thumb Metacarpophalangeal dislocation

hpi

​45 year old male right hand dominant with no significant past medical history presents by EMS after low mechanism motor vehicle crash complaining of left thumb pain.  States his left hand “jammed into the steering wheel” during the crash causing deformity to the left thumb. He denies any numbness or tingling but is unable to fully range due to pain. No prior left hand injuries. Non-smoker. 

physical exam

​Swelling and deformity to the left thumb metacarpophalangeal joint. No abrasions, laceration or ecchymosis. 2+ radial pulse. Significantly limited flexion and extension of the left thumb at the MCP. Intact flexion and extension at the PIP. 2-point sensation intact. Good capillary refill.  

Radiograph

​Dorsal dislocation of the left thumb metacarpophalangeal joint

Diagnosis and plan

​Simple metacarpophalangeal joint dislocation of the left thumb.
​Patient was given pain medication through an IV and a radial and median nerve block was done for anesthesia. The joint was then reduced successfully at bedside with initial attempt. Post-op exam essentially unchanged except significant improvement in flexion and extension at MCP. There did not seem to be any significant instability. Regardless patient was placed in a thumb spica splint and follow-up with hand clinic in 1 week.

Discussion

​Dislocation of digits are common. Dorsal MCP dislocations follow hyperextension of the affected joint with rupture of the volar plate. They are classified by direction as dorsal, volar, or lateral. 
Dorsal: distal digit displaced toward back of hand
Volar: distal digit displaced toward palm of hand
Lateral: distal digit displaced ulnar or radial direction
The most frequent direction of dislocation is a dorsal displacement.
Metacarpophalangeal dislocations are further classified by volar plate involvement.  For MCP dislocations other than the thumb this is simple (volar plate not interposed in the joint) or complex (volar plate entrapped in the joint).  For MCP dislocations of the thumb, classify as incomplete (volar plate ruptured, collateral ligament intact), simple (volar plate and collateral ligament ruptured), or complex (dislocated phalanx entrapped in intrinsic hand muscles and volar plate entrapped). Simple thumb MCP joint dislocation are in extension and reducible whereas complex dislocations are in bayonet apposition and not easily reducible. It is extremely important to obtain radiographs prior to attempting reduction to clarify whether the reduction should be attempted or referral to hand surgeon.
Emergency medicine physician should reduce the dislocation once confirmed a simple dislocation without associated open joint, fracture or entrapped volar plate.