Sonographic Changes in the Median Nerve Predict Conversion to Surgery after Corticosteroid Injection of the Carpal Tunnel

Abstract

Background: Risk factors for conversion to surgical management of moderate severity carpal tunnel syndrome are poorly understood. The authors hypothesized that sonographic findings along the carpal tunnel could predict failure of conservative management for carpal tunnel syndrome. Methods: The authors report on 96 wrists with moderate clinical signs and symptoms of carpal tunnel syndrome. Sonographic evaluation with measurement of median nerve cross-sectional area was performed at three consistent anatomic locations. The authors recorded median nerve morphology, inlet and outlet dimensions of the carpal tunnel, and maximal thickness of the transverse carpal ligament. Steroid injection was performed. Patients were followed up for a minimum of 1 year after injection and progression to surgical management was recorded. Results: A total of 54 percent (n = 52) of patients converted to surgical management within 1 year after injection. Median nerve cross-sectional area decreased over the course of the carpal tunnel from proximal to distal in 81 of 96 wrists. A greater decrease in cross-sectional area of the median nerve between the pisiform and the hamate was associated with conversion to operative intervention for carpal tunnel syndrome, with the average decrease in median nerve cross-sectional area among those whose conservative treatment failed being 5.01 mm2compared with 2.97 mm2among those who did not progress to surgical treatment. Conclusions: This study demonstrates that ultrasound may be an additional tool used by clinicians to better counsel patients about the severity and progression of their disease. Patients who demonstrate a decrease in cross-sectional area of the median nerve along the carpal tunnel demonstrate a higher likelihood of progression to operative management. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, III.