· thigh and lateral side of leg, to

 

·       
Usual
injury to sciatic nerve the most common part affected is common peroneal
component resulting in foot drop and high stepping gait

·       
The
nerve can be injured in total hip replacement (1% of cases )

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·       
Piriformis
syndrome – Due to the hypertrophy of the muscle piriformis, the sciatic nerve
is compressed, resulting in pain along the course of the sciatic nerve in the
gluteal region.

·       
Sciatica:
It is the shooting pain along the cutaneous distribution of the sciatic nerve –
pain is felt in the gluteal region or even higher, radiates along the back of
thigh and lateral side of leg, to the dorsum of foot.

·       
Compression
of sciatic nerve can occur after sitting for a long time called “sleeping foot”.

·       
The
posterior dislocation of hip joint causes injury to the sciatic nerve. When the
nerve is injured it results in excessive movement of foot and difficulty in
walking

      Applied Anatomy:

Common peroneal nerve.

Tibial nerve

·       
Terminal
branches –

The common peroneal part supplies only
the short head of the biceps femoris.

Tibial part supplies all the hamstring
muscles namely the semitendinosus, semimembranosus, long head of biceps femoris
and the ischial part of the adductor magnus.

·       
Muscular
branches

·       
Articular
branches to the hip joint.

 
Branches:

 

 

Fig. No 2

 

 

·It remnant of the axis artery of lower
limb.

·It is a branch from internal iliac artery.

·The artery to the sciatic nerve is Arteria nervi sciatica ischiadici.

            Arterial supply:

·       
It
is crossed by long head of biceps femoris.

·       
 It runs vertically downwards up to the
superior angle of the popliteal fossa at the junction of the upper 2/3 and the
lower 1/3 of the thigh where it terminates.

·       
It
lies on adductor magnus

·       
It
enters the back of thigh at the lower border of the gluteus maximus.

 
   In the thigh:

·       
The
posterior cutaneous nerve of thigh and
the inferior gluteal artery are medial to the nerve.

·       
The
structures in the gluteal region mentioned above form the sciatic bed

·       
Obturator
externus and the hip joint are separated by the quadratus femoris.

·       
Quadratus
femoris.

·       
It
then crosses posterior to tendon of obturator internus, the gamelli.

·       
Lies
on the posterior surface of ischium separated by the nerve to quadratus femoris.

·       
Upper
part of the nerve is deep to gluteus maximus.

·       
It
runs downwards passing between the ischial tuberosity and the greater
trochanter.

           In the gluteal region:

·       
It
emerges out of the pelvis via the greater sciatic
foramen below piriformis and passes down between the greater trochanter and
ischial tuberosity. Sometime it passes above or through piriformis

·       
It
lies in front of the piriformis covered by its fascia.

     
In the pelvis:

   Course and relation (Fig. No 2):

 

·       
Sometimes
the division may be above, in such a case, the tibial component passes below piriformis
and the fibular component through the piriformis

·       
It
terminates in the superior angle of popliteal fossa into tibial and common
peroneal nerves.

    
Termination:

 

 

Fig. No 1

 

      

 

Common peroneal component –  Formed by the dorsal divisions of anterior primary rami of L4, L5,
S1, S2.

Tibial component – Formed by the ventral divisions of
anterior primary rami of L4, L5, S1, S2,
S3.

·       
The
nerve is made up of 2 components: Tibial and common peroneal components (fig.no
1).

·       
Root value:
L4, L5, S1, S2, S3

·       
It
is the largest branch of the sacral plexus formed in the pelvis

     
Formation (root value):

            The sciatic nerve is the thickest nerve
in the body; 2cm wide;

1.     Describe the root value, course , relations branches and
distribution and applied anatomy of sciatic nerve