Osteonecrosis of the Upper Extremity: MRI-Based Zonal Patterns and Differential Diagnosis.

Regarding the upper extremity, osteonecrosis can relate to the humeral head and to any carpal bone, most commonly the lunate (Kienböck's disease), scaphoid (Preiser's disease and nonunion), and capitate bone (osteonecrosis of the capitate head). In children and adolescents, osteochondrosis is an important differential diagnosis at the epiphyses. Appropriate imaging of osteonecrosis depends on knowledge about blood supply, biomechanical load, and bone repair mechanisms. Contrast-enhanced MRI (ceMRI) enables the differentiation of up to three mostly band-shaped zones: necrotic tissue (proximal), hypervascular repair tissue (intermediate), and viable bone (distal). To distinguish between necrotic and repair zones, intravenous gadolinium is recommended in MRI. Osteosclerosis and insufficiency fractures in early and intermediate stages as well as osteoarthritis in advanced stages are best depicted using high-resolution CT (HRCT). The combination of HRCT and ceMRI allows for exact classification of osteonecrosis regarding morphology and viability.