The small and large psoas are muscles of the back: they are two thick, spindle-shaped muscles located in the pelvis, which are used to flex the thigh over the pelvis. They extend from the lumbar spine to the lesser trochanter, on the top of the femur, and end in a tendon common with the iliac muscle. The main function of the small and large psoas is therefore to allow flexion of the hip, flexion of the thigh on the trunk, as well as flexion and rotation of the lumbar vertebrae. In addition, it is also a postural muscle, which helps balance the body when standing. The small and large psoas can be affected by psoitis, an involuntary contraction of the psoas that can cause tendonitis, or even be the site of a hematoma or an abscess that can be drained surgically. In addition, a lesion of the psoas can occur, mainly in athletes, which can be treated. One of the best preventative treatments is to practice regular stretches of the psoas muscles.

The large and small psoas are muscles of the back, located in the pelvis, which extend from the lumbar vertebrae to the hip. Thus, the psoas muscles are located deep between the front of the hip joint and the bottom of the spine. Etymologically, the term comes from the Greek word “psoa”, which means the lower back (in anatomy, the lower back are the posterior regions of the abdomen, located to the right and left of the spine).

The greater psoas attaches above the lumbar spine and ends below at the lesser trochanter of the femur, by a large tendon common with the iliac muscle. In fact, the greater psoas and the lesser psoas are, along with the iliac, a muscle group with similar biomechanical characteristics. They are almost always contracted, since they participate in the overall postural balance when standing.

The large psoas, thick and elongated, is inserted on the spine more precisely at the level of the intervertebral discs T12 (twelfth throacic vertebra) up to L5 (fifth lumbar vertebra, located in the lower back, just above the buttocks. ). The lesser psoas muscle is present on the anterior surface of the greater psoas and runs from the twelfth thoracic vertebra to the iliopectineal eminence (which is formed by the junction of the branch of the ilion bone with that of the pubis).

The psoas muscles act on the back but also on the leg: they are used either to raise the thigh, or to tilt the bust when the leg is fixed. The main main function of the small and large psoas is therefore to allow flexion of the thigh on the trunk, or that of the trunk on the thigh, depending on the fulcrum. They also allow flexion and rotation of the lumbar vertebrae. In addition, it is also a postural muscle: it maintains the balance of the body when standing.

The greater psoas is vascularized by branches of the lumbar and circumflex iliac vessels. As for its innervation, it is done thanks to the ventral branches of the lumbar nerves, as well as some bundles of the femoral nerve at its terminal part. The small psoas is the auxiliary of the large psoas when the latter mobilizes the femur.

The psoas muscles can be the object of several abnormalities or pathologies, and thus:

• some conditions of the abdomen (such as appendicitis) cause an involuntary contraction of the psoas called psoitis. This inflammation of the psoas muscle causes tendonitis, which causes pain in the groin when the person stands, as well as, very often, lameness when walking. In addition, often flexion of the hip is also painful;
• The greater psoas can also be the site of a hematoma, in particular in the event of hypocoagulability (decrease in the coagulating power of the blood);
• In the event of spondylodiscitis (simultaneous inflammation of an intervertebral disc and adjacent vertebrae) of the lumbar spine, or in the event of bone or disc infection, the psoas may also be prone to an abscess. However, psoas abscess remains a rare disease, the first description of which dates back to 1881;
• Psoas tendinopathy is an inflammation of this tendon, at the site of the hip. It most often affects patients over the age of fifty, and most of them have hip prostheses. The pain, which occurs when the hip flexes, can be very disabling on a daily basis;
• Injury to the psoas can also occur because this muscle is used a lot in many sports, since it is the main flexor of the hip.

Preventive treatment

The goal of regular stretching of the psoas muscle is to avoid tendonitis (i.e. inflammation of the tendon), vertebral blockage, as well as diffuse pain in the hips and pelvis. This is the main stretch to do after jogging. Most of the stretching exercises used to release the psoas also work on the other hip flexor muscles of the quadriceps, adductors, and tensor fascia lata. Finally, you should know that when you stretch the iliac psoas, you also have to stretch the hamstrings, which are the antagonistic muscles.

Curative treatments in case of pathology

• The hematoma, as well as the abscess, can be drained surgically. In case of failure of percutaneous drainage of the abscess, surgical treatment remains the reference. On the other hand, in the case of abscess, treatment of the causative disease must also be carried out.
• The first treatment for psoas tendinopathy is medical: it includes analgesics and / or anti-inflammatories. In addition, the treatment is supplemented by physiotherapy. However, there is another method for treating this type of tendinopathy, when these treatments are insufficient: it is, thus, possible to practice a simple and minimally invasive surgical treatment, which allows pain relief in most cases. This act is the arthroscopic psoas tenotomy, which consists of cleaning and cutting the fibrous area of ​​tendon suffering. This operation is carried out under camera by means of two small incisions.
• Treatment of a psoas injury will first require rest, followed by rehabilitation. Finally, for lesions that take a long time to heal, an injection of PRP: plasma rich in platelets, which is blood plasma enriched in platelets thanks to centrifugation, may be considered. The rheumatologist and sports specialist, Baptiste Coustet, from INSEP, estimates on his website: “Acute muscle injuries specifically concern the athlete and involve stopping, sometimes prolonged, and the risk of recurrence.He also specifies that the treatments can prove to be long for a high level athlete. And so, Baptiste Coustet assures: “Finding treatments that can accelerate wound healing remains a challenge and injections of platelet-rich plasma may be a candidate given their safety.“. The undesirable effects of PRP remain exceptional, and it is easy to obtain by taking a small blood sample which will be reinjected locally. While at the end of 2016, studies had not yet made it possible to recommend the use of PRP in order to shorten the return to play time or decrease the risk of recurrence, since then PRP injections have proved their worth. Thus, today, muscle lesions correctly diagnosed by an imaging work-up can be effectively treated by an injection of PRP, and particularly when the treatment is initiated in the first days.
• Practicing muscle strengthening will be important, in particular, to re-muscle the damaged psoas. It may also, sometimes, be necessary to correct the posture with an osteopath, in order to avoid over-straining the muscle.
• Finally, simple dietary advice should be observed for the patient, such as sufficient hydration to help heal the tendon, and, in terms of food, the consumption of omega 3 (fish, walnut oil), d ‘antioxidants (fruits, vegetables, green tea). In addition, the limitation of “trans” fatty acids and sugars will be indicated for some time.

It is above all medical imaging which, associated with clinical signs, will define the diagnosis of psoas tendinopathy, lesion, hematoma or abscess. And so, the precise clinical diagnosis of psoas abscess in particular, its location and extent, have greatly benefited from recent imaging data: ultrasound and computed tomography. Finally, a good diagnostic test, which can also be therapeutic, concerning psoas tendinopathy, is the infiltration of corticosteroids under ultrasound.

Finally, the doctor, the physiotherapist, or the osteopath have specific tests of the psoas, in particular to distinguish between, for example, a psoitis or a joint pain of the hip. Palpation of the muscle is an effective way to tell if it is tight or painful. But it is the ultrasound that will allow us to conclude with certainty.

«The psoas is the only muscle in the human body that connects the upper and lower body“, Writes Jo-Ann Staugaard-Jones, professor of kinesiology, but also of pilates and dance, and who has dedicated a book, Le psoas, muscle vital, to what she considers “as the most important skeletal muscle in the human body“And yet, according to her,”well mistreated“. For her, the psoas “plays a crucial role in optimal postural alignment, movement and, above all, well-being«.

This author reveals it: this muscle influences, among other things, “la breathing, due to its anatomical relationship with the diaphragm“, and “up to the circulation of energy throughout the body, due to its proximity to the first three chakras of yoga philosophy“. Jo-Ann Staugaard-Jones believes that the psoas plays an important role in phenomena such as “visceral communication“, the “somatic memory”Or the emotional component associated with feelings coming from“ the guts ”.

Moreover, finally, this professor specializing in movement recalls it: the word chakra originally meant “wheel”. We can therefore see “le psoas as the core of this wheel, while the many spokes revolving around it would include the upper and lower parts of the body, physiological and metabolic functions, emotions, mind and energy“. Dr Gary Mascilak, a specialist in physical medicine, writes in the foreword to Jo-Ann Staugaard-Jones’ book: “The author gives us a precious roadmap to restore harmony between mind, body and soul, thanks to this deeply hidden treasure called the psoas.“. Finally, he adds, “this deeply central muscle is capable of influencing both mind, body and soul. Gold, it is now accepted that the balance of these three is essential to obtain an optimal state of health«.