Muscle and Joint Function After Anatomic and Reverse Total Shoulder Arthroplasty Using a Modular Shoulder Prosthesis

Abstract

Changes in joint architecture and muscle loading resulting from total shoulder arthroplasty (TSA) and reverse total shoulder arthroplasty (RSA) are known to influence joint stability and prosthesis survivorship. This study aimed to measure changes in muscle moment arms, muscle lines of action, as well as muscle and joint loading following TSA and RSA using a metal-backed uncemented modular shoulder prosthesis. Eight cadaveric upper extremities were assessed using a customized testing rig. Abduction, flexion, and axial rotation muscle moment arms were quantified using the tendon-excursion method, and muscle line-of-force directions evaluated radiographically pre-operatively, and after TSA and revision RSA. Specimen-specific musculoskeletal models were used to estimate muscle and joint loading pre-and post-operatively. TSA lateralized the glenohumeral joint center by 4.3 ± 3.2 mm, resulting in small but significant increases in middle deltoid force (2.0%BW) and joint compression during flexion (2.1% BW) (p < 0.05). Revision RSA significantly increased the moment arms of the major abductors, flexors, adductors, and extensors, and reduced their peak forces (p < 0.05). The superior inclination of the deltoid significantly increased while the inferior inclination of the rotator cuff muscles decreased (p < 0.05). TSA using an uncemented metal-backed modular shoulder prosthesis effectively restores native joint function; however, lateralization of the glenoid component should be minimized intra-operatively to mitigate increased glenohumeral joint loading and polyethylene liner contact stresses. Revision RSA reduces muscle forces required during shoulder function but produces greater superior joint shear force and less joint compression. The findings may help to guide component selection and placement to mitigate joint instability after arthroplasty.

Effect of Rotator Cuff Deficiencies on Muscle Forces and Glenohumeral Contact Force After Anatomic Total Shoulder Arthroplasty Using Musculoskeletal Multibody Dynamics Simulation

“…Although in vitro experimental studies can provide valuable information regarding joint loading with ( Parsons et al, 2002 ; Dyrna et al, 2018 ) and without rotator cuff tears ( Ackland et al, 2019 ), the experimental cost is not conductive to parameter research. Musculoskeletal multibody dynamics modeling provides a non-invasive strong platform for understanding in vivo biomechanics of the shoulder and the effects of joint replacement on function.…”

Joint-line medialization after anatomical total shoulder replacement requires more rotator cuff activity to preserve joint stability

“…Cadaveric studies have shown that implantation of a TSA can lead to lateralization of the glenohumeral joint center by 4.3 ± 3.2 mm 1 ; however, this is altered if asymmetrical reaming has to be performed for bone loss or severe retroversion in B2/B3 glenoids.…”

“…Minimizing joint lateralization intraoperatively may help to mitigate joint-contact stresses that are believed to contribute to accelerated polyethylene liner wear; however, further research is required to link joint force with component wear rates. 1 …”

Complications of Reverse Total Shoulder Arthroplasty: A Computational Modelling Perspective

“…Computational modeling of RTSA facilitates estimation of muscle and joint loading, which is currently impossible to measure non-invasively in vivo. Modeling and simulation of RTSA has played a critical role in guiding implant positioning and surgical technique [19][20][21][22], prosthesis selection [23,24], implant design [25,26], and post-operative rehabilitation prescription [27,28]. To date, most modeling and simulation tools require high levels of expertise and are generally restricted to the research setting.…”

“…For example, shoulder muscle forces during upper limb elevation can be calculated in several minutes using a subject-specific rigid body model (Figure 1A) [28,31]; however, since deformation mechanics is neglected, the internal stresses and strains in the bone and implant cannot be accurately evaluated using this method. An important utility of rigid body models has been in their capacity to estimate the influence of arthroplasty on muscle moment arms, muscle and joint forces, and range of motion (ROM) at the shoulder, which are primary indicators of implant functional performance [21,23,24,[29][30][31][32][33][34][35][36][37][38][39][40].…”