Flexor Pollicis Longus Palsy Following Both-Bone Forearm Fracture Fixation: A Case-Based and Cadaveric Evaluation.

Background: Flexor pollicis longus (FPL) palsy following both-bone forearm fracture (BBFF) is a rare complication.

Methods: A retrospective review of acute BBFF treated with open reduction internal fixation by a single surgeon from 2005 to 2023 was performed. Injury and surgical characteristics of patients with documented FPL palsy were reviewed. In addition, 10 cadaveric dissections were performed to evaluate the anatomy of the anterior interosseous nerve (AIN) and its branches. The distance of these branches from palpable elbow landmarks and variability in branching pattern were evaluated.

Results: Twenty-nine patients underwent surgery for acute BBFF. Of these, 5 (17%) had evidence of an FPL palsy either at the time of injury presentation (n = 2) or immediately following surgery (n = 3). All patients with FPL palsy sustained fractures in the middle one-third of the radius. All palsies resolved after an average of 33 days of observation. In cadaveric dissections, the average distance from the lateral epicondyle to the AIN takeoff and branch to the FPL was 5.5 and 7.6 cm, respectively. The AIN takeoff and branch to the FPL were never less than 4 and 7 cm from the lateral epicondyle, respectively.

Conclusion: Flexor pollicis longus palsy following BBFF can occur at the time of injury or following surgery. All FPL palsies involved midshaft radial fractures and were likely neurapraxia. The etiology of FPL palsy remains unclear, but cadaveric dissection suggests the FPL motor branch may be at risk from mid-to-proximal radius fracture fragments or excessive traction during surgery.