Treating posteriorly eroded glenoids with augmented baseplate or bony increased-offset reverse shoulder arthroplasty: a finite element comparison

BackgroundAugmented reverse shoulder arthroplasty (RSA) implants restore glenohumeral joint alignment in cases of asymmetric glenoid wear. However, no consensus has been reached on whether the use of metallic augmented RSA baseplates and bone graft reconstruction are equivalent in terms of implant fixation and risk of implant loosening. Therefore, the purpose of this study was to compare 2 augmented RSA designs by assessing the amount of interfacial micromotion generated under realistic physiological loading.MethodsFinite element analysis models of 9 scapulae with Walch-type B2 or B3 glenoid morphology were virtually implanted with both a metallic augmented baseplate (AUG-RSA) and using the angled bony increased-offset RSA procedure (BIO-RSA). Simulation of physiological loading was performed on each of the 18 finite element analysis models. The relative tangential and normal micromotion at the implant-to-glenoid interface was compared in each anatomical quadrant.ResultsThe AUG-RSA and angled BIO-RSA showed similar magnitudes of micromotion in most anatomical quadrants of the glenoid. Within the superior quadrant, AUG-RSA displayed a higher magnitude of mean and maximum tangential micromotion (mean: 16.6 ± 2.4 μm, P < .000; maximum: 35.1 ± 5.3 μm, P < .000). The proportion of the posterior quadrant experiencing >50 microns of micromotion was also statistically greater with AUG-RSA (5.8 ± 2.5 %, P = .047).ConclusionBecause of its statistically greater micromotion and portions of contact exceeding the accepted 50-micron threshold, the AUG-RSA may be more likely to have inhibited bone on-growth. However, the clinical importance of these differences remains unclear.     

Finite element analysis of glenoid‐sided lateralization in reverse shoulder arthroplasty

The purpose of this study was to evaluate glenoid‐sided lateralization in reverse shoulder arthroplasty (RSA), and compare bony and prosthetic lateralization. The hypothesis was that stress and displacement would increase with progressive bony lateralization, and be lower with prosthetic lateralization. A 3D finite element analysis (FEA) was performed on a commercially available RSA prosthesis. Stress and displacement were evaluated at baseline and following 5, 10, and 15 mm of bony or prosthetic lateralization. Additional variables included glenosphere size, baseplate orientation, and peripheral screw orientation. Maximum stress for a 36 mm glenosphere without bone graft increased by 137% for the 5 mm graft, 187% for the 10 mm graft, and 196% for the 15 mm graft. Likewise, displacement progressively increased with increasing graft thickness. Stress and displacement were reduced with a smaller glenosphere, inferior tilt of the baseplate, and divergent peripheral screws. Compared to bony lateralization, stress was lower with prosthetic lateralization through the glenosphere or baseplate. Displacement with 5 mm of bony lateralization reached recommended maximal amounts for osseous integration, whereas, this level was not reached until 10–15 mm of prosthetic lateralization. Baseplate stress and displacement in an FEA model is lower with a smaller glenosphere, inferior tilt, and divergent screws. Bony lateralization increases stress and displacement to a greater degree than prosthetic lateralization. It appears that at least 10 mm of prosthetic lateralization is mechanically acceptable during RSA, but only 5 mm of bony lateralization is advised. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1548–1555, 2017.

     

Intraoperative CT navigation for glenoid component fixation in reverse shoulder arthroplasty

CT navigation has been shown to improve component positioning in total shoulder arthroplasty. The technique can be useful in achieving strong initial fixation of the metal backed glenoid in reverse shoulder arthroplasty. We report a 61 years male patient who underwent reverse shoulder arthroplasty for rotator cuff arthropathy. CT navigation was used intraoperatively to identify best possible glenoid bone and to maximize the depth of the fixation screws that anchor the metaglene portion of the metal backed glenoid component. Satisfactory positioning of screws and component was achieved without any perforation or iatrogenic fracture in the scapula. CT navigation can help in maximizing the purchase of the fixation screws that dictate the initial stability of the glenoid component in reverse shoulder arthroplasty. The technique can be extended to improve glenoid component position [version and tilt] with the availability of appropriate software.