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 geometry and material property distributions were derived from CT data. Generic baseplates with two and four fixation screws were virtually implanted, after which superiorly-oriented shear loads, accompanied by a compressive load, were applied incrementally further from the glenoid surface to simulate lateralization of the COR. Relationships between lateralization, adduction range of motion (ROM), the number of fixation screws and micromotion of the baseplate (initial implant fixation) were characterized. Lateralization significantly increases micromotion (p = 0.015) and adduction ROM (p = 0.001). Using two, versus four, baseplate fixation screws significantly increases micromotion (p = 0.008). The effect of lateralization and the number of screws on adduction ROM and baseplate fixation is variable on a shoulder-specific basis. Trade-offs exist between functional outcomes, namely adduction ROM, and initial implant fixation and the negative effect of lateralization on implant fixation is amplified when only two fixation screws are used. The possibility of lateralizing the COR in order to improve functional outcomes of the procedure should be considered on a patient-specific basis accounting for factors such as availability and quality of bone stock.

Impact of Modeling Assumptions on Stability Predictions in Reverse Total Shoulder Arthroplasty

“…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.…”

“…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.…”

Clinical comparison of humeral-lateralization reverse total shoulder arthroplasty between patients with irreparable rotator cuff tear and patients with cuff tear arthropathy

“… 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.…”

Lateralized versus nonlateralized reverse total shoulder arthroplasty

“…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.…”