Piriformis sciatic nerve

The piriformis muscle is an important muscle located in the buttocks of the human body, and there is also an important nerve distribution around the piriformis muscle, which is the sciatic nerve. In a sense, the health of the piriformis muscle and the health of the sciatic nerve are directly linked. When there is a problem with the piriformis muscle, it will directly cause problems with the sciatic nerve. The following will explain in detail to readers the diseases related to the piriformis muscle and sciatic nerve.

Piriformis muscle related disorders

Piriformis syndrome: This syndrome is a group of symptoms characterized by sciatica, which is caused by mechanical compression of the sciatic nerve due to damage to the piriformis muscle, or adhesion of this section of the sciatic nerve for some reason. It manifests as pain in the affected buttocks accompanied by radiating pain in the lower limbs. Sometimes the pain is severe and unbearable, affecting rest and life. It may be aggravated by cold, fatigue, etc. During the examination, the patient was found to be in a forced position, with tenderness along the nerve path from the sciatic notch downwards, and a positive straight leg raising test; a mass could be palpated locally in the piriformis muscle, and the pain was relieved or disappeared after local closure; and piriformis tension tests (including Pace test, Thiele test, and Freiberg test) were positive. The treatment of this symptom is first conservative treatment, which can be adopted by bed rest, physical therapy, massage, acupressure and local steroid drug blockade. For those who are not responsive to conservative treatment or those with severe symptoms, surgical treatment such as piriformis muscle resection or sciatic nerve release can be adopted. The prognosis of this disease depends on whether the treatment is timely. If muscle atrophy occurs without timely treatment, the treatment effect is not ideal.

Overview

The piriformis muscle is distributed on the inner side of the pelvis, starting from the front of the 2nd to 4th sacral vertebrae, passing through the greater sciatic foramen, and ending at the top of the greater trochanter of the femur. It is innervated by the 1st and 2nd sacral nerves and its function is to control the external rotation of the thigh. This muscle is pear-shaped, with a slender tendon. Above it are the superior gluteal nerve and superior gluteal artery and vein; below it are the pudendal nerve, posterior femoral cutaneous nerve, sciatic nerve, inferior gluteal nerve, and inferior gluteal artery and vein. Various lesions of the piriformis muscle itself that compress the sciatic nerve are called piriformis syndrome.

1. Incidence: relatively common.

2. Gender: More common in women.

3. Age: middle-aged.

4. Prevalence site: Mostly on the right side.

clinical

Most cases have a history of hip sprain, and some female patients have a history of pelvic inflammatory disease. They feel that the affected limb has become shorter, they walk with a limp, and have deep swelling and pain in the buttocks radiating to the back of the thigh and the outside of the calf. Occasionally, numbness of the outer side of the calf and toes is seen. Male patients may experience discomfort in the perineum and cramping in the scrotum and testicles. Severely ill patients have severe pain, flexion of both lower limbs, inability to turn over, and inability to take care of themselves. Physical examination shows no tenderness in the waist, swelling in the piriformis area on palpation, spasmodic hypertrophy in the form of cords, local tenderness, loose surrounding tissues, pain within 60° of straight leg raising, and pain relieved when exceeding 60°. Patients with a long course of illness have gluteal muscle atrophy.

pathology

The pathological changes are inconsistent depending on the cause. Sudden excessive external rotation of the lower limbs when standing up from a squatting position or excessive abduction and external rotation of the lower limbs when carrying heavy objects can cause twisting and injury of the piriformis muscle, tendon tearing, and protective muscle spasm to compress the nerves and blood vessels, causing nerve swelling and prominent sciatica. When the piriformis muscle is mutated, the lower limbs are rotated, the muscle bundles contract, and the spaces between the muscle bundles become smaller, causing the nerve passing through the mutated piriformis muscle to be compressed and swollen. Pelvic inflammatory disease involving the piriformis muscle or chronic inflammation of the piriformis muscle can affect the nerves passing through the upper and lower holes of the piriformis muscle.

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1. X-ray manifestations: Conventional X-rays can show bone and joint abnormalities of the sacroiliac joint and greater sciatic foramen. The piriformis muscle and sciatic nerve cannot be displayed.

2. CT manifestations: In addition to detecting abnormalities in bones and joints, CT plain scan can directly observe the morphology of the piriformis muscles on both sides. When the piriformis muscle is acutely injured, it will show swelling and decreased density. If there is muscle bleeding, high-density bleeding foci can be seen. Tracing the course of the nerves, swelling of the injured nerves can be seen, which can show the extent of involvement of the piriformis muscle by pelvic lesions.

3. MRI manifestations: In addition to the morphological changes of the piriformis muscle found in CT scans, MRI can also show changes in the signal intensity of the damaged piriformis muscle. During contusion, the T1WI signal decreases and the T2WI signal intensity increases. Careful comparison of the sciatic nerves on both sides revealed that the nerve on the injured side was thickened and the T2WI signal intensity increased.

4. US manifestations: US is rarely used to examine this disease.