Sciatic nerve (L4–S3)
Nerves · L4 L5 S1 S2 S3
Thickest nerve in the body: the tibial (anterior division) and common fibular (posterior division) components travel in one sheath. Leaves the pelvis below piriformis, passes midway between the ischial tuberosity and greater trochanter, descends deep to gluteus maximus and the long head of biceps, and usually divides at the apex of the popliteal fossa (may divide anywhere from the pelvis down).
Traced from the start
Detail
- Motor (tibial part)
- Semitendinosus, semimembranosus, long head of biceps femoris, ischial part of adductor magnus
- Motor (common fibular part)
- Short head of biceps femoris
- Sensory
- No thigh skin of its own; through its branches all of the leg and foot below the knee except the medial strip (saphenous)
- Surface marking
- Midpoint between ischial tuberosity and greater trochanter; injections go in the upper outer quadrant to avoid it
When it goes wrong
Posterior hip dislocation, acetabular fracture, hip arthroplasty, or a buttock injection placed too medial or inferior
Weak knee flexion, paralysis of everything below the knee (flail foot), absent ankle jerk, anaesthesia of the leg and foot except the medial side; the common fibular part is injured most often because it is lateral and tethered at the fibular neck
Piriformis syndrome: the nerve compressed by or passing through a tight piriformis
Buttock pain with sciatica-like radiation, worse sitting and with hip internal rotation, without disc disease or back pain
Practise this structure
2 questions in the bank tagged Peripheral Nerve Injury.
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