12.21 Dislocations and joint injuries in the hand

Joints have two functions: movement and transmission of load. The failure of these functions—leading respectively to stiffness and instability—may seriously reduce hand function. But the relative importance of movement and stability varies between joints; the metacarpophalangeal (MCP) joint of the thumb needs stability more than motion, whereas motion at the proximal interphalangeal (PIP) and MCP joints of the fingers is crucial for gripping.

The effect of stiffness depends on the distance between the stiff joint and the tip of the digit. The MCP and PIP joints contribute much more to the total arc of finger motion than the distal joint. Stiffness of the DIP joint is well tolerated if the other joints are supple, and, therefore, any treatment directed at the distal joint should not risk inducing stiffness at other joints. The index finger, which performs most of its functions in a semi-extended posture for pinch against the thumb, tolerates stiffness better than the ring and little fingers, which must flex fully to the palm during power grip.

The exposed position of the hand at work, at home and at sport places its joints at risk of excessive forces that may disrupt their capsules and ligaments. These injuries are very common and may cause prolonged disability, especially at the PIP joint.

Any joint that is bruised or swollen after injury may contain a fracture or ligamentous injury. It needs both clinical and radiological examination. Palpation of an injured joint can be guided by a mental picture of the underlying anatomy; tenderness is then localized to bone, ligament attachments and tendon insertions by gentle palpation with a fine blunt object such as a pen top. Radiographs of the injured joint should include anteroposterior and true lateral views, supplemented by oblique views if necessary. Computed tomography (CT) may be useful where superimposition of adjacent rays obscures the lateral view.

Dislocations should be reduced promptly (Box 12.21.1), in order to restore circulation and reduce pressure on the skin, but the state of the nerves and vessels must be determined and recorded before any manipulation is performed or local anaesthetic block is administered. If x-ray facilities are available without delay, a radiograph should be taken before reduction; it may provide valuable evidence of injury to articular surfaces, ligament attachments, and tendon insertions. The direction of the dislocation often influences subsequent management but may not be known if the reduction was performed prior to radiographs. Open dislocations should be reduced promptly in the operating room after the wound has been irrigated; otherwise contamination may be carried into the joint as a protruding bone is reduced.

Joint laxity may be demonstrated by stress examination and documented with a stress radiograph. Laxity may be masked by muscle spasm due to pain and it may be necessary to give a local anaesthetic block before a proper examination is possible.

The DIP joint is a hinge joint. The convex bicondylar head of the middle phalanx articulates with the base of the distal phalanx, which has matching biconcave surfaces separated by a vertical median ridge. The head of the middle phalanx is attached to the base of the distal phalanx by stout collateral ligaments and by the fibrocartilaginous palmar plate, which resists hyperextension. The terminal tendon of the dorsal aponeurosis attaches to the epiphysis of the terminal phalanx, while the profundus tendon inserts into the metaphysis. Dislocations are less frequent at the DIP joint than at the PIP joint, probably because of the short lever arm of the distal phalanx and the strength of the ligamentous supports.

Dorsal dislocation is the result of rupture of the palmar plate by a hyperextension force. Reduction is occasionally blocked by interposition of the palmar plate or the flexor tendon, in which case open reduction via a dorsolateral approach is needed. Lateral stability is seldom impaired. Active flexion may begin immediately and late instability is rare.

Dorsal dislocation may be accompanied by fracture of the palmar lip of the distal phalanx; stability after reduction depends on the size of the fragment and the joint may require pinning in the reduced position. If the insertion of the profundus tendon is detached, it should be reattached via a palmar approach.

Avulsion fractures of the extensor tendon insertion (‘mallet fracture’) that involve more than 40% of the articular surface may be associated with palmar subluxation or dislocation of the DIP joint. The injury is usually the result of a blow that imparts flexion and axial compression force to the end of the finger. The subluxation is maintained by the unopposed action of the profundus tendon.

The indications for operative correction of the subluxation are controversial. Operative fixation is difficult unless there is a single large fragment. Surgical complications are common, and the results of non-operative treatment are generally good. Transarticular pinning of the reduced joint is the safest operative method.

The PIP joint is a hinge joint and is stable to lateral stress at all angles of flexion. The head of the proximal phalanx has two convex condyles that articulate with matching surfaces of the middle phalanx.

The collateral and accessory collateral ligaments form, together with the palmar plate, a three-sided box that encloses the head of the proximal phalanx (Figure 12.21.1). The PIP joint cannot be displaced unless the box-like ligament array is disrupted in at least two planes. The collateral ligament arises from a depression just dorsal to the mid-axial line of the head of the proximal phalanx and inserts into the palmar lateral tubercle at the base of the middle phalanx. The accessory collateral ligament runs obliquely from the head of the proximal phalanx into the palmar plate. The palmar plate provides a static restraint to hyperextension; it is a tough fibrocartilaginous structure that has strong attachments to the palmar-lateral corners of the middle phalanx. The central portion of the palmar plate is rather loosely attached to the periosteum of the base of the middle phalanx. Proximally, the palmar plate has a long fibrous attachment (‘check-rein ligament’) to each side of the proximal phalanx at the distal margin of the A2 pulley.

Ligament injuries to the PIP joint may be dorsal, lateral, palmar, or combined. The severity of injury varies from simple PIP joint sprains, which are common in athletes, to fracture–dislocation. Local tenderness may indicate the structures that are injured. Integrity of the extensor mechanism, collateral ligaments and palmar plate should be assessed and the joint should be observed for instability or deviation during active motion, under digital nerve block if necessary.

Hyperextension force tears the distal insertion of the palmar plate or avulses a small bone fragment from its attachment at the base of the middle phalanx. The tear propagates longitudinally within the collateral ligament, or between the collateral and accessory collateral ligaments, allowing the base of the middle phalanx to dislocate dorsally (Figure 12.21.2). The dorsal component of the collateral ligament remains intact and the joint is stable to lateral stress after reduction.

Dorsal dislocations are generally stable after reduction and require minimal treatment. The aim of treatment is early restoration of movement, but splintage in 10 degrees of flexion for 5–7 days may be useful for relief of pain. Swelling, discomfort and stiffness may persist for several months. The presence of a small avulsion fracture at the palmar lip of the base of the middle phalanx does not jeopardize stability or affect the management of this injury.

Open dislocation of the PIP joint is usually associated with a transverse palmar wound at the level of the PIP joint; the skin splits as the joint is hyperextended. The serious risk of infection and stiffness may be underestimated if it is not appreciated that the wound communicates with the joint and with the flexor tendon sheath. Patients managed in the emergency room by closed reduction and suture are at risk of disastrous joint and tendon sheath infection. The wound should be debrided and the joint irrigated in the operating room.

Flexion contracture is an unpredictable but common complication of PIP joint sprain or dislocation. The key to successful management is early recognition and treatment by static or dynamic splintage.

The combination of hyperextension and axial loading produces a fracture of the palmar edge of the base of the middle phalanx and dorsal dislocation (Figure 12.21.3). Instability is directly related to the size of the fracture fragment. Since the collateral ligaments insert into the palmar aspect of the base of the middle phalanx, involvement of more than 40% of the articular surface effectively separates the ligaments from the middle phalanx and stability is lost. Stability is also impaired by loss of conformity of the articular surfaces, especially of the palmar lip of the middle phalanx.

Swelling masks the deformity and the fracture–dislocation can be overlooked if a true lateral radiograph is not taken. Congruity of the joint surfaces is the aim of treatment; the relationship of the proximal phalanx to the middle phalanx is more important than the position of the palmar fragments. However, dorsal fracture–dislocation is a serious injury that may impair function of the PIP joint in the long term. Management is determined in part by the size and number of the fragments; however, the treatment of severe injuries remains controversial.

Fractures which comprise 10–30% of the joint surface may be stable in flexion, in which case the joint can be moved within a limited range in a splint which blocks extension. A dorsal padded aluminium splint is incorporated into a forearm cast and the splint is bent to block extension at the angle of flexion that is just sufficient to maintain a congruent reduction, usually about 50 degrees (Figure 12.21.4A). Active flexion is encouraged. The extension block is decreased by 10–15 degrees each week, provided that congruity is maintained on the lateral radiograph. The splint is worn for 4–6 weeks. Static or dynamic extension splintage may be needed to overcome a residual flexion contracture.

Operative treatment is required when congruent reduction cannot be maintained in flexion, which is usually because the fracture comprises more than 30% of the articular surface, or because treatment was delayed. There is no consensus about the best means of operative stabilization.

The reduced joint is transfixed in about 25 degrees of flexion for 3–4 weeks by a pin inserted though the bare area of the middle phalanx, just distal to the central slip insertion (Figure 12.21.4B). The simplicity of this method, which concentrates on restoring the correct relationship between the proximal and middle phalanges rather than precise reduction of the fracture fragments, has much to commend it.

Open reduction may be performed through a palmar approach, opening the flexor sheath between A2 and A4 pulleys and retracting the tendons. A single large fragment that can be reduced and held with one or more small screws, but multifragmentary fractures are challenging and may require buttressing with a cage plate and bone grafting.

Several ingenious techniques have been devised to exert traction on the middle phalanx whilst allowing movement of the PIP joint. The principle is sound but the technical aspects are demanding. The axis of motion of the device must coincide with the axis of the joint, and the device should permit joint motion without rotation of pins in the bone.

The palmar plate is used to reconstruct the articular surface of the palmar half of the middle phalanx. After excision of the bone fragments, the palmar plate is advanced into a transverse groove created in the defect in the base of the middle phalanx. The plate is held in place by a suture passed through drill holes in the middle phalanx and tied over a button on the dorsum of the finger or to a suture anchor. In late cases, it is usually necessary to excise the collateral ligaments in order to reduce the joint. The joint is immobilized for two weeks by a transarticular K– wire and then mobilized in an extension-block splint for a further two weeks. At 5 weeks, dynamic splintage may be needed to correct a flexion contracture.

The damaged palmar lip of the middle phalanx is replaced with a size-matched portion of the hamate obtained from its distal dorsal articular surface between the ring and little metacarpals, thereby restoring joint stability and allowing early movement (Figure 12.21.5). This method is the best means of reconstruction of severe and late-presenting injuries.

Palmar dislocation of the PIP joint is more serious but much less common than dorsal dislocation. A rotational force tears one collateral ligament, the palmar plate and sometimes the central slip of the dorsal aponeurosis. The joint is unstable and liable to palmar subluxation, rotation and boutonnière deformity. If the central slip remains intact, reduction may be prevented by entrapment of the head of the proximal phalanx between the central slip and the lateral band. Early recognition and treatment of this serious injury is crucial in maintaining function of the finger, in contrast to dorsal dislocation which generally does well with minimal treatment.

Entrapment of the head of the proximal phalanx may be reduced by flexion of the MCP joint, which slackens the dorsal aponeurosis. If the central slip is intact, the joint can be immobilized in extension for two weeks and then mobilized with active flexion and dynamic and/or static splintage to prevent development of a flexion contracture. The joint should be reduced and held in full extension while the injured structures heal; this is most easily and reliably achieved with a transarticular pin. Open reduction and repair may be needed for displaced intra-articular fractures, irreducibility or fixed contracture.

Laterally directed force may rupture the collateral ligament and the ipsilateral half of the palmar plate, thus disrupting the box-like ligament array and allowing lateral dislocation. If the joint surfaces are congruous on x-ray after reduction and the joint is stable during flexion and extension, early protected motion is permitted. The finger can be supported during mobilization by taping to the adjacent digit on the side of the collateral ligament injury. Late instability is rare.

Lateral and hyperextension strains of the PIP joint are frequent in athletes. The primary restraint to lateral angulation stress at the PIP joint is the collateral ligament. Under load, the ligament fails at the proximal end and the tear then extends between the between the collateral and accessory collateral ligaments before running across the palmar plate. Protected active movement with buddy taping for 2–3 weeks is sufficient in most cases. Pain, swelling and stiffness often persist for several months after lateral ligament strains. Late instability is rare, but some joints develop troublesome flexion contractures that require static and/or dynamic splintage.

Hyperextension strains may be associated with avulsion of a small flake of bone at the distal insertion of the palmar plate. Flexion contracture is a common but unpredictable consequence of hyperextension injury and may require intensive splintage and exercise.

Hyperextension laxity is uncommon but may be aggravated by pre-existing ligament laxity or previous injuries. The finger adopts a ‘swan–neck’ posture with hyperextension at the PIP joint and flexion at the DIP joint, but mechanical difficulty in initiating PIP joint flexion is usually the presenting symptom. As the finger is flexed, the PIP joint ‘hangs up’ in hyperextension, snapping down into flexion as the voluntary effort is increased. Repair of the attenuated palmar plate, if possible, or construction of a new static restraint to hyperextension is required. Tenodesis using one slip of the superficialis tendon is a simple and reliable technique.

The strong collateral ligaments and palmar plate protect the MCP joints from dislocation. The palmar plate has stout attachments to the proximal phalanx but its proximal attachment is thinner and it lacks the fibrous ‘check-reins’ of its counterpart at the PIP joint. The MCP joint resembles the PIP joint in having a box-like arrangement of collateral and accessory collateral ligaments, which insert into the edges of the palmar plate. The MCP joint is linked to adjacent rays by the deep transverse metacarpal ligaments, which are continuous with the lateral edges of the palmar plate. The primary stabilising structures are the collateral ligaments. The palmar plate resists hyperextension and only contributes to lateral stability when it is taut in extension.

Dorsal dislocation of the MCP joint of the finger is uncommon (though it is the most common dislocation in children) and may affect the index and little fingers. The middle and ring fingers are protected by adjacent digits and are seldom dislocated unless the border digit is also injured. The thin proximal attachment of the palmar plate is torn by hyperextension force but the collateral ligaments remain intact.

Dorsal dislocation of the MCP joints may be simple or complex. Simple dislocation is characterized by marked hyperextension (60–80 degrees). The palmar plate is ruptured proximally and remains attached to the proximal phalanx; it is draped over the head of the metacarpal but does not block reduction (Figure 12.21.6A). The articular surface of the base of the proximal phalanx lies in contact with the dorsum of the metacarpal head. The dislocation may be converted to the complex type by traction, which may flip the palmar plate onto the dorsum of the metacarpal head. Reduction can be accomplished by direct pressure over the dorsum of the base of the proximal phalanx in a distal and palmar direction, pushing it back over the metacarpal head. Late instability does not occur and no splintage is needed.

Complex dislocation of the MCP joint occurs when the palmar plate becomes interposed between the base of the proximal phalanx and the metacarpal head. The joint rests in modest hyperextension (20–40 degrees) (Figure 12.21.6B). Anterior displacement of the metacarpal head creates a prominence in the palm, with blanching of the palmar skin (Figure 12.21.6C), and a hollow just proximal to the base of the proximal phalanx dorsally. There may be an osteochondral fracture of the metacarpal head.

The primary block to reduction of a complex dislocation is the palmar plate, which remains attached distally to the base of the proximal phalanx and lies on the dorsal surface of the metacarpal head. Although closed manipulation is sometimes successful, open reduction is usually required.

A dorsal approach to complex MCP joint dislocation avoids the risk of digital nerve injury in the palmar approach, allows access to osteochondral fractures and is both simpler and quicker than a palmar approach. The extensor tendon is split in the midline, exposing the base of the proximal phalanx and the palmar plate as it lies on the head of the metacarpal. Longitudinal incision of the palmar plate allows the two halves to slip back over the head of the metacarpal. The MCP joint is stable after reduction. Immobilization is unnecessary and may lead to stiffness. Recurrent dislocation and late instability do not seem to occur in the fingers, though injury to the palmar plate of the thumb MCP joint may contribute to hyperextension laxity.

Complex palmar dislocation of the MCP joint is rare but may require open reduction of the entrapped palmar plate or dorsal capsule.

Locking of the MCP joint is characterized by the sudden onset of a flexion deformity that cannot be corrected passively. Locking may be acute, chronic or intermittent. Entrapment of the palmar plate on an osteophyte arising from the palmar/lateral corner of the metacarpal head is the usual cause of locking in older patients. Oblique views or CT may be needed to demonstrate the osteophyte; its removal will correct the deformity. Distension of the joint with local anaesthetic may lift the palmar plate off the osteophyte, but locking may recur. Other causes of locking include loose bodies, malunited articular fractures and entrapment of an interosseous tendon or collateral ligament on bony prominences of the metacarpal head.

The collateral ligaments and palmar plate are the primary stabilizers of the MCP joint of the thumb, but additional dynamic stability is provided by the insertion of the adductor pollicis muscle at the base of the proximal phalanx. The adductor aponeurosis lies directly over the ulnar collateral ligament and is formed from fibres that pass from the adductor muscle into the ulnar side of the dorsal aponeurosis. Stability is the most important attribute of the MCP joint of the thumb; movement is much less important provided that the basal joint is mobile. Indeed, some normal individuals have very little MCP joint flexion, but the average range is 75 degrees flexion, 20 degrees hyperextension, and 10 degrees abduction/adduction.

Dislocation of the thumb MCP joint is similar in many respects to dislocation of the index and little finger MCP joints. It results from forcible hyperextension and may be simple or complex, the latter resulting from interposition of the palmar plate. The management is the same as in the index finger. After reduction the stability of the collateral ligaments should be checked and any instability managed as described below.

Hyperextension injury of the thumb MCP joint may strain or rupture the palmar plate; comparing the range of hyperextension with the opposite thumb, using a local anaesthetic block if necessary, may identify these injuries. Strains require symptomatic treatment only. Complete ruptures should be immobilized with the MCP joint in 10–20 degrees flexion for 3–4 weeks to encourage healing of the palmar plate at its correct length. Hyperextension injuries occasionally lead to laxity and dynamic collapse of the thumb skeleton with hyperextension of the MCP joint and flexion at the IP and CMC joints. The collapse deformity can be corrected by capsulodesis or tenodesis of the MCP joint, if the joint surfaces are healthy, or by arthrodesis if the surfaces are degenerate.

Rupture of the ulnar collateral ligament is caused by forced abduction stress, with or without hyperextension. The degree of injury varies from a stable ligamentous strain to disruption of the collateral ligament, palmar plate and dorsal capsule. Motorcycle accidents, falls onto the outstretched thumb and ski-pole injuries are common causes of MCP joint ligament rupture. The ulnar collateral ligament resists laterally directed forces during pinch against the index finger; laxity of the ligament is associated with a weak painful pinch and predisposes to degenerative arthritis of the MCP joint.

The ulnar collateral ligament is usually injured at its attachment to the proximal phalanx, where it may avulse a fragment of bone, but mid-substance ruptures are occasionally seen. An anatomical peculiarity of the ulnar side of the MCP joint may account for the poor results of non-operative management of complete collateral ligament ruptures. The ligament may slip around the proximal free edge of the adductor aponeurosis as the aponeurosis slides distally at the moment of injury—the Stener lesion. The aponeurosis then separates the torn end of the ligament and its site of attachment to the proximal phalanx (Figure 12.21.7A). The Stener lesion is present in the majority of complete ulnar collateral ligament ruptures. The ulnar collateral ligament may avulse a small fragment of bone at its insertion and the presence of a Stener lesion may be inferred from the position of the fragment on x-ray.

Radiographs should be taken before stress testing is performed, lest an undisplaced fracture is displaced. If there is no fracture, the integrity of the ligament can be assessed by applying radial deviation stress and comparing the range of abduction with the opposite side (Figure 12.21.7B, C). It may be necessary to relieve pain and muscle spasm by infiltration of local anaesthetic before an adequate examination is possible. The examination should be performed in 15-degree flexion, which is sufficient to relax the palmar plate but not enough to allow rotation of the proximal phalanx during testing. The amount of laxity and the ‘end-point feel’ are compared with the uninjured side. A 30-degree excess of laxity compared to the opposite side indicates rupture of the ulnar collateral ligament and the need for operative repair.

Ligament injuries which are not associated with excess laxity, and those with undisplaced avulsion fractures, may be treated with strapping but are often more comfortable in a thumb spica cast for 3–4 weeks. Those with excess laxity should be explored and repaired via a dorsoulnar incision, protecting the branch of the superficial radial nerve that lies here. Avulsion fractures which are displaced by more than 2mm should be reduced operatively and fixed with a K-wire, interosseous wire or small lag screw, depending on the size of the fragment. If a Stener lesion is present, the distal end of the collateral ligament is usually found turned back upon itself immediately proximal to the edge of the adductor aponeurosis. The ligament is usually torn at its attachment to the palmar and ulnar corner of the base of the proximal phalanx, and may be reattached by suture to local tissues or by a suture anchor. Protection of the repair with a transarticular pin is optional. The joint is mobilized after 4 weeks but protected from stress until the 8th week. Some limitation of MCP joint flexion is common but is not disabling in a joint where stability is more important than movement.

After 2 weeks from injury, the ruptured ligament shortens and it may be difficult to achieve a secure repair. The ligament may be reconstructed with a strip of palmaris longus tendon passed in a figure-of-eight fashion though vertical drill holes in the bone on each side of the joint. In the presence of degenerative arthritis, arthrodesis is an excellent procedure that provides stable pain-free pinch. Very little disability results from loss of MCP joint movement provided that there is good motion at the basal joint.

Tears of the radial collateral ligament account for about a quarter of MCP joint collateral ligament injuries. The ligament may tear at either end and there is no counterpart of the Stener lesion on the radial side of the joint. Pain occurs when pressure is placed on the radial side of the thumb, particularly when pushing against a surface with the hand flat. Excessive ulnar deviation occurs on adduction stress. Unstable radial collateral ligament injuries should be repaired.

The CMC joints of the index and middle rays have interlocking articular surfaces and strong ligaments that allow very little movement. The base of the fourth metacarpal articulates with the radial facet of the hamate and has 10–15 degrees flexion-extension. The fifth CMC joint allows 15–20 degrees flexion as well as some rotation, aiding opposition of the thumb to the little finger and cupping of the palm. The deep branch of the ulnar nerve runs close to the palmar aspect of the fourth and fifth CMC joints, where it may suffer injury or operative damage.

Dislocation of the CMC joints of the fingers may involve one or more joints, with or without fracture of the articular surfaces, and may be associated with fracture of adjacent metacarpal bones. The displacement is usually dorsal and the fifth ray is most frequently injured, though several types of multiple dislocation have been reported (Box 12.21.8).

Examination shortly after injury will often detect the dorsal displacement that may have been noticed by the patient. However, CMC joint dislocations are easily overlooked. Contributory factors are obliteration of deformity by swelling, inadequate radiographs or their incorrect interpretation and the presence of multiple injuries. The frequent combination of a displaced metacarpal fracture with CMC joint dislocation in an adjacent ray is a pitfall; the fracture catches the eye and the dislocation is missed.

Severe swelling of the wrist after a violent injury frequently conceals a serious carpometacarpal or carpal injury. The minimum radiographic examination comprises PA, true lateral view and oblique views in 30 degrees pronation and supination from the lateral position. CT examination may be very helpful in defining the injury and particularly in determining if comminution precludes operative reconstruction of the articular surfaces.

Single CMC joint dislocations may result from blows to the hand or from falls, causing flexion and axial loading of the metacarpal. The fifth ray is most often affected. Disruption of several joints, especially the strong second and third, requires high energy trauma and these patients frequently have multiple injuries. The dislocations can usually be reduced without difficulty; stability can be assessed at the time of reduction and a K-wire inserted if necessary.

Undisplaced articular fractures of the CMC joints may be treated satisfactorily with external splintage of the wrist and protected motion of the fingers. Fracture–subluxation of the fifth CMC joint is sometimes called ‘reverse Bennett’s fracture’ because of its similarity to fracture-subluxation of the first CMC joint. The fracture line runs obliquely across the metacarpal base, leaving the radial fragment attached to the base of the fourth metacarpal and hamate by the strong intermetacarpal ligaments and allowing the shaft of the metacarpal to displace in an ulnar and dorsal direction. The sloping surface of the hamate, the obliquity of the fracture line and the pull of the extensor carpi ulnaris tendon all contribute towards redisplacement after reduction. Closed reduction can usually be achieved without difficulty using a combination of traction and direct pressure but the injury is unstable and requires percutaneous pin fixation. The aim is restoration of the relationship between the metacarpal shaft and the hamate; slight displacement of the intra-articular fracture may be accepted. Open reduction is indicated for failed closed reduction, soft-tissue interposition or late presentation, and for open injuries.

Multiple CMC joint fracture dislocations are accompanied by severe swelling which precludes effective control by external splintage. Percutaneous pin fixation may be possible but it can be difficult to achieve in the presence of swelling and reduction is sometimes blocked by interposition of soft-tissues such as the extensor carpi radialis brevis tendon. Multiple pins are required and they tend to interfere with movement of the extensor tendons if the ends are left long. The potential for stiffness of the fingers in these severe injuries demands mobilization as soon as possible. Open reduction with fixation by buried K-wires, together with screw fixation of associated metacarpal fractures and large intra-articular fragments, permits early movement and also ensures an accurate reduction.

The basal joint of the thumb is saddle-shaped. The primary stabilizing ligaments are the anterior oblique and dorsoradial ligaments, but the first intermetacarpal, ulnar collateral and posterior oblique ligaments act as secondary stabilizers.

Dislocation of the basal joint of the thumb without fracture is uncommon and results from longitudinal force applied along the metacarpal shaft to the flexed basal joint (Figure 12.21.8). The dorsoradial ligament tears and the anterior oblique ligament is stripped subperiosteally from the base and proximal shaft of the metacarpal. Immediate closed reduction and maintenance of a stable reduction in a cast is associated with a good long-term outcome, but many joints are unstable and require percutaneous pin fixation. Painful instability is common in patients presenting late and may occur despite primary pin fixation.

Late instability of the basal joint predisposes to early degenerative arthritis. An anteroposterior stress radiograph with the radial surfaces of the thumbs pressed together may demonstrate instability. The treatment of painful instability or subluxation is determined by the state of the articular surfaces. Ligament reconstruction using a distally-based strip of the flexor carpi radialis tendon is appropriate if the articular surfaces are healthy. The tendon strip is passed through a drill-hole in the base of the metacarpal so as to replicate the function of the anterior oblique ligament. If painful instability is accompanied by degenerative change, the options are trapezial excision arthroplasty with ligament reconstruction and arthrodesis. The choice of procedure will be influenced by age, the state of other thumb joints and the requirements of the patient.