A newborn is noted to have bilateral hip dislocations. Ultrasound at 4 weeks of age shows a dislocatable hip with an alpha angle of 49° and a beta angle of 67°. According to Graf classification, this hip is:

• A Type I — mature normal hip (alpha >60°)
• B Type IIb — delayed ossification in infant >3 months (alpha 50–59°)
• C Type III — subluxated hip with cartilaginous roof displacement
• D Type IIa — physiologically immature hip in infant <3 months (alpha 50–59°) ✓

Explanation

In Graf ultrasound classification of DDH: alpha angle = bony acetabular roof angle (>60° = mature); beta angle = cartilaginous roof angle. Alpha 50–59°: Type IIa = immature but acceptable in infants <3 months (physiological immaturity — may mature spontaneously); Type IIb = same alpha angle but infant is >3 months, indicating delayed ossification requiring treatment. At 4 weeks of age with alpha 49°, this is Type IIa (some references include 50° boundary as marginal; in clinical practice, alpha <50° warrants harness). Type III = subluxated with alpha <43° and beta >77° with cartilaginous roof displaced superiorly.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.