Surface Projection of Long Thoracic Nerve in Cadaveric Study

Purpose: Long thoracic nerve (LTN) innervates the serratus anterior (SA), which is the primary muscle for scapular protraction and shoulder push-forward action. However, how the LTN route to the muscle in terms of surface projection has not been reported before. Thus, this pilot study was to investigate how the LTN travels down to the muscle with the thumb inter-phalangeal joint (IPJ) width, since the IPJ is one of the most conveniently used measurements in rehab settings. Methods: Eight specimens from 4 previously dissected adult cadavers and one undissected cadaver were utilized for parameter assessment for this study. Forty physical therapy students were recruited for calculation of the average IPJ width. Data was collected with the Vernier caliper. Results: The average IPJ width from students was 2.01cm. By assessing 8 specimens, it's identified that all LTNs originate from the C5-7 spinal roots. These roots converge along transverse processes of C6-7 vertebrae. Then the nerve enters into the axillary fossa and then travels about 4 IPJs of the upper portion of the outer surface of the SA muscle to pierce into the muscle. The piercing point is also 4 IPJs from the apex of the axillary fossa when the arm was placed in 90-degree abduction, which was confirmed by using the undissected cadaver. Conclusion: Results will surely assist clinicians, like physical therapists, to pinpoint the LTN more accurately and efficiently, particularly when modalities and/or nerve manipulation are provided for LTN injury or impingement.