Trauma to the hand is exceedingly common, not infrequently resulting in metacarpal and phalangeal fractures and dislocations.  Most of these injuries can be managed nonoperatively with immobilization or controlled mobilization. For certain intra-articular fractures, displaced and angulated fractures, unstable fracture patterns, combined or open injuries, as well as irreducible and unstable dislocations, surgical intervention may be required for restoration of function and appearance.
Most metacarpal fractures occur in the active and working population, particularly adolescents and young adults. In the United States, upper extremity injuries result in over 16 million days off of work and a further 90 million days of restricted activity. Lost revenue and costs exceed 10 billion dollars. [2, 3, 4]
Patterns of injuries result from the unique anatomy of the hand. Metacarpals are long tubular bones with an intrinsic longitudinal arch and a collective transverse arch. Bones are concave on the palmar surface and are joined proximally and distally by ligamentous attachments. The second and third metacarpals are fixed rigidly at their bases, while the fourth and fifth carpometacarpal (CMC) joints are capable of at least 15° and 25° of motion, respectively. The thumb CMC saddle joint is highly mobile, and its unique motion and injury patterns are addressed more fully elsewhere (see Bennett Fracture and Rolando Fracture).
The CMC joints of the second and third metacarpals are very stable, and there is very little relative motion at these joints. The sawtooth articular arrangement combined and the strong dorsal and palmar CMC ligaments and metacarpal ligaments form very strong and relatively immobile joint capsules.
These joints are further stabilized by extensor carpi radialis longus and brevis tendon insertions on the bases of the second and third metacarpals, respectively. The insertion of the flexor carpi radialis at the base of the second metacarpal contributes as well. The articulation with the hamate and the fourth and fifth metatarsal bases allows for much freer movement, but the CMC and metacarpal ligaments are still very strong.
The insertion of the extensor carpi ulnaris (ECU) on the dorsal aspect of the ulnar fifth metacarpal base often provides a deforming force in fractures of the fifth metacarpal. Articular fractures of the base of the fifth metacarpal often occur between the metacarpal ligament insertions and the insertion of the ECU, resulting in proximal and dorsal migration of the fractured metacarpal due to the unopposed tendon action (often called "reverse Bennett fracture" due to its similarity to the injury in the thumb).
The metacarpophalangeal (MCP) joints are multiaxial condyloid joints capable of flexion, extension, and some lateral motion and circumduction. The cam-shape of the metacarpal heads leads to relaxation of the collateral ligaments in extension, permitting adduction and abduction of the finger. With about 70° of MCP joint flexion, the collateral ligaments become taut, stabilizing the finger for power pinch and grip. Increased tension in the collateral ligaments with MCP flexion can be helpful in stabilizing the metacarpal head while reducing a metacarpal neck fracture. MCP joints are routinely immobilized in at least 70° of flexion to maintain maximum stretch of these ligaments, thus lessening postimmobilization stiffness.
The volar plate is a cartilaginous structure on the palmar aspect of each MCP joint, which limits extension of the joint. The volar plate is thicker at its insertions on the proximal phalanges and weaker at the proximal metacarpal origin. Volar plates are interconnected through deep transverse intermetacarpal ligaments, which provide additional volar stability.
Metacarpal base injuries
CMC joints, especially the central joints, are quite stable. The metacarpal bases are held in position by dorsal and palmar carpometacarpal ligaments, as well as by interosseous ligaments. 
CMC dislocations may occur with or without fracture. Avulsion (chip) fractures of the metacarpal base, or fractures involving the dorsal carpus, frequently accompany CMC dislocations. A CMC dislocation should signal the examiner to look for either a fracture or dislocation of the adjacent joints. Disruption of the strong ligaments stabilizing the central CMC joints signifies high-force transmission; in these cases, the examiner must maintain an even higher level of suspicion for other injuries.
Fracture-dislocation of the fifth metacarpal base is a common intra-articular injury and has been dubbed the reverse Bennett fracture. A direct blow to the ulnar border of the hand tends to cause an extra-articular fifth metacarpal base fracture. Axial load more often results in an intra-articular or reverse Bennett fracture. Generally, the volar radial one fourth to one third of the fifth articular base remains reduced. The remainder of the metacarpal displaces in a dorsal and ulnar direction. Displacement is caused by dynamic forces, similar to that seen with Bennett fracture of the thumb. The fifth metacarpal is the most mobile of the four ulnar CMC joints; therefore, it is prone to arthrosis from articular incongruity. 
Metacarpal shaft/neck fractures
Axial loading, direct blow, or torsional loading can cause metacarpal shaft fractures. Usually, the fractures are classified anatomically as transverse, oblique, or spiral. The fracture pattern often denotes the mechanism of injury, with direct or axial injury leading to transverse or oblique fractures and torsion leading to spiral fracture.
Fractures of the fifth metacarpal neck are among the most common fractures in the hand. Usually, these fractures are caused by striking a solid object with a closed fist and thus are dubbed boxer fractures, although this injury almost never occurs during boxing. Typically, a skilled fighter fractures the index metacarpal because instead of using a "roundhouse" motion, the blow comes straight from the body along the line of greatest force transmission.
Metacarpal head injuries
Fractures of the metacarpal head are rare injuries. These fractures are intra-articular and periarticular. If displaced, metacarpal head fractures usually require open reduction and internal fixation (ORIF). Direct trauma to the joint or an avulsion injury of the collateral ligaments are the typical causes. Injuries caused by direct trauma often are comminuted.
Almost all MCP dislocations occur with the proximal phalanx displaced dorsally on the metacarpal head; there is no specific dorsal restraint to the MCP joint other than the joint capsule and extensor mechanism. The collateral ligaments remain intact, and the weak proximal insertion of the volar plate avulses from the metacarpal neck.
Injury to the metacarpals is the result of either direct or indirect trauma. The nature and direction of the applied force determines the exact type of fracture or dislocation. [2, 3] Specific injury patterns that occur from commonly seen trauma are as follows:
CMC injuries - Metacarpal base fractures and dislocations of the CMC joint commonly result from an axial load or other stress on the hand with the wrist flexed
Metacarpal shaft and neck injuries - Typically, metacarpal shaft fractures are produced by either axial loading or direct trauma, though torsional forces on the digits may also produce these injuries; metacarpal neck fractures, the most common metacarpal fractures, usually result from striking a solid object with a clenched fist
Metacarpal head injuries - Metacarpal head fractures are intra-articular injuries and result from axial loading or direct trauma; avulsion fractures at the origin of the collateral ligaments are caused by forced deviation of the flexed MCP joint
MCP dislocations - Dorsal MCP dislocations are the most frequent dislocations, resulting from forced hyperextension of the digits
Fractures of the metacarpals and phalanges constitute approximately 10% of all fractures. Metacarpal fractures account for 30-40% of all hand fractures. Fractures of the fifth metacarpal neck alone account for 10% of all fractures in the hand. The lifetime incidence of metacarpal fractures is approximately 2.5%.
Overall, results of treatment of metacarpal shaft and neck fractures have been very good. Nonunion is very rare, but malunion is common.  The resultant function despite malunion usually is good, provided that there is no rotational deformity and that the previously mentioned limits of angular deformity are adhered to.
Ozer et al compared the clinical and radiographic outcomes of intramedullary nail (IMN) fixation with those of plate-screw (PS) fixation between 2004 and 2006 in 52 consecutive closed, displaced, extra-articular metacarpal fractures.  Thirty-eight patients received IMN fixation, and 14 received PS fixation. Mean follow-up was 18 weeks in the IMN group and 19 weeks in the PS group.
The study found no significant differences in clinical outcomes between the two techniques.  Operative time was shorter in the IMN group, but loss of reduction, penetration to the MCP joint, and secondary surgery for hardware removal were higher in the IMN group. The mean and median total active motion for the IMN group were 237º and 250º; for the PS group, 228º and 248º for the PS group. The mean DASH score was 9.47 in the IMN group and 8.07 in the PS group.
Harris et al studied the records and radiographs of 59 patients who underwent reduction of boxer's fractures using longitudinal traction and subsequent immobilization in a specially molded cast.  On average, 80% of initial fracture angulation in the sagittal plane was corrected, and only 1º of this correction was lost at the discontinuance of casting (3-4 weeks). The authors concluded that this technique is highly effective in the treatment of boxer's fractures, with the advantages of this treatment including efficacy, ease, and improved patient tolerance over other casting techniques.
Liporace et al studied 48 cadaver metacarpals to biomechanically assess the strength of the bicortical interfragmentary screw versus that of the traditional lag screw for oblique metacarpal fractures using 1 of 4 methods: 1.5 mm bicortical interfragmentary (IF) screw, 1.5 mm lag screw, 2.0 mm bicortical IF screw, and 2.0 mm lag screw.  There was no significant difference between the fixation techniques with regard to displacement and ultimate failure strength, but there was a slight trend for a higher load to failure with the 2.0 mm IF screw and 2.0 mm lag screw.
This study supported previous clinical data showing that bicortical interfragmentary screw fixation is an effective treatment option for oblique metacarpal fractures.  According to the authors, this technique provides an option for stabilization of small, difficult-to-control fracture fragments in metacarpal fractures.
Souer and Mudgal reviewed 19 patients with 43 closed metacarpal fractures treated by early ORIF with 2 mm plates.  Eighteen patients recovered full range of motion (one patient was lost to follow-up). In only two metacarpals in two patients was implant removal required because of extensor irritation. Plating of multiple, closed metacarpal fractures, therefore, is a safe, reliable, and consistently reproducible treatment method, according to the authors.