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More Careful Diagnosis Needed for Transient Osteoporosis of the Hip in Men

Increased awareness and more careful analysis of magnetic resonance imaging data are needed to prevent the misdiagnosis of transient osteoporosis of the hip as avascular necrosis, particularly in men.

Transient osteoporosis of the hip (TOH) is a spontaneous skeletal disorder characterised by a sudden onset of severe pain that resolves within 6 to 8 months. It is commonly associated with pregnancy, but has also been detected in men. Disease management typically consists of symptomatic pain relief and decreased weight bearing activity and does not require further intervention.

In contrast, avascular necrosis is a progressive condition that requires early surgical intervention to prevent hip joint deformity and is a more common cause of acute hip pain than TOH.

Radiographic analysis and bone scans are most often used in the diagnosis of acute hip pain, yet these tests lack sensitivity and specificity, respectively. Furthermore, radiographic results in the early stages of TOH are often confused with avascular necrosis, which can put patients at an unnecessary risk of surgery-related complications.

MRI has emerged as a promising diagnostic tool that when analysed properly can successfully distinguish between TOH and avascular necrosis. This distinction is essential for the proper management of these conditions.

Michael D. McKee, MD, and colleagues at St. Michael's Hospital and the University of Toronto, Ontario, Canada, analysed the prevalence of misdiagnosis of TOH as avascular necrosis in 196 patients, with a particular interest in the frequency of TOH in men.

Ten men (12 hips) between the ages of 32 and 55 who were initially diagnosed with avascular necrosis were determined by this study to have TOH.

MRI data collected before referral for avascular necrosis were obtained for 9 of the men. Analysis by this study's physicians revealed changes typically seen in TOH, namely diffuse oedema, absence of focal defects, intact articular surface and absence of a double line sign, which is commonly associated with joint effusion.

Bone scans revealed uniform increased uptake at the affected femoral head extending down into the femoral neck and intertrochanteric region, and radiographic data saw either no changes or diffuse osteopaenia in the affected femoral head and periarticular acetabular bone.

Confirmation of TOH as the correct diagnosis was made through the observation of symptom resolution over time. The average time to resolution was about 6 months and complete resolution as determined by MRI was seen at an average of 7.5 months.

Dr. McKee recommends that "TOH should always be considered in the differential diagnosis of acute hip pain in young men." Undeniably, "early differentiation of TOH from avascular necrosis will avoid unnecessary surgical intervention and ensure appropriate treatment."
Can J Surg Vol 46, Number 3 (June), 2003:187-192. "Distinguishing transient osteoporosis of the hip from avascular necrosis"

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