Biomechanics Unit 4 Flashcards
what are the 5 parts of the upper limb and what does each part consist of
shoulder girdle
- clavicle
- scapula
the arm
- humerus
the forearm
- radius
- ulna
the wrist
- 8 carpal bones
the hand
- metacarpals
- phalanges
how many vertebrae are there
24
and the sacrum and the coccyx
what are the 4 articulations of the shoulder joint
glenohumeral, acromioclavicular, sternoclavicular [are synovial joints] and scapulothoracic [bone on muscle articulation]
what forms the glenohumeral articulation and why are dislocations here more common
humeral head and glenoid fossa of the scapula
glenoid fossa is particularly shallow [allows for a wide ROM], makes the articulation less stable
what is present to assist stability in the glenohumeral articulation
glenoid labrum
[also surrounded by joint capsule and rotator cuff]
what are the 4 muscles of the rotator cuff
subscapularis
infraspinatus
supraspinatus
teres minor
how does the rotator cuff aid stability
provide dynamic restraints to anterior, posterior and inferior displacement
rotator cuff pushes on the humeral head, preventing any anterior-posterior movement, thereby stabilising the joint.
what forms the acromioclavicular joint and what helps with stability
proximal acromion of the scapula and the distal clavicle
stabilised by superior and inferior acromio-clavicular ligaments which prevent the joint being pulled apart
AND ALSO the coracoclavicular ligament [between the clavicle and coracoid process of the scapula] which limits the upward movement of the clavicle
why is range of motion at the acromioclavicular joint restricted
it is restricted by the thorax and the muscle attachments
ROM limited to a few degrees during arm abduction
what forms the sternoclavicular joint
formed between the manubrium of the sternum and the proximal clavicle
what joint is the only bony connection of the shoulder girdle to the trunk
sternoclavicular joint
how does the sternoclacicular joint act on the clavicle during arm elevation
clavicle elevates at the joint
For the first 90 degrees of arm elevation
- the clavicle elevates by around 4 degrees for every 10 degrees of arm elevation
Beyond 90 degrees
- elevation of the clavicle is negligible
what happens to the clavicle during elevation and depression
clavicle rotates about an axis determined by the attachment of the costoclavicular ligament
what is the scapulothoracic articulation
bone-muscle-bone articulation between the scapula and the posterior thoracic wall
[not a joint really as there no bony or ligamentous connections between scapula and thorax]
why is the scapulothoracic articulation important to the shoulder girdle
contributes significantly to the wide range of motion of the scapula
greatly enhances the mobility of the entire shoulder complex.
what are the 2 posterior thorax muscles important to the shoulder girdle
serratus anterior
- supplied by long thoracic nerve
- holds the scapula against the thorax
- prevents winging
- strong abductor that is useful in pulling or pushing movements
subscapularis
- rotator cuff muscle
- acts to medially rotate the humerus
what are the origins/insertions of the serratus anterior and subscapularis muscle
serratus anterior
- originates on the upper 8th or 9th ribs
- inserts on the anterior surface of the scapula along its vertebral border
Subscapularis
- originates from the subscapular fossa
- inserts on the lesser tubercle of the humerus
what are the terms for the range of motion possible at the shoulder joint and what movement do they mean
shoulder elevation
- humerus away from the side of the thorax in any plane
shoulder depression
- movement of the humerus towards the side of the thorax
In SAGITTAL plane:
forward flexion
- arm moves forward
backward extension
- arm moves backwards
In CORONAL/FRONTAL plane:
abduction
- arm moves away from trunk
adduction
- arm moves towards the trunk
along LONGITUDINAL AXIS of the humerus:
internal rotation
external rotation
In TRANSVERSE/HORIZONTAL plane:
horizontal flexion
- forward motion of the arm
horizontal extenson
- backwards motion of the arm
how is the amount of elevation in the shoulder quantified
angle of elevation
- angle between axis passing through the shoulder joint centre parallel to the longitudinal axis of the trunk and the longitudinal axis of the humerus
[really just angle between arm and thorax]
what is the average ranges of shoulder joint motion [in degrees]
forward flexion - 180
backward extension - 60
range = 240
abduction - 180
adduction - 75
range = 255
internal rotation - 90
external rotation - 90
range = 180
horizontal flexion - 135
horizontal extension - 45
range = 180
all 3 synovial articulations of the shoulder joint are prone to dislocation
- what is the most common?
anterior dislocation of the glenohumeral articulation.
- head of the humerus slips forward off the shallow glenoid fossa
what is the possible MOI of an anterior dislocation of the glenohumeral articulation
arm suffers a heavy blow when the shoulder is abducted and extended horizontally
what are the 3 articulations of the elbow joint
humeroradial articulation
- capitellum of the distal humerus and the head of the radius.
humeroulnar articulation
- trochlea of the distal humerus and the trochlear fossa of the proximal ulna.
proximal radioulnar articulation
- head of the radius and the radial notch of the proximal ulna
what articulations allow the elbow joint to flex/extend in a hinge-like manner and where is the axis of rotation
humeroradial and humeroulnar articulations
axis passes through the middle of the trochlea and is roughly parallel to the line joining the lateral and medial epicondyles of the humerus
what articulation allows pronation and supination
proximal radioulnar articulation
how is pronation and supination achieved
rotation of the head of the radius in the radial notch of the ulna in a pivot-like manner
[occurs inside the ligamentous sling which binds the radius to the ulna i.e. the annular ligament]
what is the average ranges of elbow joint motion [in degrees]
extension - 0
flexion - 140
range = 140
pronation - 70
supination - 80
range = 150
what is the range of motion required at the elbow for activities of daily living
flexion = 30 - 130 degrees
supination = 50 degrees pronation = 50 degrees range = 100 degrees
the elbow is a mechanically stable joint
- how does the olecranon process add to this
well suited to resist forces in the anteroposterior and posteroanterior direction
[does not provide much resistance to forces acting in a lateral and medial direction]
what provides the side to side stability of the elbow joint
2 collateral ligaments:
- medial ligament
[prevents abduction of the elbow]
- lateral ligament
[provides limited resistance to adduction forces - is assisted by the anconeus muscle]
what is the origin and insertion of the anconeus muscle
origin
- lateral epicondyle of the humerus
insertion
- olecranon and superior portion of the ulna shaft
what is the lack of resistance of adduction forces not a massive issue in the elbow
valgus stability is much more important functionally than varus stability
the stability of the elbow joint makes a dislocation less common than a shoulder dislocation
- what MOI can cause an elbow dislocation?
fall on a outstretched arm in almost full extension can result in an anterior dislocation
[distal end of the humerus slides forward over the coronoid process]
during common daily activities, the elbow joint force can be as high 2000N
- why are such high joint forces needed?
muscle forces need to be large since the muscles generally have small moment arms compared to the moment arms of the externally applied forces