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PART TWO
Survey of common postural disorders
CHAPTER
Postural disorders and musculoskeletal dysfunction
in the upper extremities
134 Stabilizing elements of the shoulder girdle
140 Survey of common disorders of the shoulder girdle
155 Adapted physical activity for functional disorders of the shoulder joint and shoulder girdle
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The interaction of static components and dynamic muscle tendons allows the shoulder girdle to move multidirectionally on all planes. Normal movement is a result of the balanced and synchronized action of all joints and movement centers connected to the shoulder, in coordination with the spinal joints in the cervical and thoracic vertebrae (Kamkar et al., 1993) (see Ch. 2).
Many shoulder girdle movements create func- tional chain reactions in adjacent joints, specially the spine. Conversely, spinal position and the functioning of all the joints along the spine affect shoulder position.
Preceding chapters have mentioned conditions in which faulty spinal position indirectly affects shoulder girdle functioning (see Kyphosis in Ch. 2). This chapter will focus on common disorders in the shoulder girdle area and their indirect effect on spinal functioning.
The contents of this chapter are based on the anatomical and kinesiological background material about the shoulder girdle presented in Chapter 2. However, due to the functional complexity of this area, additional kinesiological information not mentioned before has been introduced into this chapter.
Stabilizing elements of the shoulder girdle
In most daily activities, the joints of the upper extremity usually do not have to bear great weight, and the evolutionary result has been alterations that in effect “sacrifice” joint stability in order to gain greater movement ranges. The consequence of this anatomical change in structure of the shoulder joint is a characteristic instability, as the articulated surface in the glenoid cavity in the scapula is very flat and not adapted to the rounded structure of the humeral head.
The osseous structure of the joint is defined as a multiaxial ball and socket in which the humeral head is four times as large as the glenoid cavity, so that only part of the humeral head is in contact with the glenoid cavity at any given joint position. Nevertheless, the shoulder joint succeeds in maintaining stability by means of passive and active systems working synergetically (Fig. 6.1). The passive system includes several structures that work statically, and they, in essence, serve as the primary stabilizers of the shoulder. The active system includes the rotator cuff muscles, which interlock with the capsule and impart dynamic stability to the joint (Hess, 2000).
Stability of the shoulder joint
Passive system
Active system
| | |
| |Glenoid labrum Joint |
| |capsule Ligaments |
| |Intra-articular |
| |pressure Osseous |
| |structure |
Figure 6.1 Passive and active systems that contribute to stabilizing the shoulder joint.
The elements stabilizing the shoulder joint
The glenoid labrum (Fig. 6.2)
This cartilaginous casing is located around the glenoid cavity, and contributes to greater shoulder stability by slightly deepening the joint.
Capsuloligamentous mechanism (Fig. 6.3)
The capsule, together with a number of ligaments, contributes to joint stability. It begins from the borders of the glenoid cavity in the scapula and reaches the anatomical neck of the humerus. When the arm is hanging in its natural anatomical position, the upper half of the humeral head comes in contact with the capsule, and the bottom half comes in contact with the glenoid cavity.
Labrum
Glenoid
Figure 6.2 Glenoid labrum.
Biceps tendon
Figure 6.3 Shoulder capsule, anterior view.
The capsule plays an important role in stabilizing the shoulder, especially at the “extremes” of the ranges of motion, so that during lateral rotation of the arm the anterior part of the capsule is stretched, and during medial rotation its rear part is stretched (Kahle et al., 1986).
Supporting ligaments (Fig. 6.4)
The ligaments connecting the various structures attached to the shoulder are extremely important for joint stability, as they limit excessive movement in all planes. These are the main ligaments that stabilize the shoulder:
Biceps tendon
Posterior capsule
Posterior band inferior glenohumeral
ligament
Superior glenohumeral ligament
Middle glenohumeral ligament
Anterior band
inferior glenohumeral ligament
Figure 6.4 Ligaments supporting the shoulder joint.
• Coracohumeral ligament – This ligament passes from the base of the coracoid process on the scapula and connects to the greater and lesser tubercles of the humerus. The ligament supports the humeral head as it resists the downward pull of gravity
• Superior glenohumeral ligament – The origin of this ligament is near the biceps brachii tendon and it connects slightly above the lesser tubercle of the humerus. This ligament strengthens the anterior superior wall of the capsule in the shoulder joint and prevents downward dislocation of the humeral head when the arm is hanging or is held close to the body
• Middle glenohumeral ligament – The origin of this ligament is somewhat medial to the lesser tubercle of the humerus and is connected to the scapula in the center of the glenoid cavity. The ligament strengthens the anterior wall of the joint capsule and limits lateral rotation of the arm. Weakness in this ligament causes instability in the anterior aspect of the joint
• Inferior glenohumeral ligament – The origin of this ligament is in the area of the glenoid cavity of the scapula and is connected to the anatomical neck of the humerus. This ligament strengthens the inferior anterior wall of the capsule, and in addition prevents dislocation of the humeral head from the joint socket; its anterior and posterior parts also limit internal and external rotation (respectively).
Intra-articular pressure (vacuum effect)
The rotator cuff muscles that encase the joint from all sides create a compression or vacuum effect that presses the humeral head into the glenoid cavity. Under normal conditions, this compression remains constant within the joint and contributes to its stability (Hess, 2000).
Osseous structure
The meeting of the scapula with the ribs facilitates a sliding movement along the wall of the thoracic cage, with the clavicle in front acting as a “supporting beam”. This support helps to stabilize the scapula when opposing muscular forces are working on it, performing medial rotation and scapular adduction. In this way, the clavicle helps to maintain shoulder stability by means of its points of connection to the scapula and the sternum.
Stabilizing muscles
Most of the muscles affecting movement and stability of the shoulder girdle are presented in full detail in the tables of muscles in Chapter 2, with reference to their points of origin and insertion. Therefore, this chapter emphasizes only those muscle actions related specifically to the shoulder joint.
Anatomically speaking, it is possible to classify the muscles that stabilize the shoulder joint into three groups.
The superficial group
Table 6.1
MUSCLE MUSCLE ACTION IN RELATION TO THE SHOULDER JOINT
Deltoid Arm abduction beyond 30°
Clavicular head and posterior scapular head help in arm adduction
Anterior muscle fibers also perform internal rotation from a position in which the arm is rotated externally
Posterior muscle fibers also perform external rotation from a position in which the arm
is rotated internally
Coracobrachialis Flexion of arm Adduction of arm
Biceps brachii Flexion of elbow (with supinated forearm) (long head) Long head participates in humeral abduction
when the humerus is in lateral rotation The short head assists in humeral adduction and flexion
The muscle contributes to joint stability by preventing the humeral head from slipping upward
Radius
Ulna
Biceps brachii
Tendon
Origin
Scapula
Insertion
Humerus
Deep group (rotator cuff) Shoulder stability depends very much on the rotator cuff encasing it. The rotator cuff muscles are an important stabilizing factor that provides active support to the joint. (As noted, full anatomical details about origins and insertions of each muscle appear in the tables of muscles in Ch. 2.)
|Table 6.2 |
|MUSCLE |MUSCLE ACTION IN RELATION TO THE SHOULDER JOINT |
|Supraspinatus |Humeral abduction from 0–30° with slight external rotation |
| |Stabilizes the humeral head in the shoulder joint |
|Infraspinatus |Lateral rotation of the humerus and arm extension |
| |Stabilizes the humeral head in the shoulder joint and contributes especially |
| |to anterior stabil- |
| |ity of the joint in positions of abduction with lateral rotation |
|Teres minor |Lateral rotation of the humerus |
| |Stabilizes the humeral head in the shoulder joint and contributes especially |
| |to anterior stabil- |
| |ity of the joint in a state of abduction with lateral rotation |
|Subscapularis |Medial rotation of the humerus and humeral adduction |
| |Stabilizes the humeral head in the shoulder joint |
The peripheral group
|Table 6.3 |
|MUSCLE |MUSCLE ACTION IN RELATION TO THE SHOULDER JOINT |
|Latissimus dorsi |Extension and adduction of the humerus in a state of flexion |
| |When the humerus is in a state of adduction it also creates medial rotation |
| |When the two sides work together they draw shoulders back and down |
|Pectoralis major |Adduction and medial rotation of the humerus Horizontal adduction of |
|Teres major |humerus (“hugging” movement) |
| |Extension, adduction and medial rotation of the humerus Synergist muscle |
| |with the latissimus dorsi |
Tables 6.1–6.3 present the main muscles affecting the shoulder joint. Other muscles working on the entire shoulder girdle appear in detail in Chapter 2.
Survey of common disorders of the shoulder girdle
In various movements, the shoulder joint acts as a link between the upper extremity and the trunk, and in terms of the skeletal system, there are interrelationships between joint position and the functioning of the muscle casing enveloping these joints. Functional impairments to the shoulder girdle are quite common in the population at large, and for the most part they involve a number of limiting factors (Glousman, 1993). A problem in the shoulder girdle may be the result of faulty functioning of any of the components connected to it.
The most common disorders of the shoulder girdle
Wing scapulae
The shoulder girdle needs to provide a combination of broad range of movements and a stable base of support for the arm. The scapula plays a central role in this function as it connects all the structures affecting shoulder movement. Imbalance in the normal position of the scapula impairs functional efficiency in all the muscles acting on it, and especially in the rotator cuff, which cannot operate optimally in such a condition. Dynamic stability of the scapula requires coordinated and well-timed muscular action, and faulty muscle functioning may cause improper positioning of the scapula and impair the shoulder joint itself.
1. Anatomical and physiological aspects of postural characteristics of scapular position
In normative conditions, scapular position forms an angle of 30° anterior to the frontal plane (Fig. 6.5). This position allows optimal movement of the arm in horizontal adduction and abduction, and
Posterior view Superior view
3° Scapular spine
Acromion
Humerus
Scapula
30°
A B
Figure 6.5 Scapular position in normal posture. (A) Scapular position on the frontal plane, posterior view. (B) Scapular position on the horizontal plane, superior view.
the scapula accompanies the movement of the arm accordingly. During horizontal adduction the scapulae move apart from one another, and the angle exceeds 30° (Fig. 6.6); during horizontal abduction the angle decreases to ................
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