Review Question - QID 6451

A 55-year-old electrician who is 5' 8" and weighs 243 lbs has severe pain in the medial side of his knee. Six months ago he underwent an arthroscopy and partial medial meniscectomy that resulted in very little improvement in symptoms. Radiographs confirmed medial femoral condyle osteonecrosis and he underwent a successful medial unicondylar knee arthroplasty and returned to work in 3 weeks. Radiographs are shown in Figures 29a and 29b. Four months after this surgery, he now reports the gradual onset of pain and swelling for the past 2 weeks. Laboratory studies, including a CBC count, erythrocyte sedimentation rate, CRP, and uric acid level, are all normal. Synovial fluid analysis reveals a WBC count of 6,500/mm3 and a RBC count of 45,000/mm3. He has difficulty weight bearing and is unable to work. What is the most likely diagnosis?