Morphology properties of scapular spine relative to reverse shoulder arthroplasty: A biomechanical study

Objective: Stress fractures of the scapular spine are often a consequence of reverse shoulder arthroplasty (RSA) reconstruction. Knowledge of the morphology and strength of the scapular spine may have potential value preoperative planning of RSA. However, the morphometric and biomechanics of the scapular spine have not been thoroughly investigated yet. This study aimed to evaluate the association between different morphology of the scapular spine and biomechanics to identify scapular spine with weaker strength that may be destroyed after RSA.Methods: Anatomical morphology of 102 dry scapulae was studied. Nine bony landmarks associated with the anatomical morphology of the scapular spine were measured. After the measurements, each specimen was loaded to failure under an axial compressive load. All the samples were analyzed at the point of failure to calculate the failure load and energy.Results: Five types of scapular spine were observed in the population. Type I (fusiform shape) was the most frequent (32.4%), and the least common type included type V (S-shape) (4.9%). The morphological parameters for type II (slender rod shape) were smaller than those for the other types. Type II scapular spine withstood the lowest failure load (381.87 +/- 25.31 N) and energy (1.45 +/- 0.56 J), followed by type V (530.98 +/- 25.26 N and 1.75 +/- 0.49 J).Conclusion: Significant variation was observed in the anatomical morphology of scapular spine. Slender rod shaped and S-shaped scapular spine bore lower load and energy, which may be the potential anatomical related factors of stress fractures after RSA.