SCIATIC NERVE INJURY

• 4 yr old child develop foot drop after dpt vaccination. how do you recognize the degree of involvement?

• The sciatic nerve, a mixed nerve, the largest in the body, derives from the fourth and fifth lumbar and the first and second sacral spinal segments. It emerges from the sacral plexus and leaves the pelvis through the greater sciatic foramen below the piriformis muscle (infrapiriform foramen). The nerve then curves laterally and downward beneath the gluteus maximus muscle; in the posterior aspect of the thigh,
• It innervates the semitendinosus (L4 to S2), semimembranosus (L4 to S2), and biceps femoris (L4 to S2) muscles (i.e., the hamstring muscles, which are flexors of the knee joint) and the adductor magnus (L2 to L4) muscle, an adductor of the thigh (which is also supplied by the obturator nerve). The nerve proceeds downward in the thigh, and at the apex of the popliteal fossa, it divides into its two terminal branches, the tibial (medial popliteal) nerve (L4 to S3) and the common peroneal (lateral popliteal) nerve (L4 to S2).
• Tibial Nerve
  • it gives off branches to the following three muscles:
• • Tibialis posterior (L4 to L5), a plantar flexor and invertor of the foot. It is tested by having the patient invert the foot against resistance or walk on the toes. Inversion should be tested with the foot in complete plantar flexion, thereby eliminating the action of the tibialis anterior.
  • Flexor digitorum longus (L5 to S2), a plantar flexor of the foot and of all the toes except the large toe. It is tested by having the patient flex the toes against resistance.
  • Flexor hallucis longus (S1 to S2), a plantar flexor of the foot and that of the terminal phalanx of the great toe.
• common peroneal nerve
• • Tibialis anterior (L4 toL5), a dorsiflexor and invertor of the foot. It is tested by having the patient dorsiflex the foot against resistance or walk on the heels.
  • Extensor hallucis longus (L5 to Sl), an extensor of the great toe and dorsiflexor of the foot. It is tested by having the patient dorsiflex the distal phalanx of the big toe against resistance.
  • Extensor digitorum longus (L5 to Sl), an extensor of the four lateral toes and dorsiflexor of the foot. It is tested by having the patient dorsiflex the toes against resistance
  • Extensor digitorum brevis (L5 to “Sl), an extensor of the large toe and three medial toes. It is tested by having the patient dorsiflex the proximal phalanges of the toes against resistance
  • The superficial peroneal nerve supplies the peroneus longus and brevis muscles (L5 to S1), which are plantar flexors and evertors of the foot

In general, sciatic lesions tend to affect the peroneal division more than the tibial division in about 75% of cases

High sciatic lesions result in the following signs (high thigh lesions may selectively involve peroneal fibers):

• Deformity. A flail foot is present because of paralysis of the dorsiflexors and plantar flexors of the foot. When the leg is passively lifted, the foot is plantar flexed and inverted (foot drop), but it also dorsiflexes loosely when the foot is passively moved back and forth.
• Atrophy. There is wasting of the hamstrings and all the muscles below the knee.
• Motor signs. There is paresis or paralysis of knee flexion (hamstrings), foot eversion (peronei), foot inversion (tibialis anterior), foot dorsiflexion (tibialis anterior and anterior leg musculature), foot plantar flexion (gastrocnemius and soleus), toe dorsiflexion (extensors of the toes), and toe plantar flexion (plantar flexors of the toes).
• Reflex signs. There is a decrease or absence of the Achilles reflex (S1 to S2), which is subserved by the tibial nerve.

Sensory signs. There are sensory changes (paresthesias and sensory loss) on the outer aspect of the leg and the dorsum of the foot (common peroneal distribution) and on the sole and the inner aspect of the foot (tibial nerve). The skin of the medial leg as far as the medial malleolus is spared because it is innervated by the saphenous nerve (a branch of the femoral nerve).

 

tibial nerve

Lesions at the popliteal fossa. Lesions of the tibial nerve at this location result in paresis or paralysis of plantar flexion and inversion of the foot, plantar flexion of the toes, and movements of the intrinsic muscles of the foot. Sensory impairment is located on the sole and the lateral border of the foot

common peroneal nerve

With lesions at the fibular head, the deep branch of the nerve is affected more commonly than the whole nerve[312, 325], although the superficial branch alone may also be affected. With common peroneal neuropathies, weakness is usually more prominent in muscles supplied by the deep peroneal nerve than in muscles supplied by the superficial peroneal nerve, likely because of differing degrees of damage to individual fascicles within the common peroneal nerve [161, 312, 325]. When both branches (deep and superficial) are affected, there is paresis or paralysis of toe and foot dorsiflexion and of foot eversion

 

The anterior tibial (deep peroneal) nerve syndrome. This nerve may be injured in isolation at the fibular head or more distally in the leg. Nerve injury results in a motor deficit (paresis or paralysis of toe and foot dorsiflexion); sensory deficit is limited to the web of skin located between the first and second toes

 

The superficial peroneal nerve syndrome. The superficial peroneal nerve may be affected in isolation by lesions at the fibular head or by lesions more distally in the leg. Paresis and atrophy of the peronei (foot eversion) and a sensory disturbance affecting the skin of the lateral distal portion of the lower leg and dorsum of the foot are present. The web of skin between the first and second toes is spared (this is the area of supply of the deep peroneal nerve).