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) andsternal 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 peripherallyand 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