Wk 1: functional anatomy and biomechanics of the shoulder girdle complex Flashcards
where does the shoulder girdle articulate?
sternum
the shoulder is…
the most mobile joint in the body
what is the alignment of the ligaments of the shoulder girdle?
vertically aligned & small
what does the shape and alignment of the ligaments affect?
decreases stability
what does optimal function of the shoulder complex require?
- optimal positioning of all joints
- ideal excursion/ mobility of all joints
- motor control of all joints
what does movement of the shoulder complex require smooth inter-relationships between?
- humerus and scapula
- scapular and clavicle
- clavicle and sternum
humerus and scapula relationship
humerus rotates about the scapula within the GH jt
scapula and clavicle relationship
scapula rotates about the clavicle at the AC jt
clavicle and sternum relationship
clavicle rotates around the sternum at the SC jt
what is the scapula resting position over the ribs?
concave
what does the scapulo-thoracic articulation provide?
base for GHJ stability & mobility
what does the scapulo-thoracic articulation act as?
muscle attachment site between shoulder complex and thoracic/ cervical spine.
what does the scapulo thoracic articulation transfer?
loads from upper limb to torso and vice versa
what ribs does the “ideal” scapular resting position sit?
between T2 and T7
how far from the thoracic midline is the ideal scap resting position?
approx 7 cm
position of the scapula
- slight UR (3)
- slight anterior rotation / tilt (8)
- internal rotation of 30
what does the ‘ideal’ scapular resting position provide?
stable, safe socket for GH jt and prevents inferior subluxation
what is the sequence of shoulder girdle movements that makes up scap UR
- scap rotates upwardly as clavicle elevates around an AXIS OF MOTION that passes through the SC jt and base of scapular spine
- clavicular elevation continues until costoclavicular ligament becomes tight. Axis of scapular upward rotation motion moves to AC jt
- the scapula continues to rotate upward at AC jt UNTIL CC ligament BECOMES TIGHT
SCAPULAR UR CONTINUES
what does tension in the coracoclavicular ligament produce?
a passive force that rotates the clavicle backwards
what does backward clavicular rotation do to the clavicle?
elevates the distal end of the clavicle and, with it, the acromion and the AC jt
what does the elevation of the distal clavicle due to backward rotation, do?
enables last few degrees of abduction
what allows continued scapular UR?
elevation of the acromion and AC jt
what does full shoulder motion require?
- thoracic extension 10-15
- rib cage mobility
- trunk/ LL strength, stability and flexibility
what does optimal function require?
- correct posture that then produces –>
- optimal length tension relationships of muscles and articular structures
what are the static/ passive stabilisers of GH stability?
- bony geometry
- glenoid labrum
- glenoid depth and orientation
- vacuum effect
- capsuloligamentous structures
what are the active stabilisers of GH stability?
neuromuscular system
what does synovial fluid in the GH jt do?
creates a wet surface between the humeral head & glenoid fossa –> keeps suction effect strong
what is the glenoid labrum?
firbo-cartilaginous tissue that deepens glenoid by 9mm superior to inferior and 2.5mm antero-posterior
what does the glenoid labrum increase?
articular surface area by 50% / adapts to accomodate movement of the HOH
what does the glenoid labrum allow for?
for attachment of GH ligaments, cuff tendons and LHB
what is the adhesion-cohesion bond?
when 2 wet surfaces come into contact with each other this creates an adhesion-cohesion bond, which provides stability to the GH articulation - compresses HOH into socket –> seals labrum and glenoid to humerus
what does negative intra-articular pressure in the GH jt do?
helps to resist anterior and superior HH translation
what does negative intra-articular pressure in the GH jt require?
intact glenoid labrum/ capsule = critical component
where does the GH capsule attach?
around glenoid rim and forms a sleeve around HOH and anatomical neck
where does the inferior position of the GH capsule lie?
in folds – important in laxity and adhesive capsulitis
what is the GH capsule reinforced by?
ligaments and RC tendons
what is the posterior GH capsule intimately reinforced by?
rotator cuff tendons (IS and TM)
what does the posterior GH capsule restrains?
flexion, abduction, IR (stops excess)
what does the superior and middle posterior capsule restrain?
IR
what does the inferior aspect of the postrior capsule restrain?
abduction +/- IR
GH ligaments
- coracohumeral ligament
- superior GH ligament
- middle GH ligament
- inferior GH ligament
what restrains 0* abduction
CHL and SGHL
what restrains 45-60* abduction
MGHL
what restrains 90* abduction
IGHL
what do the GH ligaments do?
guide and position the HOH
CORACOHUMERAL LIGAMENT
where does the CH ligament attach?
anterolateral base of the coracoid
how many bands are in the CH ligament?
2
what ligament is difficult to separate from the CH ligament
superior GH ligament
what does the CH ligament blend with?
the capsule
what does the CH ligament insert into?
and inserts into the greater and lesser tuberosities
functions of the CH ligament?
- helps support the dependent arm
- resists inferior subluxation of the GH
- becomes taut in external rotation
(ANTERIOR) SUPERIOR GLENOHUMAL LIGAMENT
where does the ligament start?
from tubercle of glenoid, anterior to HOH lesser tuberosity