A biomechanical analysis of flowable injectable calcium bone void filler on acromial tensile stresses: a method to reduce acromial stress fractures

Abstract

IntroductionAcromial fracture after reverse shoulder arthroplasty (RSA) is a known complication. These fractures are difficult to treat and negatively impact outcomes in patients who experience them. As the rate of RSA increases worldwide, it will be valuable to identify ways to decrease the risk of postoperative acromion fractures. The goal of this study was to evaluate if injecting an acromion with a synthetic bone graft substitute can strengthen the acromion and theoretically provide a means to reduce the incidence of acromial fractures after reverse shoulder arthroplasty. MethodsEight cadaveric scapulae matched pairs (n = 16) were randomly allocated to two groups with the contralateral side in the different group. The experimental group (n = 8) had synthetic bone graft filler (CERAMENT) injected while the control group (n = 8) did not. The experimental group had the injection both through an anterolateral and posterolateral corners of the acromion for filling of the acromion. Each scapulae was fixed to the base of a MTS Bionix test frame. Cantilever bending testing to failure was performed on each scapulae with a loading rate of 0.1 mm/s. Failure load (N), force (N/mm), and displacement (mm) were recorded and compared for each specimen. CT scans and fluoroscopy imaging was performed for each specimen before and after testing. ResultsAll 16 specimens were available for analysis. The experimental group was injected with 4 cc +/- 0.5 showed material-to-area ratio fill of 39% mid-acromial area and 38% of the acromial area at the Levy I-II junction. The load to failure was 396 N +/- 89 in the control group and 521 N +/-147 in the experimental group (P = .017). Displacement at failure was less for the control group at 8 mm +/- 2 mm compared to the experimental group at 12 mm +/- 4 mm (P = .051). All samples failed with Levy Type II acromion fractures. ConclusionThis biomechanical study showed that injection of 4 cc of flowable synthetic bone graft filler into the acromion increased load to failure 32% compared to control scapulae. The stiffness was greater and the displacement before failure was greater in the control group compared to the experimental group, although not statistically significant. The ability for the acromion to plastically deform a greater distance prior to failure allow for greater resistance to fracture under higher tensile loads when flowable bone graft filler is injected. Level of evidenceBasic Science Study.