Anteroposterior Centering of the Humeral Head on the Glenoid in Vivo

Abstract

In that many patients with unstable shoulders demonstrate instability in midrange positions, it is hoped that further study of living shoulders will lead to a more effective understanding of the nonligament mechanisms of shoulder stability and the ways in which these stabilizing mechanisms can be restored.

An integrated model of active glenohumeral stability

“…This is in accordance with a previous model for which the joint reaction force fell close to the superior border of the glenoid from 301 to 451 of glenohumeral abduction (Poppen and Walker, 1978). Resting muscle tone (Debski et al, 1999a;Schiffern et al, 2002), intraarticular pressure (Itoi et al, 1993) or subacromial spacer effect of the supraspinatus (Werner et al, 2006) might already be sufficient to confine these humeral head translations. After 601 of elevation, the deltoid becomes a stabilizer with a line of action approaching a perpendicular line to the glenoid surface (Ackland and Pandy, 2009).…”

“…This also suggests that an optimal muscular coordination can guarantee joint stability, while sensorimotor alterations may contribute to deficits in stability (Warner et al, 1996). Finally, it provides a theoretical background for the hypothesis that the ligaments and capsule are only secondary mechanical stabilizers (Lee et al, 2000;Myers and Lephart, 2002;Schiffern et al, 2002). The corresponding contact normal stresses obtained for each elevation degree are shown below the x-axis.…”

“…Glenohumeral stability is primarily ensured by coordinated rotator cuff action to provide concavity compression (Lippitt and Matsen, 1993). However, the study of active muscular stabilization remains neglected (Apreleva et al, 1998;McMahon and Lee, 2002;Schiffern et al, 2002) because the number of involved muscles and their infinite potential interactions makes such studies challenging, the rotator cuff muscles simultaneously move and stabilize the humerus (McMahon and Lee, 2002) and muscles can stabilize or destabilize the joint depending on joint position (Labriola et al, 2005;McMahon and Lee, 2002;Werner et al, 2007). Muscular stabilization has been studied in cadaver tests (Halder et al, 2001a;Lee et al, 2000;McMahon and Lee, 2002) restricted to a subset of muscles, or describing muscle force vector components (Ackland and Pandy, 2009;Konrad et al, 2007;Labriola et al, 2005) that cannot account for muscle timing and interaction for movement and stabilization (Veeger and van der Helm, 2007).…”

Multidirectional kinematics of the glenohumeral joint during simulated simple translation tests: Impact on clinical diagnoses

“…Furthermore, the data presented in this study for the vented shoulder demonstrate that the normal capsule allows a total range in anteroposterior translation over 30 mm at 0" and 30" of external rotation. This indicates that additional factors such as negative intra-capsular pressure, joint cohesion, and the shoulder muscles may aide the capsule as it guides the motion of the humeral head in these positions [1,15,28,34,40].…”

Automated muscle wrapping using finite element contact detection

“…(Charlton and Johnson, 2006;Garner and Pandy, 2001;Holzbaur et al, 2005;Karlsson and Peterson, 1992b;van der Helm, 1994). Although humeral head translations within the glenoid remain small in vivo (Schiffern et al, 2002;Werner et al, 2006) and are generally neglected in modeling (Veeger, 2000), they would influence the moment arms in an unstable joint. Muscle thickness was neglected (Gao et al, 2002;Ruckstuhl et al, 2009), representing only the muscle fibers closest to the joint (Favre et al, 2005(Favre et al, , 2009a.…”