Do you know that at least 6% of individuals diagnosed with low back pain have piriformis syndrome?^1,2

What is piriformis syndrome?

According to the National Institute of Neurological Disorders and Stroke piriformis syndrome is a rare neuromuscular disorder. It affects the piriformis muscle and sciatic nerve.³ Piriformis syndrome occurs when the piriformis muscle compresses the sciatic nerve. The pressure causes shooting, burning or aching pain and numbing and tingling sensation in the buttocks or along the back of the legs.⁴ Piriformis syndrome mostly happens during midlife and affects individuals from all walks of life and physical activity levels.^5-9 This disorder is increasingly common in women assigned females at birth than in men assigned males at birth with six women affected for every one man.¹⁰

It is hard to truly know how frequently this disorder occurs because the symptoms are usually identical to those of other medical conditions such as sciatica, primary sacral dysfunction (Problems or misalignment of the sacrum that affect its movement and function) or sacroiliac joint dysfunction (dysfunction of where the sacrum connects to the pelvis). These conditions all cause pain in the lower back and legs but originate from different areas.¹¹

Let’s briefly consider the anatomy of the piriformis muscle and the sciatic nerve and how they are related.

Anatomy of the piriformis muscle and sciatic nerve 

Piriformis muscle

The piriformis is a small, flat pear-shaped muscle found deep in the buttocks (gluteal). The piriformis muscle begins at the front surface of the sacrum and attaches to the top middle part of the thigh bone(femur). The piriformis muscle helps to rotate your hips and to slightly lift or bend your leg thus helping you maintain your posture during walking and standing.⁴

Sciatic nerve

The sciatic nerve is the longest and largest nerve in the body. It begins from outside the lower spine and passes through the pelvis, then into your buttocks and finally to the rear part of each leg.

The sciatic nerve divides into

• The common fibular 
• The tibial nerve

The sciatic nerve is a mixed nerve i.e. motor (movement) and sensory (sensation). This means that the motor neurons carry signals from the central nervous system to the muscles at the back of the thigh, leg and foot and to the muscles at the front and side of the leg and foot. These muscles enable you to bring your legs towards the centre of your body, bend your knee and toes, raise your foot upwards and backwards towards the shin and turn your foot away from the midline of your body. The sciatic nerve also provides sensation (sensory) to the skin of the foot, lateral lower leg and sole and some parts of the toes.¹²

Causes of Piriformis syndrome

The cause of piriformis syndrome depends on the type. There are two types – primary and secondary piriformis syndrome.¹¹

Primary piriformis syndrome: This type is caused by a variation in the morphology (i.e. the form and structure)  and path of the piriformis muscle and sciatic nerve respectively. This variation can make the sciatic nerve more susceptible to compression. However, studies on this connection have shown mixed results, as the incidence of these structural malformations in individuals with piriformis syndrome is similar to that in people without the condition. Regardless, understanding these variations is important for surgical treatment, as certain structural issues could hinder successful decompression of the sciatic nerve if not addressed.^5,13,18

 Based on Beaton and Anson's classification system there are six structural variations of the piriformis muscle and the sciatic nerve.^7,14 They are:

• Type A- The sciatic nerve passes underneath the piriformis muscle (most prevalent)
• Type B- The divisions of the sciatic nerve pass between and below the piriformis muscle
• Type C- The divisions of the sciatic nerve pass above and beneath the piriformis muscle
• Type D- The sciatic nerve passes completely between the piriformis muscle
• Type E- Divided sciatic nerve pierce through and above the piriformis
• Type F- The sciatic nerve passes completely above the piriformis muscle

The primary cause is responsible for less than 15% of piriformis syndrome among patients.

Secondary piriformis syndrome: This type is caused by external factors or events that lead to muscle or nerve irritation, such as: ^8,11,15-18

• Minor trauma (injury) to the buttocks or hip area such as overuse of the piriformis muscle due to walking long distances, running or repetitively sitting on hard surfaces for a long time
• Major trauma to the buttocks or hip area such as from a fall resulting in fracture dislocation and blunt blow  
• Poor blood supply to the surrounding tissues or the piriformis muscle and sciatic nerve
• Tumour  invasion
• Poor posture and body positioning

Piriformis syndrome is commonly caused by a major trauma to the buttocks, resulting in either inflammation or spasm of the muscle or both hence causing nerve compression.^1,8

Finally, other conditions, such as myositis ossificans, pyomyositis, patent sciatic vessels, abnormal fibrous bands, and pseudoaneurysm, have been linked to piriformis syndrome.¹⁸

Symptoms of piriformis syndrome

Patients with piriformis syndrome present with the following symptoms: ^5,8,11,15,17

• Increased pain after sitting, standing or lying  longer than 15- 20 minutes
• Pain  when standing from sitting or squatting position
• Pain that gets better with walking and gets worse with no movement
• Pain and or  sensation of burning, prickling  tingling or itching spread from the lower back to the buttocks down to the back of the thigh till above the knee
• The feeling of numbness in the foot
• Difficulty walking
• Pain associated with bowel movement
• Pain in the abdomen, pelvis and groin
• Experience pain during sex in women
• Pain on the opposite side of the sacroiliac joint 
• Pain on the same side of the hip, thigh, knee, leg, ankle and foot.
• Persistence of pain after changing position 
• Headache
• Neck Pain

FAQs

How can I tell if my condition is piriformis syndrome?

There is a likelihood of experiencing symptoms such as pain in the hips, buttocks, thigh and opposite side of the sacroiliac joint. In addition, you experience pain after walking, standing or sitting for more than 20 minutes, or severe pain while sitting or squatting. Your general practitioner will perform a physical exam to test for piriformis syndrome. If the GP suspects piriformis syndrome, they may refer you to specialists such as an orthopedic doctor, neurologist, or physical therapist for further diagnosis or advanced treatment

Can a fall cause piriformis syndrome?

It is very possible to have piriformis syndrome after a fall, especially when it happens as a result of a forceful event such as a car accident.

Can stress cause piriformis syndrome?

Yes! Excessive stress or weight on the muscle can cause spasms which could irritate the nerve.

Summary

Piriformis syndrome is a relatively rare neuromuscular disorder that affects the piriformis muscle and the sciatic nerve. There are primary and secondary causes of piriformis syndrome. This disorder is usually characterised by pain and tingling, burning, prickling, or itching sensation in the affected body parts.