Biomedical Engineering Reference
In-Depth Information
shoulder structures. Fortunately, musculoskeletal system has the ability to adapt to
the high load activities in order to achieve the best performance and avoid injury. Not
all the adaptations are considered beneficial and some of them have been involved
in the pathomechanics of shoulder pain and disability.
The throwing shoulder poses major challenges to clinicians. It is a complex of
great mobility in which static and dynamic stability depends on the synchronized
position and motion between scapula and humerus. Understanding the role of the
scapula in shoulder function and dysfunction is one of the recent directions in the
scientific community. It is accepted that changes in scapular kinematics are related
to shoulder pathology however clinical procedures to assess scapular contribution
to total shoulder motion have been poorly developed. Here is presented the
contribution of the scapula to one of the most acknowledged functional adaptations
of the throwing shoulder - the external rotation gain.
1.1
Shoulder Structure and Function
1.1.1
Glenohumeral Joint Structure and Function
The glenohumeral joint is composed by static and dynamic stabilizers. The dynamic
stabilizers of the glenohumeral joint include the rotator cuff, the scapulothoracic
muscles, and the long head of the biceps tendon, while the static stabilizers include
the osseous anatomy, the fibrocartilaginous labrum, and the glenohumeral joint
capsule [
1
-
4
]. The stability demands on these structures are even higher during
the practice of overhead sports such as tennis [
5
], volleyball [
6
], handball [
7
,
8
],
baseball [
9
-
13
], water polo [
14
] and swimming [
5
,
10
].
The mobility of the shoulder joint is the result of motion in both the glenohumeral
joint and scapulothoracic-gliding plane. Most of the thoracohumeral motion takes
place in the glenohumeral joint, which itself allows for glenohumeral elevation up
to 120
ı
and in addition the humerus is able to axially rotate about 135
ı
relative to
thescapula[
4
,
15
,
16
].
Alterations in either the anatomy of the joint, e.g. glenoid version [
17
], or
deficiencies in the intrinsic biomechanical properties of the ligamentous and/or
capsular components can cause motion abnormalities and focal contact stresses
or even develop instability [
2
,
18
]. Depending on the injured structures involved,
the direction of instability may be primarily anterior, inferior or posterior, or a
combination of these. The degree of instability may range from mild subluxation
to dislocation, with associated injuries to the bony (e.g. Hill Sachs lesion), cap-
sulolabral structures (e.g. Bankart and SLAP lesions), or both, and surrounding
musculature (e.g. rotator cuff tears and impingement). Isolated injuries are not very
common and usually one problem may lead to other [
19
,
20
].
