Peak age group = 35 -45 years
Most common location L4-L5 & L5- S1 [ NOTE : L4 -L5 > L5-S1 ]
Disc herniation can be central / paracentral and lateral. Most disc herniation that cause unilateral radicular symptoms are paracentral herniations [ ref : CODT page 231/ 3ed]
Lumber disc herniation can produce symptoms by compression of exiting nerve root or traversing nerve root at that disc level.( now have a look at the figure given below to understand what are these )
so we can say that : at L3- L4 disc, L3 root will be exiting nerve and L4 root wiil be traversing nerve root….similarly at L4-L5 disc, L4 root will be exiting and L5 root will be traversing root and so on..
LETS MOVE ON :
Now we need to understand that lateral disc herniation will affect exiting nerve root at that level. In the figure given below L4 nerve root is compressed by lateral herniation of L4-L5 DISC.
NOW LETS UNDERSTAND EFFECT OF MORE COMMNER VARIETY ie PARACENTRAL/CENTRAL DISC HERNIATION ( SEE THE FIGURE BELOW)
So its now clear that until the q mentions any specific type of herniation we assume it as paracentral ans so we can draw inference for q solving purpose that:
L3-L4 DISC HERNIATION = L4 ROOT WILL BE AFFECTED
L4-L5 DISC HERNIATION = L5 ROOT WILL BE AFFECTED
L5-S1 DISC HERNIATION = S1 ROOT WILL BE AFFECTED
But always keep in mind that q may be twisted by asking lateral disc herniation and in such condition root affected will be one level up!!!!!!!!
NOW WE SHOULD LEARN THE EFFECTS OF L5 ROOT COMPRESSION BY L4-L5 DISC HERNIATION ( SEE THE FIGURE BELOW)
Q] After lifting something heavy from ground a patient complains of back pain which is radiating to lateral leg and great toe of lower limb. most probable diagonosis is …[AIIMS MAY 2012]
A]L5-S1 DISC PROLAPSE
B]L4-L5 DISC PROLAPSE
C]L3-L4 DISC PROLAPSE
ANS= [B] L4- L5 PROLAPSE : Will cause L5 radiculopathy so back pain ( occuring at level of prolapse) will radiate to distribution of L5 root ie lateral side of leg and dorsum of foot. Furthur it will lead to sensory loss at these sites and weakness of extensor hallucis longus and other dorsiflexors. EHL is exclusively supplied by L5 root.
NOW LETS DROP DOWN OURSELVES ONE LEVEL DOWN AND SEE THE EFFECTS OF S1 NERVE ROOT COMPRESSION by L5-S1 DISC PROLAPSE(see the figure below)
Now we can summarise the effect of disc herniations at various levels ( assuming it to be of most common type ie paracentral)
1. L3-L4 DISC HERNIATION = L4 ROOT COMPRESSION = SENSORY LOSS over great toe and medial side of leg, MOTOR LOSS consisting of weakness of knee extensors , KNEE JERK becomes sluggish or absent.
2. L4-L5 DISC HERNIATION = L5 ROOT COMPRESSION = SENSORY LOSS over lateral side of leg and dorsum of foot , MOTOR LOSS consisting of weakness of EHL and foot dorsiflexors, ANKLE JERK is normal.
3. L5-S1 DISC HERNIATION = S1 ROOT COMPRESSION = SENSORY LOSS over lateral side of foot , MOTOR LOSS consisting of weakness of planter flexors , ANKLE JERK is sluggish or absent.
NOTE POINTS :
1. Straight leg raising test is performed when disc herniation is suspected . Pain on elevating affected leg ( lesegue sign +ve) is positive in more then 90% patients. Pain on opposite leg is elevated ( cross lesegue + ve ) is present in about 20 % patients.
2. MRI is study of choice for diagonosis of a herniated disc.
3. only < 10 % patients require surgial management which consists of Discectomy , Microdiscectomy, Chemonucleolysis .
SAMPLE Q : A patient presents with sensory loss over lateral leg and dorsum of foot along with weakness of extensor hallucis longus and normal ankle jerk then diagonosis among following is/are….
A] LATERAL DISC PROLAPSE L4-L5
B] PARACENTRAL DISC PROLAPSE L4- L5
C] LATERAL DISC PROLAPSE L5-S1
D] PARACENTRAL DISC PROLAPSE L5-S1
ANS = going with symptoms , L5 root is affected so it can be due to both [B] and [C].