Hip arthritis presenting as knee pain

A 68-year-old man with a history of left total knee replacement presented to his general practitioner with left knee pain. He reported pain onset after a fall in the garden. An X-ray of the knee was arranged but showed no abnormality to explain the pain. He was treated with simple analgesia. However, he reattended with the same knee pain. A further X-ray of the knee was requested, but again showed no abnormality. On his fourth presentation in 6 months, a further musculoskeletal examination was undertaken. This time the hip was also examined and showed that maximal pain was in fact on rotation of the hip joint. A subsequent X-ray of the hip showed severe osteoarthritis of the left hip with complete joint space loss and flattening of the femoral head. The patient was referred to an orthopaedic surgeon for a left hip replacement.