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Static stabilization of GHJ in the dependent arm, Dynamic Stabilization…
Static stabilization of GHJ in the
dependent arm
Humeral head resting on the fossa
Gravity imparts a caudally directed translator force on the humerus
To maintain equilibrium a cranially directed force is needed
1.Passive tension in the rotator interval capsule will stabilize the joint
2.Negative intra-articular pressure
Loss of intra articular pressure
would increases inferior translation
3.Degree of inclination
Slightly upward tilt of the glenoid fossa will produce a partial block against humeral inferior translation
*Supraspinatus
When passive forces are inadequate for GHJ stabilization muscles
are recruited for active assistance
Dynamic Stabilization of GHJ
1.Deltoid and GH stabilization
Suprapinatus, infraspinatus, teres minor and subscapuris forms the
rotator cuff muscles
Tendons of each muscle blends with and reinforce the GH capsule
Stabilize by
ITS together or individually have a similar line of pull
The perpendicular component compresses as well as rotates
3.The parallel component(sum of all 3) helps offset the superior translatory pull of the deltoid
The action of the deltoid and combined ITS muscles are nearly equal
and provides opposite forces making it a relatively stable axis of
rotation with minimal translation
2.Supraspinatus and GH stabilization
Line of action has a superior translator component
Not able to offset the upward dislocating action of the deltoid
Stabilize by
Superior location of the line of axis compared to other rotator cuff muscles
Large moment arm capable of producing a full or nearly full range of GHJ abduction
Gravity act as a synergist to the supraspinatus by offsetting the small upward translatory pull of the muscle
Longhead of Biceps brachii and GH stabilization
Runs superiorly from anterior shaft of the humerus
Through the bicipital groove between the greater and lesser tubercle
Enveloped by a tendon sheath
Tethered by the transverse humeral ligament
Attaches to the supraglenoid tubercle and superior labrum
Enters the GHJ capsule through an opening between the subscapulris and supraspinatus,
penetrates only the capsule and not the synovium
Stabilize by
Centering the head in the fossa, reducing vertical and anterior translations
Tightening superior labrum
Transmitting icreased tension to the Superior and middle GHL