Chapter 84. Metacarpophalangeal Joint Dislocation Reduction

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 the patient is reminded of on a daily basis and 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 protected location of this joint in the hand.6 Injuries to the MCP joint of the thumb are more common than 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 84-1A). 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 84-1B).

Functional Anatomy

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.

The MCP joints are resistant to ligamentous injury and dislocation because of their inherent ligamentous structure, their surrounding supporting structures, and their protected position at the base of the fingers. The volar plate is a fibrocartilaginous structure that is attached firmly to the base of the proximal phalanx. It originates just proximal to the metacarpal head where it is thin and transparent. This allows for hyperextension of the MCP joint yet makes it vulnerable to injury during dorsal dislocations.

Side-to-side stability of the MCP joint is provided mainly by the collateral and accessory collateral ligaments, and to some extent by the lumbrical and the interossei muscles and tendons.8 The collateral ligaments originate from the mediolateral recesses in the metacarpal head and travel to insert onto the base of the proximal phalanx. The eccentric configuration of the metacarpal head and the relatively fixed length of the collateral ligaments cause it to tighten when the joint is in flexion (Figure 84-2). This accounts for the limited abduction and adduction of the MCP joint in flexion as compared to the laxity in extension. The collateral ligaments of the MCP joint are most vulnerable to injury from forces directed ulnarly and dorsally. The accessory collateral ligament spans from the true collateral ligament to the volar plate, providing additional joint stability in extension. The central extensor tendon and sagittal band augment the thin dorsal capsule. The tendons of the palmar and dorsal interossei add a small degree of dynamic stability.

The interphalangeal (IP) joints are hinges and motion only occurs as flexion and extension while the MCP joints are condyloid joints. The range of motion about the MCP joint includes 120° of flexion and 30° of hyperextension. It has up to 30° of additional mediolateral laxity and a small degree of rotational laxity to facilitate an efficient grasp.9 The clinical importance of these differences is that to minimize the development of contractures after joint injuries. The preferred position of immobilization of the IP joints is in extension, whereas the MCP joints are immobilized in flexion.

The opposable thumb is an essential structure for countless activities. Despite its strong ligamentous and capsular support, the exposed positioning of the thumb makes it a frequent site of dislocations and subluxations. The MCP joint of the thumb is similar to those of the fingers but has a stronger volar plate and collateral ligaments with less side-to-side mobility.2 The MCP joint of the thumb is also a condyloid joint with a quadrilateral rather than a spherical metacarpal head that allows mainly flexion and extension. However, it also permits some degree of abduction, adduction, and rotation. There is a large variability among individuals in its range of flexion and extension.

The metacarpal head is bicondylar, with the radial condyle being slightly larger. This structural difference provides the thumb proximal phalanx with a modest degree of pronation during flexion. Its range of motion consists of 15° to 20° of extension and 80° of flexion. However, the range of motion of the MCP joint of the thumb is restricted, especially in lateral motion with only 10° of adduction and abduction.

Patterns of Injury

MCP joint dislocations are considerably less common than dislocations of the IP joints. Most MCP joint dislocations are dorsal. These were first described by Kaplan in 1957.10 A volar MCP joint dislocation is a rare finding.11 Dislocation of any of the MCP joints is possible from hyperextension injuries. The dorsal dislocation of the thumb MCP joint is the most common type of MCP joint dislocation.

Hyperextension of the MCP joint results in the rupture of the volar plate. Injuries are classified as simple (reducible with closed technique) or complex (irreducible with closed technique). Unless there is associated twisting of the finger, the collateral ligaments remain intact. Clinical and radiographic features can be used to differentiate simple from complex dislocations. In cases of simple dislocations, the joint usually hyperextends to approximately 90° and the volar plate is not interposed between the dislocated bones.12 The deformity is obvious with the finger in a claw position of extreme dorsiflexion at the MCP joint. In complex dislocations, the metacarpal and proximal phalanx usually lie more parallel to each other, with the metacarpal head causing a dimple on the volar skin and palpable underneath the skin. Clinical features that suggest a complex MCP dislocation include a proximal phalanx that is less acutely angulated than with a simple dislocation.2 The volar plate, sesamoids, flexor tendon, adductor tendons, extensor expansion, collateral ligaments, or capsule may become entrapped and prevent reduction.2 A widened joint space is seen on radiographs when the volar plate is interposed in the joint. Complex MCP dislocations occur more frequently in the index finger. They can be difficult to manage because reduction is often blocked by the interposed soft tissue.13

The MCP joint of the thumb is very mobile. Dislocations of the thumb MCP joint are more common than the MCP joints of the fingers. The MCP joint can be dorsally dislocated by a hyperextension injury or shearing forces that ruptures the volar plate, joint capsule, and at least part of the collateral ligament. The proximal phalanx will come to rest in a position dorsal to the first metacarpal. Displacement of the proximal phalanx varies from a subluxation to the complete dislocation. For the latter to occur, the volar plate and the collateral ligaments must completely tear. Volar dislocations are rare and result from extensive tearing of the dorsal capsule and the extensor pollicis brevis tendon, leaving the joint very unstable.14

A simple MCP joint dislocation can be converted into a complex one during prolonged or repeated reduction attempts, especially those in which axial traction is the primary component.2 This should not deter the EP from attempting a closed reduction for any MCP dislocation.

Radiographic Evaluation

Radiographic evaluation of all hand injuries is relatively straightforward. It should include at least three views (i.e., anteroposterior, oblique, and lateral) of the injured area. The most important radiographic error in evaluating joint injuries of the hand is failing to get a true lateral view of the injured joint. This may result in missing a fracture or a loose body in the joint.2 Radiographic examination will show an obvious dislocation in the lateral view. Anteroposterior views may reveal widening of the joint space in complex dislocations. In addition, the sesamoid bones may be seen in the joint space, a pathognomonic sign for a complex MCP joint dislocation.

All MCP joint dislocations should have an initial attempt at reduction in the ED unless they are unstable, chronic, open, or associated with a fracture. This is true even if it is suspected to be a complex MCP joint dislocation.15 Reduction of the dislocation will provide significant pain relief. If a Hand Surgeon is not immediately available, an open MCP joint dislocation should be reduced after copious irrigation with sterile saline to remove any dirt and debris.

Certain MCP joint dislocations require an immediate evaluation by a Hand Surgeon for open reduction and repair of any ligamentous or associated injuries. Closed reduction of an MCP joint dislocation should not be performed in the ED for unstable, chronic, and open injuries or if it is associated with a fracture. Instability in a joint through active range of motion indicates complete and multiple ligament disruption requiring an open surgical repair.2,17 Chronic injuries greater than 3 weeks old generally require surgical repair.16

If the closed reduction attempt is unsuccessful, repeated attempts at reduction are contraindicated as a simple dislocation can be converted to a complex dislocation requiring an open surgical reduction. The ligaments, tendons, or sesamoid bones may become entrapped by bony and soft tissue structures in and around the MCP joint and prevent the reduction. Complex dislocations usually require open surgical reduction.15,18 Open MCP joint dislocations, whether reduced in the ED or not, will require operative management after initiation of antibiotics in the ED.

There are few contraindications to the use of local anesthesia solutions.19 Relative contraindications include injection through infected skin, history of coagulopathy from heparin or warfarin therapy, factor deficiencies, liver dysfunction or bleeding disorder, or an allergy to the anesthetic medication. Another relative contraindication includes preexisting neurovascular damage prior to the procedure. Uncooperative patients can make the injection procedure technically more difficult and dangerous to perform. Procedural sedation should be considered for these patients and children.

• Povidone iodine or chlorhexidine solution
• 18 gauge needle to draw up the local anesthetic solution
• 27 or 30 gauge needle, 2 in. long
• 10 mL syringe
• Alcohol swab
• Sterile gloves
• Sterile drapes
• Local anesthetic solution without epinephrine
• Equipment and supplies for procedural sedation (Chapter 129)
• Adhesive tape, ½ in.
• Webril padding
• Casting material
• Ace bandage
• Scissors

Explain the risks, benefits, potential complications, and aftercare of the reduction to the patient and/or their representative. The patient must be aware that irreducible dislocations will require an open surgical reduction and possible repair of damaged structures within and surrounding the joint. Inform the patient that the injury can result in joint swelling for weeks to months and possibly permanent joint enlargement. Loss of motion with stiffness and residual soreness may last for months. Obtain an informed consent for the reduction procedure. An informed consent should also be obtained for procedural sedation (Chapter 129) and/or the intraarticular injection (Chapter 77) if they are performed in addition to the reduction procedure.

Clean the involved joint of any dirt or debris. Apply povidone iodine or chlorhexidine solution and allow it to dry. Perform a wrist block (Chapter 126), the instillation of the local anesthetic solution into the joint (Chapter 77), and/or procedural sedation and analgesia (Chapter 129).

Early closed reduction may be easy provided that the thumb is maintained in adduction, the fingers are flexed, and the wrist is flexed to relax the intrinsic hand muscles. The major obstruction preventing reduction of the dislocated MCP joint is the displaced volar fibrocartilaginous plate lying dorsal to the metacarpal head. Approximately 50% of MCP joint dislocations can be reduced in the ED using the closed method.

Dorsal MCP Joint Dislocations

Dorsal MCP joint dislocations (Figure 84-3A) require minimal, if any, distally applied traction for reduction. It is important to remember that applying simple traction alone as an initial maneuver risks trapping the volar plate and transforming a simple dislocation into a complex dislocation.

Hyperextend the MCP joint while simultaneously pushing the proximal end of the proximal phalanx volarly and over the metacarpal head (Figure 84-3B). This maneuver diminishes the buttonhole effect on the metacarpal neck that is accentuated by traction. Flex the MCP joint as the proximal phalanx returns to position (Figure 84-3C). Simultaneously flexing the IP joint and wrist can help to relax the flexor tendons and make the reduction easier. This maneuver can sometimes trap the displaced fibrocartilaginous plate and carry it to its normal position anterior to the metacarpal head.

If the reduction is unsuccessful, repeated attempts to reduce the dislocation are contraindicated. Consider open reduction to disengage the metacarpal head from a probable buttonhole slit in the anterior capsule and from the surrounding muscles and tendons. Consult a Hand Surgeon for these MCP joint dislocations that cannot be reduced after one attempt in the ED.

Volar MCP Joint Dislocations

Volar MCP joint dislocations (Figure 84-4A) are generally associated with collateral ligament ruptures. They are commonly irreducible due to interposition of the extensor tendons and the dorsal joint capsule. Consultation with a Hand Surgeon is often required for operative reduction.

Volar MCP joint dislocations require minimal, if any, distally applied traction for reduction. It is important to remember that applying simple traction alone as an initial maneuver risks trapping the volar plate and transforming a simple dislocation into a complex dislocation. Flex the MCP joint while simultaneously pushing the proximal end of the proximal phalanx dorsally and over the metacarpal head (Figure 84-4B). Extend the MCP joint as the proximal phalanx returns to position (Figure 84-4C).

If the reduction is unsuccessful, repeated attempts to reduce the dislocation are contraindicated. Consider open reduction to disengage the metacarpal head from a probable buttonhole slit in the anterior capsule and from the surrounding muscles and tendons. Consult a Hand Surgeon for these MCP joint dislocations that cannot be reduced after one attempt in the ED.

Clinical Assessment

Assess the collateral ligaments for stability. Because the goal of treatment is to restore functional stability, it is essential to perform a systematic evaluation of joint stability. An accurate assessment generally requires adequate pain control, even in the most cooperative patients. Active stability is tested by allowing the patient to move the joint through the normal range of motion. Completion of a full range without displacement indicates adequate joint stability. Passive stability is assessed by applying gentle radial and ulnar stress to each collateral ligament and posteroanterior stress to assess volar plate integrity. Stress testing should be performed in extension and flexion to avoid the stabilizing effect of the volar plate. Comparisons with the same joint of the uninvolved hand may assist in the diagnosis.2 Stability of the joint provides strong evidence that optimal functional recovery would result from short-term immobilization rather than surgical intervention.

Joint stability of the thumb MCP joint is tested in full extension as well as in 30° of flexion. Complete ligament disruption is suspected if the joint can be stressed in a radial direction 25° to 35° beyond a similar stress to the patient's opposite thumb MCP joint. This instability should be demonstrated in both full extension and 30° of flexion. Flexion at 30° lessens the stabilizing effects of the volar plate.2 The presence of ecchymosis suggests a complete ligament tear as well as a volar subluxation of the proximal phalanx.19

Radiographic Assessment

Postreduction radiographs are essential to demonstrate adequate reduction. Occasionally, a fracture is only visible on these views and not on the prereduction films.1,20 Joint subluxation after reduction is associated with interposed soft-tissue or severe capsular injury.

Splinting of any MCP joint dislocation should provide adequate immobilization and protection. Splinting is maintained for at least 1 week to no more than 3 weeks to prevent joint stiffness. Simple dorsal finger MCP joint dislocation injuries generally require splinting for 1 to 3 weeks with the joints in 45° to 50° of flexion.2 Volar finger MCP joint dislocations require splinting in extension for 1 to 3 weeks. The thumb should be immobilized in a thumb spica splint in 20° of flexion for dorsal dislocations and in extension for volar dislocations for 3 weeks. A proper program of gradual active range-of-motion exercises should follow splinting.18 With adequate protection and splinting of uncomplicated dislocations, athletes may return to activities within 1 to 2 weeks, sooner for low-risk sports with minor injuries, and longer for more serious injuries requiring surgery.20

Allergic reactions can occur from hypersensitivity to the local anesthetic solution. Symptoms can range from mild pruritus and urticarial rash to circulatory collapse and even death. Severe allergic reactions are extremely rare. Taking a thorough history might prevent such a reaction. The preservative in the anesthetic is often the culprit. The possibility of injury to structures in the joint may occur from improper insertion of the needle or needle movement within the joint cavity. Infection of the joint can occur when the needle penetrates unclean skin, infected skin, or infected subcutaneous tissue. If proper aseptic technique is followed, the risk of infection is negligible. Please refer to Chapters 77 and 123 regarding the complete details of local anesthetic complications and joint injection complications.

Complications of the reduction procedure are primarily related to failure of reduction, especially complex dislocations. Entrapment of ligaments, tendons, or sesamoid bones leads to an unsuccessful reduction. A simple MCP joint dislocation can be converted into a complex one during prolonged or repeated reduction attempts, especially those in which axial traction is the primary component.2 Irreducible MCP joint dislocations require an immediate evaluation by a Hand Surgeon.

Collateral ligament injuries occur infrequently and are often missed in the acute setting. The presence of an avulsion fracture from the metacarpal head or corner fracture of the base of the proximal phalanx suggests a collateral ligament injury. Consultation with a Hand Surgeon is recommended for patients with a collateral ligament injury. Some surgeons prefer immediate operative repair of these injuries. ED care involves immobilization in a gutter splint, with the MCP joint in 45° to 50° of flexion, and appropriate referral.

Ulnar collateral ligament of the thumb rupture, also known as gamekeeper's or skier's thumb, results from a laterally directed force at the thumb MCP joint. The ligament is important to the grasping function of the thumb. Early recognition of this injury is key. The diagnosis is generally made through stress testing of the reduced MCP joint. Radiographs occasionally demonstrate an avulsion-type fracture. Treatment of partial ligament tears requires splinting in a thumb spica for 6 weeks, while complete rupture requires operative repair.

Radial collateral ligament injuries of the MCP joint of the thumb are less common but equally debilitating. The usual mechanism is forced adduction with or without hyperextension. The diagnosis is generally made through stress testing of the reduced MCP joint. Radiographs occasionally demonstrate an avulsion-type fracture. Treatment of partial ligament tears requires splinting in a thumb spica for 6 weeks, while complete rupture requires operative repair.

Degenerative arthritis may occur after multiple closed reductions or an unrecognized chronic dislocation.21 Inadequate immobilization or early return to high-stress activities may result in ligamentous laxity or recurrent instability. Excessive joint contractures unresponsive to physical therapy may require surgical release.

Injuries to the MCP joints of the hand are occasionally encountered in the ED. They may be associated with significant morbidity if not properly managed. The most common dorsal MCP joint dislocation seen is that of the thumb. Volar dislocations of the MCP joints are rarely seen. A thorough understanding of the anatomy and function of the MCP joint is essential to diagnose and manage these injuries. A detailed physical assessment of the soft tissues, bones, and neurovascular structures is essential to prevent occult injuries. Radiographic evaluation is required for all potential injuries. This should include anteroposterior, lateral, and obliques views in order to not miss associated avulsion fractures or evidence of complex dislocations. All MCP joint dislocations should have an attempt at reduction, except those that are unstable, chronic, open, or associated with a fracture. A Hand Surgeon should evaluate any unstable, chronic, open, or irreducible dislocation. MCP joint dislocations reduced in the ED must be appropriately splinted and follow-up arranged with a Hand Surgeon.