Anterior Scalene Muscle Block Response Predicts Outcomes Following Thoracic Outlet Decompression

Abstract

Background: There is no definitive objective measure for diagnosis of thoracic outlet syndrome (TOS), and functional capacity testing on standardized rehabilitation exercises before and after an anterior scalene muscle block (ASMB) has the potential to serve as a predictor of response to surgery and to improve diagnostic accuracy in these cases. Methods: Patients evaluated for TOS underwent ASMB as a diagnostic test and were retrospectively reviewed. Functional capacity scores were recorded for patients performing repetitive motion exercises immediately before ASMB, 15 minutes after ASMB, and at a minimum of 6 weeks after thoracic outlet decompression (TOD). The primary outcome of interest was correlation between the pre- to post-ASMB difference and the pre-ASMB to postoperative difference with respect to 3 functional work capacity scores. Results: The average change in time-to-fatigue and work product between pre- and post-ASMB of all exercises was an increase of 39.5% and 53.8%, respectively. The greatest pre-ASMB to post-TOD difference was seen for the Extremity Abduction Stress Test with an average improvement of 109.7% and 150.4% for time-to-fatigue and work product, respectively. The degree of percent improvement post-ASMB correlated positively with the degree of percent improvement post-TOD for all exercises with respect to work product and time-to-fatigue. Conclusions: Patient response to ASMB as measured by functional capacity on rehabilitation exercises predicted objective functional outcomes following TOD. Post-ASMB outcomes correlated with post-TOD outcomes. The ASMB can be used to assist in diagnosing TOS and provide a surrogate for expectation in patients considering undergoing neurogenic TOD.