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for all 12 male participants. Data were recorded by using the 1,5-T Sigma system (GE Medical Systems,
Milwaukee, WI). From 120 images taken in the frontal plane, a total of 12 characteristic images were
identified. The humerus MRI slices were 2 mm in thickness. Data were digitized by using AutoCAD
R14 and Alice v.4.4.9 software.
27.4 Results and Discussion
These theoretical studies revealed that a migration of the humeral head in the superior-inferior direction
was related to the glenoid fossa inclination and the attachment of the lateral part of the deltoideus muscle
between the glenoid concavity and the middle deltoid attachment, during abduction ranging from 0
8
to
170
8
. Generally, the largest translations of the humerus were during abduction ranging from 0
8
to 40
8
and from 140
8
to 170
8
. The translations increased when tangents f increased from 10
8
to 90
8
for the
deltoid lateral part attached directly to the glenoid fossa (z
0). The translations were reduced when
¼
tangents f decreased from 90
for the deltoid lateral part attached directly to the glenoid
fossa. The increasing distance of muscle attachment, measured along the Z-axis, between the lateral
margin of the acromion and a point at which a tangent to the glenoid fossa crosses the Z-axis, increased
the translations of the humerus when the angle of tangent f increased from 10
8
to 170
8
. However, the
increasing distance of muscle attachment reduced the translations of the humerus when the angle of
tangent fincreased from 90
8
to 90
8
.
Parametric analyses have been provided for changing values f, z, and a. The positions of the humeral
head were calculated for the four parametric conditions: (1) f
¼
8
to 170
8
90
8
, z
0 mm (Figure 27.2a);
¼
(2) f
¼
90
8
, z
0-32 mm (Figure 27.2b); (3) f
¼
10
8
-170
8
, z
0 mm (Figure 27.2c and e); (4)
¼
¼
f
10
8
-170
8
, z
0-32 mm (Figure 27.2d and f), during arm elevation
abduction ranging from
¼
¼
/
a
increments. The humeral
head positions were related to the interactions among the distinguished geometric parameters.
For the first parametric condition, an inclination of 90
0
8
to 170
8
. The calculations were performed during arm abduction in 10
8
¼
8
with the muscle attachment in line with the
glenoid fossa (f
90
8
, z
0 mm) during abduction from 0
8
to 170
8
, the greatest inferior translation
¼
¼
was observed. For a tangent to the shape of the glenoid fossa f
90
8
and for increased angle of
¼
abduction (a)to90
8
, the humeral head positions were decreased. For increased angle of abduction
above 90
, the humeral head positions were increased. When the muscle attachment was placed
further from the glenoid fossa (f
8
0-32 mm) for the second parametric condition, the trans-
lations were smaller. The increasing distance of the muscle attachment reduced the translations of the
humerus for the whole range of arm abduction (Figure 27.4). The results revealed that for an increasing
distance of the muscle attachment to z
90
8
, z
¼
¼
24 mm the translations of the humerus head decreased up to
¼
90
8
abduction and increased above 90
8
. However, for the distance z
32 mm the trend was the opposite
¼
with the translations of the humerus head increased to 90
.
For the third parametric condition, where the angle of inclination franged from 10
8
and decreased above 90
8
8
to 170
8
with the
muscle attachment at the glenoid fossa (f
¼
10
8
-170
8
, z
¼
0 mm), all observed translations of the
humerus head were smaller than for conditions f
¼
90
8
and z
¼
0 mm. For all angles of tangent incli-
nation and increased angle of abduction to 90
8
, the humeral head translations decreased, but increased
during abduction from 90
8
to 170
8
.
For the conditions (1) f
¼
90
8
, z
0 mm; (2) f
¼
90
8
, z
0-32 mm; and (3) f
¼
10
8
-170
8
,
¼
¼
z
0 mm, a symmetry of humeral head translations was observed along the angle of arm abduction
at 90
¼
. The results revealed that the translations of the humerus head along any tangent to the glenoid
fossa were the same as for the supplementary angle to this tangent inclination. The translations were
the smallest for the supplementary angles of 10
8
8
and 170
8
(Figure 27.5).
The results of calculations for the fourth condition (f
10
8
-170
8
, z
0-32 mm) revealed another
¼
¼
symmetry. When the angle of inclination fincreased from 10
and the distance of muscle attach-
ment of the lateral part of the deltoideus increased, the humeral head translations also increased;
however, when the angle of inclination increased from 110
8
to 70
8
8
to 170
8
and the distance of the muscle
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