Piriformis Syndrome

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Original Editors - Marlies Verbruggen

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Definition/Description

Piriformis syndrome (PS) is a painful musculoskeletal condition, characterized by a constellation of symptoms that include buttock or hip pain. [4,7,9] In several articles, piriformis syndrome is defined as a peripheral neuritis of the branches of the sciatic nerve caused by an abnormal condition of the piriformis muscle (PM), such as an injured or irritated muscle.[1,9] There are more women diagnosed with Piriformis syndrome than men, the female–to–male ratio is 6:1. This ratio can be explained by the wider quadriceps femoris muscle angle in the os coxae of women. [2,3,9] There are two types of piriformis syndrome. The first type is called “Primary piriformis syndrome” : it is caused by an anatomic variation, like a split piriformis muscle, a split sciatic nerve or an anomalous sciatic nerve path. The second type is called “Secondary piriformis syndrome” : it is the result of a precipitating cause, such as a macrotrauma, microtraumata, ischemic mass effect and local ischemia.[3,9]

Clinically Relevant Anatomy

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Epidemiology /Etiology

PS is often caused by shortening or spasm of the piriformis muscle, this can result in compression or irritation of the sciatic nerve.[1,3,6] The spasm of the PM is mostly caused by direct trauma, post surgical injury, lumbar and sacroiliac joint pathologies and overuse.[1,2,3,6,7,9] In 50 % of the cases, PS is caused by a (macro)trauma to the buttock(s). Therefore we can consider trauma to the buttock(s) as the main cause of PS.[3,7] This direct trauma can cause inflammation of soft tissue or muscle spasm or both, which can result in nerve compression. [9] When there is a dysfunction of the piriformis muscle, it can cause signs and symptoms of pain in the sciatic nerve distribution, such as the gluteal area, posterior thigh, posterior leg and lateral aspect of the foot. [2] When there is an overuse of the piriformis muscle, like in long- distance walking or running or by direct compression, it can lead to microtrauma. “Wallet neuritis” is an example of direct compression : it’s a repetitive trauma from sitting on hard surfaces. [9]

Other causative factors are anatomic variations of the divisions of the sciatic nerve, anatomic variations or hypertrophy of piriformis muscle, repetitive trauma, sacro-iliac arthritis and total hip replacement.[2,3,6,7]A Morton foot can predispose the patient to developing piriformis syndrome. A fraction of the population is at high risk, particularly skiers, truck drivers, tennis players and long-distance bikers. [2]

Tonley JC [1] had another view about the cause of PS. He said:” The piriformis muscle may be functioning in an elongated position or subjected to high eccentric loads during functional activities secondary to weak agonist muscles. For example, if the hip excessively adducts and internally rotates during weight-bearing tasks, due to weakness of the gluteal maximus and / or the gluteus medius, a greater eccentric load may be shifted to the piriformis muscle. Perpetual loading of the piriformis muscle through overlengthening and eccentric demand may result in sciatic nerve compression or irritation”. [1]

Characteristics/Clinical Presentation

Patients with piriformis syndrome have many symptoms that typically consist of (chronic) buttock pain, difficulty with walking and other functional activities, pain with sitting, pain with bowel movements and dyspareunia in women. [1,2,4,6,9]. The buttock pain can radiate into the hip, the posterior aspect of the thigh and the proximal portion of the lower leg. [1] The pain in the buttock can also copy the low back pain. [2] There is an aggravation of pain with activity, prolonged sitting or walking, squatting, hip adduction and internal rotation and maneuvers that increase the tension of the piriformis muscle. [1,2,4,6] It is possible that the patient walks with a limp and that he is holding his leg in a shortened and externally rotated position while supine. [4] Piriformis syndrome is not characterized by neurological deficits typical for a radicular syndrome, such as declined deep tendon reflexes and myotomal weakness. Sometimes, when the patient is lying on his back, his ipsilateral foot is externally rotated. This can be a positive piriformis sign, also called a splayfoot. It can be the result of a contracted piriformis muscle. [3,9]

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