PBL 2 - Chronic Back Pain

Question 1

Draw a diagram of a vertebra.

Answer 1

Include:

1. Vertebral body
2. Pedicle/lamina
3. Transverse/spinous process
4. Inferior/superior articular processes
5. Inferior/superior vertebral notches

Question 2

What makes up the intervertebral disc?

Answer 2

ANULUS FIBROSIS

1. Structure: outer ring of collagen; inner layers of fibrocartilage
2. Function: limits rotation between vertebrae

NUCLEUS PULPOSUS

1. Structure: gelatinous; loose fibres surrounded by a mucoprotein gel
2. Function: absorbs compression forces

Question 3

List the ligaments on the back, and where they are found.

Answer 3

1. Anterior and posterior longitudinal ligaments (ant/post surfaces of vertebral bodies)
2. Ligamenta flava (between laminae of adjacent vertebrae)
3. Supraspinous ligament and ligamentum nuchae (connecting spinous processes from C7 to sacrum)
4. Interspinous ligaments (between adjacent spinous processes)

Question 4

List the sulci found on the outside of the spinal cord.

Answer 4

1. Anterior median fissure
2. Posterior median sulcus
3. Posterolateral sulci (formed where posterior rami of the spinal nerves leave the cord)

Question 5

Describe the features of the denticular ligaments.

Answer 5

Attach pia mater to the lateral walls of vertebral canal (function: lateral stability)

21 pairs

Question 6

List the dermatomes of important structures in the lower limb. Include:

1. Knee
2. Medial malleolus
3. Toes 1-3
4. Toes 4-5 (and lateral malleolus)

Answer 6

Knee - L3
Medial malleolus - L4
Toes 1-3 - L5
Toes 4-5 (and lateral malleolus) - S1

Question 7

List the dermatomes of important structures in the trunk. Include:

1. Posterior head and neck
2. Nipple
3. Umbilicus

Answer 7

Posterior head/neck - C2/3
Nipple - T4
Umbilicus - T10

Question 8

List the myotomes of the lower limb.

Answer 8

HIP:
Flexion - L2/3
Adduction - L2/3
Extension - L4/5
Abduction - L4/5

KNEE:
Extension - L3/4
Flexion - L5/S1

ANKLE:
Dorsiflexion - L4/5
Plantarflexion - S1/S2

TOES:
Big toe extension - L5

Question 9

What are the 4 steps in pain physiology?

Answer 9

1. Transduction
2. Transmission
3. Perception
4. Modulation

Question 10

Describe pain transduction.

Answer 10

Nociceptors (polymodal, high threshold)

1. Sensitisation - switches nociceptor from high threshold to low threshold
   a. Caused by peripheral mediators, e.g.
   - –Prostaglandins
   - –Leukotrienes
   - –Inflammatory soup
   - –Axon reflex
2. Activation - stimulates pain signals
   a. Caused by peripheral mediators, e.g.
   - –H+
   - –Histamine
   - –Axon reflex

Question 11

Describe the axon reflex.

Answer 11

1. Stimulation of nociceptors causes release of substance P and CGRP
   a. This causes vasodilation and release of bradykinin
2. Vasodilation causes plasma leakage and further inflammation
   a. This causes increased sensitisation of nociceptors
3. Bradykinin causes further activation of nociceptors

Question 12

Describe the spinothalamic pathway.

Answer 12

1. Pain stimuli from the skin activate Ad/C fibres (primary neuron)
2. Ad/C fibres (primary neuron) enter the spinal cord and terminate in the superficial dorsal horn
   a. Primary neuron then synapses onto the secondary neuron
3. Secondary neuron decussates onto the other side of the spinal cord
   a. This then travels up the spinal cord to the medulla via the anterolateral columns (NOTE: called the spinal lemniscus in the medulla)
4. Most C fibres terminate in the medulla, pons and mesencephalon
   a. This gives rise to the conscious feeling of pain
5. Secondary neuron terminates in the thalamus
   a. Secondary neuron synapses onto a tertiary neuron
6. Tertiary neuron crosses the internal capsule and enters the sensory cortex

Question 13

Describe the perception of pain.

Answer 13

SENSORY/DISCRIMINATORY
Brain areas involved:
---Thalamus
---S1 and S2
---Post. insula

COGNITIVE/AFFECTIVE

• –Ant. insula
• –Anterior cingulate gyrus
• –Prefrontal cortex

Question 14

Describe the modulation of pain.

Answer 14

1. Gate control theory
2. Descending inhibitory system/supraspinal loop
   a. Descending serotonergic/noradrenergic fibres from the pons/raphe nuclei form synapses in the spinal cord:
   - –Directly onto ascending neurons
   - –Onto inhibitory encephalin neurons
   b. Both of these synapses inhibit pain transmission
3. Endogenous opiate system of brain
   a. There are 3 types of endogenous opiates: encephalins, POMC, dynorphins
   b. These stimulate opiate receptors in the midbrain/medulla, which then activates the supraspinal loop

Question 15

Describe the mechanism of referred pain.

Answer 15

1. Visceral pain fibres have branches that synapse onto the same secondary neurons as the Ad and C fibres use in the spinal cord
2. Therefore, when the visceral pain fibres are activated, at least some pain signals are conducted through the same neurons that conduct pain from the skin
   a. This creates the feeling that the pain originates in the skin

Question 16

List the red flag signs for serious spinal injjury in back pain.

Answer 16

1. Weight loss
2. Past medical history of malignancy
3. Fever
4. Signs of systemic inflammatory disease
5. Anatomical change
6. Possible fractures – history of trauma
7. Cauda equine syndrome
8. Neurological signs (i.e. radiculopathy)

Question 17

What are the 6Ps of pain treatment?

Answer 17

1. Preventative
2. Pathology
3. Physical therapies
4. Pharmacotherapy
5. Procedural
6. Psychologically based

Question 18

Describe the analgesic ladder.

Answer 18

Step 1: paracetamol and/or NSAIDs
a. NOTE: always best to start with paracetamol, as there are fewer side effects (e.g. GI ulceration or bleeding)

Step 2: codeine, dihydrocodeine
a. NOTE: codeine is ineffective in people with a CP450/CYP 2D mutation – this is actually quite common, and means that the body can’t convert codeine into morphine

Step 2-3 transition: tramadol

Step 3: morphine, oxycodone, methadone, diamorphine, pethidine