Shoulder Part 2 Flashcards
Shoulder abduction
Where does the 60 degrees of thoracic motion occur?
Where is the axis located throughout the motion?
0-90 = early phase. Most of 30 degrees of scapular thoracic motion happens at SC joint.
90-180 = late phase. 2nd 30 degrees happens at AC joint. Axis is located at SC joint and moves through root of scapula.
Upper traps?? and serratus ant.?? contracts and pulls scapula laterally around the rib cage and superiorly.
Shoulder abduction
Where is the axis in the late phase of the motion?
How do the functions of the muscles change throughout the motion?
Late phase Axis at AC joint.
Middle and Lower traps–Axis has changed location.
As axis moves, function of lower trap changes and allows the trap to pull inf. The muscle’s involvement kicks in at 90 degrees and increases exponentially at 150 degrees.
Upper trap and Serratus Anterior is really working throughout range
What muscles are involved in shoulder abduction and what phase are they active?
Upper trap/Serratus Ant. Early phase
Upper trap/Serratus Ant./Lower trap. Late phase (some middle trap).
Deltoid and Rotator Cuff (Supraspinatus)
Explain what the frontal plane motion effect would be at the GHJ if the deltoid muscle contracted alone and unopposed by any other force? (Base your explanation on the breakdown of the deltoid resultant force vector into its component forces.
Alone and Unopposed, translation force is greater than rotation.
Explain what the frontal plane motion effect would be at the GHJ if the infraspinatus, teres minor and subscapularis muscles, as a group, contracted together and unopposed by any other force? (Base your explanation on the breakdown of these muscles combined/composite resultant force vector into its component forces.)
More rotation, less translation
How do the combined actions of the deltoid and the rotator cuff muscles produce motion at the GHJ?
Translations cancel each other out to a degree leaving rotational components to summate and create rotational motion.
What would be the effect at the GHJ if the supraspinatus muscle contracted alone and unopposed? Explain how these effects are possible again based on breakdown of resultant force vectors into component forces.
The bulk of the force would be rotation rather than rotation
What role does gravity play in working with the supraspinatus muscle during arm elevation?
Gravity and subscapular translation cancels out upward translation in the arm–deltoid and Supraspinatus.
When downward translation muscles get weak, upward translation takes over and impingement takes over.
In what osteokinematic motions does the long head of the bicep contribute to arm elevation and explain how the bicep does this? (Also, by what mechanism(s) does the long head of biceps appear to provide stabilization to the anterior GHJ?
a. Contributes flexion – Long head of tendon pulls up anteriorly on GHJ. Line of pull relative to axis of rotation.
b. Bow-string effect (mechanism) - produces a force to push the head of humerus into GHJ. Producing an anterior stabilizing effect on flexing shoulder. pg 156 fig 5-47.
How is length-tension of the deltoid maintained throughout arm elevation?
Deltoid is effective throughout full range.
Length-tension is maintained by scapular rotation. Scapula has to move. As the humerus moves to shorten the muscle, the scapula moves to lengthen the muscle.
What motion does the latissimus dorsi produce at the ST joint during open chain activity vs closed kinematic chain activity?
Latissimus Dorsi–open chain v closed chain.
Open chain–downward rotation and depression of scapula at ST joint.
Closed chain–torso/thorax/rib cage will lift up. Between shoulders.
Transfers from wheelchairs. Move along a bed. pg 153 fig 5-42 5-43. 159 fig 5-53 force couple.
What is the role of the rhomboids during arm adduction and extension from an abducted/flexed position of the GHJ?
Rhomboids also function as a huge stabilizer. Allows GHJ to move.
Contrast the strength of internal vs external rotator muscles of the shoulder. What accounts for the difference?
Internal rotators are stronger due to larger muscle mass.
What might be a potential problem with the difference in strength of the IRs and ERs?
Internal rotators generate more force than external rotators, and external rotators get injured because they can’t slow everything down in time.
