THE SCIATIC NERVE BY DR VINEETA WALDIA ASSISTANT

THE SCIATIC NERVE BY DR. VINEETA WALDIA ASSISTANT PROFESSOR DEPARTMENT OF SHARIR RACHNA H. A. M. C. H. , DEHRADUN, UK. CONTACT NO. 8006969188

INTRODUCTION The sciatic nerve is a major nerve of the lower limb. It is a thick flat band, approximately 2 cm wide. It is the largest nerve in the body and a branch of lumbo-sacral plexus.

OVERVIEW ROOT VALUE: - VENTRAL RAMI OF L 4, L 5, S 1, S 2, S 3. MOTOR FUNCTIONS: � Innervates the muscles of the posterior thigh (biceps femoris, semimembranosus and semitendinosus) and the hamstring portion of the adductor magnus (remaining portion of which is supplied by the obturator nerve). � Indirectly innervates (via its terminal branches) all the muscles of the leg and foot.

SENSORY FUNCTIONS: No direct sensory functions. Indirectly innervates (via its terminal branches) the skin of the lateral leg, heel, and both the dorsal and plantar surfaces of the foot.

ANATOMICAL COURSE The sciatic nerve is derived from the lumbosacral plexus. After its formation, it leaves the pelvis and enters the gluteal region via greater sciatic foramen. It emerges inferiorly to the piriformis muscle and descends in an inferolateral direction. As the nerve moves through the gluteal region, it crosses the posterior surface of the superior gemellus, obturator internus, inferior gemellus and quadratus femoris muscles. It then enters the posterior thigh by passing deep to the long head of the biceps femoris.

Within the posterior thigh, the nerve gives rise to branches to the hamstring muscles When the sciatic nerve reaches the apex of the popliteal fossa, it terminates by bifurcating into 1. 2. THE TIBIAL PART COMMON FIBULAR PART

THE TWO COMPONENTS OF THE SCIATIC NERVE THE TIBIAL PART- Its root value ventral division of ventral rami of L 4, L 5, S 1, S 2, S 3. THE COMMON FIBULAR OR COMMON PERONEAL PART- Its root value is dorsal division of ventral rami of L 4, L 5, S 1, S 2.

MOTOR INNERVATION Although the sciatic nerve passes through the gluteal region, it does not innervate any muscles there. However, the sciatic nerve does directly innervate the muscles in the posterior compartment of the thigh, and the hamstring portion of the adductor magnus. The sciatic nerve also indirectly innervates several other muscles, via its two terminal branches.

Tibial nerve – the muscles of the posterior leg (calf muscles), and some of the intrinsic muscles of the foot. Common fibular nerve – the muscles of the anterior leg, lateral leg, and the remaining intrinsic foot muscles. In total, the sciatic nerve innervates the muscles of the posterior thigh, entire leg and entire foot.

SENSORY INNERVATION The sciatic nerve does not have any direct cutaneous functions. It does provide indirect sensory innervation via its terminal branches: Tibial nerve – supplies the skin of the posterolateral leg, lateral foot and the sole of the foot. Common fibular nerve – supplies the skin of the lateral leg and the dorsum of the foot.

CLINICAL RELEVANCE: INTRAMUSCULAR INJECTIONS The anatomical course of the sciatic nerve must be considered when administering intramuscular injections into the gluteal region. The region can be divided into quadrants using 2 lines, marked by bony landmarks: One line descends vertically from the highest point on the iliac crest. The other horizontal line passes through the vertical line half way between the highest point on the iliac crest and ischial tuberosity. The sciatic nerve passes through the lower medial quadrant. To avoid damaging the sciatic nerve therefore, intramuscular injections are given only in the upper lateral quadrant of the gluteal region.

CLINICAL ANATOMY SLEEPING FOOT: - Sciatic nerve lies on quadratus femoris and adductor magnus, Between the two muscles the nerve lies on femur. When the nerve gets pressed between the femur and hard edge of any sitting surface there is numbness in the lower limb. INJURY: - Injury to the sciatic nerve leads to paralysis of hamstrings and all muscles of leg and foot leading to foot drop.

SCIATICA: - Is the name given when there is radiating pain in the back of the lower limb. It may be due to slip disc. PIRIFORMIS SYNDROME refers to compression of the sciatic nerve by the piriformis muscle. It is also known as deep gluteal syndrome. Clinical features include pain, numbness, muscle weakness and buttock tenderness.

SCIATICA

PIRIFORMIS SYNDROME