Femoroacetabular impingement is another cause of hip pain that may initially have a non–specific clinical presentation; however, a thorough physical evaluation should be able to identify this condition. Pain can be elicited on physical exam by passive movement of the thigh into full flexion, adduction, and internal rotation (34). Radiographs often help to identify anatomical variations such as dysplasia of the femoral neck (Fig. 6-19) or acetabular overcoverage. MR arthrography (Fig. 6-20) can be a helpful imaging study for evaluating the consequences of femoroacetabular impingement as well as thoroughly evaluating the abnormal anatomy. Intra-articular contrast helps to better delineate hyaline cartilage defects as well as labral tears. These findings, along with the clinical evaluation, help guide the appropriate treatment plan.
FIGURE 6-19. Lateral radiograph of the left hip. There is a bump along the superior margin of the left femoral head-neck junction that
Transient regional osteoporosis presents with a low– signal-makes for an aspherical configuration of the femoral head. This is intensity lesion on T1-weighted images that is similar to isch-characteristic of Cam-type femoroacetabular impingement. emic necrosis, but it typically involves both femoral head and neck and becomes hyperintense on T2-weighted images, suggesting the presence of edema. MRI demonstrates osteoarthritic subchondral sclerosis as low–signal-intensity zones in the subchondral marrow of both the femoral head and acetabulum. MRI also has been found to be very useful for identifying stress or occult fractures. These appear as low–signal-intensity areas containing an oblique or wavy line of still lower signal intensity, representing the actual fracture site. On T2-weighted images, these areas become hyperintense, suggesting that they are edema. MRI also can identify many types of soft-tissue abnormalities about the hip, including synovial cysts, periarticular bursitis, soft tissue masses and articular abnormalities such as synovial chondromatosis.