Biomechanics Unit 4 Flashcards Preview

BMSc SB > Biomechanics Unit 4 > Flashcards

Flashcards in Biomechanics Unit 4 Deck (86):

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


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

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

- 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

- 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

- arm moves away from trunk

- arm moves towards the trunk

along LONGITUDINAL AXIS of the humerus:
internal rotation

external rotation

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

- lateral epicondyle of the humerus

- 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


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

- hand tilting forwards
- hand tilting backwards
- hand tilting outwards 􏰀

- 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

- 60% occurs at midcarpal joint
- 40% in the radiocarpal joint

- 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

- 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

- no body but is composed of a ring within which an oval fossa articulates with the 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]