Psoas Syndrome

Etiology

Athletes, particularly runners and those engaging in plyometric activities (eg, kickboxing, mixed martial arts, tennis, and soccer), are at an increased risk of developing psoas syndrome due to repetitive hip flexion, often against a resisting force.[2] The pubic tubercle, often only briefly addressed in anatomy courses, may play a significant role in anterior (or internal) snapping hip and distal psoas tendinopathy. Psoas tendinitis or syndrome can also affect individuals with inflammatory or degenerative arthritis and may result from impingement of the psoas tendon against an enlarged acetabulum.[3][4] Postoperative psoas tendinitis may arise from complications such as recurrent hematomas within the iliopsoas tendon or protruding surgical screws.[5][6][7]

Anatomically, the psoas muscle originates from the transverse processes of the lower lumbar spine and extends to the pelvis and femur, functioning primarily in hip flexion and external rotation of the leg.[8][9] The iliacus muscle attaches proximally to the inner surface of the ilium, and both muscles insert on the lesser trochanter of the proximal femur.[10] In approximately 15% of individuals, the iliopsoas bursa communicates with the hip joint. During physical examination, movement of the iliopsoas tendon from medial to lateral across the femoral head may produce a snapping or clunking sound, which can lead to inflammation and fluid accumulation in the bursa, resulting in pain. Please see StatPearls' companion resource, "Anatomy, Bony Pelvis and Lower Limb: Psoas Major," for more information.

A less common etiology of psoas syndrome is malignant invasion of the psoas muscle, termed "malignant psoas syndrome."[11][12] First reported by Stevens and Gonet in 1990, this condition typically occurs in individuals with previously diagnosed, advanced-stage malignancy.[13] Malignant psoas syndrome is characterized by painful, fixed hip flexion, proximal lumbosacral plexopathy, and computed tomography (CT) evidence of tumor infiltration into the psoas muscle. The condition results in severe pain, with symptoms varying based on the extent of anatomical involvement.[13][14]

Epidemiology

The true incidence and prevalence of psoas syndrome in the general population are unknown, likely due to frequent underdiagnosis, misdiagnosis, and spontaneous symptom resolution before clinical evaluation. Female athletes may be at an increased risk, possibly due to a wider osseous pelvis. Additional risk factors include hip osteoarthritis and rheumatoid arthritis. While hip pain is relatively common in individuals aged 60 or older, psoas syndrome represents an uncommon etiology in this age group.

More data are available for psoas abscess. In a study involving 40 patients, the mean age was 60, and 67.5% were men. The in-hospital mortality rate was 5%. Half of the cases were secondary to infective spondylitis. Staphylococcus aureus was the most common causative organism, followed by Escherichia coli. Polymicrobial infections were frequently observed in secondary abscesses.[15] Postoperative iliopsoas syndrome has been reported in 4.3% of individuals following THA.[16][17] Additionally, a study of 252 patients undergoing THA identified iliopsoas tendonitis in 24% of cases.[18]

Pathophysiology

Benign psoas syndrome typically results from overstretching of the iliopsoas tendon, which may snap over the ipsilateral pubic tubercle and cause pain during hip extension. In contrast, infectious and malignant forms exhibit variable pathophysiology, depending on the extent and progression of the underlying condition. Infectious cases often originate from a primary spinal source, such as vertebral osteomyelitis, that extends to involve the psoas muscle.

History and Physical

Patients typically present with anterior groin pain that worsens with hip flexion. Due to altered gait mechanics, axial spine discomfort in the lumbosacral region may also occur. Pain may radiate to the sacrum and be accompanied by discomfort in the buttocks, pelvis, or lower back.[19] Some patients report a catching or slipping sensation in the groin when the knee is flexed to 90°. While this symptom often indicates a labral tear, it is also characteristic of iliopsoas tendinopathy.

A standard motor strength and reflex examination, including deep tendon reflexes, should be performed, along with assessment for upper motor neuron signs, muscle atrophy, and both dermatomal and peripheral sensory changes. A detailed history should investigate recent changes in workout routines, use of new athletic equipment, or modifications in coaching techniques that may suggest mechanical triggers. To assess for more serious pathology, clinicians should inquire about a history of malignancy, spinal injections (particularly discography), and intravenous (IV) drug use. A review of systems should include screening for constitutional symptoms such as fever, chills, weight loss, or night sweats.

Clinicians should maintain a low threshold for ordering diagnostic laboratory tests, including urinalysis, complete blood count (CBC) with differential, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP). When appropriate, a human chorionic gonadotropin (hCG) test should also be considered. Standard vital signs must be documented, and additional history should include questions about IV drug use, unexplained weight loss, prior ovarian cysts, or other gynecological conditions.

As the iliopsoas muscle is a primary hip flexor with proximal attachments along the lumbar vertebrae, individuals with psoas syndrome often report lower back pain during ambulation. Pain is commonly triggered by positional changes, such as transitioning from seated to standing, or difficulty maintaining an upright posture. Some patients may also experience contralateral gluteal pain. Symptoms typically worsen with activity and improve with rest, and radiating pain generally does not extend beyond the knee. A detailed medical history is essential. Although malignant psoas syndrome is rare, metastatic spread to the psoas muscle should be ruled out. Thorough history-taking is also crucial to exclude other potential causes of similar symptoms.

Patients typically do not present with overt difficulty ambulating; however, subtle signs such as a limp, slow transitions from sitting to standing, or a shuffling gait may be observed. Gait should be assessed passively, without alerting the patient, to minimize performance bias. Tightness or hypertonicity of the hip flexors, particularly the quadriceps, may be evident. A positive Ely test—performed with the patient in the prone position and the knee passively flexed—is noted when the foot does not reach the buttocks. Palpation may reveal tenderness at the insertion site of the iliopsoas on the lesser trochanter. Range of motion in hip extension is often reduced, and in chronic cases, exaggerated lumbar lordosis may be observed.

Although traditionally associated with appendicitis, a positive psoas sign—pain elicited during passive hip extension—may also indicate psoas muscle irritation and support a diagnosis of psoas syndrome. A positive Ludloff sign, demonstrated by having the patient sit with the knee extended and lift the heel of the affected leg, suggests pain localized to the iliopsoas region. The snapping hip test may also yield a positive result. With the affected hip flexed, externally rotated, and abducted, passive hip extension may reproduce pain, which further supports the diagnosis of psoas syndrome.

Evaluation

Imaging techniques such as x-rays and CT scans of the hip are typically unremarkable and unnecessary for diagnosing psoas syndrome, unless malignant psoas syndrome is suspected. In such cases, one of the diagnostic criteria proposed by Stevens and Gonet includes CT imaging showing pathological evidence of malignancy in the psoas muscle.[13]

Acute inflammatory markers, such as the ESR and non-cardiac CRP, should be assessed. A CBC with differential and platelet count is recommended when infection is suspected. A detailed history of current or past IV drug use should be obtained, and toxicology screening may be warranted. Additionally, urine hCG testing or an ovarian ultrasound may be indicated in cases of unexplained anterior groin or pelvic pain. A basic urine dipstick test is a rapid and inexpensive tool that is particularly useful for detecting blood in the urine (hematuria). This tool also helps narrow the differential diagnosis in ambiguous cases, especially when sports-related risk factors are absent.

Ultrasound can help differentiate between intra-articular and extra-articular causes of hip pain.[20] A lidocaine challenge test, performed under ultrasound or fluoroscopic guidance, may also help diagnose psoas syndrome. In this test, lidocaine is injected into the psoas tendon, and a significant reduction in pain following the injection supports the diagnosis of psoas tendonitis (or syndrome).

Iliopsoas pathology is detectable on magnetic resonance imaging (MRI) in approximately 21% of athletes presenting with groin pain.[21] If conservative management for a suspected iliopsoas injury is unsuccessful, MRI can help confirm the diagnosis. Both MRI and ultrasound typically show enlargement of the bursa and thickening of the iliopsoas tendon.[22]

Laboratory tests are typically unnecessary in diagnosing benign psoas syndrome, as the condition is primarily due to overuse and mechanical factors without changes in autoimmune markers.[23] Electrodiagnostic evaluation, including nerve conduction studies of the lateral femoral cutaneous nerve, should be considered in cases of anterior thigh pain and potential overlapping meralgia paresthetica. Needle electromyography, often performed as part of an electrodiagnostic evaluation, may also be relevant in cases of diffuse leg pain, high lumbar radiculopathy, or diabetic amyotrophy. Please see StatPearls' companion resources, "Meralgia Paresthetica and Diabetic Amyotrophy," for more information. 

Treatment / Management

First-line management for psoas syndrome includes physical therapy aimed at stretching the iliopsoas hip flexor group, strengthening the spinal and hip musculature, and identifying any triggers in the training routine that may have contributed to the tendinopathy. A study reported a 100% response rate to conservative treatment among dancers. Exercise programs, particularly those targeting hip rotation, have proven effective in reducing pain and improving activity for patients. Over-the-counter pain medications (eg, ibuprofen and acetaminophen) should be continued.[24] Adjunctive modalities such as heat, ice, therapeutic ultrasound, and electrical stimulation may also be used if beneficial and maintained empirically based on clinical response.(B2)

For athletes, adequate rest and cross-training are crucial to avoid further strain on the hip flexors; however, modifying activity can be one of the most challenging aspects of management. Runners and field athletes may benefit from aquatic therapy, particularly when the water depth reaches the midsection, which reduces pressure on the psoas while providing hydrostatic compression and preserving a sense of continued exercise. An MRI may be warranted for return-to-play decisions in cases of suspected groin pain due to iliopsoas tendon injury. Notably, MRI findings indicating muscle strain are associated with a significantly lower return-to-play rate compared to those showing peritendinitis changes.

Osteopathic manipulative therapy, therapeutic ultrasound, corticosteroid injections, and, in refractory cases, surgical release of the psoas tendon are potential treatment options for psoas syndrome. Ultrasound-guided injections can be used for both diagnostic and therapeutic purposes in cases of hip pain with an unclear origin.[25][26] Please see StatPearls' companion resource, "Osteopathic Manipulative Treatment: Muscle Energy and Counterstrain Procedure - Psoas Muscle Procedures," for more information.(B3)

For refractory cases requiring surgery, arthroscopic lengthening of the tendon can provide relief, and correction of any intra-articular pathology may also be necessary.[27] Releasing the psoas tendon from its insertion is a potential surgical option. Various approaches to surgical release have been attempted and studied, which yield similar results. Among patients who developed postoperative iliopsoas tendonitis following THA, 24% required a corticosteroid injection for pain relief, whereas 12% needed revision surgery or iliopsoas tendon release. In contrast, the treatment of malignant psoas syndrome differs significantly. Management primarily focuses on pain relief through opiates, muscle relaxants, anti-inflammatory medications, nerve blocks, epidural anesthesia, chemotherapy, radiotherapy, and, if necessary, surgery.[28] Addressing the primary tumor with gold standard treatment modalities remains critical for effective management.[29]

Antibiotic therapy and, if necessary, antituberculosis treatment are indicated for infections. An infectious disease consult may also be required, along with potential neurosurgical intervention for underlying spinal infections. General or vascular surgery may be needed for abscess management. If the abscess is clearly loculated, interventional radiology may place a drain and obtain a sample for culture to guide appropriate antimicrobial therapy.

Differential Diagnosis

The differential diagnosis of anterior hip or inguinal pain is broad and can vary by sex. Symptoms of psoas syndrome often resemble those of a symptomatic herniated disc, hernia, ovarian cyst, or lumbar spine issues. Other musculoskeletal conditions to consider include hip arthritis and femoral bursitis. Additionally, snapping hip syndrome (coxa saltans) should be considered in the differential diagnosis.[30]

Visceral causes of pain present with symptoms similar to those of psoas syndrome and should be considered in the differential diagnosis. These include prostatitis, diverticulitis, salpingitis, nephrolithiasis, and pregnancy-related causes such as ectopic pregnancy. A well-regarded reference on right lower quadrant pain explicitly lists psoas tendonitis among the differential diagnoses.[31] Additionally, hip labral tears can mimic psoas syndrome, often presenting with a catching or slipping sensation and pain reproduced by knee flexion, making clinical distinction challenging during physical examination.

The ureter lies medial to the psoas muscle. As a result, patients with a renal stone may often experience symptoms similar to psoas syndrome due to irritation of the psoas muscle from a stone located within the ureter. Similarly, the appendix can be located anterior to the psoas muscle, and in some cases of appendicitis, the psoas muscle may also become irritated, contributing to similar symptoms.

A significant overlap exists between snapping hip syndrome, psoas syndrome, iliopsoas bursitis, hip impingement, iliopsoas tendonitis, and hip labral pathology, which can complicate both diagnosis and treatment. On examination, weakness in hip flexion of an abducted hip may be observed in both snapping hip syndrome and iliopsoas syndrome. Finally, malignant psoas syndrome should remain in the examiner’s differential diagnosis. Although rare, it should not be overlooked, especially when accompanied by other presenting symptoms or a history of primary cancer.

Toxicity and Adverse Effect Management

Conservative management and therapies typically carry minimal risk. However, overly aggressive treatment early on may trigger a symptom flare, leading to therapy discontinuation and potential reluctance to resume treatment. Monitoring patient tolerance and maintaining effective communication between the patient and therapist can help mitigate this risk. Therapeutic ultrasound can cause skin burns if high settings are used in continuous (nonpulsed) mode and the transducer is left stationary; however, such incidents are rare when administered by trained therapists.

Injections carry risks such as vascular or nerve injury, steroid reactions, and post-injection pain. Fluoroscopy often involves the use of a contrast agent, which may pose a risk of renal toxicity, although the typical dose is limited to 1 to 2 mL. Ultrasound guidance may not reliably detect inadvertent vascular uptake, and aspiration for blood has been shown to be insufficient for excluding it.

Bupivacaine (Marcaine) carries a higher risk of cardiac toxicity compared to lidocaine in the event of inadvertent vascular uptake, a risk that can be mitigated by avoiding its use. Procedures involving bupivacaine should be performed in facilities equipped with appropriate emergency equipment (eg, code cart) and staffed by personnel trained in Basic Life Support (BLS) and Advanced Cardiovascular Life Support (ACLS) to manage potential periprocedural complications. In rare instances where bupivacaine use is deemed necessary, the facility must be prepared for "lipid rescue." For this reason, bupivacaine is increasingly avoided in outpatient procedural clinics.[32]

Prognosis

The vast majority of patients diagnosed with psoas syndrome due to overuse and benign etiologies respond well to conservative management and achieve full recovery. However, postoperative pain in the psoas muscle following THA may require more advanced treatments to restore function. Patients undergoing this procedure are typically not high-performance athletes. Treatment options in these cases may include corticosteroid injections and tendon release. The prognosis for malignant psoas syndrome varies significantly, depending on factors such as the degree of tumor infiltration (primary or secondary) and the progression of the underlying malignancy.

Complications

Untreated iliopsoas syndrome can result in chronic pain and decreased athletic performance. Over time, recurrent inflammation may lead to tendon degeneration, contributing to long-term functional limitations. A potential consequence of untreated iliopsoas syndrome is the development of reflex sympathetic dystrophy, which is a form of complex regional pain syndrome that can arise from persistent musculoskeletal irritation. Recurrent tendonitis of the iliopsoas tendon is another concern, particularly when underlying mechanical factors remain unaddressed. Persistent inflammation may lead to a flexion contracture, resulting in secondary impairment and potential disability if not managed appropriately.

Local anesthetics and corticosteroids, although often necessary for treatment, can lead to secondary hyperglycemia. Additionally, inadvertent intravascular uptake may cause local anesthetic toxicity. This risk is heightened with agents such as bupivacaine, which has greater cardiac toxicity than lidocaine. This underscores the importance of performing such procedures in facilities equipped for emergencies, including those prepared for lipid rescue.

Injection-related complications may also include potential injury to neurovascular structures; however, this risk is significantly minimized when procedures are performed under fluoroscopic or ultrasound guidance. Despite imaging, inadvertent vascular uptake remains a concern, emphasizing the need for careful procedural technique.[33] Postprocedural complications from platelet-rich plasma (PRP) are rare and usually limited to localized effects at the injection site.