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
what bones form the wrist
distal radius
carpal bones
proximal ends of the metacarpals
what are the carpal bones
proximal row
- scaphoid
- lunate
- triquetrum
pisiform
distal row
- trapezium
- trapezoid
- capitate
- hamate
[in the order of ‘some lovers try positions that they cannot handle’]
where is the pisiform bone located and what is its function
anteriorly to the triquetrum [projects anteriorly on the little finger side of the hand as a small rounded elevation]
insertion point of the flexor carpi ulnaris muscle
- pisiform bone increases the lever arm of the muscle
what is the function of the flexor carpi ulnaris muscle
flexes and adducts the wrist
the wrist is a relatively stable joint
- what is its stability derived from?
intricate ligamentous structures
and the precise opposition of the multifaceted articular surfaces
[rather than from any inherent bony stability]
what are the articulations of the wrist joint
radiocarpal joint
mid-carpal joint
carpo-metacarpal joint
intercarpal joint
what makes the radoiocarpal joint and movements does it allow
lunate and scaphoid articulate with the distal end of the radius
[condyloid joint, whereby an oval-shaped condyle fits into an elliptical depression]
allows flexion and extension, abduction and adduction and circumduction
what is the ulnocarpal space
where the triquetrum articulates with the distal ulna via a triangular shaped inter-articular disc
what the movements possible at the wrist
flexion - hand tilting forwards extension - hand tilting backwards abduction - hand tilting outwards
adduction
- hand tilting inwards
range of movement possible at wrist in degrees
flexion = 80-90 extension = 70-80
abduction = 15-20 adduction = 35 range = 50
what joints does flexion and extension at the wrist occur at
Flexion:
- 60% occurs at midcarpal joint
- 40% in the radiocarpal joint
Extension:
- 2/3rds at radiocarpal joint
- 1/3rds at midcarpal joint
what is the range of movement needed at the wrist for daily activity
10 degrees of flexion to 35 degrees of extension
[For immobilised wrist joints a fixed extension of around 15 degrees allows most activities of daily living to be performed]
what its the hand composed of
5 metacarpals
14 phalanges [3 for each finger, 2 at the thumbs]
what are the joints of the hand
carpometacarpal joints [CMC joints] intermetacarpal joints metacarpophalangeal joints [MCP joints] proximal interphalangeal joints [PIP joints] distal interphalangeal joints [DIP joints]
what are the CMC joints formed by
carpal bones of the wrist and the metacarpals of the hand
why is the 1st CMC joint, between trapezium and 1st metacarpal at base of thumb, of great significance?
allows the thumb to oppose the fingers giving the human hand much greater dexterity
is a saddle joint which allows the first metacarpal to flex and extend, and abduct and adduct
what are each CMC joints surrounded by
joint capsules which are reinforced by several ligaments
what are intermetacarpal joints
irregular articulations formed between the proximal ends of adjacent metacarpals
share joint capsules of CMC joints
what are MCP joints
formed by the rounded distal heads of the metacarpals and the concave proximal ends of the phalanges
condyloid joints
[form the knuckles of the hand]
what stabilised the MCP joints
joint capsule and strong collateral ligament
MCP joint of the thumb is strengthened by an additional dorsal ligament.
what type of joints are the PIP and DIP joints
hinge joints
- only only flexion and extension
[the thumb has only one interphalangeal (IP) joint]
the second and third metacarpals of the hand are basically immobile
- what range of movement is possible at the 4th and 5th metacarpals
10 to 15 degrees at the fourth
20 to 30 degrees at the fifth.
[of flexion/extension]
what range of movement is possible at the MCP joints
flexion-extension and abduction-adduction.
max flexion = 90 degrees
extension = varies depending on laxity of persons ligaments
what range of movement is possible at the DIP and PIP joints
only permit flexion-extension
largest amount of flexion is possible at the PIP joints
PIP = 100-110 degrees flexion
DIP = 90 degrees flexion
what is extension at the DIP and PIP beyond neutral position termed
hyperextension
- dependent largely on ligament laxity
what is the range of motion available at the thumb in degrees
[MCP joint, CMC joint]
MCP joint
- flexion = 30-90
- extension = 15
CMC joint
- flexion [thumb moving across palm] = 15
- extension [thumb moves away from pals] = 20
- abduction [when thumb moves away from hand and points towards the roof] = 60
- adduction [thumb moves to touch little finger] = ?
where are the principal muscles that control the movements of the digits located
in the forearm
- distal tendons cross the wrist and possibly several joints of the digits before they are inserted
what is the function of the flexor digitorum profundus
flex the distal interphalangeal joints
[originates from the anterior aspect of the ulna and has insertions on the distal phalanges]
what happens as the wrist changes position
it also alters the functional lengths of the muscle tendons that cross it
what is an example of the wrist changing position affecting the tendons that cross over it
when the wrist is straight the fingers can be easily clenched into a tight fist
however, if the wrist is flexed first of all then it becomes difficult to fully flex the fingers
[the range of wrist flexion is also dependent on whether the fingers are straight or flexed]
what is an example of whether the fingers are flexed or extended affecting the position of the wrist
With the fingers extended the wrist can flex to almost 90 degrees
but with the fingers clenched into a fist the range of wrist flexion is significantly reduced.
what are the segments of the spinal column
7 Cervical vertebrae
C1 to C7
12 Thoracic (dorsal) vertebrae T1 to T12
5 Lumbar vertebrae
L1 to L5
Sacrum and Coccyx
(5 and 4 fused vertebrae)
what is the anatomy of the vertebrae
All have a flat, rounded body placed anteriorly and centrally
[VERTEBRAL BODY] and arch of bone [NEURAL ARCH], that forms the SPINAL FORAMEN
All have a SPINOUS PROCESS that projects inferiorly in the posterior midline and 2 TRANSVERSE PROCESSES that project laterally
what passes through the spinal foramen
the spinal cord
what is the function of the spinous and transverse processes on the vertebraes
provide anchorage sites for the ligaments and muscles which stabilise and move the spine.
Each vertebra articulates with each adjacent vertebra at 3 points
- what are the articulations
main articulation is at the vertebral body via an intervertebral disc
Other 2 articulations = facet joints - 1 above and below
[The upper facets articulate with the lower facets of the vertebra above, and the lower facets articulate
with the upper facets of the vertebra below]
what is the function of intervertebral discs
dual role of bearing and distributing loads and of restraining excessive motion.
what are the specific names for C1 and C2 and what are there features
C1 - ATLAS
- no body but is composed of a ring within which an oval fossa articulates with the axis
C2 - AXIS
- has an articular process, the dens, which protrudes superiorly from the vertebral body.
- atlas rotates about the dens but the motion is restricted by several ligaments that are attached to the top of the dens
[small synovial joint is formed between the anterior tip of the dens and the oval fossa of the atlas]
what are each thoracic vertebrae attached to
a pair of ribs
- head of each rib articulates with the body and the tubercle of each rib articulates with the transverse process
[second through to ninth ribs articulate with the body of the vertebra above. These articulations allow the ribs to move up and down as we breathe]
why do lumbar vertebrae have bigger vertebral bodies compared to the rest
they are subjected to significantly greater loads than the vertebrae in the rest of the spine
what forms the sacrum and the coccyx
sacrum - formed by fusion of 5 vertebrae
coccyx - formed by fusion of 4 or 5 vertebrae
why is the sacrum important
is the link between the lumbar spine and the pelvic girdle
junction between sacrum and the lumbar spine is very mobile.
sacrum is joined to pelvis by 2 fibrous joints that allow only a small amount of relative motion
what is the range of movement in the spine in regards to flexion and extension
flexion = bending forwards extension = bending backwards
range varies between spinal segments
greatest in CERVICAL spine = 21 degrees between C4 & C5
smallest in THORACIC spine = 3 degrees between T9 and T10
in LUMBAR spine =
max range of flexion = 10 degrees
max range of extension = 4 degrees
what is the range of motion of lateral bending in the spine
lateral bending = side to side in frontal plane
CERVICAL spine = most mobile
THORACIC spine = least mobile
[there is no lateral bending between first 2 cervical vertebrae atlas and axis]
the lumbar spine carries the highest loading in the spine
- what can increase loading
bad posture
[The load during standing is defined as 100% during upright standing. Note that during sitting the loading is actually larger than during upright standing and how slumping forwards can almost double the load.]
why does bad posture increase lumbar loading
The moment arm of the upper body mass about the lumbar spine is increased in the case of relaxed sitting due to the backward tilt of the pelvis
The flexion moment must be counterbalanced by an extension moment produced by the posterior back muscles
larger the moment arm is the greater the muscle forces need to be
muscles produce a compressive load on the spine which increases with increasing muscle force
Thus any change in posture that causes the upper body to be in a position offset from the lumbar spine effectively increases the load that it must carry
how does the loading change in the lumbar spine during lifting an object
load on lumbar spine is increased in accordance with the increase in the moment arm produced by weight of the object being lifted
how can the load of the lumbar spine be reduced during lifting
bending the knees and keeping the object closer to the body.
what makes up the intervertebral discs
inner nucleus pulposus
outer annulus fibrosus
what makes up the inner nucleus pulposus and what is its function
- formed by a strongly hydrophilic (water- loving) gel that is enmeshed in a random collagen matrix
- internal pressure balances the applied compressive stress
- If the applied stress is increased water is driven out of the disc until a new steady state is reached [decreased stress then disc rehydrates]
what makes up the outer annulus fibrosus
- tough layer which surrounds the nucleus pulposus
- composed of collagen fibres
- form concentric layers (lamellae) with alternating orientations of the collagen fibres
- arrangement resists high bending and torsional loads
how does the amount of rotation vary as you go down the spine
amount of rotation generally decreases down the spine
the range of rotation is considerably larger between the atlas (C1) and axis (C2) than between any other vertebrae - due to their unique structure
[no rotation between atlas (c1) and the occipital bone of the skull]
