Early syphilis: a cause of mono-arthritis of the knee.

The number of syphilis cases has increased in the UK in recent years, but many clinicians have limited experience in the diagnosis and treatment of this disease. If early diagnosis is not made and treated promptly with antibiotics, the disease may remain latent until the more serious manifestations of tertiary syphilis develop. We present the case of a 27-year-old man who presented with an acute mono-arthritis secondary to syphilis. The condition responded to antibiotic therapy. Orthopaedic surgeons should be aware of the diagnosis and consider it in patients with an acute arthropathy.