Unit 4 - Biomechanics of the upper limb & spine

Question 1

What 2 bones make up shoulder girdle?

Answer 1

Clavicle & scapula

Question 2

What 4 articulations make up the shoulder joint & what type of articulations are they?

Answer 2

3 synovial:
  - glenohumeral
  - acromioclavicular
  - sternoclavicular
1 bone-on-muscle-on-bone joint:
  - scapulothroacic

Question 3

What type of joint is the glenohumeral?

Answer 3

Ball (humeral head) & socket (glenoid fossa of scapula)

Question 4

What structures aid stability of the glenohumeral joint?

Answer 4

Glenoid labrum (thick cartilagenous rim)
Capsule
Rotator cuff

Question 5

What muscles make up the rotator cuff & what is its function?

Answer 5

Muscles:

• Subscapularis
• Infraspinatus
• Supraspinatus
• Teres minor

Pushes on humeral head, providing dynamic restraints to anterior, posterior & inferior displacement

Question 6

What structures stabilise the AC joint?

Answer 6

Superior & inferior AC ligaments which prevent joint being pulled apart

2 parts of the coracoclavicular ligament which limits movement of clavical

RoM limited to a few degrees during arm abduction (restricted by thorax & muscle attachments)

Question 7

How much does the clavicle elevate during arm elevation?

Answer 7

~4 degrees for every 10 of arm elevation (for first 90 of arm elevation - past 90 clavicle elevation is negligible)

Question 8

Why does the clavicle rotate?

Answer 8

During arm elevation/depression clavicle rotates about longitudinal axis due to attachment of costoclavicular ligament

Question 9

Why is the scapulothoracic articulation not a true joint?

Answer 9

No direct bony/ligamentus connections

Question 10

What 2 muscles separate scapula from posterior thorax?

Answer 10

Serratus anterior:

• originates on upper 8/9 ribs & inserts on anterior surface of scapula along vertebral boarder
• helps hold scapula against thorax (preventing winging) & is a strong abductor (for pulling/pushing)

Subscapularis:

• originates from subscapular fossa & inserts on lesser tubercle of humerus
• medially rotates humerus

Question 11

What is the range of motion of the shoulder in the sagittal plane?

Answer 11

Forward flexion - 180

Backward extension - 60

Question 12

What is the range of motion of the shoulder in the coronal plane?

Answer 12

Abduction - 180

Adduction - 75

Internal rotation - 90

External rotation - 90

Question 13

What is the range of motion of the shoulder in the transverse plane?

Answer 13

Horizontal flexion - 135

Horizontal extension - 45

Question 14

What is the most common type of shoulder dislocation?

Answer 14

Anterior dislocation of glenohumeral joint

Heavy blow when arm abducted & extended. If blow too heavy/muscles too weak –> dislocation

Arm & shoulder acting as 1st class lever with resistance to dislocation at a disadvantage

Question 15

What 3 articulations make up the elbow joint?

Answer 15

Humeroradial

Humeroulnar

Proximal radioulnar

Question 16

How much extension & flexion are possible at the elbow?

Answer 16

Extension - 0
Flexion - 140 (40 between arm & forearm when fully flexed)

Humeroradial/ulnar articulations allow hinge movement - axis of rotation through middle of trochlea

Question 17

What articulation in the elbow allows for pronation & supination?

Describe hoe it comes about

Answer 17

Proximal radioulnar

Rotation of radial head in radial notch of unla in pivot-like manner (occurs in annular ligament - ligamentous sling wich binds through radius to ulna)

Longitudinal axis passes through radial head & distal unla articular surface - rotation about this axis results in migration of distal radius around ulna

Question 18

What is the max RoM for pronation & supination of forearm?

Answer 18

Pronation - 70

Supination - 80

Question 19

How is stability achieved at the elbow?

Answer 19

Olecranon process holding trochlea like a spanner & nut (for anterior-posterior stability)

2 collateral ligaments:

• medial (ulnar): most important, preventing abduction
• lateral: provides limited resistance to adduction. Aided by anconeus muscle located on lateral aspect of elbow (weakness doesn’t cause problem as valgus stability more important)

Question 20

What bones make up the carpals?

Answer 20

Scaphoid
Lunate 
Triquetrum
Pisiform
Trapezium
Trapezoid
Capitate
Hamate

Question 21

What is the function of the pisifrom?

Answer 21

Is the insertion point of flexor carpi ulnaris (flexes & adducts wrist)

Increases lever arm of flexor carpi ulnaris - decreasing the force required from the muscle

Question 22

What articulations are involved in the wrist?

Answer 22

Radiocarpal
Midcarpal
Carpometacarpal
Intercarpal

Question 23

Describe the radiocarpal joint

Answer 23

Condyloid joint - oval shaped condyle of radius fits into eliptical depression between lunate & scaphoid

Allows flexion, extension, abduction, adduction & circumduction

Question 24

Describe the range of motion at the wrist

Answer 24

Flexion: 80-90 (40% at radiocarpal & 60% at midcarpal)

Extension: 70-80 (67% at radiocarpal & 33% at midcarpal). Most critical movement

Abduction: 15-20

Adduction: 35

Question 25

What articulations are found in the hand?

Answer 25

``` Carpometacarpal Intermetacarpal Metacarpophalangeal Proximal interphalangeal Distal interphalangeal ```

Question 26

Describe 1st carpometacarpal joint

Answer 26

Saddle joint between trapezium & 1st metacarpal at base of thumb Most freely moving CMC joint & allows thumb to oppose fingers giving great dexterity All CMC joints surrounded by joint capsule & reinforced by ligaments

Question 27

Describe intermetacarpal joints

Answer 27

Irregular articulations formed by prox ends of adjacent metacarpals Share joint capsules of CMC joints

Question 28

Describe metacarpophalangeal joints

Answer 28

Condyloid - rounded distal heads of metacarpals & concave prox ends of phalanges Forms the knuckles Each enclosed in a capsule & stabilised by strong collateral ligaments (MCP of thumb strengthened by additional dorsal ligament)

Question 29

What type of joints are DIP & PIPs?

Answer 29

Hinge joints allowing only flexion/extension

Question 30

Describe the range of motion in the: - Metacarpals? - MCPs? - DIP/PIPs?

Answer 30

Metacarpals - 2nd & 3rd immobile while a small amount of flexion/extension is allowed in 4th & 5th MCPs - allow flex/extension & add/abduction. Max flex ~90 & extension varies between individuals depending on ligament laxity PIPs - flexion 100-110 DIPs - flexion 90 (extension for both depends on ligament laxity)

Question 31

Describe the range of motion at the thumb

Answer 31

MCP does not allow as much flexion as fingers (30-90) but has more extension CMC joint: - flexion (thumb across palm) - 15 - extension (thumb away from side of palm) - 20 - abduction (thumb away from palm) - 60 - small degree of rotation

Question 32

What is the interaction between hand and wrist movements?

Answer 32

As wrist changes positions it alters lengths of tendons crossing from forearm into wrist When wrist straight fingers can be easily clenched however if wrist is flexed it becomes difficult to fully flex fingers (and vice versa)

Question 33

What common features do unfused vertebrae have (bar C1 & 2)?`

Answer 33

Vertebral body - flat round central body Neural arch - arch of bone that forms spinal foramen Spinous process - projects inferoposteriorly 2x transverse processes - project laterally

Question 34

At what points to adjacent vertebrae articulate?

Answer 34

Vertebral body via intervertebral disc 2x facet joints - synovial joints either side of the arch

Question 35

Describe the nucleus pulposus

Answer 35

Lies in centre of intervertebral discs Formed by strongly hydrophilic gel enmeshed in random collagen matrix Gel produces high water content & elevated nucleus pressure which balances compressive stress If applied stress increases, water is driven out of disc until new equilibrium is reached (disc rehydrates when stress decreases)

Question 36

Describe the annulus fibrosis

Answer 36

Tough layer that surrounds nucleus pulposus composed of collagen fibres forming concentric layers (lamellae) with alternating orientations Arrangement resists high bending & torsional loads

Question 37

How are C1 & C2 different to other vertebrae?

Answer 37

C1 (atlas) - no body, composed of a ring withing which an oval fossa articulates with axis C2 (axis) - has dens which protrudes superiorly & forms small synovial joint with oval fossa of atlas

Question 38

At which points of the thoracic vertebrae do the ribs articulate with?

Answer 38

Head of each rib with vertebral body Tubercle of each rib with transverse process

Question 39

Describe motion in the spine: - flexion-extension? - lateral bending? - rotation?

Answer 39

Flexion-extension: - varies between different regions (cervical>thoracic) - extent of flexion & extension also varies between regions Lateral bending: - similarly cervical has greatest Rom & thoracic least - no lateral bending between C1 & 2 Rotation: - decreases down spine - greatest between C1 & 2

Question 40

How can you explain higher load on spine when sitting compared to standing?

Answer 40

Moment arm of upper body weight about lumbar spine increases during sitting due to backward tilt of pelvis This moment must be counter balanced by extension moment produced by posterior back muscles (producing compressive load)