Definition
- Progressive decrease in femoral neck shaft angle from a primary defect of ossification in the medial femoral neck
- Distinct from congenital coxa vara with femoral deficiency and from acquired causes
Epidemiology
- About 1 in 25,000 births
- Bilateral in a third to a half
Clinical Features
- Painless limp after walking age
- Trendelenburg gait, waddling when bilateral
- Leg length difference when unilateral
- Reduced abduction and internal rotation
- Prominent greater trochanter
- Usually presents between walking age and 6 years
Investigations
- Triangular metaphyseal fragment in the inferomedial neck, the inverted Y (Fairbank triangle)
- Hilgenreiner epiphyseal (HE) angle measured on AP pelvis
- Normal HE angle is under about 25 degrees
- Neck shaft angle is reduced and the neck is short
Management
| HE angle | Management |
|---|---|
| Under 45 degrees | Observe, likely to resolve |
| 45 to 60 degrees | Observe for progression |
| Over 60 degrees or progressive | Valgus subtrochanteric osteotomy aiming for HE angle under 38 degrees |
- Neck shaft angle under 100 degrees is also an indication for surgery
- Recurrence is more likely if correction is inadequate
Differential Diagnosis
- Congenital femoral deficiency
- Skeletal dysplasias
- Rickets and SUFE
- Skeletal dysplasias such as cleidocranial dysplasia and spondyloepiphyseal dysplasia
- Rickets and osteogenesis imperfecta
- Malunited femoral neck fracture and slipped upper femoral epiphysis
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.