Simulated joint and muscle forces in reversed and anatomic shoulder prostheses

Abstract

Reversed shoulder prostheses are increasingly being used for the treatment of glenohumeral arthropathy associated with a deficient rotator cuff. These non-anatomical implants attempt to balance the joint forces by means of a semi-constrained articular surface and a medialised centre of rotation. A finite element model was used to compare a reversed prosthesis with an anatomical implant. Active abduction was simulated from 0 degrees to 150 degrees of elevation. With the anatomical prosthesis, the joint force almost reached the equivalence of body weight. The joint force was half this for the reversed prosthesis. The direction of force was much more vertically aligned for the reverse prosthesis, in the first 90 degrees of abduction. With the reversed prosthesis, abduction was possible without rotator cuff muscles and required 20% less deltoid force to achieve it. This force analysis confirms the potential mechanical advantage of reversed prostheses when rotator cuff muscles are deficient.

Implant Design Variations in Reverse Total Shoulder Arthroplasty Influence the Required Deltoid Force and Resultant Joint Load

“…Our results, however, were similar to those in a computational study by Terrier et al [28] (60% BW), who also simulated partial cuff deficiency. Despite humeral lateralization's effect of reducing required deltoid force, it did not markedly reduce joint load magnitude.…”

“…In addition, increased joint loading has been linked with greater implant wear and fixation failure [4]. Initial research in the biomechanical performance of RTSA focused on individual commercially available implant configurations [2,3,19,22,28], although some studies have addressed individual design parameters at numerous values (such as humeral version at 10°, 20°, 30°) [16][17][18]24]; however, there are little data regarding how these parameters interact with one another and influence joint and muscle-loading outcomes.…”

Bony Increased-offset Reversed Shoulder Arthroplasty: Minimizing Scapular Impingement While Maximizing Glenoid Fixation

“…The two basic biomechanical principles of the Grammont RSA are a medialization of the glenohumeral center of rotation and a lowering of the humerus [6]. These principles reduce torque on the glenoid component and increase the deltoid lever arm, overcoming weak or absent rotator cuff musculature [5,34]. However, a number of problems and complications, attributed to the medialized design, have been reported in the literature One author (PB) declares a commercial association (Tornier) that might pose a conflict of interest in connection with the submitted article.…”

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).…”