An algorithm to allow humerus translation in the indeterminate problem of shoulder abduction

Abstract

The shoulder is one of the most complex joints of the human body, mainly because of its large range of motion, but also because of its active muscular stabilisation. Actually, the numerous stabilizing muscles and degrees of freedom yield indeterminate biomechanical models. To solve this indeterminate, most models use reverse dynamics with a simplified ball-socket joint, preventing therefore the natural humerus translation. In this paper, an algorithm was specifically developed to solve the indeterminate problem by a feedback control of muscle activation, allowing the natural humerus translation. Abduction was considered in the scapular plane, accounting for the three deltoid parts and the rotator cuff muscles. The major aim of this study was to validate the numerical algorithm, which was here restricted to two-dimensions in order to compare the numerical solution to a known algebraic one. This comparison gave a relative error below 0.1%. The joint reaction force was comparable to other models and the humerus translation was in agreement with in vivo or in vitro studies.

Total shoulder arthroplasty: Downward inclination of the glenoid component to balance supraspinatus deficiency

“…The joint force was maximal at approximately 90 of abduction, when the arm weight moment force is maximal. 22,23 However, the contact pressure was maximal at approximately 60 of abduction, because the contact pattern was less centered than at 90 of abduction. Although the downward inclination of the glenoid component partly balanced the supraspinatus deficiency regarding joint stability, this potential advantage was counterbalanced by an important increase of the cement stress.…”

“…15 The details of this algorithm are described in 2 previous articles and can be summarized as follows. 22,23 The elevation movement is controlled through a shortening of the middle deltoid. The force induced within the middle deltoid is then considered as the reference force to constrain the force within the other muscles, according to the predefined muscle ratios.…”

Importance of the subscapularis muscle after total shoulder arthroplasty

“…We developed an optimization module for an existing musculoskeletal model of the glenohumeral joint allowing gleno-humeral translations (Terrier et al, 2008). This optimization module minimizes the difference between experimentally measured muscular activities and predicted ones.…”

“…This problem is particularly present for the shoulder, which has a wide range of motion, and many muscles. As for other joints, three techniques are used: 1) group muscles to suppress the indeterminacy (Inman et al, 1944), 2) use inverse dynamics coupled with optimization of a cost function (Charlton and Johnson, 2006;Dickerson et al, 2007;Favre et al, 2005;Holzbaur et al, 2005;Karlsson and Peterson, 1992;Terrier et al, 2010;van der Helm, 1994), or 3) use forward dynamics with electromyography (EMG) measurements as input (Langenderfer et al, 2005;Laursen et al, 1998;Terrier et al, 2008).…”

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

“…A scapulo-humeral rhythm of 2:1 was assumed to replicate the motion of the scapula and the correct alignment of the muscle action relative to the arm weight. Detail of this numerical musculoskeletal model and its validation can be found in technical (Terrier et al, 2007;Terrier et al, 2008b) and clinical application papers (Terrier et al, 2008a;Terrier et al, 2009aTerrier et al, , 2009bTerrier et al, 2010).…”