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MSK T3 > Anatomy of the Shoulder Complex > Flashcards

Anatomy of the Shoulder Complex Flashcards

1
Q

What are the four joints of the shoulder complex?

A

Glenohumeral (GH), Acromioclavicular (AC), Sternoclavicular (SC), and Scapulothoracic (ST) joints.

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2
Q

What is the only articulation between the upper limb and the trunk?

A

Sternoclavicular (SC) joint.

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3
Q

What nerves predominantly innervate the shoulder complex?

A

Brachial plexus (C5-T1) and supraclavicular nerves (C3-C4).

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4
Q

What compensatory areas are often affected by faulty shoulder mechanics?

A

The neck and lumbar spine.

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5
Q

What is the normal ROM for shoulder flexion and abduction?

A

160-180 degrees.

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6
Q

What is the normal ROM for external and internal rotation of the shoulder?

A

External: 80-90 degrees, Internal: 60-100 degrees.

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7
Q

What is the closed-packed position for the GH joint?

A

Full abduction and external rotation.

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8
Q

What is the loose-packed position for the GH joint?

A

55 degrees abduction, 30 degrees horizontal adduction.

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9
Q

What is the capsular pattern for the GH joint?

A

Lateral rotation, abduction, medial rotation, flexion.

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10
Q

Why is the scapular plane significant?

A

• 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.

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11
Q

What type of joint is the GH joint?

A

Synovial, multi-axial, ball-and-socket joint.

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12
Q

What structure deepens the GH socket and improves articulation?

A

Fibrocartilaginous glenoid labrum.

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13
Q

What ligament forms a protective vault over the humeral head?

A

Coracoacromial ligament.

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14
Q

What happens if the coracoacromial ligament thickens?

A

It can contribute to impingement syndrome due to repetitive trauma or excessive superior translation of the humeral head.

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15
Q

What type of joint is the AC joint?

A

Synovial, plane joint.

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16
Q

What movements affect the AC joint?

A

Upward rotation, downward rotation, winging, anterior tipping.

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17
Q

What ligaments support the AC joint?

A

Superior and inferior AC ligaments, coracoclavicular ligaments (conoid and trapezoid).

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18
Q

What type of joint is the SC joint?

A

Triaxial, saddle joint with a disc.

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19
Q

What movements affect the SC joint?

A

Elevation, depression, retraction, protraction.

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20
Q

Why is clavicle fracture more common than SC dislocation?

A

The SC joint has very strong ligamentous support.

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21
Q

Is the ST joint a true joint?

A

No, it is an articulation between the scapula and thoracic spine.

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22
Q

What is required for optimal shoulder function?

A

A stable scapula.

23
Q

What are the motions of the scapula?

A

Elevation, depression, protraction, retraction, upward rotation, downward rotation.

24
Q

What are the movements at the GH joint?

A

• Flexion
• Scaption
• Abduction
• Extension

25
Q

What are the movements at the SC joint?

A

• Inferiorly
• Posteriorly

26
Q

What are the movements at the AC joint?

A

• Moves with scapula (superiorly with posterior rotation)
• Superiorly, anteriorly
• Moves with scapula (anteriorly and inferiorly)

27
Q

What are the movements at the ST joint?

A

• Upward rotation
• Protraction
• Posterior tipping
• Downward rotation
• Retraction
• Anterior tipping

28
Q

How do scapular muscles influence arm movements?

A

Scapular muscles control the position of the scapula, allowing scapulohumeral muscles to maintain an effective length-tension relationship to stabilize and move the humerus.

29
Q

How does improper scapular positioning affect the humerus?

A

Improper scapular positioning (e.g., downward rotation, protraction, anterior tipping) changes the position of the humerus, leading to internal rotation and abduction.

30
Q

What is the function of the rhomboids?

A

Downward rotation and retraction of the scapula.

31
Q

What is the function of the upper traps?

A

Elevation and upward rotation of the scapula.

32
Q

What is the function of the middle traps?

A

Retraction of the scapula.

33
Q

What is the function of the lower traps?

A

Depression and upward rotation of the scapula.

34
Q

What is the function of the serratus anterior?

A

Protraction and upward rotation of the scapula; keeps the scapula fixed to the ribcage (weakness causes winging).

35
Q

What is the function of the levator scapula?

A

Elevation and downward rotation of the scapula.

36
Q

What muscles attach to the coracoid process and affect scapular mechanics?

A

• Pectoralis minor
• Biceps brachii (short head)
• Coracobrachialis

37
Q

What happens if the pectoralis major is short?

A

It contributes to excessive internal rotation, restricting humeral abduction and flexion.

38
Q

What is the anatomical function of the supraspinatus?

A

Initiates GH abduction and compresses the humeral head in the glenoid fossa.

39
Q

What is the anatomical function of the infraspinatus?

A

GH external rotation and opposes abduction; compresses the humeral head.

40
Q

What is the anatomical function of the subscapularis?

A

GH internal rotation and opposes abduction; compresses the humeral head.

41
Q

What is the anatomical function of the teres minor?

A

GH external rotation and adduction; opposes abduction of the arm; compresses the humeral head.

42
Q

What is the anatomical function of the teres major?

A

GH internal rotation, adduction, and extension; opposes abduction of the arm.

43
Q

What is the anatomical function of the deltoid?

A

GH abduction; anterior fibers flex GH; posterior fibers extend GH.

44
Q

What is the anatomical function of the latissimus dorsi?

A

GH internal rotation, adduction, extension; also extends the lumbar spine.

45
Q

What three key structures reside under the hook of the acromion and coracoacromial ligament?

A

• Supraspinatus tendon
• Subacromial bursa
• Biceps long head tendon

46
Q

What factors can contribute to impingement in the subacromial space?

A

• Acromial shape
• Weak external rotators
• Weak scapular depressors
• Laxity and instability

47
Q

How does the shape of the acromion affect impingement?

A

A hooked acromion reduces the subacromial space, increasing the risk of impingement.

48
Q

How does the deltoid’s insertion affect humeral movement?

A

The deltoid has a superior pull on the humerus, whereas the supraspinatus exerts an inferomedial force, compressing the humeral head into the glenoid fossa.

49
Q

What happens when the rotator cuff is weak or inefficient?

A

The deltoid translates the humerus superiorly, which can lead to compression and impingement in the subacromial space.

50
Q

What role does the biceps long head tendon play in stabilizing the humeral head?

A

It helps prevent superior translation of the humeral head, especially if the rotator cuff is weak.

51
Q

What is the movement ratio for humeral abduction and scapular motion?

A

• 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).

52
Q

What movement occurs at the clavicle during humeral abduction?

A

The clavicle elevates and posteriorly rotates.

53
Q

What are some common scapulohumeral dysfunctions?

A

• 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).

MSK T3 (9 decks)

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