Rupture of the Flexor Digitorum Superficialis at the Musculotendinous Junction Due to a Forearm Fracture: A Case Report

Abstract

We report a case of a forearm fracture in which the flexor digitorum superficialis (FDS) of the small finger was found to be ruptured at its musculotendinous junction. Although experimental models and studies emphasize that such traumas present with rupture at the musculotendinous junction or at the bony insertion, the literature supports only the latter. Such ruptures of the musculotendinous junction may be misdiagnosed. Case ReportA 22-year-old male was referred to our clinic for ulnar nerve palsy following closed trauma of the right forearm sustained in a car accident. The injured hand was the dominant one. Radiological evaluation revealed fracture of the distal third of the radius and ulna (►Fig. 1). Clinical examination revealed a sensory deficit of the ring and small finger as well as reduced adduction strength (M4) of the thumb. Active flexion of the small finger had reduced strength. The patient underwent open reduction and internal fixation of the radius and ulna. Via the extended anterior forearm approach, we explored the distal half of the ulnar nerve. The ulnar nerve was intact with an epineural hematoma. During exploration of the ulnar nerve, we found that the FDS tendon of the small finger was avulsed from its musculotendinous junction (►Fig. 2). The injury was not a result of a laceration from a bony fragment, considering that the level of the fracture was far more distal than the tendon avulsion. We performed a sideto-side suturing of the ruptured tendon to the FDS of the ring finger in the proper flexion. We must stress that the patient had no underlying pathologies that could have contributed to this tendon rupture.Six months postoperatively, the patient had clinical and radiological signs of fracture union. Grip strength of the injured hand was 90% and lateral pinch strength was 60% of the contralateral side. Mild hypothenar atrophy was still present. Patient had full range of motion of wrist and digits, no sensory deficit of the small and ring finger, and no claw deformity. DiscussionIn a retrospective analysis of 80 flexor tendon ruptures, it was reported that only eight (10%) occurred on the FDS alone, of which only one case involved the FDS of the small finger and only two cases were located at the musculotendinous Keywords ► flexor digitorum superficiallis ► musculotendinous junction ► rupture AbstractWe present a case of a closed distal-third forearm fracture, in which the flexor digitorum superficialis was found ruptured at its musculotendinous junction. We diagnosed the ruptured tendon during the exploration of the ulnar nerve for observed preoperative palsy. Although there are numerous reports about avulsions at the bony insertions, there are very few about avulsion at the musculotendinous junction in the literature. This consideration leads to the conclusion that this kind of rupture may be more frequent than recognized.