Our study demonstrates that tri-cortical scapular spine auto-graft restores the bony stability of the shoulder in cases with large glenoid defects.
Shoulder instability is a common complication of shoulder dislocation, especially in young patients. Glenoid bone loss following glenohumeral dislocation is a frequent contributor to instability in these patients. The Latarjet procedure, in which the coracoid process is utilized for bony augmentation of the glenoid, is an established treatment method, however, this is a technically difficult procedure that significantly alters the local anatomy. The purpose of our cadaveric study was to evaluate if the scapular spine is a good local alternative for auto-graft augmentation of the glenoid in shoulder instability. We hypothesized that tri-cortical scapular spine auto-graft can restore the joint reaction forces of the glenohumeral joint in resisting anterior shoulder dislocation.
We obtained 6 matched pairs of fresh-frozen cadaver shoulders. Skin, subcutaneous tissues, and muscle were removed from the specimens, leaving intact the rotator cuff musculature and shoulder capsule. Utilizing a customized testing device, the humerus was translated 1cm anteriorly on the glenoid under 25N of axial compression force. The peak reaction force of the glenohumeral joint was then measured under three conditions: 1) an intact glenoid 2) after a bone defect measuring 25% of the maximal width of the glenoid was made in the anterior-inferior glenoid 3) after size-matched glenoid augmentation with a scapular spine tri-cortical auto-graft. The primary outcome was the change in peak joint reaction forces between the defect state and the augmented state.
One matched pair was removed from final analysis secondary to anatomic concerns that conflated test results. Each of the 10 remaining specimens showed a significant decrease in peak reaction force after the glenoid defect was created as compared to the intact state (p=0.00001). All specimens showed an increase in peak joint reaction force in the augmented state as compared to the defect state (p=0.00001). On average, the augmented state restored 81% of the peak reaction force of the glenohumeral joint compared to the intact state, a non-significant difference (p=0.068).
The scapular spine is a local alternative to the coracoid process for bony augmentation of glenoid defects in shoulder instability. The scapular spine may have advantages over the coracoid in that it does not have direct muscular attachments and it is easily accessible without disturbing major neurovascular structures. The results of our cadaveric study confirm that auto-graft harvested from the scapular spine significantly increases the bony restraint to anterior shoulder dislocation in shoulders with glenoid bone loss.