Relationship Between Insertion Torque and Compression Strength in the Reverse Total Shoulder Arthroplasty Baseplate

Reverse shoulder arthroplasty is a well-established procedure, however, there is limited data in the literature regarding adequate insertion torque and the resulting compression for glenoid baseplate fixation. In this biomechanical study, we evaluated the relationship between insertion torque and baseplate compression by simultaneously measuring the insertion torque and axial compressive forces generated by two reverse shoulder arthroplasty baseplates with central screw design. Three different bone surrogates were chosen to mimic clinical scenarios where differences in compression achieved during baseplate insertion may exist due to varying bone quality. Epoxy resin sheets were combined with the bone surrogates to simulate the glenoid vault. A digital torque gauge was used to measure insertion torque applied to the baseplate, while compression data were collected continuously from a load cell. A strong positive correlation was found between baseplate compression and insertion torque. Among the lower density bone surrogates, neither baseplate design reached maximum insertion torque (6.8 Nm) due to material strip-out. This phenomenon did not occur in denser bone surrogates. Both baseplate designs experienced a significant increase in mean baseplate compression as insertion torque increased and were found to behave similar in the denser bone surrogates. The results presented here suggest that larger compressive forces can be achieved with an increase in insertion torque in denser bone surrogates, but caution must be used when trying to achieve fixation in poor-quality bone. Clinically, this could be useful preoperatively to minimize baseplate failure, and in further studies regarding baseplate design for improved initial fixation and stability. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:871-879, 2020     

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.

     

Bone preserving technique for reverse arthroplasty: The preferred management option for osteoarthritis with glenoid bone loss in patients 70 and older

Elderly patients with shoulder arthritis and glenoid bone loss represent a challenging patient population. Surgical treatment options include hemiarthroplasty, anatomic total shoulder arthroplasty (TSA) with bone grafting or augmentation, and reverse total shoulder arthroplasty (RSA). The RSA has multiple advantages compared to anatomic TSA, particularly in an older patient population with glenoid bone loss.RSA with an augmented glenoid baseplate is ideal for the treatment of patients who have glenoid bone loss. The augmented base plate has many advantages including bone preservation, longer central and peripheral screws, ability to dial the augment to match the region of bone deficiency, and lateralization to improve tensioning on the deltoid and rotator cuff. Additionally, a bone preserving RSA is possible with an augmented glenoid baseplate in patients with no glenoid bone loss.     

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.     

The risk of suprascapular and axillary nerve injury in reverse total shoulder arthroplasty: An anatomic study

PurposeImplantation of a reverse total shoulder arthroplasty (rTSA) places the axillary and suprascapular nerves at risk. The aim of this anatomic study was to digitally analyse the location of these nerves in relation to bony landmarks in order to predict their path and thereby help to reduce the risk of neurological complications during the procedure.MethodsA total of 22 human cadaveric shoulder specimens were used in this study. The axillary and suprascapular nerves were dissected, and radiopaque threads were sutured onto the nerves without mobilizing the nerves from their native paths. Then, 3D X-ray scans of the specimens were performed, and the distance of the nerves to bony landmarks at the humerus and the glenoid were measured.ResultsThe distance of the inferior glenoid rim to the axillary nerve averaged 13.6 mm (5.8–27.0 mm, ±5.1 mm). In the anteroposterior direction, the distance between the axillary nerve and the humeral metaphysis averaged 8.1 mm (0.6–21.3 mm, ±6.5 mm).The distance of the glenoid centre to the suprascapular nerve passing point under the transverse scapular ligament measured 28.4 mm (18.9–35.1 mm, ±3.8 mm) in the mediolateral direction and 10.8 mm (−4.8 to 25.3 mm, ±6.1 mm) in the anteroposterior direction. The distance to the spinoglenoid notch was 16.6 mm (11.1–24.9 mm, ±3.4 mm) in the mediolateral direction and −11.8 mm posterior (−19.3 to −4.7 mm, ±4.7 mm) in the anteroposterior direction.ConclusionsImplantation of rTSA components endangers the axillary nerve because of its proximity to the humeral metaphysis and the inferior glenoid rim. Posterior and superior drilling and extraosseous screw placement during glenoid baseplate implantation in rTSA place the suprascapular nerve at risk, with safe zones to the nerve passing the spinoglenoid notch of 11 mm and to the suprascapular notch of 19 mm.     

Computed tomography–based three-dimensional modeling of glenoid bone preservation with augmented baseplates

BackgroundReverse total shoulder arthroplasty (rTSA) is a treatment option for a variety of shoulder pathologies, including rotator cuff arthropathy, glenohumeral arthritis, and irreparable rotator cuff tears and fractures. There has been substantial improvement in rTSA implants and surgical techniques, such as augmented baseplates that preserve bone tissue. In this study, we used three-dimensional modeling to determine the extent of bone preservation with augmented baseplates in rTSA.MethodsComputed tomography scans from 50 consecutive patients before they underwent rTSA were used to create three-dimensional models of each glenoid. The virtual positions of reverse shoulder baseplate implants followed strict parameters for adequate fixation as determined through consensus among 4 fellowship-trained shoulder specialists. Parameters for adequate fixations included 100% backside contact, neutral scapular version, and 10° of inferior tilt. The 4 baseplate options trialed on each glenoid were a nonaugmented baseplate, a small 10° half-wedge augment, a medium 20° half-wedge augment, and a large 30° half-wedge augment. The extent of volumetric glenoid bone removal and lateralization of the baseplate was calculated for each scenario.ResultsPreoperative computed tomography imaging showed a mean of 10.7° of retroversion and a reverse shoulder arthroplasty angle of 21.3°. A medium augment (20° half wedge) was determined as optimal in 29 cases, and a large augment (30° half wedge) was considered optimal for the remaining 21 cases. The use of augmented baseplates was calculated to preserve 54% glenoid bone stock (1989 ± 650 mm³ bone removal vs. 4439 ± 1636 mm³ with nonaugmented baseplate; P < .001). The surgeon-selected augmented baseplate was on average 4.1 mm lateral in comparison to the nonaugmented baseplate.ConclusionsThe use of augmented baseplates reduces the volume of bone that needs to be removed in rTSA. Furthermore, augmented baseplates result in relative lateralization of the glenosphere, which has been theorized to improve soft tissue tension and limit impingement and scapular notching. Further exploration of the impact of augmented baseplates on clinical outcomes is needed.