Biomechanical Modeling of the Shoulder - Fundamentals and Assessment Tools for Occupational Ergonomics - page 561

Y

z

O

f

Z

z '

y '

A A

y y

b

Q Q

γ 3

b

90 − b γ 2

R R

α

S S

90 − f

R M R S

γ 1

L 1

L 2

C

α

P

FIGURE 27.1 A planar model of the glenohumeral joint with the glenoid inclination and the distance of the
deltoideus lateral part attachment.

glenohumeral joint was restrained only by the deltoid lateral part, (4) the glenohumeral joint reaction
force acts perpendicular to the articular surface, (5) friction at the joint was omitted. Reference axes
Y-Z were fixed in the scapula at the center of the lateral margin of the acromion, where the Y-axis
was parallel to the longitudinal axis of the thorax.
The main feature of the approach was combining the possible mutual geometric relations, including
the position of the humerus, the inclination of the tangents to the glenoid surface, the radius of the
humerus, the angle between the middle deltoid attachment, and the muscle contact with the
humerus, with the conditions for equilibrium of the structure during static loading.
These relations are:

g 1 ¼ sin 1 R
L 1

(27 : 1)

!

y
sin f

z cos f

g 2 ¼ tan 1

(27 : 2)

R z sin f