FRACTURE OF METACARPALS
The carpal and metacarpal bones form a longitudinal arch within the osseous framework of the hand, with transverse arches formed by the metacarpals. The treatment of metacarpal fractures must restore the architecture of the hand so that the metacarpals of the mobile groups the thumb on the radial side and the ring and small fingers on the ulnar side maintain their important relationship with the stable central ray, which includes the metacarpals of the index and long fingers.
Fracture Of Metacarpal Neck
The most common metacarpal fracture occurs at the neck of the fifth metacarpal. Although often called the boxer fracture, it is more aptly named the “street fighter (brawler)” fracture because trained boxers attempt to strike their opponent with the radial side of the hand, which is more stable than the ulnar side. Most fractures of the neck of the fifth metacarpal are significantly comminuted on the volar side, resulting in apex dorsal angulation at the fracture site. These fractures are usually treated with closed reduction and immobilization in an ulnar gutter splint, which holds the metacarpophalangeal joint in 70 to 90 degrees of flexion.
Most fractures heal satisfactorily. Maintaining adequate rotational alignment is important, but some residual dorsal angulation is acceptable because the flexible ulnar side of the hand can adapt to slight deformity. Some extensor lag commonly persists after fracture healing. Open reduction is indicated only if rotational alignment cannot be maintained or the fracture angulates greater than 60 degrees. In any fracture of this type, the physician must carefully search for a laceration of the adjacent metacarpophalangeal joint caused by impact with a tooth; lacerations could lead to significant infection and marked disability if left untreated. Careful examination of a fight wound over the metacarpophalangeal joint requires a high index of suspicion as the extensor tendon laceration from a tooth is more proximal than the skin laceration when the hand is examined in the extended position; during making of a fist the tendon and skin laceration line up as does the cartilage injury to the metacarpal head.
Fracture Of Metacarpal Shaft
Most transverse fractures of the metacarpal shaft are angulated dorsally by the pull of the intrinsic muscles of the hand. The metacarpals of the long and ring fingers, however, are stabilized by the adjacent border metacarpals and their deep transverse metacarpal ligaments; therefore, they do not generally shorten even if the fracture is comminuted. Oblique or spiral fractures of the metacarpals of the small and index fingers do tend to shorten because they are not adequately splinted by stable metacarpals on either side.
Fractures of the metacarpal shaft can be treated adequately with immobilization in a plaster cast, with the metacarpophalangeal joint flexed 70 degrees and the proximal interphalangeal joint in full extension. This “position of function” relaxes the pull of the intrinsic muscles and allows the physician to monitor apposition, length, and rotational alignment of the metacarpals. Massive crush injuries of the hand, with multiple fractures and considerable soft tissue damage, require open reduction and internal fixation. Surgical repair allows early active motion and produces a good functional result.
Mobility of the carpometacarpal joint of the thumb is essential for adequate hand function. Therefore, treatment of all fractures of the thumb must achieve and maintain good reduction and alignment. Two particularly troublesome fractures are intra-articular fractures of the base of the first metacarpal.
Type I Intra-articular Fracture (Bennett Fracture)
This fracture within the joint is often associated with proximal dislocation of the metacarpal shaft. The abductor pollicis longus tendon inserts on the base of the metacarpal of the thumb and tends to abduct and pull the metacarpal shaft proximally. The very strong volar ligament, which is attached to the base of the articular facet of the metacarpal, maintains the alignment of the proximal fragment with the trapezium.
Bennett fractures usually require surgical fixation because reduction is difficult to maintain in a plaster cast. If a very small fragment of the metacarpal base remains on the ulnar side, the dislocated metacarpal can be reduced easily by applying traction and holding the thumb in abduction. The reduction is maintained with Kirschner wires inserted percutaneously. If the intra-articular fragment is very large, open reduction should be considered to restore the anatomy of the joint to as normal as possible. The reduction can be stabilized with screws, Kirschner wires, or a small buttress plate.
Often, a small displaced fragment appears innocuous on the radiograph, and the dislocation is missed. The most important aspects of the treatment of Bennett fractures are recognizing that the injury is a fracture dislocation rather than just an intra-articular fracture and achieving and maintaining an adequate reduction.
Type II Intra-Articular Fracture (Rolando Fracture)
This comminuted fracture involves the articular surface of the metacarpal. Unlike the type I fracture, there is no significant proximal displacement of the metacarpal shaft. The comminution extends radially along the base of the metacarpal of the thumb and distally to the insertion of the abductor pollicis longus tendon.
In a Rolando fracture, the amount of comminution determines the method of treatment. If there are two or three large fragments that can be adequately reduced, open reduction and internal fixation can be attempted.
Usually, however, good reduction is achieved only with great difficulty. Extensive comminution of the base of the metacarpal indicates the need for skeletal or skin traction to maintain the reduction.
Intra-articular fractures of the base of the thumb often lead to osteoarthritis of the carpometacarpal joint. Arthrodesis of the carpometacarpal joint of the thumb may be required later to relieve pain and instability.
Types III and IV Fractures
Type III fractures of the first metacarpal are extra-articular; that is, they do not involve the joint. Type IV (epiphyseal) fractures commonly occur in children and involve the growth plate; they should be recognized as extra-articular, not intra-articular, fractures. Extra-articular fractures are treated with closed reduction and immobilization; they rarely require surgery.