Review Question - QID 211424

The patient has sustained a 4th and 5th carpometacarpal joint (CMCJ) dorsal fracture-dislocation with an associated dorsal hamate fracture. The 5th metacarpal is displaced dorsally and proximally by the pull of the extensor carpi ulnaris (ECU), which inserts on the base of the 5th metacarpal and is innervated by the PIN.

CMCJ fracture-dislocations are often missed on initial presentation. Radiographs should be carefully scrutinized for shortening of the metacarpals on the AP view. On the lateral view, metacarpal base subluxation or small fragments of the hamate may be present dorsally. Reduction is typically obtained with a local block, wrist extension, and pressure over the base of the metacarpal. Reduction may often then be maintained within a well-molded splint. However with more extensive joint involvement or soft tissue disruption, maintenance of reduction by closed means may be difficult and unreliable. Moreover, cases in which there is delayed presentation or those which do not stay reduced following closed reduction and splinting require percutaneous fixation or potentially even open with internal fixation.

Zhang et al. evaluated the management of patients presenting with acute (20) and chronic (6) ulnar CMCJ fracture dislocations. All of those who received acute treatment were successfully managed conservatively with reduction and splinting. However, 50% (3 of 6) of the injuries treated in a delayed fashion failed conservative management and necessitated operative stabilization. The authors concluded that early reduction was paramount in avoiding surgical intervention and attaining the best outcomes.

Gehrmann et al. reviewed 16 cases of 4th/5th and 23 cases of 5th CMCJ fracture-dislocations. The authors managed all cases with reduction and percutaneous pinning. They found that the two cohorts had comparable DASH scores and functional outcomes. The authors concluded that reduction of the ulnar CMCJ consistently resulted in excellent outcomes at one year follow-up.

Figure A shows an AP radiograph of an ulnar fracture dislocation at the CMCJ. Note the shortening of the ulnar two metacarpals.
Figure B shows a lateral radiograph of an ulnar fracture dislocation at the CMCJ. The metacarpals are dislocated dorsally.

Incorrect Answers:
Answer 1: The AIN innervates the deep flexors, but not the extensors.
Answer 2: The radial nerve innervates the ECRL but the remainder of the extensors are innervated by the PIN.
Answer 4: The ulnar nerve innervates the FDP to the ulnar two digits as well as intrinsic muscles in the hand, but not the ECU.
Answer 5: There is not a nerve by this name.