Sonographic evaluation of the posterior interosseous nerve in a patient with wrist drop
Journal
American Journal of Physical Medicine and Rehabilitation
Journal Volume
97
Journal Issue
7
Pages
e68
Date Issued
2018
Author(s)
Abstract
A 24-yr-old lady was involved in a traffic accident and sustained a left humeral shaft displaced comminuted fracture. She underwent open reduction and internal fixation of the fracture. Intraoperatively, the radial nerve was noted to be intact at the fracture site. However, a left wrist drop was observed soon after the surgery, where there was no active wrist and finger extension on examination. The orthopedist referred the patient to the physiatrist for evaluation and treatment. Ultrasound was performed for the tracking of the radial nerve and a focal swelling of the posterior interosseous nerve (PIN) was noted within the supinator muscle, with enlarged hypoechoic fascicles of the nerve in both the short and long axis views (see Video). A comparison was done with the asymptomatic side to confirm the swelling (Fig. 1). There was no structural discontinuity of the radial nerve demonstrated. Electrodiagnostic studies were consistent with an acute and severe left radial neuropathy at the upper arm level, with some electrophysiologic evidence of neural regeneration. The patient was managed conservatively as there was no structural discontinuity. She made significant neurologic recovery over 5 months where the wrist and finger extension improved to grade 4 on manual muscle testing.FIGURE 1: A, Short axis view of the posterior interosseous nerve within the supinator muscle. The enlarged hypoechoic fascicles can be seen. B, Longitudinal axis view of the posterior interosseous nerve within the supinator muscle.The radial nerve divides to form the PIN and superficial branch of the radial nerve at the radio-capitellar joint, passes under the extensor carpi radialis brevis muscle, through the arcade of Frohse before entering the supinator muscle. The deep branch further divides and innervates the extensor muscles of the dorsal compartment of the forearm and hand after exiting the supinator muscle.1 Compression of the deep branch usually presents with painless wrist and finger extension weakness. Ultrasound may show a flattening of the nerve as it enters the supinator muscle; however, the cross-sectional area of the nerve remains the same and hence should not be interpreted as an entrapment.2 This was similarly observed in the asymptomatic side of this study's patient. A case series of 10 patients with PIN syndrome were examined sonographically. Four of the patients had compression and hypoechoic swelling of the PIN at its entry to the supinator muscle, whereas one patient had swelling upon exiting from the supinator.3 Ultrasound is useful in the evaluation of suspected PIN syndrome as it allows for real time and continuous dynamic tracking of the PIN to confirm continuity and morphology of the nerve.
SDGs
Publisher
Lippincott Williams and Wilkins
Type
note