Thumb injuries are not as common as those occurring in the fingers. The authors present the case of a patient who had an isolated avulsion of the extensor pollicis brevis that resulted in metacarpophalangeal joint instability, with intact radial and ulnar collateral ligament.
Keywords: Congenital hand deformities; Joint instability; Metacarpophalangeal joint; Thumb.
Lesões no polegar não são tão comuns como aquelas nos dedos. Os autores relatam um caso em que a paciente sofreu uma avulsão isolada do extensor curto do polegar que resultou em instabilidade da articulação metacarpofalângica do polegar, com ligamento colateral ulnar e radial intacto.
Palavras-chave: Deformidades congênitas da mão; Instabilidade articular; Articulação metacarpofalângica; Polegar.
Note: Study conducted at University of South Florida, Tampa, United States.
A 17 y.o. female with no significant past medical history came into the ED after direct trauma to the dorsal aspect of the left thumb. Initial X-ray revealed a volar dislocation of the left thumb Metacarpophalangeal joint (MCPJ), with no fractures.
After reduction, patient was splinted. In her follow-up appointment, she complained of worsening pain, weakness, and decreased range of motion in the left thumb. On inspection, there was swelling on the MCPJ dorsal-ulnar aspect, pain on the MCPJ dorsal-ulnar aspect, decreased MCPJ stability and grip strength. MRI ordered to evaluate the possibility of damage to the ulnar collateral ligament.
MRI indicated an avulsion at the insertion point of the EPB with proximal phalanx volar subluxation, as well as an intact ulnar collateral ligament (UCL) (Fig. 1).
Fig. 1. (Left) A T2 weighted sagittal MRI the thumb indicated an avulsion at the insertion of the EPB (*) and a volar dislocation of the proximal phalanx. (Right) T2 weighted MRI in an A/P view of the thumb, showing the UCL to be intact (**).
Surgery was recommended. In surgery, the EPL was reinserted through a dorsal approach (Fig. 2). A SonicAnchor (Stryker) was then inserted into the dorsal aspect of the proximal phalanx, the dorsal capsule and the EPB repaired. The stability of the MCPJ was tested with no subluxation or instability. Patient was immobilized for 3 weeks and AROM started.
Fig. 2. Surgical steps, reinsertion EPB at the base of the proximal phalanx (A to D).
Upon physical examination of the patient, due to the significant loss of stability as well as a swelling on the dorsal-medial aspect of the thumb, it was previously thought there would be an injury to the UCL. With the results of the MRI as shown above, it was clear that the UCL remained intact and that an avulsion at the distal attachment of the EPB was present. However, due to the unified fibrous canal that contains the EPB and the APL, it was interesting to note that there was not a simultaneous avulsion of the APL at the base of the first metacarpal (the distal attachment of the APL). With previous literature not reporting an isolated avulsion of the EPB, a surgical approach was taken to treat the avulsion.
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