Identification of the Sensory Dependent Locations of the Shoulder Joint to Optimize Surgical Approaches and Reduce Postoperative Pain: A Systematic Review.

INTRODUCTION: Treatment of post-surgical pain is predicated by an understanding of pain generators. The purpose of this review is to identify sensory dependent areas of the shoulder and discuss their correlation in treating postoperative pain.

MATERIALS AND METHODS: Pubmed, Embase, and Cochrane Database of Systemic Reviews were searched (key terms: "Nociception" or "sensory pain receptors" or "pain map" or "neuroanatomy and shoulder" or "rotator cuff") to identify studies in the current literature (1966-2018) regarding sensory innervation of the shoulder and rotator cuff. The search was limited to the English language, human studies, and publication types to reviews and clinical studies. Articles written in other languages besides English, animal studies, abstracts, and conference notes were excluded. Each search result was investigated for relevant physiological information of the nerve endings and nociceptors as well as pertinent information and figures that illustrated the location of the identified receptors.

RESULTS: A total of 12 articles were identified that addressed the sensory innervation of the shoulder. The shoulder capsule has the highest sensory nerve density. The attachment sites between the labrum and the capsule and glenoid rim were also found to be highly sensory dependent, in contrast to the peri-core zone at the capsulolabral junction, which was found to be less concentrated with fascicles and sensory nerve endings. The subacromial bursa is also a highly sensory dependent structure, with a more concentrated neural network on the coracoacromial side compared to other quadrants of the bursa. Cutaneous locations of sensory fibers on the shoulder are best defined by mapping the pressure pain threshold (PPT) of various locations on the shoulder. The most sensory dependent locations of the shoulder were found to be the posterior border of the acromion, the glenohumeral joint, the anterior deltoid, and the upper trapezius.

CONCLUSION: This review examined the origin of pain in the shoulder, the location of cutaneous pain receptors, and receptors in each major part of the shoulder. Providing analgesia to these densely innervated areas of the shoulder can potentially reduce pain associated with surgical trauma. In addition, knowledge of the sensory dependent areas of the shoulder may elicit consideration of alternative incision sites and surgical protocols to decrease the insult to nociceptors in these locations. These changes could possibly decrease the narcotic requirement in the postoperative period.