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Complex Dislocations of the MP Joint

- See Simple Dislocations of the MP joint

- Discussion:
    - by definition, an irreducible MP dislocation;
    - involves infolding of the proximally disrupted volar plate between metacarpal head and base of proximal phalanx;
    - complex dislocations occur most commonly in index finger followed in incidence by thumb & small finger &, rarely, long & ring fingers;
    - mechanism of injury:
            - proximal phalanx hyperextends causing volar plate and capsule rupture; off proximal metacarpal head;
            - further hypertextension, volar plate completely dislocates & comes to lie on dorsum of the metacarpal head;
            - flexors tendons are displaced further ulnarly by the radially and palmarly displaced metacarpal head;
            - metacarpal head may be forced thru fibers of palmar aponeurosis and becomes button-holed between 4 structures:
                   - lumbrical;
                   - flexor tendon (lies on ulnar side of dislocated digit);
                   - transverse bands of natatory ligaments lie taut distally;
                   - superficial transverse ligament lie taut proximally;
            - hyperextension of MCP joint may cause volar plate disruption at its proximal (metacarpal attachment);

- Exam:
    - NV compromise:
           - neurovascular bundle may be tented over top of dorsally dislocated metacarpal head;
    - joint is appears slightly hyperextended, w/ proximal phalanx lying on dorsum of metacarpal head
    - finger lies of ulnar deviation w/ digit partially overlapping adjacent digit;
    - puckering of the volar skin is a common finding;
           - puckering may be subtle w/ index dislocation;
           - in thumb skin dimple is located over thenar eminence;

- Radiographics:
    - most useful view is true lateral;
    - widened joint space results from interposition of volar plate or interposed sesamoid within joint (in children older than 10 yrs);
           - presence of sesamoid in joint space indicates presence of volar plate with in joint;

- Non Operative Treatment:
    - attempt at reduction:
           - adequate anesthesia is a requirement;
           - perform reduction w/ wrist flexed which relaxes tension on flexor tendons;
           - simple MP dislocations can be reduced by initial MCP hyperextension & then dorsal pressure on proximal phalanx in conjunction with wrist flexion;
           - w/ complex dislocations, it is essential that the articular surfaces are firmly opposed;
           - proximal phalanx is then pushed over the articular surface of the metacarpal;
           - finger should be stable following reduction;
           - MCP needs to be splinted for 3 to 4 weeks to prevent hyperextension (this is best achieved with a hand based MP joint splint);

- Operative Treatment:
    - dorsal approach: (preferred technique)
          - this approach avoids injury to the digital nerves and allows for fixation of  metacarpal fractures (if one is present);
          - involves spliting the volar plate longitudinally;
          - using the dorsal approach, the volar plate is identified and split vertically;
    - volar approach:
          - skin is reflected proximally to metacarpal neck;
          - avoid injury to the digital nerves;
          - palmar fascia and natatory ligaments are split longitudinally;
          - proximally the superficial transverse ligament is incised;
          - expose lumbrical muscle & flexor tendon sheath;
          - volar plate is is retrieved and opposed to metacarpal or deep fascia;
          - immobilize in 60 deg of flexion to prevent collateral ligament shortening

Complex dislocations of the metacarpophalangeal joint.

A simplified technique for treating the complex dislocation of the index metacarpophalangeal joint.

Complex dislocation of the metacarpo-phalangeal joint of the index finger: a comparison of the surgical approaches.