Psoas Syndrome

Etiology

Psoas syndrome is more commonly seen in athletes but can occur in the general population as well. The prevalence is higher in runners and athletes partaking in plyometric exercises. Activities that result in repetitive hip flexion can result in underlying psoas syndrome.[1] Psoas syndrome occurs in patients with either inflammatory or degenerative arthritis, as well. 

Separately, psoas tendinitis or syndrome can occur with the impingement of the psoas tendon against an oversized acetabulum.[2][3] Furthermore, post-operatively psoas muscle tendinitis (syndrome) can occur for a variety of reasons ranging from recurrent hematomas in the iliopsoas tendon to protruding surgical screws.[4][5][6] 

The location of the psoas muscle is in the lower lumbar area of the spine and has attachment points along the pelvis and femur. The primary action of the psoas muscle is it serves as a hip flexor and an external rotator of the leg. The psoas muscle proximal attachment is along with the transverse processes of the lumbar spine. Separately, the iliac muscle proximal attachment is along the inner surface of the ilium. Both muscles then insert on the medial aspect of the proximal femur, on the lesser trochanter. In 15% of people, the iliopsoas bursa communicates with the hip joint. Any snapping or clunking which may occur on physical exam as the patient's leg moves from flexion to extension is due to the iliopsoas tendon moving medially to lateral on the femoral head. The snapping of the iliopsoas muscle leads to inflammation and or fluid accumulation in the iliopsoas bursa. 

Epidemiology

The incidence and prevalence of psoas syndrome in the general population are unknown. However, female athletes are at higher risk, as well as patients with hip osteoarthritis or rheumatoid arthritis. Generally speaking, hip pain is relatively common in patients 60 years of age or older, but psoas syndrome is an uncommon cause.

The reported prevalence of iliopsoas syndrome postoperative following a total hip arthroplasty is 4.3% in patients.[7][8] A study of 252 total hip arthroplasty patients showed the incidence of iliopsoas tendonitis to be 24% of cases.[9]

History and Physical

Patients will often complain of back pain in the lumbosacral region. Radiation down into the sacrum or up the lumbar vertebra can occur — the location of the pain is described as buttock pain, pelvic pain, or groin pain. The patient may endorse a feeling of catching or slipping in the groin when their knee flexed to 90 degrees. Pain and a sense of "catching" in the groin with the knee flexed to 90 degrees suggests a labral tear but also may be seen with iliopsoas tendinopathy.

Given the iliopsoas muscle is a hip flexor, a history significant for back pain with walking occurs with psoas syndrome. Pain often occurs with changing positions, moving from a sitting to a standing position, or difficulty standing upright. Patients may also complain of pain in the gluteal region of the contralateral side of the injury. Symptoms are made worse with activity but improve with rest. The radiating pain often stops at the knee.

Patients can ambulate with a limp or shuffling gait. On exam, hip flexors such as the quadriceps may be hypertonic or tight on palpation. There may be tenderness to palpation on the psoas insertion site at the lesser trochanter. Separately, the patient may have a decreased range of motion in leg extension. Chronic changes can include exaggerated lumbar lordosis.

On exam, the Ludloff sign may be positive. The examiner directs the patient to sit with their knee in extension, then lift their heel of the affected leg. When pain is reproducible with this maneuver, it is a positive sign. Separately a snapping hip sign may be positive in psoas syndrome as well. On exam, have the patient place their affected hip in a flexed, externally rotated, and abducted position. The provider then passively puts the affected hip into extension. The associated pain is a positive test and suggestive of psoas syndrome.

Evaluation

X-rays of the hip are often negative in the case of psoas syndrome and often unwarranted.

Ultrasound can be helpful in the diagnostic evaluation of intraarticular versus extra-articular origins of hip pain.[10] A lidocaine challenge test can also be useful in diagnosing psoas syndrome when the diagnosis is unclear. Under ultrasound guidance, lidocaine gets injected into the psoas tendon. Reduced pain following an injection is suggestive of psoas tendonitis (syndrome).

In 21% of athletes experiencing groin pain, iliopsoas pathology was apparent on MRI.[11] If patients do not respond to conservative management for suspected iliopsoas injury, an MRI could be beneficial in the diagnosis. MRI and US often show enlargement of the bursa as well as thickening of the iliopsoas tendon.[12][13]

Labs are often unnecessary in the evaluation of psoas syndrome.[12]

Treatment / Management

Typical treatment includes physical therapy focused on stretching and strengthening the spine and hip joints alongside the psoas muscle. One study found 100% of dancers responded to conservative management. Exercise programs that the patient can do at home with a focus on hip rotation have demonstrated effectiveness in reducing pain and improving activity for patients in pain. Continue over-the-counter pain medications, such as ibuprofen and acetaminophen.[1][14][1](B2)

For athletes with suspected groin pain secondary to an iliopsoas tendon injury, an MRI could be warranted for an expected return to play management. MRI changes consistent with muscle strain correlated with a significantly decreased return to play for their respective sport compared to peri-tendinitis changes seen on MRI.[11]

Other treatment modalities include osteopathic manipulative therapy (OMT)[15], therapeutic ultrasound, corticosteroid injections, and in refractory cases, surgical release of the psoas tendon. Ultrasound-guided injections can serve both diagnostic and therapeutic treatment for hip pain of unclear origin.[10][16][17](B3)

For refractory cases requiring surgery, arthroscopic lengthening of the tendon can be completed for relief, and correcting intra-articular pathology can be done.[18] Furthermore, the release of the psoas tendon from the insertion is also a possible surgical option. Multiple different approaches have been attempted and studied with similar results. 

Of the reported 24% of patients who developed postoperative iliopsoas tendonitis following total hip arthroscopy, 50% of them required a corticosteroid injection to help relieve pain, while 12% required revision or iliopsoas release.[9]

Differential Diagnosis

Symptoms of psoas syndrome can often mimic a symptomatic herniated disc of the lumbar region. Other musculoskeletal causes on the differential for suspected psoas syndrome include arthritis of the hip and femoral bursitis. Snapping hip syndrome or coxa saltans should also be considered as part of the differential.[19]

There can also be visceral causes of pain, which present similar to psoas syndrome. Visceral causes of pain include prostatitis, appendicitis, diverticulitis, salpingitis, nephrolithiasis, and colon cancer. A labral tear of the hip also presents with a slipping or catching feeling in the hip, as well as the reproduction of pain with knee flexion, making distinguishing it from psoas syndrome on exam difficult. 

Medial to the psoas muscle is the ureter; thus, patients with a renal stone can often experience symptoms similar to psoas syndrome due to irritation of the psoas muscle secondary to a stone within the ureter. Similarly, the appendix can lie anterior to the psoas muscle. In the case of appendicitis, the psoas muscle can once again become irritated. 

There can be considerable overlap between snapping hip and psoas syndrome, iliopsoas bursitis, hip impingement, iliopsoas tendonitis, and hip labral pathology. Thus making the diagnosis difficult.[18][16]

On exam, weakness in hip flexion of an abducted hip can be seen in either snapping hip or iliopsoas syndrome.[1]

Prognosis

The vast majority of patients diagnosed with psoas syndrome respond to conservative management and have a full recovery. However, postoperative pain of the psoas muscle following total hip arthroscopy may require more advanced therapies for pain relief. These therapies include corticosteroid injections and tendon release. 

Complications

• Chronic pain for untreated iliopsoas syndrome and decreased athletic performance
• Recurrent tendonitis of the iliopsoas tendon
• Damage to neurovascular structures for patients when a clinician performing a psoas tendon corticosteroid injection does not utilize ultrasound guidance.