Femur chondrosarcoma misdiagnosed as acute knee arthritis and osteomyelitis—Further developing a hitherto unreported complication of tumor embolic ischemic ileal perforation after arthroscopic lavage

The differentiation between osteomyelitis and bone tumor may be difficult due to their overlapping clinical and radiological features. A 25-year-old lady presented with left knee pain and joint effusion associated with redness and hotness. A sub-optimally taken plain radiograph showed mixed osteolytic and osteoblastic lesion in the left lower femur with surrounding soft tissue swelling. Since the clinical diagnosis was acute osteomyelitis and arthritis, arthroscopic lavage was performed as a diagnostic and therapeutic procedure. The removed loose bodies and fibrinous tissue showed pathological features suspicious of chondrosarcoma. Subsequent MRI revealed an infiltrative tumor eroding through the cortex and joint cartilage. En bloc excision of the left lower femur, upper tibia including the knee joint and patella was performed, and the final diagnosis was grade 2 chondrosarcoma. The patient developed bilateral pulmonary metastasis 33 months after operation. Five months later, she suffered from a hitherto undescribed complication of ischemic perforation of the terminal ileum secondary to tumor embolic arterial obstruction with no macroscopic intestinal or peritoneal tumor deposit. The patient developed multiple brain metastases and died 43 months after initial presentation.Our case illustrates that malignant bone tumor as a differential diagnosis of acute osteomyelitis and arthritis merits recognition and exclusion before arthroscopic lavage, which may enhance tumor dissemination and in our patient results in embolic ischemic ileal perforation.