A man with a human bite to the finger

A 29 year old man presented to the emergency department with increasing pain, redness, and swelling of his right middle finger. Two weeks previously he had been bitten during an alleged assault, but had not sought medical attention.

Examination of the digit showed a discharging sinus at the distal inter-phalangeal joint level on the dorsal surface, with swelling, localised erythema, tenderness, and reduced active and passive motion (30 degrees active and passive flexion compared with 45 degrees on the opposite side).

Systemically, the patient was apyrexial and had normal vital signs. Routine investigations showed a normal white cell count, a C reactive protein of 52 (normal range: < 5 mg/L). He had two radiographs taken—anteroposterior and lateral. The lateral radiograph is shown.

(1) What does the radiograph show?

(2) Based on the case history and radiograph, what diagnosis does this patient have?

(3) What other investigations may be helpful?

(4)