BMS271 - Shoulder Flashcards
Shoulder Complex
The shoulder complex consists of four articulations all of which contribute to the mobility of the upper limb
- Scapulothoracic joint (ST)
- Sternoclavicular joint (SC)
- Acromioclavicular joint (AC)
- Glenohumeral joint (GH)
Scapulothoracic Joint (ST)
Not a true anatomical joint, scapula glides over thorax
- No joint capsule, synovial membrane, fibrous tissue or articular cartilage
- Scapula and rib cage separated by layers of muscle and connective tissue
- Scapulothoracic motion linked with AC and SC joint motion
- Elevation/depression
- Protraction/retraction
- Upward/downward rotation
- Scapular motion increases upper limb ROM
- Contact between scapula and thorax maintained by musculature
- Movement of scapula ensures glenoid fossa is in best position for mobility of upper limb
- Stability of scapula is also important for rolling and sliding of humeral head on glenoid cavity
- During various tasks the scapula needs to be mobile or stable and is ideally always in good contact with the thorax: all this depends on the action of the muscles attached to the scapula
Sternoclavicular Joint (SC)
- Only point of direct attachment of pectoral girdle and axial skeleton
- Saddle synovial joint (acts like ball and socket)
- Joint capsule contains articular disk (fibrocartilage)
- Joint supported by anterior and posterior sternoclavicular ligaments, the interclavicular ligament and costoclavicular ligament
- Allows elevation/depression, protraction/retraction and rotation of the clavicle
- Movement of the clavicle is linked to movement of the scapula
Sternoclavicular Joint Articular Disk
- Separates joint into two separate synovial cavities
- Improves contact b/w incongruent bony surfaces
- Attached to clavicle, sternum, 1st costal cartilage and joint capsule = provides stability
- Acts as hinge to provide mobility
- Allows rotation of clavicle 30-55° posteriorly from neutral
- Provides shock absorption
Acromioclavicular Joint (AC)
- Plane synovial joint
- Joint contains disk of variable size/shape
- Weak capsule supported by the acromioclavicular ligament (reinforced by trapezius tendon)
- Allows protraction/retraction of the scapula around a vertical axis ie glenoid fossa ends up facing anteriorly when protracted
- Also allows tipping of the scapula ie scapula is elevated and must adhere to thorax, which is curved; results in inferior angle of scapula protruding
Coracoclavicular Ligament
Has two parts: conoid and trapezoid ligaments
Both parts support the AC joint and allow the rest of the upper limb to be suspended from the clavicle
Trapezoid ligament
- lateral portion of Coracoclavicular Ligament
- quadrangular
- nearly horizontal
- prevents overriding and narrowing of angle b/w clavicle and scapula (from above)
Conoid ligament
- medial portion of Coracoclavicular Ligament
- triangular
- nearly vertical
- restricts vertical movement of clavicle,
- prevents widening of the angle b/w clavicle and scapula
Glenohumeral Joint
- Shallow ball and socket joint
- Glenoid fossa slightly deepened by glenoid labrum, a rim of fibrocartilage
- Neither surface is perfectly spherical,
- incongruence means that head of humerus may roll and/or slide
- With upper limb at rest coracohumeral ligament and superior capsule resist gravity whilst the rest of the capsule and glenohumeral ligaments are relaxed
- During abduction and lateral rotation the joint capsule twists and tightens, reinforced by the anterior, middle and inferior glenohumeral ligs. Closed packed position
- GH joint stability relies heavily on muscular support
- The glenohumeral joint allows flexion/extension, abduction/adduction and medial and lateral rotation
- The coracoacromial arch (coracoid process, acromion and coracoacromial ligament) is superior to the GH joint and prevents impact trauma and superior dislocation
- Subacromial bursa allows free movement of structures beneath the arch
Closed packed position of joint
= maximal congruence
= maximal tension in joint capsule
= maximal stability
Scapulohumeral Rhythm
Shoulder complex capable of 180 ° of abduction
- GH component : ST component = 2:1
- That is; the glenohumeral joint contributes roughly 120 ° of motion, and the scapulothoracic contributes 60°
- Much variation b/w individuals
- Scapula component small during first 30°
- Full abduction requires mobility of the upper thoracic and cervical regions of the spine
Pectoralis Major
Attachments:
- clavicular head: medial half of clavicle
- sternocostal head: anterior surface of sternum, costal cartilages 1-6
- intertubercular sulcus
Actions:
- adducts and medially rotates humerus,
- draws scapula anteriorly and inferiorly
- clavicular head alone flexes humerus,
- sternocostal head alone extends humerus from flexed position
Innervation:
lateral and medial pectoral nerves (clavicular head C5, C6, sternocostal head C7 and C8, T1)
Pectoralis Minor
Attachments: - ribs 3-5 near costal cartilages - coracoid process Actions: - stabilises scapula by drawing it anteriorly and inferiorly Innervation: - medial pectoral nerve (C8 and T1)
Subclavius
Attachments:
- junction of 1st rib and 1st costal cartilage
- inferior surface of middle third of clavicle
Actions:
- anchors and depresses clavicle
Innervation:
- nerve to subclavius (C5 and C6)
Serratus Anterior
Attachments: - lateral aspect of ribs 1-8 - medial border of scapula Actions: - protract scapula, - rotate scapula superiorly (lower fibres), - hold scapula to thorax Innervation: - long thoracic nerve (C5, C6 and C7)
