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MCP (Metacarpophalangeal) Dislocation



Ovid: 5-Minute Sports Medicine Consult, The


MCP (Metacarpophalangeal) Dislocation
Jessica Stumbo
Basics
  • The metacarpophalangeal (MCP) joints are relatively stable joints, especially in flexion.
  • Stability is provided by collateral ligaments on either side of the joint and the volar plate. The collateral ligaments are lax in extension and taut in flexion. The volar plate has a firm distal attachment to the proximal phalanx and a less stable proximal attachment to the metacarpal. It is the proximal attachment that is disrupted in a dislocation (1,2,3).
  • The index finger, thumb, and 5th finger are most vulnerable to dislocations.
Description
  • An MCP joint dislocation involves dislocation of the proximal phalanx in relation to the distal metacarpal.
  • Requires disruption of stabilizing structures
  • Dislocations may occur dorsally (most common), laterally (uncommon), or volarly (rare).
  • The typical mechanism for a dorsal dislocation is hyperextension at the MCP joint. With hyperextension, there is rupture of the volar plate from its proximal attachment, and due to the anatomy of the joint, there is also proximal dorsal translocation of the base of the proximal phalanx over the distal metacarpal (3).
  • Classification of dislocations: (3)
    • Simple dorsal: Articular surfaces are in partial contact, and there is no soft tissue interposed in the joint.
    • Complex dorsal: The volar plate or other tissue is interposed between articular surfaces and is, by definition, an irreducible dislocation.
    • Lateral: Results from an injury to the collateral ligament, either ulnar (UCL) or radial collateral ligament (RCL). The collateral ligaments of the thumb are more commonly injured than the collateral ligaments of the fingers (4).
    • Volar: Rare, but may result from severe or repetitive blows to knuckle, leading to rupture of dorsal capsule with subsequent volar displacement of the proximal phalanx
Epidemiology
  • MCP dislocations are much less common than proximal interphalangeal dislocations because of support from surrounding structures and protected position (2,3).
  • Usually occurs in index finger, thumb, or 5th finger.
  • Nearly always a single digit, but multiple digits may be involved.
Risk Factors
  • Contact and ball-handling sports
  • Prior history of injury or dislocation
Diagnosis
History
  • Will complain of pain, loss of function, and usually an obvious deformity
  • Dorsal dislocation generally results from forced hyperextension of digit, as in striking the heel of an opponent while diving to make a tackle, or a fall on an outstretched hand (1,3,5)[C].
  • Lateral dislocation is caused by an ulnarly or radially directed blow to the MCP joint, usually while in a flexed position (3,5)[C].
  • Volar dislocation may be seen with punching in boxing and martial arts.
Physical Exam
  • Evaluate and document neurovascular status before and after reduction attempts.
  • With dorsal dislocations, the metacarpal head is volarly displaced and will be easily palpable in the palm (1)[C].
  • Simple dorsal: There is obvious deformity, with the phalanx resting at 60–90 degrees of hyperextension over the head of the metacarpal (2)[C].
  • Complex dorsal: Much more subtle deformity, with only slight hyperextension (10–15 degrees) of the phalanx; may find dimpling or puckering of the palmar aspect of the finger where the volar plate is caught between the ends of the bones (proximal phalanx and head of metacarpal). This is pathognomonic for a complex dislocation; slight ulnar deviation of the involved digit also may be noted (1,2,6)[C].
  • Lateral: Swelling and tenderness along the ulnar or radial side of the MCP joint; assess for injury and laxity of the collateral ligaments by stressing the ligament with the MCP joint in flexion (4,5)[C].
  • Volar: Obvious deformity, with the phalanx positioned palmar to metacarpal
Diagnostic Tests & Interpretation
Imaging
  • Anteroposterior (AP), lateral, and oblique views of involved digit (not the entire hand) generally show deformity, joint space widening, and any accompanying fracture.
  • Brewerton view (MCP joint flexed to 65 degrees, with the dorsum of the proximal phalanx flat against the film cassette and the beam angled 15 degrees ulnar to radial) helpful in identifying collateral ligament avulsion fractures and fractures of the metacarpal head (2,3,4)[C]
  • Presence of a sesamoid in the widened joint space of the involved digit is pathognomonic for a complex dorsal dislocation (because sesamoids are embedded in the volar plate) (1,2)[C].
  • In skeletally immature patients, it is important to image the contralateral side in order to adequately evaluate for growth plate injuries.
  • In skeletally mature patients, stress radiographs are sometimes utilized. Stress x-rays should only be done after static x-rays to prevent nondisplaced fractures from becoming displaced fractures. In the thumb, MCP joint laxity >30–35 degrees on stress x-rays is usually associated with a complete collateral ligament tear. Stress x-rays are not typically utilized in the skeletally immature patient because those patients are more likely to have a growth plate injury.
  • Postreduction views: AP, lateral, and oblique to evaluate for joint congruity and/or fracture
  • Up to 50% of MCP joint dislocations may have a concomitant fracture of the proximal phalanx base and/or the metacarpal head.
Differential Diagnosis
  • Fracture of phalanx or metacarpal
  • Tendon rupture
  • Disruption of volar plate
Ongoing Care
Follow-Up Recommendations
After successful closed reduction, most MCP dislocations should be followed up with an orthopedic surgeon or hand surgeon within a week.
Patient Education
Warn patients that finger and hand swelling can take months to resolve.
Prognosis
Prognosis of most MCP dislocations is good as long as identified early and managed appropriately.
See Also
Thumb Ulnar Collateral Ligament Sprain and MCP Collateral Ligament Sprain
Codes
ICD9
834.01 Closed dislocation of metacarpophalangeal (joint)


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