Pectoral Girdle and Shoulder Flashcards
What is the pectoral girdle?
Scapula (anchored to chest wall by soft tissue and muscles) and clavicle connect the UL to the axial skeleton
What is the glenohumeral joint?
Ball and socket synovial joint between head of humerus and glenoid fossa (cavity) of scapula
What is the stability of the GH joint compromised by?
Incongruent joint surfaces (i.e. a poor fit)/ Thin and lax joint capsule
What is the stability of the GH joint improved by?
Glenoid labrum
Ligaments
Biceps tendon
Rotator cuff muscles
Where is the GH joint weakest?
Joint is weakest inferiorly
What prevents superior displacement of the humerus?
Coraco-acromial arch:
Acromion +coracoid process+ coracoacromial ligament
What two joints does the clavicle form part of?
The clavicle is palpable throughout its length. The lateral one third is concave, but the medial two thirds are convex. The ends of the clavicle can be felt projecting to the acromion of the scapula laterally (forming the acromioclavicular joint) and the manubrium of the sternum medially (forming the sternoclavicular joint).
What are the scapula articulations? Where is the scapula?
The scapula is a flat triangular bone, which lies on the back of the rib cage between the second and seventh ribs. It articulates with the humerus at the glenoid fossa to form the shoulder (glenohumeral) joint. The dorsal surface of the scapula is divided into supraspinous and
infraspinous fossae by the spine of the scapula. The posterior surface of the spine widens laterally to become continuous with the flattened acromion. Fracture of the scapula is uncommon.
Where do clavicular fractures occur?
The clavicle acts to transmit forces from the upper limb to the axial skeleton. Given its relative size, this leaves it particularly susceptible to fracture. The most common mechanism of injury is a fall onto the shoulder, or onto an outstretched hand.
With the clavicle arbitrarily divided into thirds:
15% of fractures occur in the lateral third
80% occur in the middle third
5% occur in the medial third.
After a fracture, the lateral end of the clavicle is displaced inferiorly by the weight of the arm, and displaced medially by the pectoralis major. The medial end is pulled superiorly by the sternocleidomastoid muscle.
Management of a clavicular fracture can be conservative (e.g. sling immobilisation) or operative (e.g. open reduction and internal fixation, ORIF). In ORIF, the supraclavicular nerves are often sacrificed – resulting in a post-operative numb patch over the shoulder.
What movements can the scapula make?
Far from lying inert on the chest wall, the scapula moves relatively freely so that the inferior angle can be moved laterally and cranially from the anatomical position. This movement brings the face of the glenoid cavity upwards and thus allows the arm to be lifted above the head. The scapula and clavicle can be considered to move together as a unit, usually moving the shoulder joint itself into a different position.
Additionally, the scapula can move up and down (elevation and depression), forwards (protraction = reaching the arm out in front, as if to push open a door, or throw a punch) and backwards (retraction = ‘squaring’ the shoulders) over the chest wall. These movements consequently move the upper limb and are achieved by muscles attached to the pectoral girdle, trunk, head and neck. In all these movements, the humerus moves with the scapula.
What are the superficial dorsal muscles of the pectoral girdle?
trapezius and latissimus dorsi
Trapezius - origins, insertions and innervation?
Trapezius is a large muscle with lots of bony attachments.
Originates from the skull, nuchal ligament, superior nuchal line and the spinous processes of C7-T12. The fibres attach to the clavicle, acromion and the scapula spine.
The fibres attach to the clavicle, acromion (upper) and the scapula spine (middle and lower).
The upper fibres of the trapezius elevate the scapula and rotates it during abduction of the arm. The middle fibres retract/adduct the scapula and the lower fibres pull the scapula inferiorly/depress.
Innervation: Motor innervation is from the accessory nerve (CNXI). It also receives proprioceptor fibres from C3 and C4 spinal nerves.
All fibres retract the scapula during abduction of humerus past horizontal
Latissimus Dorsi- origins, insertions, actions and innervation?
large, flat, triangular muscle that sweeps over the lumbar region and lower thorax and converges to a narrow tendon that inserts on the anterior surface of the humerus. In taking this path, it contributes to the posterior wall of the axilla (armpit).
origin – arising from the spinous processes of T7-L5, iliac crest, thoracolumbar fascia and the inferior three ribs. The fibres converge into a tendon that attaches to the intertubercular sulcus of the ant humerus.
Innervation: Thoracodorsal nerve (long scapular N C6,7,8)).
Actions: Extends, adducts and medially rotates the humerus.
What are the deep dorsal muscles of the pectoral girdle?
Levator scapulae
Rhomboid major
Rhomboid minor
Where do the deep dorsal muscles of the pectoral girdle attach?
The medial border of the scapula, deep to trapezius
