Biomechanical Modeling of the Shoulder - Fundamentals and Assessment Tools for Occupational Ergonomics - page 559

27
Biomechanical
Modeling of the
Shoulder

27.1 Introduction . ............................. 27-1
27.2 Methods ................................. 27-2
Theoretical Consideration † Method of Geometrical
Description
27.3 Data Collection ............................ 27-7
27.4 Results and Discussion ...................... 27-8
27.5 Conclusions

Krystyna
Gielo-Perczak
Liberty Mutual Research
Institute for Safety

. ............................. 27-11

27.1 Introduction

At present, it is difficult to establish a unifying integrative approach in the study of glenohumeral stability
and upper extremity strength. The glenohumeral joint is the most mobile articulation of the human
body, involving interacting and interrelated geometric variables relating bones, muscles, and ligaments,
that needs further exploration and understanding. The purpose of the current study was to propose
a method of geometrical description of the glenoid fossa in order to deduce an unrecognized inter-
relationship between glenoid concavity and the deltoid attachment on the glenohumeral head position.
It supports the concept of a new biomechanical parameter, the dynamic glenohumeral stability index
proposed by Lee and An, 16 which considers not only the force vectors generated by the deltoid muscle
but also the concavity compression mechanism. Recent analyses of the glenohumeral joint have not
focused on the contribution of geometric parameters like the shape of the glenoid fossa, radius of the
humerus, the attachment of the deltoideus lateral part in relation to the glenoid fossa, and the angular
measure of the articular surface of the humerus head.
The concavity of the glenoid fossa plays a significant role in the stability of the glenohumeral joint
as was revealed in recent experiments by Lee and An. 16 A labrum may not contribute to glenohumeral
stability as much as was previously assumed, as also was found by Halder et al. 8 It has been shown that the
glenohumeral joint exhibits ball-and-socket kinematics; however, its motion is coupled with translation
of the humeral head on the glenoid which requires a certain degree of mismatch of the articulating
surfaces and leads to variations in the joint-contact area. 8,9,11,17
Gagey and Hue 5,6 recently analyzed the mechanics of the deltoid muscle and suggested that the deltoid
acts on the humeral head like a cable on a pulley. They pointed out “the downward-oriented force applied

27-1