What is Piriformis Muscle?

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What is Piriformis Muscle?

The piriformis is the smaller muscle in the gluteus, located deep in the middle of the gluteal region, in the same plane as the gluteus medius. It originates from the front of the sacrum by three muscle teeth. The muscle teeth attach to the bony surface between the anterior sacral foramen and the groove extending from the anterior sacral foramen. It also arises from the gluteal surface of the ilium near the posterior inferior iliac spine and the adjacent sacroiliac joint capsule and sometimes the pelvic surface of the sacrotuberous ligament. Muscles exit the pelvis from the greater sciatic foramen and substantially fill the foramen, which is an important reference point for the structure above and below it. The piriformis muscle inserts on the medial side of the superior border of the greater trochanter by means of the round tendon. The tendons are located posteriorly and posteriorly in the obturator internus and common cress tendon and are often partially fused with them. The piriformis also fuses with the gluteus medius.

Piriformis Muscle and Sciatic Nerve

The piriformis muscle is one of the posterior groups of hip muscles. Behind the hip joint capsule originates from the anterior side of the sacrum, exits the greater sciatic foramen, and ends on the medial side of the greater trochanter. This muscle works with other muscles to externally rotate the thigh. Innervated by the muscular branches of the sacral plexus (sacral 1-3).

The sciatic nerve travels below the piriformis muscle when it passes through the sciatic foramen magnum. When the sciatic nerve is injured, it is easy to stimulate the surrounding piriformis muscle to produce inflammatory edema.

Piriformis Muscle Structure: superior gluteal nerve, superior gluteal artery, vein.

Body Surface Projection: The line connecting this point to the greater trochanter of the femur.

Piriformis Syndrome: Hip and leg pain caused by compression of the sciatic nerve.

Diagnostic Points: Patients often have lower extremity injuries or a history of chronic strain.

Anatomy

The piriformis muscle is located on the posterior wall of the lesser pelvis and is triangular in shape. It originates from the anterior side of the 2nd to 5th sacral vertebrae. The muscle fibers concentrate outward, exit the lesser pelvis through the greater sciatic foramen, and insert at the top of the greater trochanter of the femur. In near immobilization, this muscle contracts to abduct, externally rotate and extend the thigh. During distal fixation, one side is contracted to turn the pelvis to the same side; both sides are contracted to tilt the pelvis posteriorly. The piriformis muscle is innervated by the muscular branches of the sacral plexus (S1-S3).

Piriformis Trigger Point

Starting Point: sacrum-pelvic surface.
Insertion: Greater trochanter of femur.
Trigger Point Location: connect the line between the posterior superior iliac spine and the tip of the coccyx. On this line, 2cm away from the posterior superior iliac spine, make a line connecting the greater trochanter of the femur. Score this line in 3 copies, and the junction of the inner and middle 1/3 is the trigger point.
Referred Pain: ① sacroiliac joint; ② buttocks; ③ posterior 1/3 of the thigh.

Piriformis Syndrome

Intrinsic is a group of syndromes mainly caused by sciatica caused by mechanical compression of the sciatic nerve due to piriformis muscle damage, or adhesion of this segment of the sciatic nerve for some reason. Manifested as hip pain on the affected side accompanied by radiating pain in the lower extremity, sometimes the pain is severe and unbearable, affecting rest and life. It can be aggravated by cold and fatigue. During the examination, it was found that the patient was in a forced position, from the sciatic notch downward, there was tenderness along the path of the nerve, and the straight leg raising test was positive; the piriformis muscle was partially palpable, and the pain was relieved or disappeared after partial closure; the piriformis muscle Stress tests (including Pace test, Thiele test, and Freiberg test) were positive. For the treatment of intrinsic symptoms, conservative therapy can be used first, and measures such as bed rest, physiotherapy, massage, massage, and local steroid blockade can be used; for patients with ineffective conservative treatment and severe symptoms, piriformotomy or sciatic nerve release can be used Surgery and other surgical treatments. Intrinsic prognosis depends on whether the treatment is timely. If muscle atrophy occurs without timely treatment, the treatment effect is not ideal.

Piriformis Syndrome

The piriformis muscle distributes on the inner side of the lesser pelvis, originates from the front of the second to fourth sacral vertebrae, passes through the sciatic foramen, and inserts at the top of the greater trochanter of the femur. It is innervated by the 1st and 2nd sacral nerves and functions to control the external rotation of the thigh. The muscle is shaped like a pear, with long and slender tendons. Above it are the superior gluteal nerve and superior gluteal artery and vein; below it is the pudendal nerve, posterior femoral cutaneous nerve, sciatic nerve, inferior gluteal nerve, and inferior gluteal artery and vein. Various lesions of the piriformis itself compress the sciatic nerve, which is called piriformis syndrome.

Incidence: more common.
Gender: more common in women.
Age: middle age.
Predisposing site: more common on the right side.

Clinical Examination

Most of the cases had a history of hip sprain, and a few female patients had a history of pelvic inflammatory disease. The affected limbs became shorter, limping when walking, and pain in the deep hip, radiating to the back of the thigh and the outer side of the calf. Male patients may have perineal discomfort and scrotal testicular pain. Severely ill patients have severe pain, flexion of both lower limbs, unable to turn over, unable to take care of themselves, physical examination of the waist without tenderness, palpation of piriformis area swelling, spasm, and hypertrophy in the form of cords, local tenderness, loose peripheral tissues, straight leg elevation 60. The pain is painful within and the pain is relieved when it exceeds 60 ° and the gluteal muscle atrophy in the elderly.

Pathology

Pathological changes are inconsistent according to different etiologies.

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 may cause twisting of the piriformis muscle, tearing of the tendon, and protective spasm of the muscles compressing the nerves and blood vessels, causing swelling of the nerves, and prominent sciatica.

When the piriformis muscle is deformed, the lower limbs are rotated, the muscle bundles are contracted, and the gap between the muscle bundles becomes smaller so that the nerve passing through the variant piriformis muscle is compressed and swelled. Pelvic inflammatory disease involving the piriformis muscle or chronic inflammation of the piriformis muscle can affect the passage of the nerve through the upper and lower foramen of the piriformis muscle.

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