Bonnet’s sign is defined as pain elicited upon adduction of the thigh, typically observed in patients with sciatica. This sign indicates irritation or compression of the sciatic nerve, often due to herniated lumbar discs or other causes of lumbosacral nerve root compression.

Pathophysiology

• Adduction of the thigh stretches the sciatic nerve along its course from the lumbosacral spine to the lower limb.

• In cases of nerve root compression or inflammation (commonly L4–S3), this maneuver increases mechanical tension on the sciatic nerve, eliciting pain radiating along its distribution.

• The sign reflects nerve irritation rather than primary muscular pathology.

Examination Technique

• Patient positioning: Supine, relaxed.

• Maneuver:

  1. Flex the patient’s hip and knee slightly.

  2. Gently adduct the thigh across the midline.

• Assessment: Observe for pain radiating along the posterior thigh, leg, or foot consistent with sciatic nerve distribution.

• Interpretation: Reproduction of sciatic pain constitutes a positive Bonnet’s sign.

Clinical utility

• Indicator of sciatica: Helps confirm nerve root involvement in patients with suspected lumbar disc disease.

• Adjunct to other tests: Often used alongside Lasègue’s sign (straight leg raise), Bragard’s sign, and slump test for comprehensive assessment of sciatic nerve irritation.

• Localization: Can assist in differentiating nerve root vs. muscular pain in the lower limb.

Differential Diagnosis

Management

• Underlying cause treatment:

  • Lumbar disc herniation: Conservative management (NSAIDs, physical therapy, epidural steroid injections), surgical decompression if severe.

  • Piriformis syndrome: Stretching, physiotherapy, local injections, or surgical release in refractory cases.

  • Spinal stenosis: Conservative care or surgical decompression based on severity.

• Pain control: Analgesics, nerve blocks, and activity modification.

• Rehabilitation: Stretching, strengthening, and ergonomic education to prevent recurrence.

Pediatric considerations

• Rare in children; may be associated with trauma, infection, or congenital spine disorders.

• Assessment should be gentle, and observation for refusal to bear weight may be an alternative indicator.

Geriatric considerations

• Older adults may have degenerative spine disease causing sciatica.

• Positive Bonnet’s sign should be interpreted in conjunction with imaging and functional assessment due to coexisting comorbidities.

Limitations

• Not entirely specific; pain may also originate from muscular, hip joint, or pelvic pathology.

• Should be used as part of a comprehensive neurologic and musculoskeletal evaluation.

Patient counseling

• Explain that the maneuver assesses nerve irritation and is safe when performed gently.

• Advise the patient to report any radiating pain immediately during the test.

• Discuss potential treatment options for underlying causes once identified.

Conclusion

Bonnet’s sign is a valuable clinical indicator of sciatic nerve irritation, particularly in lumbar disc herniation and related conditions. When combined with other neurologic and orthopedic tests, it helps guide diagnosis and management of lower limb radicular pain.

References

1. Bonnet F. Sciatica and its Clinical Examination. Paris: Masson; 1828.

2. Buttaro TM, Tybulski J, Bailey PP, Sandberg-Cook J. Primary Care: A Collaborative Practice. St. Louis (MO): Mosby Elsevier; 2008. p. 444–447.

3. Deyo RA, Mirza SK. Clinical practice. Lumbar disc herniation. N Engl J Med. 2016;374:1763–1772.

4. Hoppenfeld S, deBoer P, Buckley R. Physical Examination of the Spine and Extremities. 3rd ed. New York, NY: Appleton & Lange; 2000.

5. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 9th ed. Philadelphia, PA: Wolters Kluwer; 2020.