A Cadaveric Model Evaluating the Influence of Bony Anatomy and the Effectiveness of Partial Scapulectomy on Decompression of the Scapulothoracic Space in Snapping Scapula Syndrome.

Background: Snapping scapula syndrome (SSS) is caused by bony and/or soft tissue impingement in the scapulothoracic articulation. Surgical resection of the superomedial angle (SMA) plus bursectomy can provide relief in most cases; however, the amount needed to achieve adequate scapulothoracic space decompression (SSD) is unknown.

Purpose: The aim of this study was to evaluate the effectiveness of partial scapulectomy and the influence of bony anatomy on SSD. It was hypothesized that the anterior offset and costomedial angle would correlate with the amount of bony resection needed to achieve adequate SSD.

Study Design: Controlled laboratory study.

Methods: Twenty pairs (n = 40) of shoulder specimens (mean age, 58 years [range, 41-64 years]; 10 male and 10 female specimens) were included. The scapula shape, medial scapula corpus angle (MSCA), anterior offset, and costomedial angle were obtained from computed tomography scans. Specimens were dissected, and each bare bony scapula was rigidly mounted. Points were collected using a 3-dimensional measuring arm. An SMA point and theoretical resection points (incremental 1-cm points up to 3 cm) proceeding laterally and medially were collected. The scapular plane was interpolated using points from the posterior scapular body. The horizontal distances of the anterior offset and each resection point to the scapular plane were calculated. The difference between the native anterior offset and the offset after resection represented the SSD. Adequate SSD was set at 5 mm. One-way analyses of variance and Pearson correlations were used with statistical significance set at P < .05.

Results: The maximum SSD with 3-cm resection was significantly correlated with the anterior offset ( R = 0.83, P < .001) as well as the costomedial angle ( R = -0.43, P = .006) but not the MSCA ( R = -0.11, P = .495) or scapula shape ( F = 0.39, P = .681). For the 5 scapulae with an anterior offset of less than 20 mm, a 5-mm SSD was not achieved. For 18 of 30 (60%) scapulae with an anterior offset between 20 mm and 35 mm, 3-cm resection provided at least a 5-mm SSD. For the 5 scapulae with an anterior offset of greater than 35 mm, 2-cm resection resulted in at least a 5-mm SSD in all cases.

Conclusion: The anterior offset of the scapula appeared to be the most important bony parameter to consider during preoperative planning and the evaluation of SSD with partial scapulectomy.

Clinical Relevance: The results of this study may help surgeons with preoperative planning of surgical decompression of the scapulothoracic space for patients with symptomatic SSS.