Anatomic safe zones for arthroscopic snapping scapula surgery: quantitative anatomy of the superomedial scapula and associated neurovascular structures and the effects of arm positioning on safety

Abstract

Background: Neurovascular anatomy has not been previously quantified for the arthroscopic snapping scapula approach with the patient in the most frequent patient position (“chicken-wing” position). The purposes of this study were (1) to determine anatomic relationships of the superomedial scapula and neurovascular structures at risk during arthroscopic surgical treatment of snapping scapula syndrome (SSS), (2) to compare these measurements between the arm in the neutral position and the arm in the chicken-wing position, and (3) to establish safe zones for arthroscopic treatment of SSS. Methods: Eight fresh-frozen cadaveric hemi-torsos (mean age, 55.8 years; range, 52-66 years) were dissected to ascertain relevant anatomic structure locations including the (1) spinal accessory nerve, (2) dorsal scapular nerve, and (3) suprascapular nerve. A coordinate measuring device was used to collect data on the relationships of anatomic landmarks and at-risk structures during the surgical approach. Results: The dorsal scapular nerve was a mean of 24.4 mm medial to the superomedial scapula in the neutral position and 33.1 mm medial in the chicken-wing position (P < .001); the dorsal scapular nerve was 21.7 mm medial to the medial border of the scapular spine in the neutral position and 35.5 mm medial in the chicken-wing position (P < .001). The mean distance from the superomedial angle to the spinal accessory nerve intersection at the superior scapular border was 16.5 mm in the neutral position and 15.0 mm in the chicken-wing position (P = .031). The average distance from the superomedial angle to the closest point of the spinal accessory nerve was 11.6 mm and 10.4 mm in the neutral position and chicken-wing position, respectively (P = .039). Conclusion: Neurologic structures around the scapula vary significantly between the neutral arm position and the chicken-wing position commonly used in the arthroscopic treatment of SSS. The chicken-wing position improves safe distances for the dorsal scapular nerve during medial-portal placement and should be considered as a primary position for arthroscopic management of SSS.