Ans. a (1st metacarpal). (Ref. Maheshwari, Orthopaedics, 2nd/pg.98)RENNET'S FRACTURE# Bennet's fracture is an oblique intra-articular fracture of the base of 1st metacarpal with subluxation or dislocation of the metacarpal.# Rx by accurate reduction & restoration of the smooth joint surface is important as any abnormality in congruity of the articular surface will lead to osteoarthritis. Following methods are used for treatment:# (1). Closed manipulation & plaster cast.# (2). Closed reduction & percutaneous fixation under X-ray control.# (3). Open reduction & internal fixation with K-wire/screw may be necessary in some cases.Bennett's fractureAn oblique fracture at the base of the first metacarpal that involves the first carpometacarpal joint space. Such a fracture is often unstable, as the distal fragment is distracted by the unopposed abductor pollicis longus muscle, and may require surgical intervention.Rolando's fractureA fracture similar to Bennett's fracture with comminution of the metacarpal. This injury is actually less prone to displacement of the distal fragment due to the comminution of the thumb base and is less likely to require surgical fixation than is a Bennett's fracture.Game keeper's (skier's) thumbForced abduction of the thumb can result in disruption of the ulnar collateral ligament of the metacarpophalangeal joint (MCP) of the thumb, a major stabilizer of the thumb.Boxer's fractureFractures of the fourth and fifth metacarpals are common and are usually the result of punching a hard object. The fracture may involve the midshaft or distal end of the bone, and is usually dorsally angulated.