Quantifying the competing relationship between adduction range of motion and baseplate micromotion with lateralization of reverse total shoulder arthroplasty
Abstract:Lateralizing the center of rotation (COR) of reverse total shoulder arthroplasty (rTSA) could improve functional outcomes and mitigate scapular notching, a commonly occurring complication of the procedure. However, resulting increases in torque at the bone-implant interface may negatively affect initial fixation of the glenoid-side component, especially if only two fixation screws can be placed. Shoulder-specific finite element (FE) models of four fresh-frozen cadaveric shoulders were constructed. Scapular geo… Show more
“…Finite element analysis (FEA) simulations are often used for replicating the test setup per ASTM F2028-14, to determine worst case configuration for physical testing or to make comparisons among different designs or configurations. Several FEA studies have been performed to study the effect of implant designs, lateralization, inferior tilt of glenoid, and degree of joint conformity on glenoid baseplate-bone micromotion ( Hopkins et al, 2008 ; Virani et al, 2008 ; Hopkins and Hansen, 2009 ; Suárez et al, 2012 ; Chae et al, 2016 ; Denard et al, 2017 ; Elwell et al, 2017 ; Geraldes et al, 2017 ). The complexity of the FEA models has increased with time due to improvements in computing power and software technologies.…”
Section: Introductionmentioning
confidence: 99%
“…However, results from FEA can be critically dependent on the modeling assumptions. In particular, one commonly used simplification in rTSA modeling studies is de-featuring of the screw threads from the screw shafts and the screw holes in the bone ( Hopkins et al, 2008 ; Virani et al, 2008 ; Hopkins and Hansen, 2009 ; Suárez et al, 2012 ; Chae et al, 2016 ; Denard et al, 2017 ; Elwell et al, 2017 ; Geraldes et al, 2017 ). The screw shafts are modeled as cylinders, virtually implanted in the cylindrical holes created in the bone.…”
Reverse total shoulder arthroplasty (rTSA) is commonly used in the shoulder replacement surgeries for the relief of pain and to restore function, in patients with grossly deficient rotator cuff. Primary instability due to glenoid loosening is one of the critical complications of rTSA; the implants are designed and implanted such that the motion between the glenoid baseplate and underlying bone is minimized to facilitate adequate primary fixation. Finite element analysis (FEA) is commonly used to simulate the test setup per ASTM F2028-14 for comparing micromotion between designs or configurations to study the pre-clinical indications for stability. The FEA results can be influenced by the underlying modeling assumptions. It is a common practice to simplify the screw shafts by modeling them as cylinders and modeling the screw-bone interface using bonded contact, to evaluate micromotion in rTSA components. The goal of this study was to evaluate the effect of three different assumptions for modeling the screw-bone interface on micromotion predictions. The credibility of these modeling assumptions was examined by comparing the micromotion rank order predicted among three different modular configurations with similar information from the literature. Eight configurations were modeled using different number of screws, glenosphere offset, and baseplate sizes. An axial compression and shear load was applied through the glenosphere and micromotion at the baseplate-bone interface was measured. Three modeling assumptions pertaining to modeling of the screw-bone interface were used and micromotion results were compared to study the effect of number of peripheral screws, eccentricities, and baseplate diameter. The relative comparison of micromotion between configurations using two versus four peripheral screws remained unchanged irrespective of the three modeling assumptions. However, the relative comparison between two inferior offsets and baseplate sizes changed depending on the modeling assumptions used for the screw-bone interface. The finding from this study challenges the generally believed hypothesis that FEA models can be used to make relative comparison of micromotion in rTSA designs as long as the same modeling assumptions are used across all models. The comparisons with previously published work matched the finding from this study in some cases, whereas the comparison was contradicting in other cases. It is essential to validate the computer modeling approach with an experiment using similar designs and methods to increase the confidence in the predictions to make design decisions.
“…Finite element analysis (FEA) simulations are often used for replicating the test setup per ASTM F2028-14, to determine worst case configuration for physical testing or to make comparisons among different designs or configurations. Several FEA studies have been performed to study the effect of implant designs, lateralization, inferior tilt of glenoid, and degree of joint conformity on glenoid baseplate-bone micromotion ( Hopkins et al, 2008 ; Virani et al, 2008 ; Hopkins and Hansen, 2009 ; Suárez et al, 2012 ; Chae et al, 2016 ; Denard et al, 2017 ; Elwell et al, 2017 ; Geraldes et al, 2017 ). The complexity of the FEA models has increased with time due to improvements in computing power and software technologies.…”
Section: Introductionmentioning
confidence: 99%
“…However, results from FEA can be critically dependent on the modeling assumptions. In particular, one commonly used simplification in rTSA modeling studies is de-featuring of the screw threads from the screw shafts and the screw holes in the bone ( Hopkins et al, 2008 ; Virani et al, 2008 ; Hopkins and Hansen, 2009 ; Suárez et al, 2012 ; Chae et al, 2016 ; Denard et al, 2017 ; Elwell et al, 2017 ; Geraldes et al, 2017 ). The screw shafts are modeled as cylinders, virtually implanted in the cylindrical holes created in the bone.…”
Reverse total shoulder arthroplasty (rTSA) is commonly used in the shoulder replacement surgeries for the relief of pain and to restore function, in patients with grossly deficient rotator cuff. Primary instability due to glenoid loosening is one of the critical complications of rTSA; the implants are designed and implanted such that the motion between the glenoid baseplate and underlying bone is minimized to facilitate adequate primary fixation. Finite element analysis (FEA) is commonly used to simulate the test setup per ASTM F2028-14 for comparing micromotion between designs or configurations to study the pre-clinical indications for stability. The FEA results can be influenced by the underlying modeling assumptions. It is a common practice to simplify the screw shafts by modeling them as cylinders and modeling the screw-bone interface using bonded contact, to evaluate micromotion in rTSA components. The goal of this study was to evaluate the effect of three different assumptions for modeling the screw-bone interface on micromotion predictions. The credibility of these modeling assumptions was examined by comparing the micromotion rank order predicted among three different modular configurations with similar information from the literature. Eight configurations were modeled using different number of screws, glenosphere offset, and baseplate sizes. An axial compression and shear load was applied through the glenosphere and micromotion at the baseplate-bone interface was measured. Three modeling assumptions pertaining to modeling of the screw-bone interface were used and micromotion results were compared to study the effect of number of peripheral screws, eccentricities, and baseplate diameter. The relative comparison of micromotion between configurations using two versus four peripheral screws remained unchanged irrespective of the three modeling assumptions. However, the relative comparison between two inferior offsets and baseplate sizes changed depending on the modeling assumptions used for the screw-bone interface. The finding from this study challenges the generally believed hypothesis that FEA models can be used to make relative comparison of micromotion in rTSA designs as long as the same modeling assumptions are used across all models. The comparisons with previously published work matched the finding from this study in some cases, whereas the comparison was contradicting in other cases. It is essential to validate the computer modeling approach with an experiment using similar designs and methods to increase the confidence in the predictions to make design decisions.
“… 12 To evaluate functional recovery after RTSA, active forward flexion has been emphasized to be a key factor providing patient satisfaction and maintenance of activities of daily living. 8 , 22 , 38 However, in addition to active forward flexion, internal rotation and external rotation play important roles and are known to be contributing factors to postoperative satisfaction after RTSA. 23 Therefore, it seems that there was no difference in clinical results between the 2 groups in our study regardless of the preoperative status of the subscapularis tendon or tendon repair.…”
Background
This study aimed to compare the clinical and radiologic outcomes between patients with irreparable cuff tears (ICTs) and those with cuff tear arthropathy (CTA) after reverse total shoulder arthroplasty (RTSA) with a humeral-lateralization prosthesis.
Methods
A total of 127 patients with ICTs and CTA who underwent RTSA were enrolled and matched at a 1:2 ratio by propensity score. Preoperative shoulder function was assessed for all patients. Radiologic parameters including the acromion–deltoid tuberosity (ADT) distance, lateral humeral offset, and scapular notching were evaluated.
Results
Thirty-four patients in the ICT group and 68 patients in the CTA group were matched for comparison. Preoperatively, mean active forward flexion in the ICT group (89.7° ± 29.4°) was significantly better than that in the CTA group (65.5° ± 24.0°,
P
< .001). In the CTA group, fatty infiltration of the supraspinatus was worse (3.7 ± 0.5) and the ADT distance was shorter (134.0 ± 12.0 mm) compared with the ICT group preoperatively (3.3 ± 0.8 [
P
= .008] and 140.7 ± 12.5 mm [
P
= .001], respectively). There was no significant difference in postoperative functional or radiologic outcomes between the 2 groups. However, gains in active forward flexion (37.9° in ICT group vs. 61.5° in CTA group,
P
< .01) and abduction (42.1° in ICT group vs. 60.6° in CTA group,
P
< .01) were significantly greater in the CTA group than in the ICT group.
Conclusions
Shoulder function was significantly improved after RTSA regardless of the preoperative diagnosis. Postoperatively, radiologic findings were not significantly different between the 2 groups. Due to the fact that preoperative range of motion and rotator cuff status were better in patients with ICTs, improvements in active forward flexion and abduction were significantly greater in patients with CTA.
“…4,44,45 This potentially leads to a higher risk of baseplate loosening, glenosphere unscrewing, and migration. 46 The importance of adequate screw fixation of the baseplate with COR lateralization has been emphasized in multiple studies. 4,47,48 Studies have shown that joint load magnitude is either decreased or unchanged with humeral lateralization.…”
Throughout the history of reverse total shoulder arthroplasty, the extent of lateral offset has changed considerably from “too lateral” to “too medial” and has been lately swinging back towards a point somewhere in between. Nonlateralized designs minimize shear forces on the glenoid and decrease force required by the deltoid. Glenoid lateralization decreases impingement and scapular notching and improves range of motion. Humeral lateralization achieves a more anatomic position of the tuberosities while maintaining a nonlateralized center of rotation. Several factors play a role in choosing the extent of lateral offset and method of lateralization.
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