Psoas Sign: Technique and Clinical Significance
The psoas sign is elicited by having the patient lie supine and either actively flex the hip against resistance or by passively extending the hip; pain with either maneuver indicates irritation of the psoas muscle and suggests retroperitoneal or pelvic pathology, most commonly appendicitis when located in the right lower quadrant.
How to Elicit the Psoas Sign
The psoas sign can be tested using two distinct methods:
Active method: With the patient supine, ask them to actively flex the right hip against your hand providing resistance. Pain during this maneuver is considered positive 1.
Passive method: With the patient lying on their left side, passively extend the right hip by pulling the right leg backward. Pain elicited during passive extension also constitutes a positive sign 2.
Both techniques work by stretching or contracting the psoas muscle, which lies in the retroperitoneum. When inflamed structures (such as an inflamed appendix) are adjacent to or involve the psoas muscle, these movements cause pain 3, 4.
Clinical Significance of a Positive Psoas Sign
Primary Indication: Appendicitis
A positive psoas sign significantly increases the likelihood of acute appendicitis, particularly when the appendix is retrocecal or in a pelvic location 1, 2.
The presence of a positive psoas sign, along with fever or migratory pain to the right lower quadrant, suggests increased likelihood of appendicitis 1, 2.
However, the classic triad of fever, flank pain, and limitation of hip movement (positive psoas sign) is present in only approximately 30% of patients with psoas-related pathology 4, 5.
The psoas sign is more specific than sensitive—its presence is helpful for diagnosis, but its absence does not exclude appendicitis 2.
Other Retroperitoneal Pathologies
A positive psoas sign is not specific to appendicitis and can indicate various retroperitoneal processes:
Psoas abscess: The most important alternative diagnosis, which can actually simulate acute appendicitis with similar presentation 3, 4, 5.
Retroperitoneal hematoma: Can cause psoas irritation and obscuration of the psoas muscle contour on imaging 1, 6.
Retroperitoneal tumors or adenopathy: May involve or compress the psoas muscle 6.
Inflammatory lesions: Including pyelonephritis or other retroperitoneal infections 6, 4.
Critical Clinical Pitfalls
Do Not Rely on the Psoas Sign Alone
Physical examination findings should never be used in isolation for diagnosis—imaging is essential, particularly CT scan which has 90-100% sensitivity and 94.8-100% specificity for appendicitis 7.
The psoas sign has limited sensitivity; many patients with appendicitis will not demonstrate this finding 2.
Only one patient in a 10-year review of psoas abscesses presented with the classic triad including positive psoas sign 4.
Psoas Abscess Can Masquerade as Appendicitis
Psoas abscess is an underdiagnosed condition with vague, nonspecific symptoms that can closely mimic acute appendicitis 3, 5.
In one case series, only 30% of patients with psoas abscess were correctly diagnosed on initial presentation to the emergency department 5.
CT scan is the diagnostic standard for differentiating psoas abscess from appendicitis and other retroperitoneal pathology 4, 5.
Ultrasound performed by experienced clinicians can identify psoas abscess in patients with sepsis and nonspecific abdominal/flank pain, though CT remains superior 5.
Diagnostic Algorithm When Psoas Sign is Positive
Assess for appendicitis risk factors: Right lower quadrant pain, fever, migratory pain pattern, anorexia/nausea 1, 7.
Obtain laboratory studies: Complete blood count (leukocytosis is common but nonspecific), C-reactive protein 7, 4.
Proceed directly to imaging—do not delay based on clinical assessment alone:
- CT abdomen/pelvis with IV contrast is the gold standard for adults with suspected appendicitis or retroperitoneal pathology 1, 7.
- Ultrasound may be considered as first-line in younger patients, though sensitivity is lower (87.1%) 7.
- MRI shows 96% sensitivity and specificity for appendicitis, particularly useful in pregnant patients 1, 7.
Consider psoas abscess if patient has prolonged symptoms (mean 10.6 days), sepsis, or risk factors such as diabetes, immunosuppression, or recent urological procedures 4, 5.
Evaluate for other retroperitoneal pathology if appendicitis is excluded: hematoma, tumor, inflammatory conditions 1, 6.