Hand injuries are among the most common injuries encountered in the Emergency Department (ED). They are responsible for 5% to 10% of ED visits, with approximately 6% of these patients having significant injuries.1,2 Many hand injuries occur from sports-related events or in the workplace. Data suggest that hand injuries account for 19% of lost-time injuries and 9% of workers’ compensation cases.3 Approximately 3 to 4 million working days are lost each year as a result of hand injuries.4 It is estimated that 10% of patients with hand injuries require referral to a hand specialist.5 Proper motion and function of the hand are intimately related to normal anatomic alignment. The Emergency Physician (EP) must be skilled in the diagnosis and management of injuries about the hand. An improperly managed hand injury can result in significant disability that may include chronic pain, decrease range of motion, stiffness, joint swelling, deformity, or early degenerative arthritis.
Dislocations of the metacarpophalangeal (MCP) joint are relatively uncommon due to the relatively protected location of this joint in the hand.6 Injuries to the MCP joint of the thumb are more common than injuries to the other digits. Most of these injuries are to the collateral ligaments rather than a true dorsal or volar dislocation.7 The spectrum of injury to the ligaments extends from a minor stretch or sprain to a complete disruption.
The deformity caused by a joint dislocation is classified by the position of the distal skeletal unit in relation to its proximal counterpart. A dorsal MCP joint dislocation describes a dislocation in which the proximal phalanx is displaced in a dorsal direction relative to the metacarpal bone (Figure 106-1A). A volar MCP joint dislocation describes a dislocation in which the proximal phalanx is displaced in a volar direction relative to the metacarpal bone (Figure 106-1B).
Dislocations are classified by the position of the distal skeletal unit in relation to its proximal counterpart. A. Dorsal MCP joint dislocation. B. Volar MCP joint dislocation.
ANATOMY AND PATHOPHYSIOLOGY
The metacarpals are tubular bones structurally divided into a head, neck, shaft, and base. When viewed in the sagittal plane, the metacarpal head has an increasing diameter beginning dorsally and extending along the articular surface to the volar side. When viewed in the coronal plane, the metacarpal head is pear-shaped or dumbbell-shaped, with the volar surface extending out of each side. The metacarpal head is broader in volar orientation which results in increasing bony stability as the joint is flexed. The volar plate, collateral ligaments, dorsal capsule, deep transverse intermetacarpal ligament, extensor tendon, and intrinsic tendons provide additional support and stability to the MCP joint.