- 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.