MR Imaging of the Hip: An Update on Bone Marrow Edema

Abstract

Bone marrow edema (BME) represents a frequent and easily detected MR imaging finding that is recognized as a common source of pain. It is considered a nonspecific finding that constitutes a central component of a wide spectrum of pathologies affecting the hip joint, showing high variability in terms of prognosis and treatment requirements. Solid knowledge of the various BME patterns and associated imaging findings indicative of these conditions can aid in differentiation. Additionally, correlation with clinical and laboratory data are essential for arriving at a final diagnosis in several cases. In this review, we describe the disease characteristics and imaging findings and also highlight the differential diagnostic clues regarding common hip disorders associated with BME including avascular necrosis, transient osteoporosis, stress injuries, and infectious/inflammatory disorders.

Imaging of the Hip

“…Within the epiphysis, the junction of the reactive zone with the articular subchondral bone plate undergoes increased bone resorption which can lead to early fracture of the overlying cartilage at these locations and subsequent subchondral fracture. This is often the earliest manifestation of an impending articular collapse [6,7]. Progressive fragmentation of the articular surface and secondary osteoarthritis are almost inevitable due to cortical flattening and collapse.…”

“…Imaging has an important role in ON evaluation, allowing early detection, assessment of severity and prognosis, treatment options, and postoperative follow-up [7]. Radiographs are the initial imaging method in the evaluation of the patient with hip pain, however, are insensitive for early changes of ON [6]. In late stage ON, the radiographic features are often characteristic and usually do not require further imaging workup.…”

“…As the disease progresses, a subchondral fracture with a crescentic appearance (crescent sign) may be visualized. Eventually this will lead to articular surface collapse and development of secondary osteoarthritis [6].…”

“…Subchondral insufficiency fractures (SIF) of the femoral head are a cause of marked mechanical hip pain and typically occur in the older, osteoporotic population. These fractures may progress to advanced collapse and therefore should be recognized on imaging and distinguished from osteonecrosis [6]. The MR imaging findings of SIF are that of a low signal subchondral line that parallels the articular surface and extensive bone marrow edema of the femoral head/neck (Fig.…”

“…Many consider this to be a "transient painful marrow edema." These conditions have basic characteristics which include sudden onset of pain in middle-aged men and in pregnant/post-partum women, spontaneous with gradual resolution of symptoms with conservative treatment (6-8 months), and presence of bone marrow edema on MRI [6]. This is typically a unilateral process but, however, can involve the contralateral side.…”