A 44-year-old man presented with progressively worsening left thigh pain of 8 years' duration. The patient's medical history was significant for a diagnosis of osteoid osteoma of the left femur treated elsewhere 24 years previously. At that time, the patient underwent open incisional biopsy ( Fig. 1), curettage, and autogenous iliac crest bone grafting without stabilization. The patient had no complications after surgery and was in good health until 8 years before this visit when he began to experience intermittent left thigh pain which gradually increased in frequency and severity. By the time the patient presented to us, he described a dull pain present most of the time punctuated by intermittent sharp pain. The patient could not identify any particular palliative or provocative factors for the pain. Acetaminophen provided minimal relief. He had experienced some decrease in his energy level but denied any fevers, chills, night sweats, skin changes, abdominal pain, diarrhea, unintentional weight loss, or decrease in appetite.On physical examination, the patient appeared healthy and had a normal gait. He had full active and passive ROM of the left hip, knee, and ankle without limitation. Motor testing and sensation in the left lower extremity were normal. Distal pulses were present and normal in the left lower extremity. There was exquisite tenderness to palpation over a several-centimeter diameter region of the anterior and lateral left mid-thigh, but there was no palpable mass in that extremity or any skin lesions at this site or elsewhere. The patient had increased thigh pain with provocative testing, including resisted hip flexion, extremes of hip rotation, and with full passive hip flexion.One month before presentation to our institution the patient had sought care from his primary care physician. The physician ordered radiographs (Fig. 2). A CT scan (Fig. 3) and bone scan (Fig. 4) were obtained subsequently and the patient was sent to us for additional orthopaedic care.Based on the history, physical examination, and imaging studies, what is the differential diagnosis at this point?
Imaging InterpretationThe radiographs (Fig. 2) and CT images (Fig. 3) of the left femur showed a geographic 3-cm diaphyseal radiolucency