Tuesday, September 11, 2018

Anatomy of the Posterior Cutaneous Nerve of the Thigh

The posterior cutaneous nerve of the thigh (small sciatic nerve) arises from the sacral plexus from S1-S3. The posterior cutaneous nerve of the thigh exits from the pelvis through the greater sciatic notch below the piriformis muscle. The nerve descends below the gluteus maximus muscle along with the inferior gluteal artery. It runs into the back of the thigh beneath the fascia lata and over the long head of the biceps femoris muscle to the back of the knee. The nerve then pierces the deep fascia and accompanies the short saphenous vein to the middle of the back of the leg. The posterior cutaneous nerve of the thigh innervates the distal part of the gluteal region, the skin of the perineum and the posterior part of the thigh.
The nerve can become compressed when passing through the tunnel below the piriformis muscle and under the gluteus maximus muscle. This may result in sensitivity disturbances of the innervation area of the nerve. Causes of the syndrome may be hypertrophy or abnormality of the piriformis muscle such as entrapment below the piriformis which compresses the nerve. Compression of the nerve can also occur due to prolonged sitting. During the clinical examination, pain and sensitivity will be evident. Pain and sensitivity disturbances are characteristic of the nerve distribution site in the posterior part of the thigh down the knee. This disturbance can be from hyperesthesia to hypoesthesia or burning sensation similar to meralgia paresthetica of the lateral cutaneous nerve of the thigh.

Differential diagnosis include piriformis syndrome. The patient should avoid sitting for long periods of time, especially on a hard base. Treatment consists of physical therapy, massage, and injection. Surgery is rarely needed.