Quantitative Assessment of Scalene Muscle Block for the Diagnosis of Suspected Thoracic Outlet Syndrome

Purpose To measure changes in upper limb work and power capacity before and after anterior scalene muscle block (ASMB) to suggest thoracic outlet syndrome caused by costoclavicular space compression. Methods We evaluated 34 patients disabled by symptoms suggesting thoracic outlet syndrome. An ASMB. was performed via a supraclavicular injection. The sternocleidomastoid muscle was injected as a control. We captured data obtained from work simulator measurements before and after ASMB. Each patient performed a push pull test with the forearm at waist level (test 1), an overhead bar push pull test with the arm elevated (test 2), and the extremity abduction stress test with repetitive hand gripping during static arm elevation (test 3). We measured the work product, time to fatigue, and power generation. Sensory testing was performed after ASMB to rule out improved performance associated With possible sensory nerve block. Results In contrast to sternocleidomastoid injection controls, symptomatic and functional improvement was noted in all patients (n = 34) after ASMB. Work product measurement improved 93%, 108%, and 104% for tests 1, 2, and 3, respectively. Time to fatigue and power output also increased after the block. Conclusions Temporary symptomatic improvement after ASMB may be anticipated in patients with TOS. This study documents a significant concurrent increase in upper limb motor function after the block. Increased work and power measurements after ASMB may draw diagnostic inference regarding a dynamic change in the scalene muscle and the costoclavicular space associated with symptomatic thoracic outlet syndrome. (Copyright (C) 2015 by the American Society for Surgery of the Hand. All rights reserved.)