Lecture 7
Static Stabilization of the Glenohumeral Joint
Dynamic Stabilization of the Glenohumeral Joint
Musculature of the Shoulder
Kinetics of the Shoulder
Static Stabilization of shoulder with UE in dependent position

Superior joint capsule and coracohumeral ligament prevent inferior dislocation

If the passive counterforce of the structures is insufficient, the supraspinatus will be recruited.

Paresis of supraspinatus

creep of passive structures
 reduced joint stability
Passive structures supporting the G-H joint:
Anterior Dislocation resisted by:

Anterior glenohumeral joint capsule (slack) – weak

Glenohumeral ligaments (superior, middle, inferior) – weak between superior and middle (foramen of Weitbrecht)

Biceps tendon

Most common form of dislocation WHY?
Posterior Dislocation resisted by:

Posterior glenohumeral capsule

RTC tendon
Superior Dislocation resisted by:

Acromion

Coracoacromial ligament
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Inferior Dislocation resisted by:

Inferior glenohumeral joint capsule (slack) –weakest

Second most common form of dislocation
Musculature of the shoulder joint
Equilibrium at the G-H joint is function of :
1.
Prime movers
2.
Gravity
3.
Compressors/steerers
4.
Joint reaction force/friction force
Deltoid

Primarily translates humerus superiorly

Assists in rotation of the humerus for flexion and abduction
Rotator Cuff (SITS)

Infraspinatus, subscapularis, and teres minor (oblique
RTC) provides inferior translation of the humeral head nearly counteracting the Deltoid.

Provides down and in force to create force couple with
Deltoid

Provides compressive force in G-H joint (stabilizers)

Teres minor and infraspinatus provide external/lateral rotation to permit full elevation.

Horizontal steerers – steer the humeral head anteriorly - posteriorly

Supraspinatus

Acutally causes a superior translation of humeral head.

Provides compressive force (stabilizer)

Significant abductor
2


Steering muscle – counteracts acts gravity to vertically steer the humeral head
Injury Model in RTC Tendon

Critical zone – between supraspinatus tendon and coracohumeral ligament

Area of maximal tensile strength and vascular anastomoses between osseous and muscular vessels

Area becomes ischemic when arm is in dependent position
(12 to 18 hours /day)

Ca++ deposits

degeneration/tears

Latissimus dorsi

Depresses shoulder complex

Adduction, medial rotation, extension, depression

Seated push-ups, crutch walking
Pectoralis major

Sternal portion parallels the latissimus to depress the shoulder complex
Pectoralis minor

Depresses and rotates scapula downward
Teres major

Adduction, medial rotation, extension, depression – active only in static positions of the humerus
Rhomboids

Counteract pull of teres major and contribute to depression

Adduct and assist in downward rotation of the scapula

Work eccentrically to control scapula during upward rotation
(stabilizing synergists)
3

Suprascapular n. block (supraspinatus and infraspinatus)

35%

force in scaption at 0 deg

60%

force in scaption at 60 deg

30%

force in scaption at 150 deg

50%

force in external rotation
Axillary n. block

35%

force in elevation at 0 deg

60-80%

force in elevation at 150 deg

45%

force in external rotation
Kinetics
Arm at 90 abduction

Deltoid force = 8 x .09BW = .72BW

Rotator cuff = 9.6 x .09BW = .86BW

G-H reaction force = 10 x .09BW = .9BW
With Deltoid only active:
Straight arm at 90 abduction

G-H joint reaction force = .5BW
Arm at 90 abduction while holding a weight 2.5% of BW;

G-H joint reaction force = BW
Arm at 90 abduction with elbow flexed to 90 degrees

G-H joint reaction force = .25BW
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