Bones of the Pectoral Girdle, Acromioclavicular & Sternoclavicular Joints

acromioclavicular acromioclavicular joints clavicle coracoaromial arch pectoral girdle pelvic girdle sc joint scapula shoulder girdle sternoclavicular

Bones of the Pectoral Girdle Physiotherapy Solihull Simon Evans

The Shoulder Girdle

  • Evolutionary change in function of upper limb from one of locomotion to a tool for manipulation
  • Upper Limb attached to trunk via Pectoral Girdle (compare with Pelvic Girdle for lower limb) consisting of two freely mobile bones 
    • Clavicle
    • Scapula
  • Sole true articulation between Upper Limb and Trunk is via Sternoclavicular Joint 

The Clavicle

  • Lies horizontally, acting as a strut to hold the Upper Limb away from the body
  • Medial (sternal) end is convex anteriorly 
  • Lateral (acromial) end is concave anteriorly
  • Note identifiable and palpable bony points

The Scapula

  • Large flat bone situated on the posterior thoracic wall
  • Note the glenoid fossa (for the shoulder joint)
  • Note subscapular fossa (on costal surface) and 
  • Spine of scapula dividing the supraspinous & infraspinous fossae (on dorsal surface)
  • Scapula and clavicle articulate via the lateral end of the clavicle and the acromion process (see facet)

The Humerus

  • Typical long bone
  • Comparable with femur
  • Note anatomical and surgical neck of humerus and the Intertubercular sulcus

Joints of the Shoulder Girdle

  • Note differences between pectoral and pelvic girdles - relate to respective function
    • Pelvic girdle - rigid and very stable poor for mobility
    • Pectoral girdle - movable giving increased range to the Upper Limb
  • This is achieved by the presence of joints within the pectoral girdle and between the girdle and the axial skeleton
    • The Sternoclavicular
    • and the Acromioclavicular Joints

The Sternoclavicular Joint

  • Sole true articulation between Upper Limb & Axial Skeleton - Synovial, saddle joint.
  • Between sternal end of the clavicle - larger of the 2 surfaces (convex superiorly - inferiorly concave antero-posteriorly) and  sternal facet - on manubrium of sternum above facet for 1st rib (reciprocally concavo-convex)
  • All surfaces covered with fibrocartilage 
  • Poor congruency of facets improved by intra-articular disc - attached firmly to clavicle above and to 1st costal cartilage below
  • Blends with, the capsule peripherally and thinnest centrally (occasionally perforated)...(angled at 45 degrees)

The SC Joint

  • Functions of the disc:
    • i) Improve congruency
    • ii) Shock absorption and weight dissipation,
    • iii) Provide stability to the S/C joint (prevents the clavicle from sliding superiorly and medially along the sternal, facet)
  • Capsule - Attached to articular margins - Very strong except inferiorly
  • Synovial Membrane - Lines the capsule in the 2 separate cavities
  • Attached to articular margins and to the margins of the disc

Ligaments of the SCJ

  • 4 ligaments to consider: 
    • Anterior Sternoclavicular ligament - Thickening in anterior capsule
      • from the superior and anterior part of the clavicle running obliquely to the anterior aspect of the manubrium (blends with the tendon of Sterno-cleido-mastoid) 
    • Posterior Sternoclavicular Ligament - Weaker than anterior SCL
      • Reinforces posterior capsule, mirroring the anterior SCL
    • Interclavicular Ligament - As name suggests passes from clavicle to clavicle
      • Reinforces both superior capsules
      • Some fibres attach to the superior aspect of the manubrium as they pass over it.
    • Costoclavicular Ligament
        • Very strong ligament made up of 2 layers which are separated by a bursa
        • Anterior and posterior fibres are orientated obliquely to each other
        • Inferiorly attach to the 1st rib and adjacent part of costal cartilage
        • Superiorly attaches to the roughened area on the inferior aspect of the medial, clavicle
        • Functionally very important primarily limiting elevation, of the clavicle but also playing a role in, preventing anterior and posterior displacement

    Movements of the SCJ

    • Elevation and depression – describes movement of lateral end of clavicle
    • Axis of motion through the costoclavicular ligament (see saw effect)
    • Protraction and retraction - Axis passes vertically through costoclavicular ligament
    • Axial rotation
      • Axis is through the length of the clavicle
      • Occurs passively as a result of rotation, of the scapula causing increased tension, in, coracoclavicular ligament
      • (usually in conjunction with lateral rotation during arm elevation)

    The Acromioclavicular Joint

    • Synovial plane joint between lateral end of clavicle and tip of the acromion process
    • Articular surfaces:
      • Oval facets on respective bones
      • Clavicular facet is usually flat but may be convex
      • Acromial facet is reciprocally shaped
    • Both surfaces are covered with fibrocartilage
    • Capsule attaches to articular margins - strongest superiorly and lined with synovial membrane
    • An intra-articular disc partly divides the joint - when present may extend down into the joint from the capsule above and is wedge shaped (Its function is to improve congruency of the joint surfaces)

    Ligaments of the ACJ

    • Thickenings in capsule are described as superior & inferior AC ligaments
    • Fibres orientated parallel to capsular fibres - superior part is most important as it prevents superior displacement of 1ateral end of clavicle 
    • Coracoclavicular Ligament:
      • Very strong ligament uniting the lateral end of the clavicle to the coracoid process...
      • Divided into...
        • Conoid Ligament - Fan, shaped from root of coracoid process to conoid tubercle
        • Trapezoid ligament - Stronger part - quadrilateral in shape from the roughened area on the superior surface of the coracoid to trapezoid line
    • AC joint is prone to dislocation/trauma

    The Coracoacromial Arch

    • The Corocoid process, acromion and the coracoacromial ligament together form and arch known as the coracoacromial arch whose function is to spread the loading during upward movement of the humerus
    • A number of structures pass under the coracoacromial arch and as such are prone to impingement during shoulder movements

    See More Articles on the Human Anatomy - Click HereBones of the Pectoral Girdle Physiotherapy Solihull Simon Evans

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