A 55 year old postmenopausal female, previously in good health, had an abrupt onset of right knee pain. This was managed by her general practitioner for three months, with analgesics and non-steroidal anti-inflammatory drugs (NSAIDs). She had no recollection of any trauma. As the symptoms failed to resolve, she was referred to the orthopaedic service. On history, the knee pain was deep seated, sharp, and intermittent. It was made worse on exertion and relieved by rest. There was no associated musculoskeletal or neurological abnormality. On physical examination, she looked well. The knee joint appeared normal without any restriction of motion. All movements of her lumbar spine were normal. Examination of the hip joint was negative except for painful restriction of internal and external rotation. Blood tests including full blood count, erythrocyte sedimentation rate, and bone profile were normal. Specific tests for rheumatoid factor, antinuclear antibodies, brucella antigen, HLA B-27, and thyroid function tests were all negative. Radiographic examination of the lumbar spine, knee, and the hip (fig 1) revealed no abnormality. An isotope bone scan of the pelvis is shown (fig 2). Arthrocentesis of the hip joint yielded few millilitres of clear yellow fluid with no bacteria seen on acid-fast, fungal, or Gram stains. Culture for aerobic, anaerobic, acid-fast, and fungal organisms was also negative. A bone biopsy under general anaesthesia gave unremarkable results. Finally, a magnetic resonance imaging (MRI) scan was conducted (fig 3).
Radiograph of the pelvis at three months since onset of symptoms.
Radionuclide bone scan of the pelvis.
(A) Coronal T1 weighted MRI image and (B) coronal T2 weighted MRI image.
Questions
What are the findings on the bone scan and the MRI scans?
What is the diagnosis?
