Pain....what is Pain??

In taking clinical history many of the students still confused what is meant by referred pain, radicular pain and sciatica.

Both referred pain and radicular pain are pain that is felt in a region remote from the actual source of pain.However the referred pain is the pain that is PERCEIVED by the brain through the afferents that converge on second-order neurons or third order in CNS that happen also to receive afferents from the region to which the pain is referred.
There is NO direction connection between the actual source of pain and the area that pain is felt.The connection is by cortical perception hence has distinct characteristic:

• dull,deep ache or pressure-like in quality
• diffuse,deep and indistinct border(wide area)
• fixed in location
• no actual dermatomal distribution
  

Whereas radicular pain is a type of neurogenic pain and sciatica is an example of radicular pain
Pain is felt in the periphery territory of the affected nerve.However it differs from the referred pain is that:

• it does not involve the stimulation of nerve endings
• it does not involve convergence
• there is a direct connection from the actual source of pain and the region that is felt through the conduction of the affected nerve

Hence the radicular pain has the following characteristics:

• shooting, lancinating and electric in nature
• distributed along a narrow band not more than two inches wide
• it travels into lower limbs
• it follows dermatomal distribution

Referred pain can occur by either two mechanism:

• somatic referred pain(sources lie in the tissues or structures of body wall(soma) or limbs)
• visceral referred pain(sources lies in the organs or blood vessels)

The somatic referred pain can arises from facet joints,disc,sacroiliac joint and felt over the gluteal region and beyond. However usually this referred pain reaches up to the knee and seldom go beyond it.For practical purposes referred pain is more common that the radicular pain.

NB
Similarly many are confused between foot drop and equinus foot or ankylosis with arthrodesis.
Foot drop=a disability(unable to actively dorsiflex the ankle)
equinus foot=a deformity where hindfoot is higher than the forefoot.
ankylosis=fusion of the joint due to pathological process
arthrodesis=fusion of the joint through surgical means