PAIN & PAIN CONTROL THEORIES

Managing Pain

What is Pain?“An unpleasant sensory & emotional experience associated with actual or potential tissue damage, or described in terms of such damage” –

The International Association for the Study of Pain

Subjective sensationPain Perceptions – based on expectations, past experience, anxiety, suggestions

Affective – one’s emotional factors that can affect pain experienceBehavioral – how one expresses or controls painCognitive – one’s beliefs (attitudes) about pain

Physiological response produced by activation of specific types of nerve fibersExperienced because of nociceptors being sensitive to extreme mechanical, thermal, & chemical energy. Composed of a variety of discomforts One of the body’s defense mechanism (warns the brain that tissues may be in jeopardy)Acute vs. Chronic –

The total person must be considered. It may be worse at night when the person is alone. They are more aware of the pain because of no external diversions.

Where Does Pain Come From?Cutaneous Pain – sharp, bright, burning; can have a fast or slow onset

Deep Somatic Pain – stems from tendons, muscles, joints, periosteum, & b. vessels

Visceral Pain – originates from internal organs; diffused @ 1st & later may be localized (i.e. appendicitis)

Psychogenic Pain – individual feels pain but cause is emotional rather than physical

Pain Sources

Fast vs. Slow Pain – Fast – localized; carried through A-delta axons in skin

Slow – aching, throbbing, burning; carried by C fibers

Nociceptive neuron transmits pain info to spinal cord via unmyelinated C fibers & myelinated A-delta fibers.

• The smaller C fibers carry impulses @ rate of 0.5 to 2.0 m/sec.

• The larger A-delta fibers carry impulses @ rate of 5 to 30 m/sec.

Acute vs. Chronic

What is Referred Pain?Occurs away from pain site

Example: Kerr’s sign

Types of referred pain:Myofascial Pain – trigger points, small hyperirritable areas within a m. in which n. impulses bombard CNS & are expressed at referred pain

• Active – hyperirritable; causes obvious complaint• Latent – dormant; produces no pain except loss of ROM

Sclerotomic & Dermatomic Pain – deep pain; may originate from sclerotomic, myotomic, or dermatomic n. irritation/injury

• Sclerotome: area of bone/fascia that is supplied by a single n. root• Myotome: m. supplied by a single n. root• Dermatome: area of skin supplied by a single n. root

TerminologyNoxious – harmful, injurious

Noxious stimuli – stimuli that activate nociceptors (pressure, cold/heat extremes, chemicals)

Nociceptor – nerve receptors that transmits pain impulsesPain Threshold – level of noxious stimulus required to alert an individual of a potential threat to tissuePain Tolerance – amount of pain a person is willing or able to tolerate

Accommodation phenomenon – adaptation by the sensory receptors to various stimuli over an extended period of time (e.g. superficial hot & cold agents). Less sensitive to stimuli.

Hyperesthesia – abnormal acuteness of sensitivity to touch, pain, or other sensory stimuli Paresthesia – abnormal sensation, such as burning, pricking, tingling

Inhibition – depression or arrest of a function

Inhibitor – an agent that restrains/retards physiologic, chemical, or enzymatic action

Analgesic – a neurologic or pharmacologic state in which painful stimuli are no longer painful

Questions to Ask about Pain

P-Q-R-S-T formatProvocation – How the injury occurred & what activities the painQuality - characteristics of pain – Aching (impingement), Burning (n. irritation), Sharp (acute injury), Radiating within dermatome (pressure on n.)?Referral/Radiation –

Referred – site distant to damaged tissue that does not follow the course of a peripheral n.Radiating – follows peripheral n.; diffuse

Severity – How bad is it? Pain scaleTiming – When does it occur? p.m., a.m., before, during, after activity, all the time

Pattern: onset & duration

Area: location

Intensity: level

Nature: description

Pain Assessment ScalesVisual & Numeric Analog Scales None Severe

0 10Locate area of pain on a picturesMcGill pain questionnaire

Evaluate sensory, evaluative, & affective components of pain

• 20 subcategories, 78 words

McGill Pain Questionnaire

78 words that describe pain are grouped into 20 sets and divided into 4 categories representing dimensions of the pain experience

Completion may take 20 minutes Administered every 2-4 weeks

Goals In Managing Pain

To control acute pain and protect patient from further injury while encouraging progressive exercise in a supervised environment.Reducing pain is an essential part of treatment

Goals In Managing Pain

Encourage body to heal through exercise designed to progressively increase functional capacity and to return the patient to work, recreational and other activities as swiftly and safely as possible

Transmission of Pain

Types of Nerves

Neurotransmitters

Types of Nerves

Afferent (Ascending) – transmit impulses from the periphery to the brain

First Order neuron

Second Order neuron

Third Order neuron

Efferent (Descending) – transmit impulses from the brain to the periphery

First Order NeuronsStimulated by sensory receptorsEnd in the dorsal horn of the spinal cordTypes

A-alpha – non-pain impulsesA-beta – non-pain impulses

• Large, myelinated• Low threshold mechanoreceptor; respond to light touch & low-

intensity mechanical infoA-delta – pain impulses due to mechanical pressure

• Large diameter, thinly myelinated• Short duration, sharp, fast, bright, localized sensation (prickling,

stinging, burning)C – pain impulses due to chemicals or mechanical

• Small diameter, unmyelinated• Delayed onset, diffuse nagging sensation (aching, throbbing)

Neural Transmission (First Order Neurons)

First order or primary afferents transmit impulses from the sensory receptor to the dorsal horn of the spinal cord

Afferent First Order Neurons

Second Order NeuronsReceive impulses from the FON in the dorsal horn

Lamina II, Substantia Gelatinosa (SG) - determines the input sent to T cells from peripheral nerve

• T Cells (transmission cells): transmission cell that connects sensory n. to CNS; neurons that organize stimulus input & transmit stimulus to the brain

Travel along the spinothalmic tract Pass through Reticular Formation

TypesWide range specific

• Receive impulses from A-beta, A-delta, & C

Nociceptive specific• Receive impulses from A-delta & C

Ends in thalamus

Neural Transmission (Second Order Neurons)

Second order afferent fibers carry sensory messages from the dorsal horn to the brain Second order afferent fibers are categorized as wide dynamic range or nociceptive specific

Neural Transmission(Second Order Neurons)

Wide dynamic range second order afferents receive input from A, A and C fibers.

Second order afferents serve relatively large, overlapping receptor fields

Nociceptive specific second order afferents respond exclusively to noxious stimulation

• Receive input only from A and C fibers

Third Order Neurons

Begins in thalamus

Ends in specific brain centers (cerebral cortex)

Perceive location, quality, intensity

Allows to feel pain, integrate past experiences & emotions and determine reaction to stimulus

Neural Transmission(Third Order Neurons)

•All of these neurons synapse with third order neurons which carry information to various brain centers where the input in integrated, interpreted and acted upon

Descending NeuronsDescending Pain Modulation (Descending Pain Control Mechanism)Transmit impulses from the brain (corticospinal tract in the cortex) to the spinal cord (lamina)

Periaquaductal Gray Area (PGA) – release enkephalinsNucleus Raphe Magnus (NRM) – release serotonin

The release of these neurotransmitters inhibit ascending neurons

Stimulation of the PGA in the midbrain & NRM in the pons & medulla causes analgesia.Endogenous opioid peptides - endorphins & enkephalins

NeurotransmittersChemical substances that allow nerve impulses to move from one neuron to anotherFound in synapses

Substance P - thought to be responsible for the transmission of pain-producing impulsesAcetylcholine – responsible for transmitting motor nerve impulsesEnkephalins – reduces pain perception by bonding to pain receptor sitesNorepinephrine – causes vasoconstriction 2 types of chemical neurotransmitters that mediate pain

• Endorphins - morphine-like neurohormone; thought to pain threshold by binding to receptor sites

• Serotonin - substance that causes local vasodilation & permeability of capillaries• Both are generated by noxious stimuli, which activate the inhibition of pain

transmission

Can be either excitatory or inhibitory

Sensory ReceptorsMechanoreceptors – touch, light or deep pressure

Meissner’s corpuscles (light touch), Pacinian corpuscles (deep pressure), Merkel’s corpuscles (deep pressure)

Thermoreceptors - heat, coldKrause’s end bulbs ( temp & touch), Ruffini corpuscles (in the skin) – touch, tension, heat; (in joint capsules & ligaments – change of position)

Proprioceptors – change in length or tensionMuscle Spindles, Golgi Tendon Organs

Nociceptors – painful stimuli mechanosensitivechemosensitive

Sensory Receptors

Nerve Endings“A nerve ending is the termination of a nerve fiber in a peripheral structure.” (Prentice, p. 37)

Nerve endings may be sensory (receptor) or motor (effector).Nerve endings may be:

Respond to phasic activity - produce an impulse when the stimulus is or , but not during sustained stimulus; adapt to a constant stimulus (Meissner’s corpuscles & Pacinian corpuscles)

Respond to tonic receptors produce impulses as long as the stimulus is present. (muscle spindles, free n. endings, Krause’s end bulbs)

Superficial – Merkel’s corpuscles/disks, Meissner’s corpusclesDeep – Pacinian corpuscles,

Nerve EndingsMerkel’s corpuscles/disks -

Sensitive to touch & vibration

Slow adapting

Superficial location

Most sensitive

Meissner’s corpuscles – Sensitive to light touch & vibrations

Rapid adapting

Superficial location

Pacinian corpuscles -Sensitive to deep pressure & vibrations

Rapid adapting

Deep subcutaneous tissue location

Krause’s end bulbs – Thermoreceptor

Ruffini corpuscles/endingsThermoreceptor

Sensitive to touch & tension

Slow adapting

Free nerve endings -Afferent

Detects pain, touch, temperature, mechanical stimuli

NociceptorsSensitive to repeated or prolonged stimulationMechanosensitive – excited by stress & tissue damageChemosensitive – excited by the release of chemical mediators

Bradykinin, Histamine, Prostaglandins, Arachadonic Acid

Primary Hyperalgesia – due to injurySecondary Hyperalgesia – due to spreading of chemical mediators

Pain Control TheoriesGate Control Theory

Central Biasing Theory

Endogenous Opiates Theory

Gate Control TheoryMelzack & Wall, 1965Substantia Gelatinosa (SG) in dorsal horn of spinal cord acts as a ‘gate’ – only allows one type of impulses to connect with the SONTransmission Cell (T-cell) – distal end of the Second or neurons (SON)

If A-beta neurons are stimulated – SG is activated which closes the gate to A-delta & C neuronsIf A-delta & C neurons are stimulated – SG is blocked which closes the gate to A-beta neurons

Gate Control TheoryGate - located in the dorsal horn of the spinal cord

Smaller, slower n. carry pain impulses

Larger, faster n. fibers carry other sensations

Impulses from faster fibers arriving @ gate 1st inhibit pain impulses (acupuncture/pressure, cold, heat, chem. skin irritation).

Brain

Pain

Heat, Cold, Mechanical

Gate (T cells/ SG)

Gate Control Theory Sensory information

coming from A fibers is transmitted to higher centers in brain

“Pain message" carried along A & C fibers is not transmitted to second-order neurons and never reaches sensory centers

Central Biasing Theory

Descending neurons are activated by: stimulation of A-delta & C neurons, cognitive processes, anxiety, depression, previous experiences, expectationsCause release of enkephalins (PAG) and serotonin (NRM)Enkephalin interneuron in area of the SG blocks A-delta & C neurons

Endogenous Opiates TheoryLeast understood of all the theoriesStimulation of A-delta & C fibers causes release of B-endorphins from the PAG & NRM

Or

ACTH/B-lipotropin is released from the anterior pituitary in response to pain – broken down into B-endorphins and corticosteroids

Mechanism of action – similar to enkephalins to block ascending nerve impulses

Examples: TENS (low freq. & long pulse duration)

Mechanisms of Pain Control

The theories presented are only models Pain control is the result of overlapping mechanisms Useful in conceptualizing the perception of pain and pain relief

Pain Management

Therapeutic modalities can be used to

Stimulate large-diameter afferent fibers( TENS, massage, analgesic balms)

Decrease pain fiber transmission velocity (cold, ultrasound)

Stimulate small-diameter afferent fibers and descending pain control mechanisms (accupressure, deep massage, TENS)

Pain ManagementTherapeutic modalities can be used to Stimulate release of endogenous

opioids through prolonged small diameter fiber stimulation with TENS

Goals in Managing Pain

Reduce pain!

Control acute pain!

Protect the patient from further injury while encouraging progressive exercise

Other ways to control pain

Encourage central biasing – motivation, relaxation, positive thinking

Minimize tissue damage

Maintain communication w/ the athlete

If possible, allow exercise

Medications