Glenohumeral kinematics following total shoulder arthroplasty: A finite element investigation

Abstract

ABSTRACT:The osseous geometry of the glenohumeral joint is naturally nonconforming and minimally constrained, and the joint's stability is maintained by action of the rotator cuff muscles. Damage to these muscles is often associated with joint degeneration, and a variety of glenoid prostheses have been developed to impart varying degrees of stability postoperatively. The issues of conformity and constraint within the artificial shoulder have been addressed through in vivo and in vitro studies, although few computational models have been presented. The current investigation presents the results of three-dimensional finite element analyses of the total shoulder joint and the effects of design parameters upon glenohumeral interaction. Conformity was shown not to influence the loads required to destabilize the joint, although it was the principal factor determining the magnitude of humeral head translation. Constraint was found to correlate linearly with the forces required to dislocate the humeral head, with higher constraint leading to slightly greater humeral migration at the point of joint instability. The model predicts that patients with a dysfunctional supraspinatus would experience frequent eccentric loading of the glenoid, especially in the superior direction, which would likely lead to increased fixation stresses, and hence, a greater chance of loosening. For candidates with an intact rotator cuff, the models developed in this study predict that angular constraints of at least 148 and 6.58 in the superoinferior and anteroposterior axes are required to provide stable unloaded abduction of the humerus, with larger constraints of 188 and 108 necessitated by a dysfunctional supraspinatus. The tools developed during this study can be used to determine the capacity for different implant designs to provide resistance to excessive glenohumeral translations and reduce the potential for instability of the joint, allowing surgeons to optimize postoperative functional gains on a patient by patient basis. ß

Importance of the subscapularis muscle after total shoulder arthroplasty

“…Numerical shoulder models have already been used to analyze and improve TSA (Couteau et al, 2001;Gupta et al, 2004;Hopkins et al, 2007;Lacroix et al, 2000;Terrier et al, 2009). In particular, the problem of rotator cuff tears or muscle deficiencies has also been investigated with numerical tools.…”

Differences in reconstruction of the anatomy with modern adjustable compared to second-generation shoulder prosthesis

“…Due to this, many groups call for this anatomy to be repaired as precisely as possible when implanting a humeral prosthesis in order to achieve optimal postoperative joint function [1,4,5,7,8,10,13,15,16,18,20,22,23]. Others go further and insist on reconstruction of the centre of rotation specifically [17].…”

Importance of polyethylene thickness in total shoulder arthroplasty: A finite element analysis

“…This 2D study compares rather well with our predictions, at least qualitatively. In a 3D numerical study, the effect of the thickness was evaluated for 2, 6 and 10 mm (Hopkins et al, 2007a(Hopkins et al, , 2007b. This study reported a nearly constant peak contact pressure of about 8 MPa.…”

“…For the shoulder joint, the optimal thickness of the glenoid component has been only evaluated in two finite element analyses, which actually predict different effect of glenoid component thickness (Hopkins et al, 2007a(Hopkins et al, , 2007bSwieszkowski et al, 2003). None of these two studies focused on the thickness question.…”

“…The authors showed that increasing the polyethylene thickness from 4 to 7 mm reduced the contact stress by about 25%. The second study focused on polyethylene wear prediction as a function of various design parameters (Hopkins et al, 2007a(Hopkins et al, , 2007b. In this study, glenoid components with 2, 6 and 10 mm of polyethylene thickness were evaluated.…”