Allis’ sign refers to observable changes in the alignment or tension of the femoral region that indicate either a fracture of the femoral neck in adults or congenital hip dislocation in infants.

• In adults: Relaxation or depression of the fascia lata between the iliac crest and greater trochanter due to fracture of the femoral neck.

• In infants: Unequal leg lengths indicating hip dislocation.

Pathophysiology

• Adult fracture: Fracture of the femoral neck leads to shortening and lateral displacement of the femur, causing the fascia lata and surrounding soft tissues to relax. This results in detectable depression when firm pressure is applied between the iliac crest and greater trochanter.

• Infant hip dislocation: Developmental dysplasia of the hip causes the femoral head to displace from the acetabulum, resulting in asymmetry of the lower extremities and apparent shortening of the affected leg.

Examination Technique

Adult

1. Patient positioning: Supine with legs extended and relaxed.

2. Palpation: Place a finger firmly over the fascia lata between the iliac crest and greater trochanter.

3. Assessment: Press gradually; if the finger sinks deeply, the sign is positive, indicating possible femoral neck fracture.

Infant

1. Patient positioning: Place the infant supine with the pelvis flat.

2. Leg flexion: Flex both knees and hips, keeping the feet even.

3. Assessment: Compare knee heights; discrepancy suggests a dislocated hip on the shorter leg.

Clinical utility

• Adult: Provides a quick, bedside indication of femoral neck fracture, especially in elderly patients or those with trauma.

• Infant: Useful for early detection of developmental dysplasia of the hip, allowing prompt orthopedic intervention.

• Adjunct tool: Should be interpreted alongside radiographic studies for confirmation.

Differential diagnosis

Pediatric considerations

• Perform gentle palpation to avoid discomfort or injury.

• Early detection of hip dislocation is critical to prevent long-term gait abnormalities and degenerative joint disease.

Geriatric considerations

• Femoral neck fractures are common in elderly patients with osteoporosis or low-energy falls.

• Allis’ sign may be more evident due to decreased soft tissue mass.

• Prompt recognition aids early surgical intervention, reducing morbidity and mortality.

Limitations

• Positive Allis’ sign is not definitive; imaging (X-ray, ultrasound, or MRI) is required for confirmation.

• False negatives may occur with obese patients, significant muscle mass, or incomplete dislocation/fracture.

• In infants, leg asymmetry may also result from limb length discrepancy or neuromuscular conditions.

Patient counseling

• Explain that the test is a screening maneuver, not a definitive diagnosis.

• Advise caregivers of infants about the importance of follow-up imaging and orthopedic referral if the sign is positive.

• In adults, emphasize fall prevention and early mobilization post-diagnosis.

Conclusion

Allis’ sign is a valuable clinical tool for detecting femoral neck fractures in adults and hip dislocation in infants. While simple and non-invasive, it should always be confirmed with appropriate imaging and used as part of a comprehensive musculoskeletal or pediatric assessment.

References

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

2. McRae R, Esser MP. Practical Orthopaedic Examination. 7th ed. Edinburgh: Churchill Livingstone; 2010.

3. Beaty JH, Kasser JR. Rockwood and Wilkins’ Fractures in Children. 9th ed. Philadelphia (PA): Wolters Kluwer; 2016.

4. Canale ST, Beaty JH. Campbell’s Operative Orthopaedics. 14th ed. Philadelphia (PA): Elsevier; 2021.

5. O’Brien J, Herring JA. Tachdjian’s Pediatric Orthopaedics. 5th ed. Philadelphia (PA): Saunders; 2013.