What is the Piriformis Muscle?

The piriformis is a smaller muscle in the gluteal muscle, located in the middle of the gluteal region, deeper, and in the same plane as the gluteal muscle. Three muscle teeth are raised in front of the sacrum, and the teeth are attached to the bone surface between the anterior iliac foramen and the groove extending from the anterior iliac foramen. The joint capsule, sometimes also from the pelvic surface of the sacrotuberous ligament. The muscle penetrates the pelvis from the large ischial hole and fills the hole, which becomes an important reference point for the structure above and below it. The piriformis stops at the medial edge of the upper trochanter by a round tendon. The tendon is located behind and behind the obturator and common diaphragm tendons, and often merges in part. The piriformis can also be fused with the gluteal muscle. The sciatic nerve travels under the piriformis when passing through the sciatic foramen. When the sciatic nerve is damaged, it is easy to stimulate the surrounding piriformis to produce inflammatory edema.

The piriformis is one of the posterior hip muscles. Behind the hip joint capsule, it starts from the front side of the sacrum, exits the ischia, and ends on the medial side of the greater trochanter. This muscle works in conjunction with other muscles to externally rotate the thigh. It is dominated by the muscular branches ( 1 ~ 3) of the iliac plexus.

Chinese name: Piriformis
Foreign name: piriformis
Overview: From the front of the 2nd, 3rd and 4th vertebrae

Piriformis: Superior gluteal nerve, superior gluteal artery, vein
Body surface projection: The connection from this point to the greater trochanter of the femur
Piriformis syndrome: Hip and leg pain caused by compression of the sciatic nerve
Key points for diagnosis: Patients often have lower limb injuries or a history of chronic strain

Anatomy of the piriformis

The piriformis muscle is located in the posterior wall of the small pelvis and is triangular in shape. It starts from the anterior side of the 2nd to 5th vertebrae. When nearly fixed, this muscle contracts, allowing the thighs to abduct, rotate outward, and extend. When distantly fixed, one side shrinks, causing the pelvis to turn to the same side; the two sides shrink, causing the pelvis to tilt backwards. The piriformis is dominated by the muscular branches (S1 to S3) of the diaphragm.

Piriformis trigger point

1. Starting point: pelvic surface.

2. Stop: the greater trochanter of the femur.

3. Trigger point position: the posterior superior iliac spine and the tip of the coccyx are connected at this line 2 cm away from the posterior superior iliac spine, and then connected to the greater trochanter of the femur. Rate this line 3 points, with the trigger point at the junction of the inner and middle 1/3.

4. Involved pain: sacroiliac joint; hip; posterior thigh

Piriformis and piriformis-related diseases

Piriformis syndrome: It is a group of symptoms mainly due to sciatica due to piriformis injury, resulting in mechanical compression of the sciatic nerve, or due to adhesion of the sciatic nerve for some reason. It manifests as pain in the affected hip with radiation pain in the lower limbs. Sometimes the pain is severe and unbearable, which affects rest and life. May be aggravated by cold and fatigue. During the examination, the patient was found to be in a forced posture, with a downward sciatic notch, tenderness along the nerve path, and a straight leg elevation test was positive; the piriformis muscles could be partially palpated, and the pain was reduced or disappeared after local closure; piriformis muscles Stress tests (including Pace test, Thiele test, and Freiberg test) were positive. For the intrinsic treatment, the first conservative treatment can be adopted, such as bed rest, physical therapy, massage, massage, and local steroid blocking. For patients who fail to respond to conservative treatment and those with severe symptoms, piriformomy or sciatic nerve release can be used. Surgery and other surgical treatment. The intrinsic prognosis depends on whether the treatment is timely, and the treatment effect is unsatisfactory if muscle atrophy occurs after untimely treatment.

Overview of the piriformis

The piriformis is distributed on the inner side of the small pelvis, starting from the front of the 2nd to 4th sacral vertebrae, passing through the foramen foramen and ending at the top of the greater trochanter. It is innervated by the first and second phrenic nerves, and its function is to control external rotation of the thigh. The shape of this muscle is like a pear. The tendon is slender, and the superior gluteal nerve and superior gluteal artery and vein are located above it; Piriformis itself is called piriformis syndrome by various lesions compressing the sciatic nerve.

1. Incidence: More common.

2. Gender: Women are more common.

3. Age: Middle-aged.

4. Frequent sites: more common on the right.

Piriformis clinical

Most cases had a history of hip sprains, and some female patients had a history of pelvic inflammatory disease. They consciously shortened the affected limbs, walked lamely, and swollen the buttocks. They radiated to the back of the thigh and the outside of the calf, and occasionally numbness of the outer leg and toe numbness. Male patients may have perineal discomfort and scrotal testicle pain. Severely ill patients have severe pain, flexion of both lower limbs, can not turn over, life can not take care of themselves, physical examination of the waist without tenderness, palpation of piriformis area swelling, spasm hypertrophy shows a cord-like shape, local tenderness, weekly tissue relaxation, straight leg elevation 60 There is internal pain. When it exceeds 60 °, the pain is reduced, and the gluteal muscles of the elderly are atrophic.

Piriformis pathology

Pathological changes are inconsistent according to the cause.

Sudden excessive external rotation of the lower extremity when standing in the squatting position or excessive abduction of the lower extremity when carrying heavy objects, distorts and damages the piriformis muscles, tendons torn, and muscle protective spasms compress the nerve blood vessels, causing the nerves to swell and the sciatica to stand out.

When the piriformis is mutated, the lower extremity is rotated, the muscle bundle is contracted, and the muscle bundle space is reduced, which makes the nerve passing through the mutant piriformis muscle swell. Pelvic inflammation involving the piriformis or chronic inflammation of the piriformis can affect the passage of nerves in the upper and lower foramen of the piriformis.

Piriformis image

1. X-ray manifestations: conventional X-ray films can show abnormal bones and joints of sacroiliac joints and foramen. Can not show piriformis and sciatic nerve.

2.CT manifestations: Except for abnormalities in bone and joints, plain CT scans can directly observe the morphology of piriformis muscles on both sides. Piriformis muscles show swelling and reduced density during acute injury. If muscle bleeding shows high-density hemorrhage, look for nerves. The nerve swelling of the injured can be seen during walking, and it can show the extent of pelvic lesions affecting the piriformis.

3. MRI manifestations: Except for the morphological changes of the piriformis on CT scan, the signal intensity of the damaged piriformis can be seen. The T1WI signal decreases and the T2WI signal intensity increases during contusion. By carefully controlling the sciatic nerve on both sides, it can be seen that the injured side nerve is thickened and the T2WI signal intensity is increased.

4.US performance: US is rarely used in the examination of this disease.