This injury, described by Bennett in 1882, is a fracture subluxation of the first carpo-metacarpal joint, with a sizeable palmar anterior marginal fracture fragment. The causative mechanism is axial overload along the first metacarpal with simultaneous flexion. The palmar oblique ligament holds the palmar marginal fragment in its anatomical position.
The remainder of the first metacarpal is adducted and supinated by adductor pollicis. The metacarpal as a whole is also displaced proximally by the abductor pollicis longus muscle. The treatment goals are to reposition the first metacarpal in the carpo-metacarpal joint, and to restore the articular surface.