Ulnar carpometacarpal dislocations, a complication to be reckoned

Clinical History

A 39-year-old man came to our department complaining of continuous pain of the right hand and wrist with inability to flex and extend it and swollen skin.
The patient suffered from an ulna-radius fracture 5 months before (Fig. 1) treated with surgery and immobilization (Fig.2).
After plaster removal, symptoms appeared; physiotherapy was not successful.

Imaging Findings

A hand and wrist X-ray (Fig. 3) showed results of ulna-radius fracture with bone callus formation, without any soft tissue specific findings except for a subtle lateral displacement of long axis between F1 over 5th MTC bone.
CT scan (Fig.4) showed:
- bone loss in the anatomical snuff box,
- irregular cortical bone due to severe chondropathy,
- scapho-lunate diastasis (Terry-Thomas sign) due to ligament lesion,
- posterior dislocation of the base of the fourth metacarpal bone with detachment of a bone fragment,
- posterior subluxation of the base of the fifth metacarpal bone,
- osteoporosis of carpal, metacarpal bones and distal part of radius and ulna, due to presence of algodystrophy.
3D volume rendering (Fig. 5) images helped to highlight CT findings and to plan surgical treatment.

Discussion

Carpometacarpal joints(CMJ) are extremely stable because of their arthrodial morphology, the supporting ligaments (dorsal-metacarpal, palmar-metacarpal, and the two sets of interosseous ligaments), tendinous insertions and carpal bone alignment [1]. Pure CM dislocation (CMD) is extremely rare, fracture-dislocations (especially I and V range) are more common, together accounting for less than 1% of traumatic injuries of wrist and hand [2].
CMD affects mostly men between 20 and 40 years of age. The most common cause is high energy trauma with flex-extension mechanism.
Physical examination shows swelling and deformity of anatomical shape, pain, functional impairment, shortening of the fingers, preternatural rotation and neurological complications if compressed the deep branch of the ulnar nerve.
CMD may be divided into:
- dorsal (85% of cases),
- volar,
- lateral,
- divergent.
Imaging findings are essential to diagnose CMD: lateral, postero-anterior, oblique X-ray with prone hand at 30-45 degrees may reveal severe cases. On a lateral hand X-ray image the angle between the index and small metacarpal bone shaft and between the long and small metacarpal shaft may be used as screening to diagnose ulnar-sided CMD, when the angle is greater than 10° diagnosis and other imaging examination should be performed [3].
CT scan with 2D or 3D volume rendering is essential because X-ray underestimates the bone and joint injuries (fracture-dislocation), so CT is the preferred diagnostic imaging method for complete assessment of these injuries [4]. MRI shows ligament injuries.
CMD may lead to severe disability of the hand so treatment of choice should be early reduction and metacarpal resting [5].
CMD treatment is essentially surgical, both closed and open reduction may be administered.
Closed reduction, under fluoroscopic guidance, is usually successful in dislocations <10 days old, to ultimate stability percutaneous Kirschner wires or pinning may be necessary [6]. When the injury is older than three weeks or CMD is associated with major fractures open reduction (OR) is recommended.
OR starts with a longitudinal dorsal incision over the dislocated CMJ. After the lateralization of extensor carpal ulnaris, CMJ is well appreciable and any osteochondral debris may be removed. If fractures are present they need to be fixated. CMJ is then anatomically reduced and treated with Kirschner wires that could be removed after six weeks. In case of severe intra-articular comminution, an arthrodesis may be considered, with risk of future impairment and osteoarthritis [7].
During follow-up, X-ray examinations (to assure the correct alignment of the CMJ, to avoid secondary dislocations, prevalent in the first two weeks after surgery) and early rehabilitation (to avoid future impairment) is recommended [8].

Differential Diagnosis List

Final Diagnosis

Ulnar IV carpometacarpal dislocation, due to car accident

URL:	https://eurorad.org/case/10858
DOI:	10.1594/EURORAD/CASE.10858
ISSN:	1563-4086