Barlow Test: Screening, Technique, and Significance for Infant Hip Dysplasia

What is the Barlow Test for Hips?

The Barlow test is a specialized clinical maneuver primarily used in infants to screen for developmental dysplasia of the hip (DDH), a condition where the hip joint has not formed properly. It aims to identify a hip that is unstable and prone to dislocating by gently attempting to displace the femoral head posteriorly out of the acetabulum.

Introduction to the Barlow Test

The Barlow test is a cornerstone of the newborn and infant physical examination, specifically designed to detect instability in the hip joint. Named after Dr. Thomas Barlow, who described it in 1962, this test is crucial for the early identification of Developmental Dysplasia of the Hip (DDH). DDH encompasses a spectrum of conditions ranging from mild instability to complete dislocation of the hip joint, where the head of the femur (thigh bone) is not properly seated within the acetabulum (hip socket). Early diagnosis and intervention are paramount for preventing long-term complications and ensuring healthy hip development.

Relevant Anatomy and Biomechanics

To understand the Barlow test, a brief review of hip anatomy is beneficial. The hip is a ball-and-socket joint, formed by the spherical head of the femur fitting into the cup-shaped acetabulum of the pelvis. In infants, the hip joint is primarily cartilaginous and more pliable, making it susceptible to developmental issues. DDH occurs when there is an abnormal relationship between the femoral head and the acetabulum, which can be due to a shallow acetabulum, laxity of the joint capsule and ligaments, or other factors. The Barlow test specifically assesses the integrity of this ball-and-socket relationship by attempting to provoke a posterior dislocation.

How the Test is Performed

The Barlow test requires a gentle, precise technique performed by a trained healthcare professional. The infant should be calm and relaxed, ideally not crying, as muscle tension can interfere with the assessment.

• Patient Positioning: The infant is placed supine (on their back) on a firm surface. The examiner stands at the infant's feet.
• Examiner's Hand Placement:
  • Grasp each leg individually, ensuring the hips are flexed to 90 degrees and the knees are also flexed.
  • Place your thumb on the infant's lesser trochanter (medial aspect of the thigh, near the groin) and your fingers on the greater trochanter (lateral aspect of the thigh, below the hip bone). This hand position allows for controlled manipulation of the femoral head.
  • The examiner's other hand can stabilize the infant's pelvis.
• The Maneuver:
  • With the hip flexed to 90 degrees, gently adduct the hip (bring the thigh towards the midline of the body).
  • Simultaneously, apply gentle, but firm, posterior pressure along the long axis of the femur, pushing the femoral head towards the examination table.
  • The aim is to feel if the femoral head slips or "clunks" out of the acetabulum posteriorly.

Key Point: The test is performed one hip at a time. It is crucial to be gentle, as excessive force can cause injury or distress to the infant.

Interpreting the Results

The interpretation of the Barlow test is based on the sensation felt by the examiner's hands:

• Negative Barlow Test: This is the desired outcome. The hip remains stable throughout the maneuver, and there is no sensation of the femoral head slipping or dislocating from the acetabulum.
• Positive Barlow Test: A positive test is indicated by a palpable "clunk," "clunking sensation," or "slip" as the femoral head dislocates posteriorly out of the acetabulum. This sensation often feels like the femoral head "pops out" of the socket. This signifies hip instability and indicates a dislocatable hip.

Important Distinction (Barlow vs. Ortolani): The Barlow test provokes a dislocation, meaning it attempts to push an unstable hip out of its socket. It is often performed in conjunction with the Ortolani test, which reduces an already dislocated hip by bringing the femoral head back into the acetabulum with a distinct "clunk." While both tests assess DDH, they evaluate different aspects of hip stability.

Clinical Significance and Implications

A positive Barlow test is a critical finding that warrants immediate attention and further medical evaluation. The implications include:

• Early Diagnosis of DDH: A positive test suggests the presence of DDH, indicating that the hip joint is not stable and is at risk of dislocation.
• Prevention of Long-Term Complications: Untreated DDH can lead to significant problems as the child grows, including:
  • Abnormal gait patterns (e.g., limping)
  • Leg length discrepancy
  • Chronic hip pain
  • Early onset osteoarthritis in adulthood
  • The need for more complex and invasive surgical interventions later in life.
• Referral for Imaging and Specialist Consultation: A positive Barlow test typically prompts further diagnostic imaging, such as a hip ultrasound (preferred for infants under 4-6 months due to the cartilaginous nature of the hip) or X-rays (for older infants). Referral to a pediatric orthopedist is also standard practice.
• Prompt Treatment: Depending on the severity, treatment for DDH can range from non-invasive methods like the Pavlik harness (which holds the hips in a flexed and abducted position to encourage proper development) to more invasive surgical procedures in older children. The earlier treatment begins, the higher the success rate and the less invasive the treatment typically is.

Limitations and Considerations

While the Barlow test is a valuable screening tool, it has certain limitations:

• Operator Dependence: The accuracy of the Barlow test relies heavily on the skill, experience, and gentle technique of the examiner. Forceful or incorrect maneuvers can lead to false positives, false negatives, or even injury.
• Age Sensitivity: The test is most reliable in the first few weeks and months of life. As an infant ages, the hip capsule and surrounding ligaments naturally tighten, making the hip less dislocatable. Beyond 3-4 months of age, the test becomes less sensitive, and other clinical signs or imaging may be more indicative of DDH.
• Not a Standalone Diagnosis: A positive Barlow test indicates a dislocatable hip, but it is not the sole diagnostic criterion for DDH. It must be considered in conjunction with other clinical findings, a thorough medical history, and confirmatory imaging studies.
• Transient Instability: Some newborns may exhibit a transient hip instability that resolves spontaneously without intervention. However, any instability warrants careful monitoring.
• Not for Adults: The Barlow test is specifically designed for infants and is not used in adults, as adult hip anatomy and common hip pathologies differ significantly.

Conclusion

The Barlow test is an indispensable component of the infant physical examination, serving as a critical screening tool for developmental dysplasia of the hip. By identifying hips that are unstable and prone to dislocation, it allows for early intervention, which is key to optimizing outcomes and preventing long-term orthopedic complications. While requiring precise technique and interpretation, its role in safeguarding infant hip health underscores its importance in pediatric care. Any positive finding on a Barlow test necessitates prompt follow-up with a healthcare professional for further evaluation and management.