Biomech Unit 4

Question 1

What are the 4 articulations of the shoulder joint?

Answer 1

Glenohumeral,
Acromioclavicular,
Sternoclavicular,
Scapulothoracic

Question 2

Describe the glenohumeral joint and what provides its stability?

Answer 2

Humeral head articulates in the glenoid fossa (which is very shallow to allow a large range of movement - prone to dislocations due to shape)

Stability

• thick fibrous joint capsule
• glenoid labrum makes the socket deeper (cartilaginous ring)
• rotator cuff forms a cuff round both sides of the joint preventing ant-post movement

Question 3

What are the muscles of the rotator cuff?

Answer 3

Subscapularis
Teres minor
Infraspinatus
Supraspinatus

Question 4

Describe the acromioclavicular joint

What provides its stability?

Answer 4

Synovial joint where lateral clavicle articulates with the acromion of the scapula

Has a very limited ROM due to the thorax +
muscle attachments

Stability:

• superior + inferior acromioclavicular ligaments
• coracoclavicular ligament

Question 5

Describe the sternoclavicular joint.

What provides its stability?

Answer 5

Synovial joint; manubrium of sternum against medial clavicle

when elevate arm, the clavicle elevates at the sternoclavicular joint (can feel with finger)

Stability

• anterior sternoclavicular ligament
• costoclavicular ligament
• interclavicular ligament

Question 6

Describe the scapulothoracic articulation

Answer 6

Not a joint as is a bone-muscle-bone articulation (rather than bone-ligament)

Scapula - serratus anterior + subscapularis - posterior thoracic wall

Question 7

What is the angle of elevation of the shoulder joint?

Answer 7

The angle it is from the thorax

Question 8

What is the difference between internal/external rotation and horizontal flexion/extension?

Answer 8

Int/ext rot: elbow flexed at 90º elbow next to thorax, rotation towards/away from body

Horizontal flex/ext: arm out at side in line with shoulder (at 90º from trunk), forward/backwards movement of hand

Question 9

Which shoulder joints does dislocation occur at and which is the most common?

Answer 9

Glenohumeral, sternoclavicular, acromioclavicular

Anterior dislocation of shoulder most common

Question 10

How does anterior dislocation of the glenohumeral joint usually occur?

Answer 10

A blow to the hand whilst in a fully abducted position with horizontal extension (arm up + back like climbing)

The arm pivots around the acromion in this position - if the ligaments are too weak or the force is too strong, then dislocation occurs

Question 11

What type of joint is the elbow and what are the articulations?

Answer 11

Hinge joint

Proximal radioulnar,
Humeroradial
Humeroulnar

Question 12

How does pronation/supination occur?

Answer 12

Pronation: distal radius slides over the ulna (held together by triangular fibrocartilage), proximal radius rotates in the radial notch of the ulna (held in place by annular ligament - ligamentus sling)

Supination: slides back to its original position

Question 13

What provides ant/post stability and lat stability in the elbow joint?

Answer 13

Ant/post
- olecranon process; part of the trochlear notch which holds the trochlea like a nut

Lat

• collateral ligaments (medial/ulnar + lateral collateral)
• (MCL prevents abduction, LCL prevents adduction)

Question 14

What forces are experienced by the elbow joint? Why is this?

Answer 14

Up to 2000N
Dress/eating = 300N

As there is a small moment arm from the elbow to muscle insertion compared to the moment arm to externally applied forces (ie in the hands) - 3rd class lever

Question 15

What are the bones of the wrist (carpal bones)?

mnemonic

Answer 15

Scaphoid, Lunate, Triquetrium, Pisiform,
trapezium, Trapezoid, capitate, hamate

(some lovers try positions that they cannot handle)

Question 16

What is the purpose of the pisiform?

Answer 16

Insertion point of flexor carpi ulnaris (increases the lever arm similarly to the patella in the knee)
Flexes + adducts the wrist

Can feel under the pinky side of the wrist

Question 17

What type of joint is the 1st carpometacarpal joint (which bones is it between)? Why is it significant?

Answer 17

Saddle joint (trapezium - 1st metacarpal) - for flexion, extension abduction + adduction
Allows opposition of the thumb (makes it the most mobile carpometacarpal joint)

Question 18

What are the joints in the hand?

Answer 18

Carpometacarpal
Intermetacarpal
Metacarpophalangeal
Interphalangeal (proximal + distal (except thumb))

Question 19

How do hand and wrist motion interact? Give an example

Answer 19

Motion of the fingers are controlled by muscles in the forearm who’s tendons cross the wrist
If the wrist changes position it affects the functional length of the muscles tendons

If wrist straight, easy to form a fist; if wrist flexed, the difficult to flex fingers into a fist

If fingers in a fist, hard to flex the wrist

Question 20

How many of each vertebra are there?

Answer 20

7 Cervical
12 Thoracic
5 Lumbar 
5 sacral
4 coccygeal

Question 21

Describe the anatomy of a typical vertebrae

Answer 21

Larger vertebral body,
Spinal foramen for the spinal cord
Neutral arch surrounding the foramen, contains;
- 1x spinous process (sticks out posteriorly)
- 2x articular processes (stick out laterally)

Articulate with adjacent vertebrae via facet joints (synovial joints) from the neutral arch

Question 22

What are the 2 parts of the intervertebral discs?

Answer 22

Annulosis fibrosis: tough outer layer - made of collagen fibres

Nucleus pulposis: soft centre layer - made of hydrophilic gel in a collagen matrix

Question 23

Describe the atlas/axis

Answer 23

Atlas = C1
Has no vertebral body

Axis = C2
Has an additional odontoid process on which the atlas sits (can rotate slightly)

Question 24

Describe the vertebrae of the thoracic spine

What are the articulations of the ribs and how does this affect mobility?

Answer 24

These vertebrae also attach to a pair of ribs

The head of the rib articulates with the vertebral body (and of the vertebra above) and the tubercle with the transverse process of the vertebra

Allow the ribs to move up and down as we breathe,
Gives extra rigidity to the thoracic spine which limits mobility to very little flexion/extension/rotation

Question 25

Describe how the lumbar vertebrae are adapted to their function

Answer 25

They have larger vertebral bodies as they support larger loads

Question 26

Describe the motion of the sacrum/coccyx

Answer 26

Between lumbar spine and sacrum is very mobile joint (link between spine + pelvic girdle)
Sacrum/coccyx are fused into 2 bones so no mobility
Sacrum is joined to pelvis by 2 fibrous joints so there is very limited motion

Question 27

How much flexion/extension motion does the cervical spine have vs the thoracic?

Answer 27

Cervical spine has the most motion (21º) where as the thoracic is the most limited (3ª)

Question 28

Does the amount of flexion/extension in the vertebral column vary?

Answer 28

Yes

In lumbar spine there is up 10º flexion but 4º extension

Question 29

How does the body contribute towards bending of the spine?

Answer 29

During bending, the pelvis tilts forward to achieve further flexion (tilts backwards too)

Question 30

Where does most lateral bending occur?

Answer 30

Cervical spine (no lateral bending between C1/C2 - atlas/axis)

Question 31

Where does rotation of the head come from?

Answer 31

Between C1/C2 (there is no rotation between atlas and occipital bone)

Question 32

How does the rotation in the vertebral column vary?

Answer 32

Greatest at the top (C1/C2) and reduces down the spine

Question 33

What body position has the least and the greatest loading on the spine? Why is this?

Answer 33

Least = lying (no loading)
Most = relaxed sitting (more than erect sitting - the centre of mass of the upper body is the most forward so the spinal muscles must contract more to counter this, this increases the loading on the spine)

Question 34

Why is the loading of the spine greater during sitting than standing?

Answer 34

During sitting, the pelvis is tilted posteriorly and the centre of mass is forward in front of the body, this increases the moment arm to the spine so the spinal muscles need to contract further to balance this - this increases the compressive loading on the spine

During standing the pelvis is tilted anteriorly so the centre of mass is closer to the spine and therefore the compressive loading on the spine to counter the COM is smaller

Question 35

How does bad lifting technique affect the loading on the spine?

Answer 35

Poor technique (leaning forwards at the hips) increases the loading on the spine and increases the chance of injury

The moment arm is greater so the muscle action must be stronger to balance this which creates a larger compressive load on the spine

Question 36

At which wrist joints does most flexion + extension occur?

Answer 36

Flexion: mostly in the mid carpal (60%), the rest in the radoiocarpal
Extension: mostly in the radoiocarpal (67%), rest in the mid carpal (33%)