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Shoulder, Sternoclavicular, Acromioclavicular, Taut when, Referring to…
Shoulder
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Shoulder complex
Sternoclavicular joint
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Movements
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Athrokinematics
Saddle joint
Depression/Elevation
- Convex on Concave
- Roll and slide in opposite directions
Protraction and Retraction
- Concave on convex
- Roll and slide in same direction
Acromioclavicular joint
Plane synovial joint with three rotational and three translational degrees of freedom
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Scapulothoracic joint
- Not a true joint
- Positioned between the scapula and the posterior-lateral aspect of the thoracic wall
- No joint capsule, separated by muscles e.g. subscapularis
- Positioned ribs 2 to 7 in anatomical position
- ‘Resting’ posture of the scapula is
- 10° of anterior tilt
- 5-10° of upward rotation
- 30-40° of internal rotation
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Glenohumeral joint
- Joint between the scapula and humerus
- Ball-and-socket’
- Glenoid fossa covers only one-third of humeral head to allow greater freedom of movement
Mobility
Articulating surfaces
- Not pure ball-and-socket joint, unlike the hip
- Contribution from scapular movements
- Lined with articular cartilage, which serves as lubricant
Joint capsule
- Volume is about 2x humeral head size
- Synovial membrane lines the inner wall of the capsule
Stability
Ligaments
- Glenohumeral capsular ligaments, or the glenohumeral ligament complex
- Coracohumeral ligament
Superior GH ligament
- External rotation
- Inferior and anterior translation of humeral head
- Extreme extension will cause head to translate anteriorly, because convex on concave
Middle GH ligament
- External rotation
- Anterior translation of humeral head
during 45-90° abduction
Inferior GH ligament
- Anterior band
- Posterior band
- Connecting axillary pouch
- Anterior band
- 90° abduction + full external rotation
- Anterior translation of humeral head
- Posterior band
- 90° abduction + full internal rotation
- Axillary pouch
- 90° abduction + anterior-posterior and inferior translations
Coracohumeral
ligament
- External rotation
- Inferior translation of humeral head i.e. flexion
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Glenoid labrum
- Fibrocartilage
- Covering the rim of glenoid fossa
- Deepening the depth of glenoid fossa (attributing about 50% of the depth)
- Prone to injury
- Superior part loosely attaches to the rim of glenoid fossa
- 50% of the fibres of biceps brachii long head tendon are direct extensions of superior glenoid labrum; excessive tension (e.g. overhead movement) can tear superior glenoid labrum
- Result? SLAP (superior labrum anterior and posterior) tear or lesion which is an injury to the glenoid labrum. Tears of the superior labrum near to the origin of the long head of biceps were first noted in throwing athletes
Muscles
- Rotator cuff (subscapularis, supraspinatus, infraspinatus and teres minor)
- Long head of biceps brachii
- Anteriorly - subscapularis
- Superiorly - supraspinatus
- Posteriorly - infraspinatus, teres minor
- Rotator cuff muscles form a cuff over humeral head to actively stabilizes GH joint during all dynamic activities
- Rotator cuff muscle tendons blend into joint capsule
- ‘Weak’ areas are inferiorly and rotator (cuff) interval
- Rotator interval may be reinforced by biceps brachii long head tendon, coracohumeral ligament and parts of the GH capsular ligaments
Movements
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Flexion and extension, internal and external rotation in 90° abduction
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Referring to slide 18
- The rope indicates a muscular force that holds the glenoid fossa in a slightly upward-rotated position.
- In this position the passive tension in the taut superior capsular structure (SCS) is added to the force produced by gravity (G), yielding the compression force (CF).
- The compression force applied against the slight incline of the glenoid “locks” the joint.
- With a loss of upward rotation posture of the scapula (indicated by the cut rope), the change in angle between the SCS and G vectors reduces the magnitude of the compression force across the GH joint.
- As a consequence, the head of the humerus may slide down the now vertically oriented glenoid fossa. The dashed lines indicate the parallelogram method of adding force vectors.
SCS is needed to lock the joint in place
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