Introduction

There are reports of lower back pain affecting up to 84% of adults worldwide.¹ It is a common, but debilitating condition that can be difficult to find the root of. Psoas syndrome is one of the rarer causes of back pain.

The psoae are twin muscles that connect the lower spine to the thigh bones and play a huge part in hip movement and posture. Psoas syndrome is a condition in which an individual injures one or both of their psoae and consequently experiences back hip, or groin pain. It tends to affect athletes who use their hips in their sport, arthritis sufferers, and those who have undergone hip replacements. The back pain experienced due to psoas syndrome may travel up or down the spine. It can occur when changing positions (like sitting) or when stationary (like standing up straight).

Due to its rare nature, the condition is not widely known. This article aims to help you get all the information and guidance you need to understand why you might develop Psoas syndrome, how you can prevent it, and what to do if you’ve been diagnosed with it.

The psoas muscles (the psoae)

The two psoas (pronounced so-ezz) muscles are in the lower back and hips, one on each side of the spine. These muscles connect the upper body to the lower body. Each psoas muscle consists of the psoas major and the psoas minor. The psoas major is the bigger muscle and is the focus of this article. The psoas minor muscles are supplementary muscles that reside along the front of the psoas majors, and are only present in about half of the population.

The psoas muscle attaches to the spine in the lower back, close to the skin surface, and stretches down deep inside the body. The muscle reaches through the pelvis to the hip joints, where it connects to the iliacus muscle. The other end of the iliacus muscle is attached to the top of the pelvis. Together, the psoas muscle and the iliacus muscle form the iliopsoas muscle -  which is why you may hear iliopsoas syndrome used interchangeably with psoas syndrome.

The function of the iliopsoas muscles is to stabilise the lumbar spine in the sitting position and to flex the thigh in the standing position. It is also responsible for flexing the hip, rotating the hip outwards, and moving the thigh away from the body.²

Causes of psoas syndrome

Psoas syndrome is an injury caused by overuse of or trauma to, the psoas muscles. For example, the psoas muscle tendons can become inflamed due to pressure or repetitive rubbing. Psoas syndrome is a form of tendinitis and is thus caused by irritation in the tendons - the tissues which help muscles move the bone.²

Psoas syndrome/injury is seen in athletes who utilise their hips, like dancers, runners, high jumpers, and others who frequently perform kicking motions. It is more common in adolescents experiencing a growth spurt and in individuals assigned female at birth (AFAB). In a study performed on dancers, it was found that dancers under the age of 18 were 1.8 times more likely to suffer from Psoas syndrome than those over 18, and dancers who were assigned AFAB were 2.9 times more likely to suffer from Psoas syndrome than those assigned male at birth (AMAB).³

Additionally, it is more likely to affect those suffering from inflammatory or degenerative arthritis in the hips.

Psoas syndrome can occur postoperatively in those with a hip replacement. However, the frequency of Psoas syndrome in these patients is unclear. One study shows that 4.3% of hip replacement recipients experienced psoas syndrome; this figure was 24% in another study.^4,5

Another potential cause of psoas syndrome is an oversized acetabulum (hip joint). This is where the femur is connected.

Symptoms of psoas syndrome

Back pain

Back pain is complex and difficult to diagnose. The vertebrae in the spine are linked by joint capsules, ligaments, tendons, and muscles, as well as intervertebral discs between them. With so many moving parts, there is a lot of room for a variety of injuries.

Some potential causes of back pain are:¹

• Nerve damage
• Muscle strain
• Bone fracture
• Joint weakness
• Slipped disc
• Bad posture
• Psychological conditions, like stress and depression
• Substance use

Inflammation in the psoas muscles can cause lower back pain. This pain may travel up or down the spine, and is particularly common between the bottom of the spine and the glutes. It may also feel stiff. This pain can occur when changing positions, like going from sitting to standing. It can also be present when standing upright.⁶

Other symptoms

Psoas syndrome causes pain in the back, the hips, and the groin.

The psoas major is the primary muscle involved in tucking the knee(s) close to the chest. It attaches to a nodule on the top of the thigh bone. Individuals with psoas syndrome may feel tenderness in this area when it is pressed on (or otherwise subjected to pressure). They may also experience a decreased range of motion when extending the leg, and clicking of the hips.⁶ Pain in the hips may result in the injured shuffling or limping.

Psoas syndrome is one of the most common causes of groin pain in athletes. One study found that among a group of athletes experiencing groin pain, 10% had tendon inflammation in the psoas and 11% had the strain in the psoas.⁷ Due to the psoas muscles’ influence on the hip flexors, psoas syndrome can cause groin pain when the hip is stretched or flexed. Further, when the knee is flexed at a right angle, there may be a feeling of ‘slipping’ or ‘catching’ in the groin. This could be due to swelling of the iliopsoas, but it can also be caused by a labral tear. All of these symptoms will most likely worsen with activity and improve with rest.⁶

Diagnosing psoas syndrome

As lower back pain can have a range of underlying causes, a diagnosis of psoas syndrome is often a differential diagnosis - meaning that a healthcare professional will first investigate many other possibilities to rule out more likely conditions or injuries. An X-ray or a CT scan may be considered; these cannot diagnose psoas syndrome, but they would rule out other causes of lower back pain, like arthritis, fractures, and tumours.

Physical examination

A physical examination would involve a healthcare professional asking about your medical history, activities, and habits. They may need to press around the lower back to find abnormalities, and tenderness, and investigate the pain further. They may also require the patient to demonstrate their range of motion.

Ultrasound Scan

If a physical examination does not confirm a diagnosis, a healthcare professional may elect ultrasound imaging to investigate further as it is harmless and returns real-time, dynamic imaging. An ultrasound can reveal any thickening of the iliopsoas tendon, and the enlargement of any bursa. A bursa is the collection of lubricating fluid at a joint.

Lidocaine challenge test with ultrasound

This test involves injecting lidocaine (a local anaesthetic) into the psoas tendon with assistance from an ultrasound. If the patient’s pain is reduced after the psoas is anaesthetised, a diagnosis of psoas syndrome is indicated. The ultrasound is used to guide the needle towards the psoas muscle using a freehand technique.

MRI (magnetic resonance imaging) scan

An MRI could be used to produce an image of joints, tissues and bones. It can allow a healthcare professional to determine if you have muscle strain or tendonitis in the psoas. Recovering from tendonitis will take longer than recovering from muscle strain. It is important to differentiate between the two to prevent patients from returning to their normal activities too early and causing further damage.⁷

Treating psoas syndrome

Physical therapy

Conservative management (avoiding surgery or other invasive procedures) is the primary treatment for psoas syndrome. It has proven to be an effective treatment strategy. A study was performed on dancers suffering from psoas syndrome who were prescribed physical therapy involving stretching of the hip flexor, modifying their dancing to reduce the number of leg extensions and rest. Under this conservative management, 100% of the 49 participants showed improvement and a positive response to treatment.³

Another kind of physical therapy offered to Psoas syndrome patients is a therapeutic ultrasound. This is used to heat soft tissues, like muscles and tendons, to increase circulation and reduce pain.

Exercise programs

A healthcare professional may prescribe exercises that stretch and strengthen the psoae. Any physical exercise should be discussed with a healthcare professional beforehand, as strenuous exercise may worsen the condition.

Osteopathic manipulative treatment

Osteopathic manipulative therapy involves applying gentle pressure to injured muscles to improve their alignment and healing.

Pain management

Over-the-counter pain management like ibuprofen can provide short-term relief for back, hip, and groin pain.

Corticosteroid injections

Steroid injections provide pain relief and reduce inflammation and swelling. Similar to diagnosis by lidocaine challenge test, a healthcare professional would use an ultrasound to guide the injection into the psoas muscles. However, unlike the lidocaine test, corticosteroid injections can provide long-term relief. These injections are helpful to those experiencing psoas syndrome after a hip replacement, preventing the need for further surgery.

Surgical release of the psoas tendon

This procedure is also known as a tenotomy. The tendon is divided to relieve pain and lengthen it. It’s only to be performed in severe cases. Other methods of treatment should be tried before resorting to surgery.

Preventing psoas syndrome

Psoas syndrome can be prevented in athletes if the following measures are taken:

• Stretching before exercise
• Increasing flexibility
• Improving posture
• Gradually increasing exercise intensity, rather than suddenly performing an intense workout

It is unclear what exactly causes some individuals to develop psoas syndrome after a hip replacement. To prevent negative side effects after a hip replacement, you should follow your doctors’ advice on recovery. This may include walking, working with a physiotherapist, resting, avoiding low chairs, not crossing your legs, and not twisting your hips. 

Summary

• Psoas syndrome is a condition in which someone experiences back, hip, or groin pain due to inflammation or irritation in the psoas muscles
• There are two psoas muscles. They both attach to the lower spine and each stretch down to the top of a thigh bone. These muscles assist with stabilising the spine when sitting, flexing the thigh when standing, and general hip movement
• Psoas syndrome occurs due to muscle overuse or trauma
• Psoas syndrome is common in athletes (particularly dancers or runners) but it also is seen in individuals post-hip replacement
• Psoas syndrome can be diagnosed by a physical exam, an ultrasound, an anaesthetic injection into the psoas muscles to see if the pain originates from there, or an MRI
• Treatment involves physical therapy, rest, modified or reduced exercise, pain medication, and, in extreme cases, surgical release of the psoas tendon
• This condition can be prevented in athletes by stretching before exercise, improving posture, and gradually building up to intensive exercise