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.