This study demonstrates the viability of the scapular spine as a bone autograft source for glenoid augmentation, by using CT imaging in vivo to show that the scapular spine's dimensions are comparable to other common sources: the coracoid and iliac crest.
Structural bone graft is often necessary in surgical intervention for glenoid instability. Current graft options, such as coracoid autograft (Latarjet procedure), iliac crest autograft, and allograft, have drawbacks such as pain, multiple surgical sites, impact on surrounding structures, cost, and resorption. The scapular spine could potentially address some of these issues and serve as a bone autograft donor site due to its close proximity to the glenohumeral joint, ease of surgical approach, and low functional necessity. This study aims to quantify the size and geometry of the scapular spine in comparison to the iliac crest and coracoid, current alternatives for autologous bone graft harvest. Previous studies have separately described the dimensions of these structures; however, no study has compared these structures within the same patients, using a single measurement modality.
Patients were included if they had a fine-cut CT performed which included bilateral scapular spines, coracoids, and iliac crests. The scapular spine was measured at 4 equidistant locations spanning from the scapular spine root to the spinoglenoid notch. Scapular spine height was from scapular body to tip of the spine and spine width was from the superior to inferior surfaces. The iliac crest was measured at 4 locations, each 3cm apart. Coracoid height, width, and length were also measured. Dimensions of the 3 structures were obtained using 3D reconstructive software (Syngo.via; Siemens, Erlangen, Germany).
21 CT exams were included, providing 42 lateralities for analysis. Mean age 34 [18-71]. 12 males, 9 females. Mean scapular spine length, 87.8mm. Sequential heights of the scapular spine (medial to lateral): 7.1mm, 17.0mm, 28.1mm, 39.5mm. Sequential scapular spine widths: 12.7mm, 10.0mm, 10.5mm, 13.3mm. Sequential scapular spine cortical thickness: 2.3mm, 3.1mm, 2.5mm, 3.2mm. Coracoid length, width, height, cortical thickness: 30.7mm, 16.3mm, 11.8mm, 2.5mm. Sequential iliac crest width (medial to lateral): 15.0mm, 16.0mm, 18.2mm, 12.7mm. Sequential iliac crest cortical thickness: 2.3mm, 3.0mm, 3.6mm, 3.0mm.
The scapular spine's dimensions in this study were comparable to the other structures analyzed, and appropriate for consideration as an autograft source. The scapular spine had greater dimensions at the two lateral locations, with mean widths of 10.5 and 13.3mm , and mean heights of 28.1 and 39.5mm. Length was sufficient as to not be a limiting factor. In other studies, Iliac crest grafts used for shoulder instability are typically contoured to approximate dimensions of 20mm x 8mm x 8mm. The coracoid graft used in the Bristow-Latarjet procedure is approximately 26.4mm x 14.1mm x 9.3mm. These results suggest that the scapular spine may indeed provide adequate bone stock for use in glenoid augmentation procedures. Surgeons may need to be cautious of harvesting scapular spine graft too far laterally, to prevent destabilization of the acromion. Future cadaver studies would be useful in evaluating effects on acromial stability, and developing a surgical technique for graft transfer.
The scapular spine has dimensions sufficient for use as a structural bone graft in glenoid instability surgery. Surgeons may use the dimensions described in this paper when choosing a location for harvest.