Question

A 42-year-old woman is brought to the emergency department after tripping over a rug and falling onto her right arm. She reports severe, sharp pain and an inability to move her right arm. Vital signs are within normal limits. Physical examination reveals an obvious deformity and significant swelling over the middle-to-distal aspect of the right arm. Upon initial neurologic evaluation, the patient has full active extension of the right wrist and fingers, and sensation is intact to light touch over the dorsum of the hand. Radial and ulnar pulses are 2+ and capillary refill is less than 2 seconds. Radiographs of the right upper extremity demonstrate a displaced, spiral fracture of the distal third of the humeral shaft. An orthopedic surgery resident performs a closed reduction in the emergency department, and a coaptation splint is applied. Post-reduction radiographs confirm acceptable alignment of the fracture fragments. Thirty minutes later, during a routine neurovascular reassessment, the patient is unable to actively extend her right wrist or digits. Sensation to light touch is now decreased over the dorsal web space between the thumb and index finger. Distal pulses remain 2+. Which of the following is the most appropriate next step in management?