly demonstrated fracture in nine of nine patients; the precise configuration of the fracture line was delineated in eight patients. MR imaging was useful in excluding fractures in 14 of 14 patients, who were subsequently followed up clinically for a minimum of 3 months. Radionuclide scans were positive in four of four patients with fractures and equivocal in one patient who was subsequently demonstrated to have no fracture. Additional imaging studies were requested by clinicians in all cases in which the bone scan was positive. The results of this study suggest that MR imaging can provide a rapid, cost-effective, and anatomically precise diagnosis of hip fracture in patients with normal or equivocal initial radiographs. The specificity of the diagnosis achieved can obviate supplemental imaging examinations, with their attendant additional expense and radiation exposure.

A kinematic magnetic resonance (MR) imaging technique for assessment of malalignment of the patella, involving the acquisition of multiple sequential axial images of the patellofemoral joint during the early increments of passive knee flexion, was used to evaluate 130 patients (235 symptomatic patellofemoral joints) showing clinical evidence of having patellar tracking abnormalities. Twenty-three of the patellofemoral joints had undergone previous surgical procedures for patellar realignment. In addition, 14 (28 patellofemoral joints) asymptomatic control subjects were studied. Normal patellar tracking was observed in all of the asymptomatic subjects and in 43 (17%) of the 260 patellofemoral joints in the patient population, 18 (7%) of which were symptomatic. Sixty-nine (26%) of the patellofemoral joints had lateral subluxation of the patella, 106 (41%) had medial subluxation of the patella, 21 (8%) had excessive lateral pressure syndrome, 19 (7%) had lateral-to-medial subluxation of the patella, and two (1%) had dislocation of the patella. Of the 235 patellofemoral joints with suspected abnormalities, 217 (93%) had patellar malalignment. Of the 23 patellofemoral joints that had undergone prior surgery, 20 (87%) had abnormal patellar tracking. Thirteen of 14 (93%) patellofemoral joints that had undergone a prior arthroscopic lateral retinacular release had a medially displaced patella.

In a prior study of marathon runners, we noticed that MR scans of the knee frequently each of the three groups was statistically significant at p < .05. In each case with hematopoietic bone marrow hyperplasia, the distal femur was the only area affected, while the epiphysis and proximal tibia were uninvolved. This pattern of affected bone marrow with hyperplasia of the hematopoietic marrow may be useful for the differential diagnosis.

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