Thigh pain in a 53-year-old woman.

A 53-year-old woman presented with 3 months of progressively worsening right medial thigh pain. She reported having constant severe pain and a burning sensation in the upper thigh. Her pain was worse at night, often awakening her from sleep. Initially, she experienced some relief with aspirin, ibuprofen, and naproxen; however, these no longer provided relief. She obtained partial pain relief with acetaminophen. She had a history of mild, blunt trauma to the left torso approximately 1 month before presentation, but no history of trauma to the affected limb. She denied any back pain, fever, chills, night sweats, or weight loss. Physical examination revealed a well-developed woman with no obvious deformity. Right antalgic gait was noted. There was no edema, erythema, skin warmth, or palpable mass on examination of the right thigh. Deep palpation did not change her symptoms. There was full and painless active and passive range of motion of the right hip and knee. Neurovascular examination, strength, and tone were normal. Magnetic resonance images of the right hip and thigh (Fig. 1), CT scans of the right proximal femur (Fig. 2), and a total body bone scan (Fig. 3) were available from the referring physician. Plain radiographs had not been performed at the time of the initial evaluation. Based on the history, physical examination, and the imaging studies, what is the differential diagnosis?