Anatomy of the Shoulder Complex Flashcards
What are the four joints of the shoulder complex?
Glenohumeral (GH), Acromioclavicular (AC), Sternoclavicular (SC), and Scapulothoracic (ST) joints.
What is the only articulation between the upper limb and the trunk?
Sternoclavicular (SC) joint.
What nerves predominantly innervate the shoulder complex?
Brachial plexus (C5-T1) and supraclavicular nerves (C3-C4).
What compensatory areas are often affected by faulty shoulder mechanics?
The neck and lumbar spine.
What is the normal ROM for shoulder flexion and abduction?
160-180 degrees.
What is the normal ROM for external and internal rotation of the shoulder?
External: 80-90 degrees, Internal: 60-100 degrees.
What is the closed-packed position for the GH joint?
Full abduction and external rotation.
What is the loose-packed position for the GH joint?
55 degrees abduction, 30 degrees horizontal adduction.
What is the capsular pattern for the GH joint?
Lateral rotation, abduction, medial rotation, flexion.
Why is the scapular plane significant?
• Less tension on the GH capsule.
• Greater elevation possible than in sagittal or frontal planes.
• No GH rotation needed for full overhead ROM.
• Less risk of tubercular impingement.
What type of joint is the GH joint?
Synovial, multi-axial, ball-and-socket joint.
What structure deepens the GH socket and improves articulation?
Fibrocartilaginous glenoid labrum.
What ligament forms a protective vault over the humeral head?
Coracoacromial ligament.
What happens if the coracoacromial ligament thickens?
It can contribute to impingement syndrome due to repetitive trauma or excessive superior translation of the humeral head.
What type of joint is the AC joint?
Synovial, plane joint.
What movements affect the AC joint?
Upward rotation, downward rotation, winging, anterior tipping.
What ligaments support the AC joint?
Superior and inferior AC ligaments, coracoclavicular ligaments (conoid and trapezoid).
What type of joint is the SC joint?
Triaxial, saddle joint with a disc.
What movements affect the SC joint?
Elevation, depression, retraction, protraction.
Why is clavicle fracture more common than SC dislocation?
The SC joint has very strong ligamentous support.
Is the ST joint a true joint?
No, it is an articulation between the scapula and thoracic spine.
What is required for optimal shoulder function?
A stable scapula.
What are the motions of the scapula?
Elevation, depression, protraction, retraction, upward rotation, downward rotation.
What are the movements at the GH joint?
• Flexion
• Scaption
• Abduction
• Extension
What are the movements at the SC joint?
• Inferiorly
• Posteriorly
What are the movements at the AC joint?
• Moves with scapula (superiorly with posterior rotation)
• Superiorly, anteriorly
• Moves with scapula (anteriorly and inferiorly)
What are the movements at the ST joint?
• Upward rotation
• Protraction
• Posterior tipping
• Downward rotation
• Retraction
• Anterior tipping
How do scapular muscles influence arm movements?
Scapular muscles control the position of the scapula, allowing scapulohumeral muscles to maintain an effective length-tension relationship to stabilize and move the humerus.
How does improper scapular positioning affect the humerus?
Improper scapular positioning (e.g., downward rotation, protraction, anterior tipping) changes the position of the humerus, leading to internal rotation and abduction.
What is the function of the rhomboids?
Downward rotation and retraction of the scapula.
What is the function of the upper traps?
Elevation and upward rotation of the scapula.
What is the function of the middle traps?
Retraction of the scapula.
What is the function of the lower traps?
Depression and upward rotation of the scapula.
What is the function of the serratus anterior?
Protraction and upward rotation of the scapula; keeps the scapula fixed to the ribcage (weakness causes winging).
What is the function of the levator scapula?
Elevation and downward rotation of the scapula.
What muscles attach to the coracoid process and affect scapular mechanics?
• Pectoralis minor
• Biceps brachii (short head)
• Coracobrachialis
What happens if the pectoralis major is short?
It contributes to excessive internal rotation, restricting humeral abduction and flexion.
What is the anatomical function of the supraspinatus?
Initiates GH abduction and compresses the humeral head in the glenoid fossa.
What is the anatomical function of the infraspinatus?
GH external rotation and opposes abduction; compresses the humeral head.
What is the anatomical function of the subscapularis?
GH internal rotation and opposes abduction; compresses the humeral head.
What is the anatomical function of the teres minor?
GH external rotation and adduction; opposes abduction of the arm; compresses the humeral head.
What is the anatomical function of the teres major?
GH internal rotation, adduction, and extension; opposes abduction of the arm.
What is the anatomical function of the deltoid?
GH abduction; anterior fibers flex GH; posterior fibers extend GH.
What is the anatomical function of the latissimus dorsi?
GH internal rotation, adduction, extension; also extends the lumbar spine.
What three key structures reside under the hook of the acromion and coracoacromial ligament?
• Supraspinatus tendon
• Subacromial bursa
• Biceps long head tendon
What factors can contribute to impingement in the subacromial space?
• Acromial shape
• Weak external rotators
• Weak scapular depressors
• Laxity and instability
How does the shape of the acromion affect impingement?
A hooked acromion reduces the subacromial space, increasing the risk of impingement.
How does the deltoid’s insertion affect humeral movement?
The deltoid has a superior pull on the humerus, whereas the supraspinatus exerts an inferomedial force, compressing the humeral head into the glenoid fossa.
What happens when the rotator cuff is weak or inefficient?
The deltoid translates the humerus superiorly, which can lead to compression and impingement in the subacromial space.
What role does the biceps long head tendon play in stabilizing the humeral head?
It helps prevent superior translation of the humeral head, especially if the rotator cuff is weak.
What is the movement ratio for humeral abduction and scapular motion?
• 0-30° abduction: Almost all movement comes from the GH joint.
• 30-90° abduction: ~2:1 movement ratio (humerus: scapula).
• 90-180° abduction: ~1:1 movement ratio (humerus: scapula).
What movement occurs at the clavicle during humeral abduction?
The clavicle elevates and posteriorly rotates.
What are some common scapulohumeral dysfunctions?
• Early movement of scapula/greater upward rotation (GH capsule tightness).
• Inadequate upward rotation (impingement, rotator cuff problems, serratus anterior weakness).
• Winging (weak serratus, rhomboids).
• Tipping (short pec minor or biceps/coracobrachialis).
• Excessive clavicular elevation (excessive UFT activation, weak LFT or serratus).
