shoulder joint complex, SC joint anatomy, Biomechanics of SC joint, AC joint anatomy, Biomechanics of AC joint, ST joint anatomy, GH joint anatomy

1. THE SHOULDER
COMPLEX

2. INTRODUCTION
• Connects the upper limb to the axial skeleton
• Composed of the clavicle, scapula and humerus.
• Has greater mobility and less stability
• Anteriorly, the clavicle reaches the sternum and articulates with it at the
sterno-clavicular joint
• The clavicle and the scapula are united to each other at acromio-clavicular
joint

4. STERNO- CLAVICULAR JOINT
• Plane Synovial joint
• Compound joint
• Saddle shaped surface
• 3 degree of freedom
• It has a synovial capsule, joint disk and three major ligaments
• Medial end of the clavicle, clavicular notch of the manubrium sterni and the upper surface
of the first costal cartilage
• Clavicular surface is convex from above downwards and slightly concave from front to back
and vice versa for sternal surface

5. • The superior portion of the medial clavicle does not contact the manubrium;
serves the attachment of the SC joint disk and the inter clavicular joint.
• At rest, the SC joint space is wedge- shaped and open superiorly

8. SC DISK
• Has a fibrocartilage joint disk or meniscus
• Increases congruence between joint surfaces
• Upper portion is attached laterally to the clavicle on a rough area above and
posterior
• Lower portion is attached inferiorly to the sternum, first costal cartilage and anterior
and posterior aspects to the fibrous capsule
• In elevation and depression of the clavicle, the medial end of the clavicle rolls and
slides in relation to the stationary disk (upper point of the disk serving as a pivot
point

9. • In protraction/retraction the SC disk and medial clavicle rolls and slide
together on the manubrium facet (lower part serving as pivot point)
• Disk is part of manubrium in elevation/depression and part of the clavicle
in protraction/retraction
• Mechanical axis for these two movements located at the more laterally
located costo- clavicular ligament

12. SC JOINT LIGAMENTS
1. SC ligament
• Anterior and posterior SC ligaments reinforce the capsule
• Primary function is to check anterior and posterior translatory movements
of the medial end of the clavicle
• Attached laterally to the margins of the articular surface of the clavicle, and
medially to the margins of the articular surface of the sternum

14. 2. Costo- clavicular ligament:
• Very strong ligament
• Between the clavicle and the first rib
• Attached above to the rough area on the inferior aspect of the medial end of the clavicle
• Inferiorly to the first costal cartilage and to the first rib
• Has two segments or laminae
• Anterior segment is directed laterally from the first rib to the clavicle.
• Posterior segment is directed medially from the first rib to the clavicle

15. • Both segments check elevation of the lateral end of the clavicle and when
the limits of the ligament are reached inferiorly glide the medial clavicle.

17. 3. Inter- clavicular ligament
• Passes between the sternal ends of the right and left clavicles
• Resists excessive depression of the distal clavicle and superior glide of the
medial end of the clavicle.

19. • Blood supply: internal thoracic and suprascapular arteries
• Nerve supply: medial supraclavicular nerve

20. BIOMECHANICS
1. ELEVATION/DEPRESSION OF THE CLAVICLE:
• Occur around an approximately AP axis
• Between a convex clavicular surface and a concave surface
• With elevation the lateral end of the clavicle rotates upward and medial end
slides inferiorly and with depression lateral end of the clavicle rotates
downwards and medial end slides superiorly.

22. 2. PROTRACTION/RETRACTION OF THE CLAVICLE:
• Occurs around an approximately vertical axis
• With protraction, the lateral end of the clavicle rotates anteriorly and the
medial end of the clavicle is expected to slide anteriorly
• With retraction, the lateral end of the clavicle rotates posteriorly and the
medial end of the clavicle is expected to slide posteriorly

24. 3. Anterior and posterior rotation of the clavicle:
• Occurs as a spin between the saddle shaped surfaces of the medial clavicle
and manubrio- costal facet
• The clavicle can rotate in only posterior direction from the neutral, bringing
the inferior surface of the clavicle to face anteriorly.
• From its fully rotated position, the clavicle can rotate anteriorly again to
return in neutral.

26. ACROMIO- CLAVICULAR JOINT
• Plane synovial joint
• 3 rotational and translational degrees of freedom
• Has a joint capsule and 2 major ligaments, a joint disk may or may not be
present
• Formed by the articulation between a small facet at the lateral end of the
clavicle and on the medial margin of the acromion process of the scapula

27. AC JOINT CAPSULE AND LIGAMENTS
1. CAPSULE:
• Weak
• Can not maintain integrity of the joint
• Superior AC ligament assists the capsule in apposing articular surfaces and in controlling A-
P joint stability
2. Coracoclavicular ligament:
• Provides joint stability
• Divided into lateral portion (trapezoid ligament), and a medial portion (conoid ligament)

28. i. Trapezoid ligament:
• Quadrilateral in shape
• Nearly horizontal in orientation
• Provides the majority of resistance to posterior translator forces applied to the distal clavicle
ii. Conoid ligament:
• Triangular in shape
• Vertically oriented
• Provides the primary restraint for the AC joint in the superior and inferior directions

29. • Both portions of the coracoclavicular ligament limit upward rotation of the
scapula at the AC joint
• Blood supply: suprascapular and thoracoacromial arteries
• Nerve supply: lateral supraclavicular nerve

31. BIOMECHANICS OF AC JOINT
1. Internal and external rotation:
• IR/ER of the scapula in relation to the clavicle occurs around approximately
vertical axis through the AC joint
• IR= glenoid fossa of the scapula anteromedially
• ER= glenoid fossa of the scapula posterolaterally

33. 2. Anterior and posterior tipping:
• Anterior/posterior tipping or tilting of the scapula in relation to the clavicle
around an oblique coronal axis.
• Anterior tipping: acromion tipping forward and the inferior angle tipping
backward.
• Posterior tipping: acromion tipping backward and the inferior angle tipping
forward

35. 3. Upward/ downward rotation:
• Occur about an oblique A-P axis approximately perpendicular to the plane
of the scapula.
• Upward rotation: tilts the glenoid fossa upward
• Downward rotation: tilts the gelnoid fossa downward.

37. SCAPULOTHORACIC JOINT
• Formed by the articulation of the scapula with the thorax
• Not a true anatomic joint; functional joint
• The articulation depends on the integrity of the anatomic AC and SC joint
• Normally the scapula rests at a position on the posterior thorax approximately 2
inches from the midline, between the second through seventh ribs
• IR 30 degrees to 45 degrees from the coronal plane
• Anterior tipping approximately 10 degrees to 20 degrees from vertical

38. BIOMECHANICS OF ST JOINT
1. Upward/downward rotation: As AC joint
2. Elevation/depression:
• Elevation: shrugging the shoulder up
• Depression: depressing the shoulder downward
3. Protraction/retraction:
• Translatory motions
• Protraction: vertebral border away from the midline
• Retraction: vertebral border towards the midline.

40. SHOULDER JOINT
• Ball and socket joint
• Synovial type of joint
• 3 rotational and 3 translational degree of freedom
• Has a joint capsule, ligaments and bursae
• Articulation is between the humeral head and the glenoid fossa of the scapula
• Stability is maintained by:
a. The coracoacromial arch
b. The RC muscles of the shoulder
c. The glenoid labrum

41. • Humeral head faces medially, superiorly and posteriorly
• Angle of inclination: 130 degrees to 150 degrees
• Angle of torsion: 30 degrees

43. GLENOID LABRUM
• Attached to the periphery of the glenoid fossa
• Total articular surface of the glenoid fossa is enhanced by the glenoid labrum
• Superiorly is loosely attached
• Inferior portion is firmly attached and relatively immobile.

45. GH CAPSULE
• Very loose
• Permits free movements
• Taut superiorly and slack anteriorly and inferiorly
• Twists on itself and tightens when the arm is abducted and internally rotated (CPP
of the GH joint)
• Medially, attached to the scapula beyond the supraglenoid tubercle and the margins
of the labrum
• Laterally, attached to the anatomical neck of the humerus
• Inferiorly extends down to the surgical neck
• Superiorly deficient for passage of the tendon of the long head of the biceps brachii

46. • Anteriorly reinforced by the superior, middle and inferior GH ligaments.
• Superior GH ligament: passes from the superior glenoid labrum to the upper
neck of the humerus deep to the coracohumeral ligament
• Middle GH ligament: runs obliquely from the superior anterior labrum to the
anterior aspect of the proximal humerus below the superior GH ligament
• Inferior GH ligament complex: anterior and posterior bands and axillary
pouch

49. GH LIGAMENTS
1. Coracohumeral ligament: extends from the root of the coracoid process to
the neck of the humerus opposite the greater tubercle; gives strength to
the capsule
2. Transverse humeral ligament: bridges the upper part of the bicipital groove
of the humerus; tendon of the long head of the biceps brachii passes deep
to the ligament

51. CORACOACROMIAL ARCH
• Formed by the coracoid process, the acromion and the coracoacromial ligament
• Forms an osteoligamentous vault that covers the humeral head and forms a space
within which the subacromial bursa, the RC tendons and the portion of the tendon
of the long head of the biceps brachii
• Protects the structures beneath it from the direct trauma from above.
• Prevents the head of the humerus from dislocating superiorly, because an
unopposed upward translator force on the humerus would cause the head of the
humerus to hit the coracoacromial arch

52. • As a consequence, however, the contact of the humeral head with the
undersurface of the arch can cause painful impingement or mechanical
abrasion of the structures lying in the subacromial space.
• When the subacromial space is narrowed, the impingement of the RC
tendons and subacromial bursa during elevation of the humerus increases.

54. BURSAE
1. Subacromial (subdeltoid) bursa
• These bursa separate the supraspinatus tendon and head of the humerus
from the coracoid process, acromion, coracoacromial ligament and deltoid
muscle
• Permits smooth gliding between the humerus and supraspinatus tendon
2. Subscapularis bursa
3. Infraspinatus bursa

56. 1. Blood supply:
• Anterior circumflex humeral vessels
• Posterior circumflex humeral vessels
• Suprascapular vessels
• Subscapular vessels

57. 2. Nerve supply:
• Axillary nerve
• Musculocutaneous nerve
• Suprascapular nerve