L2: Shoulder Anatomy and Biomechanics Flashcards
What are the 5 functions of the shoulder?
- position the hand away from and towards the body
- provide us with an evolutionary advantage
- Load bearing – compression, traction
- Fastest joint in the body with rotation (9000o/sec)
- Greatest ROM in the body
What are 3 evolutionary advantages?
Compared to non-human primates, humans have a distinct evolutionary advantage:
- increased rotation ROM
- humeral torsion = increased ER
- more lateral orientation of the glenoid
This means that we have a greater capacity to throw
What is stability VS mobility in the UL?
What are 5 charcteristics of the shoulder complex?
- Multi-joint and multidirectional
- Need to consider major anatomical structures
- brachial plexus
- large vessels posterior to proximal clavicle
- Age changes
- Individual variation in structure and movement- Ranges of GHJ and scapula movements –> a lot of asymmetry
- Stability mechanisms
What are the 7 components of the shoulder complex?
- Glenohumeral joint (GHJ)
- Acromioclavicular joint (ACJ)
- Sternoclavicular joint (SCJ)
- Scapulothoracic joint
- Thoracic spine
- Cervical spine
- Lumbar spine
What are 5 components that are involved in elevation?
- Scapulothoracic joint
- Glenohumeral joint
- Clavicle (ACJ, SCJ)
- Thoracic spine
- Lumbar spine & pelvis
TrA activates first in shoulder flexion –> whole body activation
What does the suprascapula nerve (C5,6) innervate? Where does it travel?
What does the suprascapula nerve (C5,6) innervate? Where does it travel?
- Originates from the superior trunk of the brachial plexus
- Passes through the suprascapular foramen to reach the posterior scapula, where it lies in the plane between the bone and the muscle
- Innervates supraspinatus, then passes through the greater scapular notch (between the root of the spine and the glenoid cavity) to terminate in and innervate the infraspinatus
- Generally has no cutaneous branches
Which area on the suprascapular nerve is most commonly impinged?
Greater scapular notch
What does the axilliary nerve (C5,6) innervate? Where does it travel?
- Originates from the posterior cord of the brachial plexus
- Passes inferiorly & laterally along the posterior wall to exit the axilla through the quadrangular space, then passes posteriorly around the surgical neck of the humerus
- Innervates deltoid and teres minor
- Branches into superior lateral cutaneous nerve (loops around posterior margin of deltoid to innervate skin in that region)
- Accompanied by posterior circumflex humeral artery
What does the accessory nerve (CN XI) innervate? Where does it travel?
Innervates trapezius and sternocleidomastoid (with contributions from cervical plexus C2-4)
What does the long thoracic nerve (C5,6,7) innervate? Where does it travel?
Innervates serratus anterior
Traction injury –> winging of medial border
What does the dorsal scapular nerve (C4,5) innervate? Where does it travel?
Innervates rhomboid major, rhomboid major, and levator scapulae
The shoulder is a remarkable complex, but there is a trade off
between____ and _____.
mobility; stability
The shoulder complex consists of the ____, ____, ____ and
_____ joint… but also need to consider the thoracic spine, cervical spine,
lumbar spine and pelvis
GHJ, ACJ, SCJ, scapulothoracic
The shoulder is highly innervated… need to be aware of nerves as a source of ____ and ____ , as this has implications for management
pain; dysfunction
What are 6 characteristics of sternoclavicular joint?
- Only articular attachment of the shoulder girdle to the axial skeleton
- Costoclavicular and capsular ligaments
- Movement: rotation and translation (AP, sup/inf)… clavicle on the articular disc moves more than disc on the sternum
- Close to rib 1
- Neurovascular bundle
- Subclavius muscle
What are 2 injuries with the sternoclavicular joint?
- posterior dislocation (direct force e.g. MVA, sport) – emergency
- Can get arthritis or injury to ligament
- anterior dislocation (indirect force e.g. fall on shoulder)
- Due to neurovascular bundle
What are the 3 mechanical movements of the sternoclavicular joint?
What are 3 characteristics of the acromioclavicular joint?
- Plane type synovial joint between distal clavicle and acromion
- Movement: accessory (elevation/depression; forward/backward shear)
- Scapula rotates at the ACJ
What are 3 passive supports from ligaments in the ACJ?
- Acromioclavicular
- Coracoclavicular
- Trapezoid
- Conoid
- Coracoacromial ligament
What are 2 dynamic (indirect) support from muscles in the ACJ?
- Deltoid
- Upper trapezius
What are 3 steps that occur during arm elevation in the ACJ mechanics?
- Clavicle elevates distally and retracts and rotates posteriorly
- 30o of elevation occurs at the ACJ
- 15o early in movement
- 15o after 135o of arm elevation
- Minimal movement of the clavicle between 90-135o
What are 2 characteristics of the GHJ?
- Joint with the largest ROM in the human body… BUT sacrifices stability for mobility
- Large ball and smaller pearshaped socket (disproportionate)
What are the GHJ mechanics?
What is the GHJ at the end of range?
most stability comes from capsuloligamentous structures
What is the GHJ through range?
- capsule relaxed
- most stability comes from muscle
What are 6 structures contributing to passive stability in the GHJ?
- glenoid orientation
- surface tension
- negative intra-articular pressure
- labrum (fibrous)
- capsuloligamentous structures
- osseo-ligamentous coracoacromial arch (superior)
What are 2 structures contributing to dynamic stability in the GHJ?
- rotator cuff
- scapular orientation (dynamic control of glenoid position)
What are 3 characteristics of the concavity of glenoid fossa (GHJ passive stability)?
- retroverted 7o (posterior facing), upwardly tilted 5o
- if glenoid fossa is anteriorly tilted, increased risk of instability
- position of glenoid largely driven by position/control of the scapula
What are 2 characteristics of the surface tension (GHJ passive stability)?
- cohesive bond between joint surfaces, limiting free fluid movement
- allows translation but prevents distraction
What is a characteristic of the negative intra-articular pressure (GHJ passive stability)?
Draws capsule inward & tightens fibres
What are 5 characteristics of the labrum (GHJ passive stability)?
- made of pliable fibrocartilage
- blends with long head of biceps (LHB) and superior glenohumeral ligament (SGHL)
- deepens socket by 50%
- 25% of humeral head contacts glenoid
- 75% of articular surface of humeral head is in contact with labrum & glenoid
- provides stability in mid-range
- nociceptive nerve supply
What are the 6 capsuloligamentous structures of the GHJ?
- Coracoacromial ligament
- Coracohumeral ligament
- Transverse humeral ligament
- Superior GH ligament
- Middle GH ligament
- Inferior GH ligament