- Hip dysplasia: Any abnormality in the shape, size and orientation of the femoral head, acetabulum or both
- Unstable hip: Tight fit between femoral head and acetabulum is lost and the femoral head is able to move within/outside the confines of the acetabulum
- Subluxation of hip: Incomplete contact between articular surfaces of the femoral head and acetabulum
- Dislocated hip: No contact between femoral head and acetabulum
- Teratologic dislocation of hip (TDH): Very marked and advanced changes in hip joint at birth and is in a fixed dislocated position
- Associated with other severe malformations: Spina bifida, arthrogryposis multiplex congenita, lumbosacral agenesis, chromosomal abnormalities, diastrophic dwarfism, Larsen syndrome and other rare syndromes
Risk factors:The etiology of DDH is multi factorial. There are a number of predisposing factors that lead to the development of DDH
- Female sex (4x more risk)
- Intrauterine crowding:
- Breech presentation (M/significant risk factor)
- First born child
- Hereditary ligament laxity
- Neuropediatric disorders with abnormal muscle tension: Cerebral palsy, myelomeningocele and arthrogryposis
- Swaddling (postnatal positioning): Wrapping infants in blankets or similar cloths so that movement of the limbs is tightly restricted.
- Primary acetabular dysplasia
Clinical presentations of DDH depend on the age of the child.
- Newborns: Hip instability
- Infant: Limited hip abduction on examination
- Older children and adolescents: Limping, joint pain, and/or osteoarthritis
ComplicationsRepeated, careful examination of all infants from birth and throughout the first year of life until the child begins walking is important to prevent late cases.
A failed diagnosis of DDH may follow one of four clinical patterns:
- Spontaneous reduction
- Hip subluxation
- Hip dislocation
- Dysplastic changes whilst remaining located
American Academy of Pediatrics (AAP), the American Academy of Orthopaedic Surgeons(AAOS), the Pediatric Orthopaedic Society of North America(POSN), and the Canadian Task Force recommends screening newborn for DDH.
Barlow & Ortolani provocation test:Newborn screening tests for congenital hip dysplasia
Examination of an older child:Includes careful assessment of extremities for asymmetric skin folds or leg length discrepancy in case of unilateral hip dislocation.
- Galeazzi (Allis) sign: Identifies real or apparent length of the femur by comparing the knee height while hip and knee are flexed and feet flat on the table.
- Asymmetry of thigh or gluteal folds
- Discrepancy of leg lengths
Ultrasonography:Preferred technique for clarifying physical findings, evaluating a high-risk infant, and monitoring DDH as it is followed and treated.
- Graf method: Quantitative classification system
- Harcke & Suzuki methods: Qualitative definitions
- Terjesen method: Both quantitative and qualitative descriptions
Plain radiography:The ossification center of the femoral head appears by the age of 4-6 mo. At this stage radiographs become more reliable.
- Hilgenreiner’s line: Line through tri-radiate cartilages
- Perkin’s line: Drawn at lateral acetabular margin and is perpendicular to Hilgenreiner’s line
- Shenton’s line: Curved line that begins at the lesser trochanter, goes up the femoral neck, and connects to a line along the inner margin of the pubis.
- Acetabular index: Junction of Hilgenreiner’s and a line drawn along the acetabular surface.
- Normal: 27.5° (newborn), 23.5° (6 months) and 20° (2 years)
- 30°: Upper limit of normal
Differential diagnosis:Other conditions causing leg length discrepancies
- Proximal femoral focal deficiency
- Femoral neck fracture
- Coxa vara
- Residual effects of infective arthritis
Treatment depends on age at presentation and outcomes are much better when the child is treated early, particularly during the first six months of life.