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The joints of the shoulder girdle and shoulder form the shoulder joint complex. This complex consists of the humerus, scapula, clavicle, sternum, as well as the sternoclavicular, acromioclavicular, and glenohumeral joints. Most movements of the arm at the glenohumeral joint (shoulder) requires a coordinated movement with the shoulder girdle (scapula and clavicle with associated joints), “moving as a unit”. This coupling of shoulder girdle movement with shoulder joint movement is called scapulohumeral rhythm.
Specifically, the shoulder girdle consists of the manubrium, scapula, and clavicle, as well as the sternoclavicular (SC) and the acromioclavicular (AC) joints. The scapulothoracic articulation (STA) is not a true joint but is frequently used to simplify movement analysis of the shoulder girdle.
The scapulothoratic articulation refers to the movement that occurs between the scapula moving on the ribcage. Movement of the scapula cannot occur without movement of the sternoclavicular and acromioclavicular joints. Again, this is not a true joint but often used to simplify movement analysis of the shoulder girdle.
Figure 6
Stages of Development of Acquired Musculoskeletal Deformities
Kyphosis is defined as an excessive posterior curvature (rounding) of the thoracic spine associated with thoracic extensor muscle weakness, usually accompanied with a forward head and rounded shoulders. Upper Crossed Syndrome describes a specific muscle imbalance pattern, with some components similar to kyphosis, and is defined as tightness of the upper trapezius, levator scapulae, and pectoralis major, and weakness of the rhomboids, serratus anterior, middle and lower trapezius, and the deep neck flexors, especially the scalene muscles.
When evaluating a muscle for its strength and range of motion, and to prescribe an exercise program for improvement, the application of some basic principles help the evaluator to effectively apply forces to control movement of the person/limb being evaluated and to better isolate a desired muscle for a better analysis of its functionality. This becomes essential when seeking to appropriately apply forces to strengthen (or stretch) the target musculature.
Question: How would you apply this principle to the hamstring muscle group, triceps brachii muscle, and
pectoralis major muscle?
Note: On the following pages, skeleton illustrations are provided so students may draw on the associated muscles to help them in their learning of the muscle’s origin, insertion and muscle line of pull.
As the shoulder joint performs:
The shoulder girdle and shoulder joint work together in performing upper extremity movements. However, movement of the shoulder girdle is not dependent on shoulder joint movement by shoulder muscles. During the linear movements of scapular elevation/depression and protraction/retraction, it is possible to move the shoulder girdle up, down, laterally, or medially without moving the humerus. However, shoulder joint movements must accompany the angular movements of scapular upward and downward rotation. The following chart identifies the scapular movements that must occur during various shoulder joint movements.
It is important to note though that the muscles of the shoulder girdle are essential in providing a stabilized or fixated scapula so the muscles of the shoulder joint will have a stable base (bone) from which to exert a pulling force to cause shoulder movement. As such, the shoulder girdle muscles contract to maintain the scapula in a relatively static position (static stabilization) during many shoulder joint movements. As the shoulder joint moves through more extreme ranges of motion, the shoulder girdle muscles contract to move the shoulder girdle (dynamic stabilization) into a more functional position so that further shoulder joint movement can occur, while still providing a stabilizing effect on the scapula. The result is that most shoulder joint motion requires coordinated joint action of the scapula and clavicle.
This coupled action between the shoulder girdle and shoulder joint (collectively the shoulder joint complex) is referred to as scapulohumeral rhythm. Without this coupled action the shoulder joint would be limited to only 120° abduction, and high reaching movements would be very restricted. As such, when a person fully abducts the arm 180°, in reality only 120° of motion occurred at the shoulder joint, and 60° was due to scapular motion (upward rotation) at the scapulothoracic articulation with the arm “going along for the ride.”
Figure 19
Scapula Rotation
Brachial Plexus: Innervation of the Upper Extremity
As previously mentioned, spinal nerves contain both motor fibers and sensory fibers. The motor fibers innervate certain muscles, while the sensory fibers innervate certain areas of skin. A skin area innervated by the sensory fibers of a single nerve root level is known as a dermatome. A muscle or group of muscles predominately innervated by the motor fibers of a single nerve root level is known as a myotome.
Nerves are typically injured through compression or tensile/stretching forces. When a nerve root in the brachial or lumbosacral plexus is damaged, certain patterns of motor and sensory deficits occur in the corresponding limbs. Dermatomes and myotomes are used to evaluate these deficits when nerve root injury is suspected.
To test for nerve root damage, the corresponding dermatome supplied by that nerve root may be tested for abnormal sensation (Hypoesthesia = decreased sensation, Hyperesthesia = excessive sensation, Anesthesia = loss of sensation, and Paresthesia = numbness, tingling, burning sensation). To test for sensitivity of a dermatome, a pin, cotton ball, paper clip, the pads of the fingers, or fingernails may be used. The patient, with their eyes closed, should be asked to provide feedback regarding their response to the various stimuli. All tests should be compared bilaterally. A cutaneous distribution pattern is an area or patch of skin innervated by a specific sensory peripheral nerve. This nerve maybe be made up of sensory fibers from one or more nerve root levels.
The myotomes may be tested, in the form of isometric resisted muscle testing, for weakness of a particular group of muscles. Results may indicate lesion to the nerve root level, or intervertebral disc herniation pressing on the spinal nerve roots. All tests should be compared bilaterally.
**Link to view myotome testing procedures: (www.youtube.com/watch?v=rKiTwagLYck)
Deep Tendon Reflex (DTR): C5-C6: Biceps Brachii C7-C8: Triceps Brachii
likely damaged?
your hand - What is the involved muscle group? What is the prime mover for this?