Shoulder Mechanics 10/8 Flashcards
Glenohumeral joint
Is designed for maximum motion at the expense of decreased stability
Scapulothoracic articulation
Scapulothoracic rhythm - the first 30 degrees of shoulder abduction occur at the glenohumeral joint
Thereafter, for every 2 degrees of motion at the glenohumeral joint, there is 1 degree of motion at the scapulothoracic articulation
If the scapulothoracic articulation is restricted (frequently associated with thoracic spine and rib dysfunction), the glenohumeral joint may have to compensate with increased motion
- Predisposes to instability, impingement, rotator cuff tendonitis and tear
- Need to treat dysfunction in the thoracic spine and ribs to allow the scapulothoracic articulation to optimally function (somatic dysfunction contributes to imbalance in the muscles affecting scapular motion and scapular stability)
Sternoclavicular joint
Frequently forgotten but does move especially in response to scapular motion
- Capable of anteroposterior, superoinferior and rotational motion
- May become restricted with shoulder injury (can see infections or other causes of inflammation in the SC joint)
- Posterior dislocation can compromise important neurovascular structures
Acromioclavicular Joint
Allows anteroposterior, superoinferior and rotational motion
May become restricted with shoulder injury
- Frequently becomes separated when someone lands or is hit on the point of the shoulder
Where does the brachial plexus course?
C5-T1
- between the anterior and middle scalene muscles
- between the first rib and the clavicle
- underneath the pectoralis minor muscle
Somatic dysfunction affecting the cervical spine, upper thoracic spine, upper ribs, scalene muscles, clavicle and pectoralis minor can all have a negative impact on the brachial plexus and upper extremity function
Flexors of the shoulder
- Pectoralis major muscle – C5-T1
- Deltoid muscle (anterior portion) - C5, 6 (axillary nerve)
- Coracobrachialis muscle - C5, 6, 7 (musculocutaneous nerve)
Primary extensors of the arm
- Latissimus dorsi muscle – C6, 7, 8 (thoracodorsal nerve)
- Teres major muscle – C5, 6, (lower subscapular nerve)
- Deltoid muscle (posterior portion) – C5, 6 (axillary nerve)
- Long head of triceps brachii muscle – C6, 7, 8 (radial nerve)
Primary abductors of arm
Deltoid muscle – C5, 6 (axillary nerve)
Supraspinatus muscle – C4,5, 6 (suprascapular nerve)
Primary adductors of arm
- Pectoralis major muscle – C5-T1
- Latissimus dorsi muscle – C6, 7, 8 (thoracodorsal nerve)
- Teres major muscle – C5,6 (lower subscapular nerve)
- Long head of triceps brachii muscle – C6, 7, 8 (radial nerve)
primary external rotators
- Pectoralis major muscle – C5-T1
- Latissimus dorsi muscle – C6, 7, 8 (thoracodorsal nerve)
- Teres major muscle – C5,6 (lower subscapular nerve)
- Long head of triceps brachii muscle – C6, 7, 8 (radial nerve)
Primary internal rotators of shoulder
- Subscapularis muscle – C5, 6, 7 (upper and lower subscapular nerves)
- Pectoralis major muscle – C5-T1
- Latissimus dorsi muscle – C6, 7, 8 (thoracodorsal nerve)
- Deltoid muscle – C5, 6 (axillary nerve)
- Teres major muscle – C5, 6 (lower subscapular nerve)
What are the four rotator cuff muscles?
The four rotator cuff muscles (supraspinatus, infraspinatus, teres minor and subscapularis) act in concert to keep the head of the humerus centered in the glenoid fossa during motion
If any one of the rotator cuff muscles is out of balance, or if the scapulothoracic joint is not moving in concert with the glenohumeral joint (scapulothoracic rhythm), the glenohumeral joint will be less stable and more predisposed to injury
How is arterial supply, venous supply, and lymphatic drainage affected?
Upper extremity arterial supply may be affected by somatic dysfunction of the anterior and middle scalene muscles, upper thoracic and cervical vertebrae, upper ribs, clavicles and fascia of the neck and upper extremity
Ultimately occurs via the subclavian and brachiocephalic veins
Pass anterior to the scalene muscles
Somatic dysfunction anywhere along the course of the venous drainage can lead to congestion in the upper extremity
Somatic dysfunction affecting the thoracic inlet can produce a mechanical restriction to lymph flow (low pressure system) and congestion in the upper extremities – reduces healing
how does upper thoracic dysfunction affect sympathetic innervation?
- Upper thoracic somatic dysfunction increases sympathetic tone to upper extremity
- Decreased lymphatic drainage
- May lead to increased swelling within the upper extremity, impairing function and recovery
Mechanisms of throwing
- Scapular retraction stimulated by ipsilateral hip and trunk (thoracic) extension. Stable scapula is necessary for optimal rotator cuff function
- Engagement of the gluteal muscles helps stabilize pelvis – contributes to scapular stabilization and control
- Scapular stabilization also directly involves such muscles as lower trapezius, lower rhomboids and serratus anterior
- Weak gluteal muscles or altered muscle firing patterns (from somatic dysfunction) can destabilize the pelvis, contributing to shoulder injury
- Psoas major muscle tension alters hip extension, contributes to scapular destabilization and is frequently involved with shoulder (rotator cuff) injury.
- The presence of somatic dysfunction anywhere along the entire kinetic chain will reduce effective force transference to the shoulder - remember the anatomy trains
- To compensate and maintain the same performance, more force will have to be generated by the shoulder, predisposing this area to overuse, breakdown and injury
- Which muscles fire to decelerate the glenohumeral joint (braking mechanism)? Posterior shoulder muscles – especially posterior deltoid and teres minor.
