Cause of long thoracic nerve palsy: A possible dynamic fascial sling cause

Long thoracic nerve palsy can result from sudden or repetitive external bio mechanical forces. This investigation describes a possible dynamic cause fr om internal forces. Six Fresh cadaveric shoulders (3 Female, 3 male, 4 left , 2 right) with full range of motion were systematically dissected to evalu ate the anatomic course of the long thoracic nerve. In all specimens a tigh t Fascial band of tissue arose from the inferior aspect of the brachial ple xus, extended just superior to the middle scalene muscle insertion on the f irst rib, and presented a digitation that extended to the proximal aspect o f the serratus anterior muscle. With progressive manual abduction and exter nal rotation, the long thoracic nerve was found to "bow-string" across the fascial band. Medial and upward migration of the superior most aspect of th e scapula was Found to Further compress the long thoracic nerve. Previous i nvestigations have reported that nerves tolerate a 10% increase in their re sting length before a stretch-induced neuropraxia develops. Previous studie s postulated that long thoracic nerve palsy resulted from the tethering eff ect of the scalenus medius muscle as it actively or passively compressed th e nerve; however, similar neuromuscular relationships occur in many other a natomic sites without ill effect. We propose that the cause of long thoraci c nerve palsy may be this "bow-stringing" phenomenon of the nerve across th is tight fascial band. This condition may be further exacerbated with media l and upward migration of the superior aspect of the scapula as is commonly seen with scapulothoracic dyskinesia and Fatigue of the scapular stabilize rs. Rehabilitation for long thoracic nerve palsy may therefore benefit from special attention to scapulothoracic muscle stabilization.