A 3-month-old female infant is brought to the pediatric orthopedic clinic for routine developmental screening. On examination, the Barlow test is positive on the left side. Which is the most common site of hip dislocation in developmental dysplasia of the hip (DDH)?

Explanation

## Most Common Direction of Hip Dislocation in DDH **Key Point:** In developmental dysplasia of the hip (DDH), the femoral head most commonly dislocates in a **posterosuperior** direction. Among the options provided, **posterior dislocation (Option B)** is the correct answer, as posterior displacement is the defining and primary component of DDH dislocation. ### Anatomical Basis The hip joint is inherently unstable in infants due to: - Shallow acetabulum with deficient posterior wall - Ligamentous laxity (especially in females due to maternal relaxin) - Relative weakness of the joint capsule posteriorly - The femoral head is displaced posteriorly (and superiorly) by the pull of hip flexors, adductors, and the iliopsoas muscle ### Why Posterior is the Correct Answer Here Standard orthopedic references (Tachdjian's Pediatric Orthopaedics, Campbell's Operative Orthopaedics) classify DDH dislocation as **posterior** (or posterosuperior). The superior component is a *secondary* consequence of muscle pull after posterior displacement occurs. Among the four options given, **posterior dislocation** is the only anatomically recognized primary direction in DDH. ### Clinical Correlation **High-Yield:** The **Barlow test** (adduction + posterior pressure) detects instability by reproducing the posterior displacement. The **Ortolani test** (abduction + anterior lift) reduces the posteriorly dislocated femoral head back into the acetabulum — both tests confirm the posterior direction of pathological displacement. ### Risk Factors for DDH | Risk Factor | Relative Risk | |---|---| | Female sex | 4–8× higher | | First-born | 1.5–2× higher | | Family history | 10–25× higher | | Breech presentation | 10–25× higher | | Oligohydramnios | Increased | **Clinical Pearl:** The Barlow and Ortolani tests are most sensitive in the first 3 months of life. After 3 months, secondary muscle contractures develop and these tests may become negative even in true DDH. ### Why Other Directions Are Incorrect - **Anterior dislocation:** Extremely rare in DDH; occurs only with severe trauma or neuromuscular disorders - **Superior dislocation:** Not a *primary* dislocation pattern; superior migration is a secondary deformity if DDH is untreated — it is not the initiating direction - **Medial dislocation:** Not a recognized pattern in DDH; medial displacement is not anatomically favored **Reference:** Tachdjian's Pediatric Orthopaedics, 5th edition; Campbell's Operative Orthopaedics, 13th edition — both classify DDH as a posterior (posterosuperior) dislocation with posterior as the primary directional descriptor.