A Cadaveric Investigation of the Dorsal Scapular Nerve

Dorsal scapular nerve (DSN) syndrome is often associated with sharp, dull, or aching pain in the upper extremity and back. The primary cause of pain is the entrapment of this nerve at the middle scalene muscle. Even though there is clinical evidence that DSN syndrome exists, it is often overlooked during clinical diagnosis. The purpose of this study is to locate the surface projection of the DSN relative to the middle scalene muscle while using the laryngeal prominence as a reference point. From 20 embalmed adult cadavers, 23 DSN were dissected and documented regarding its spinal root origins, anatomical route, and muscular innervations. A transverse plane through the laryngeal prominence was established to measure the distance of the DSN as it enters, crosses, and exits the middle scalene muscle. Approximately 70% of the DSNs originated from C5, 22% branched from C4, and 8% from C6. In regards to the route of the DSN in relation to the middle scalene muscle, 74% of the DSNs pierced this muscle, 13% crossed this muscle anteriorly, and 13% traveled posterior to this muscle. About 48% of the DSNs supplied the levator scapulae muscle only and 52% innervated the levator scapulae and both the rhomboid muscles. The average distances from a transverse plane of the laryngeal prominence to where the DSN entered, crossed, and exited the middle scalene muscle were 1.50 cm (±0.88 cm), 1.79cm (±0.89 cm), and 2.08 cm (±0.96 cm) respectively. Injection studies were performed on 10 un-dissected embalmed cadavers to verify the accuracy of our surface projection measurements of the DSN relative to the middle scalene muscle. These injections were performed at approximately 2.08 cm (~1 thumb interphalangeal joint width) from the transverse plane of the laryngeal prominence. Dissections at these injection sites revealed that the scalene muscles were consistently located. The middle scalene muscle was accurately located in approximately 50% of the injections. The goal of this research is to understand the variability in DSN's anatomy as well as introduce a method that will assist clinicians to efficiently pinpoint and therefore treat patients with DSN entrapment.