The psoas sign is a classical physical examination maneuver used to detect retrocecal appendicitis or other causes of retroperitoneal irritation . It elicits pain by stretching or contracting the iliopsoas muscle , which lies posterior to the peritoneum, adjacent to the retrocecal appendix .
Anatomical Basis
- Psoas Major Muscle
- Location : Retroperitoneal, extending from the lumbar vertebrae to the lesser trochanter of the femur
- Innervation : Direct branches of the lumbar plexus (L1–L3)
- Iliacus Muscle
- Originates from the iliac fossa and joins the psoas major to form the iliopsoas
- Innervation : Femoral nerve (L2–L4)
🧠 High-Yield Tip : The iliopsoas lies close to retroperitoneal structures such as the appendix (especially if retrocecal), kidneys, ureters, and iliac vessels—explaining the diagnostic utility of this test.
How to Perform the Psoas Sign
Two Methods:
- Passive Extension Test :
- Patient lies on their left side
- Examiner extends the right thigh passively
- Stretching the psoas muscle causes pain if the appendix is inflamed and retrocecal
- Active Flexion Against Resistance :
- Patient lies supine
- Asked to lift the right leg against the examiner’s resistance
- Pain elicited in the right lower quadrant suggests irritation of the psoas muscle
✅ Positive Psoas Sign : Pain is elicited during either maneuver → Suggests retrocecal appendicitis or another retroperitoneal pathology
Clinical Significance
| Condition | Mechanism of Pain |
|---|---|
| Retrocecal Appendicitis | Inflamed appendix irritates the psoas muscle |
| Psoas Abscess | Local infection or TB causing inflammation |
| Iliac Vessel Hemorrhage | Hematoma compresses retroperitoneal structures |
| Retroperitoneal Tumors | Mass effect or infiltration into psoas region |
🔬 Differentiation Pearl : A positive psoas sign is not pathognomonic for appendicitis. Always interpret in clinical context.
Appendicitis and Psoas Sign
- In retrocecal appendicitis (where the appendix lies behind the cecum), classic right lower quadrant (RLQ) pain may be absent or vague
- Instead, pain may be felt in the right flank or back
- In these cases, the psoas sign may be the only physical clue
🔍 USMLE Key Point : Psoas sign is more helpful in retrocecal than pelvic appendicitis , where other signs (e.g., obturator sign) may be more useful
Other Physical Signs in Appendicitis
| Sign | Description | Interpretation |
|---|---|---|
| McBurney's point tenderness | Pain at 1/3 from ASIS to umbilicus | Classic for appendicitis |
| Rovsing’s sign | RLQ pain with LLQ palpation | Peritoneal irritation |
| Obturator sign | Pain with internal rotation of flexed hip | Pelvic appendix irritation |
| Rebound tenderness | Pain when releasing pressure on RLQ | Suggests peritoneal inflammation |
Diagnostic Accuracy
- Sensitivity : ~16–29% (low)
- Specificity : ~89–95% (high)
📌 Clinical Application : The psoas sign is not sensitive but adds specificity when combined with other signs. Use it in patients with atypical appendicitis presentation or flank pain .
Differential Diagnosis for Positive Psoas Sign
- Retrocecal appendicitis
- Psoas abscess
- Hemorrhage of iliac artery/vein
- Retroperitoneal tumor or hematoma
- Vertebral osteomyelitis or discitis
High-Yield Summary Table
| Feature | Detail |
|---|---|
| Muscle tested | Iliopsoas (psoas major + iliacus) |
| Maneuver | Passive extension or active flexion |
| Positive sign | Pain in RLQ or right flank |
| Appendicitis type detected | Retrocecal |
| Other possible causes | Psoas abscess, hemorrhage, tumor |
| Innervation of psoas | Lumbar plexus (L1–L3) |
| Innervation of iliacus | Femoral nerve (L2–L4) |
Clinical Pearl
🚨 Do not rely on a single sign. Combine physical findings, lab tests (e.g., WBC count, CRP), and imaging (ultrasound or CT abdomen) for accurate diagnosis of appendicitis.
