Effects of tilt and glenosphere eccentricity on baseplate/bone interface forces in a computational model, validated by a mechanical model, of reverse shoulder arthroplasty (original) (raw)
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Accuracy of obtaining optimal base plate declination in reverse shoulder arthroplasty
Journal of Shoulder and Elbow Surgery, 2012
Background: Reverse total shoulder arthroplasty has shown promising early and midterm results; however, complication rates remain a concern. Glenoid loosening and notching, for example, can be deleterious to the long-term success. A 15 inferior inclination angle has been shown to offer the most uniform compressive forces across the base plate and the least micromotion at the base plate-glenoid interface. The inferior inclination angle may also avoid scapular notching. The purpose of this study was to determine the accuracy of obtaining 15 of inferior inclination of the base plate. Methods: The radiographs of 138 reverse total shoulder patients were included. Overall, glenoid inclination and change in inclination from preoperative radiographs were measured using a previously described standardized method. Measurements were obtained by 2 orthopedic surgeons, who repeated all measurements 3 weeks apart. The final angle and change in inclination were averaged. Results: Seventy-two patients had pre-and postoperative radiographs of sufficient quality to accurately measure inclination. Average pre-and postoperative inclination measured À4.8 (À27.2 to 28.1) and À13.3 (À22.8 to 43.6), respectively. The average change in inclination was À8.5 (À53.7 o to 34.6 o). No scapular notching was observed, which may relate to the lateralized center of rotation of the implant used in this study. Discussion: Overall, the average decrease in inclination was very close to the intended target value using the standard guide. However, patients with preoperative superior glenoid erosion from advanced rotator cuff tear arthropathy appeared to be consistently tilted superiorly, suggesting the standard guide may be inadequate in these patients.
BMC Musculoskeletal Disorders, 2019
BackgroundLittle is known about the strains at the glenoid near the bone-implant interface in reverse shoulder arthroplasty. The purpose of the current study was to evaluate the strains on the glenoid bone under a compressive load after implantation of three different sizes of metal-backed baseplates in either inferior or superior position in combination with three different sizes of glenospheres and three different glenosphere designs.MethodsThree sizes of baseplates (small, medium, large) were implanted in thirty-six paired human cadaveric scapulae either inferior, flush with the glenoid neck, or with a 5 mm superior offset. Glenospheres were available in three sizes (36 mm, 39 mm, 42 mm) and designs (standard, 4 mm lateralized, 2.5 mm inferiorized). Specimens were mounted in a servo-hydraulic testing apparatus at a 60° angle between the glenoid and actuator holding the humeral component. Four strain-gauge rosettes were placed around the glenoid rim to measure strains transferred ...
Journal of Shoulder and Elbow Surgery, 2008
We developed biomechanical and finite element models, using high-strength polyurethane foam blocks, to represent the glenoid bone/baseplate junction to determine if increasing the distance between the glenoid bone and the center of rotation of the glenosphere increases baseplate motion during static loading in the reverse shoulder design. Although there was a general trend toward increased baseplate motion with increasing distance from the glenoid to the center of rotation, in vitro mechanical testing revealed no significant difference between the 7 glenosphere types tested, with average baseplate motion during 1000 load cycles ranging from 90 mm to 120 mm. Results from the finite element analysis strongly correlated with the in vitro mechanical testing. The magnitude of baseplate motion occurring in a modeled representation of bone under simulated physiologic loading conditions was similar for the 7 reverse shoulder glenoid components tested in this study.
Journal of Shoulder and Elbow Surgery, 2014
Background: In this glenoid loosening study, we compared the fixation strength of multiple generic reverse shoulder glenoid baseplates that differed only in backside geometry and shape and size to optimize design from a fixation perspective. Methods: The fixation strength of 4 generic baseplates was quantified in a low-density polyurethane substrate to isolate the contribution of baseplate profile and size (25 mm circular vs 25 Â 34 mm oval) and backside geometry (flat back vs curved back) on fixation using 2 center-of-rotation glenospheres (0 mm and 10 mm lateral). The cyclic test simulated 55 of abduction as a 750 N load was continuously applied to induce a variable shear and compressive load. Before and after cyclic loading, baseplate displacement was measured in the directions of the applied static shear and compressive loads. Each generic baseplate was cyclically tested 7 times with each offset glenosphere for a total of 56 samples. Results: Circular baseplates were associated with significantly more shear displacement in both the superior-inferior (SI) and anterior-posterior (AP) directions after cyclic loading than oval baseplates. No such significant differences in fixation were observed between flat-back and curved-back baseplates. Circular baseplates were also associated with significantly more SI and AP shear displacement with 10 mm glenospheres than with 0 mm glenospheres. No significant difference in SI or AP motion was observed with oval baseplates between 0 mm and 10 mm glenospheres. Discussion: Our results suggest that baseplate shape and size affects fixation strength more than backside geometry. The 25 Â 34 mm oval baseplates showed better fixation characteristics than their 25 mm circular counterparts; no discernible difference in fixation was observed between flat-back and curved-back baseplates. No institutional review board approval was required (biomechanical evaluation in polyurethane bone-substitute substrate blocks).
Journal of Shoulder and Elbow Surgery, 2019
Background: Avoiding superior inclination of the glenoid component in reverse shoulder arthroplasty (RSA) is crucial. We hypothesized that superior inclination was underestimated in RSA. Our purpose was to describe and assess a new measurement of inclination for the inferior portion of the glenoid (where the baseplate rests). Methods: The study included 47 shoulders with rotator cuff tear arthropathy (mean age, 76 years). The reverse shoulder arthroplasty angle (RSA angle), defined as the angle between the inferior part of the glenoid fossa and the perpendicular to the floor of the supraspinatus, was compared with the global glenoid inclination (b angle or total shoulder arthroplasty [TSA] angle). Measurements were made on plain anteroposterior radiographs and reformatted 2dimensional (2D) computed tomography (CT) scans by 3 independent observers and compared with 3-dimensional (3D) software (Glenosys) measurements. Results: The mean RSA angle was 25 AE 8 on plain radiographs, 20 AE 6 on reformatted 2D CT scans, and 21 AE 5 via 3D reconstruction software. The mean TSA angle was on average 10 AE 5 lower than the mean RSA angle (P < .001); this difference was observed regardless of the method of measurement (radiographs, 2D CT, or 3D CT) and type of glenoid erosion according to Favard. In Favard type E1 glenoids with central concentric erosion, the difference between the 2 angles was 12 AE 4 (P < .001). Conclusion: The same angle cannot be used to measure glenoid inclination in anatomic and reverse prostheses. The TSA (or b) angle underestimates the superior orientation of the reverse baseplate in RSA. The RSA angle (20 AE 5) needs to be corrected to achieve neutral inclination of the baseplate (RSA angle ¼ 0). Surgeons should be aware that E1 glenoids (with central erosion) are at risk for baseplate superior tilt if the RSA angle is not corrected.
Reverse total shoulder arthroplasty component center of rotation affects muscle function
Journal of Shoulder and Elbow Surgery, 2014
Background: Medialization of the glenohumeral center of rotation alters the moment arm of the deltoid, can affect muscle function, and increases the risk for scapular notching due to impingement. The objective of this study was to determine the effect of position of the glenosphere on deltoid efficiency and the range of glenohumeral adduction. Methods: Scapulohumeral bone models were reconstructed from computed tomography scans and virtually implanted with primary or reverse total shoulder arthroplasty implants. The placement of the glenosphere was varied to simulate differing degrees of ''medialization'' and inferior placement relative to the glenoid. Muscle and joint forces were computed during shoulder abduction in OpenSim musculoskeletal modeling software. Results: The average glenohumeral joint reaction forces for the primary total shoulder arthroplasty were within 5% of those previously reported in vivo. Superior placement or full lateralization of the glenosphere increased glenohumeral joint reaction forces by 10% and 18%, respectively, relative to the recommended reverse total shoulder arthroplasty position. The moment arm of the deltoid muscle was the highest at the recommended baseline surgical position. The baseline glenosphere position resulted in a glenohumeral adduction deficit averaging more than 10 that increased to more than 25 when the glenosphere was placed superiorly. Only with full lateralization was glenohumeral adduction unaffected by superoinferior placement. Discussion/Conclusion: Selecting optimum placement of the glenosphere involves tradeoffs in bending moment at the implant-bone interface, risk for impingement, and deltoid efficiency. A viable option is partially medializing the glenosphere, which retains most of the benefits of deltoid efficiency and reduces the risk for scapular notching.
JSES Open Access, 2019
glenoid baseplate fixation cyclic bench testing ASTM 2028 testing effect of screw length on rTSA baseplate fixation effect of screw number on rTSA baseplate fixation Level of evidence: Basic Science Study; Biomechanics Background: Little guidance exists regarding the minimum screw length and screw quantity necessary to achieve fixation in reverse total shoulder arthroplasty (rTSA); to that end, this study quantified the displacement of 2 different sizes of glenoid baseplates using multiple different screw lengths and quantities of screws in a low-density polyurethane bone-substitute model. Methods: Testing of rTSA glenoid loosening was conducted according to ASTM F 2028-17. To independently evaluate the impact of screw quantity and screw length on rTSA glenoid fixation for 2 different sizes of glenoid baseplates, baseplates were constructed using 2 screws, 4 screws, or 6 screws (with the latter being used for the larger baseplate only) with 3 different poly-axial locking compression screw lengths. Results: Both sizes of glenoid baseplates remained well fixed after cyclic loading regardless of screw length or screw quantity. Baseplates with 2 screws had significantly greater displacement than baseplates with 4 or 6 screws. No differences were observed between baseplates with 4 screws and those with 6 screws (used for the larger baseplate). Both sizes of baseplates with 18-mm screws had significantly greater displacement than baseplates with 30-or 46-mm screws. For larger baseplates, those with 30-mm screws had significantly greater displacement than those with 46-mm screws in the superiorinferior direction. Discussion: For the 2 different sizes of baseplates tested in this study, rTSA glenoid fixation was impacted by both screw quantity and screw length. Irrespective of screw quantity, longer screws showed significantly better fixation. Irrespective of screw length, the use of more screws showed significantly better fixation, up to a point, as the use of more than 4 screws showed no incremental benefit. Finally, longer screws can be used as a substitute for additional fixation if it is not feasible to use more screws.
International Orthopaedics, 2018
Background Severe glenoid bone loss remains a surgical challenge. This condition is known to be associated with high rates of glenoid component failure. Purpose The objective of this study was to evaluate clinical and radiological outcomes of a lateralized metal-backed 15.2-mm keeled baseplate prolonged by a thin 24.8-mm metallic post fixed directly in the subscapularis fossa in primary cases of reverse shoulder arthroplasty (RSA) for severe glenoid bone loss and in revision cases. Materials and methods Between January 2011 and December 2014, 51 shoulders (50 patients) underwent primary or revision RSA using this baseplate. Forty-five shoulders in 44 patients were followed for a minimum of two years (mean, 33 months; range, 24-60 months). The mean age of the patients was 76 years (range, 55-93 years). Outcome measures included pain, range of motion, Constant Score, and complications. Results The complication rate was 12% in primary cases and 25% in revision cases. One glenoid implant (4%) failed in primary cases and one glenoid implant (5%) failed in revision cases. Pain and range of motion were significantly improved in both groups. The mean Constant Score improved from 24 (± 7) to 62 (± 9) in primary cases and from 24 (± 10) to 58 (± 12) in revision cases. Conclusion A lateralized metal-backed 15.2-mm keeled baseplate prolonged by a thin 24.8-mm metallic post fixed directly in the subscapularis fossa may provide satisfactory mid-term outcomes in patients with large glenoid bone defects where initial press-fit of a regular baseplate is impossible to obtain.
Improving glenoid-side load sharing in a virtual reverse shoulder arthroplasty model
Journal of Shoulder and Elbow Surgery, 2013
Background: The goal of glenoid fixation in reverse shoulder arthroplasty (RSA) is to provide a stable environment to allow bony ingrowth into the baseplate. When this does not occur, eventual baseplate failure is likely. This study aims to determine the additional implant-bone contact achieved when the glenosphere undersurface is in contact with the glenoid and if this increase in implant-bone contact improves stability through load sharing with respect to baseplate fixation. We hypothesize that substantial increases in contact area are possible and that this increased contact area will improve baseplate stability through load sharing. Methods: A computer-assisted design program was used to create 3-dimensional models of 7 currently available RSA devices. Total implant-bone contact area was compared in 2 conditions: (1) baseplate flush with bone and no additional glenosphere contact, or (2) baseplate and glenosphere undersurface in contact with bone. Next, finite element models were created from a commercially available system. Micromotion and stress were computed for each size of implant in the 2 conditions. Results: All devices tested can achieve increased total contact area when the glenosphere is in contact with bone. Stress and micromotion were reduced when comparing condition 2 with condition 1 in all sizes of one commercially available system. The average micromotion decreased 37%, from 98.04 to 61.97 mm. Larger glenospheres experienced a greater reduction in micromotion. Likewise, average von Mises stress decreased 26%, from 3.29 to 2.42 MPa. Conclusion: Increasing glenosphere size and allowing glenosphere undersurface contact increased overall implant-bone contact area and baseplate stability.
Journal of Orthopaedic Research, 2019
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 sheet 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 was 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 This article is protected by copyright. All rights reserved. Accepted Article 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.