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Developmental Dysplasia of the Hip
Overview
Developmental dysplasia of the hip (DDH) (aka congenital hip dislocation) constitutes a variety of developmental anomalies of the hip.
Note that hip joint laxity and acetabulum immaturity are expected in newborns within the first few weeks of life; however, persistent abnormalities are considered pathologic.
Nomenclature
The following describe various hip anomalies:
- Dislocation - the femoral head has complete loss of contact with the acetabulum (at rest and with maneuvers).
- Subluxation is essentially a partial dislocation.
- Dislocatable - the femoral head is in normal position at rest but is unstable - it can be dislocated with examination maneuvers.
- Subluxatable essentially means partially dislocatable (mild hip instability/laxity).
- Reducible - the femoral head is dislocated at rest but can be brought back into contact with the acetabulum with manipulation.
- Dysplasia - the hip joint is misshapen, typically the acetabulum is shallow (due to excess articular cartilage).
Pathogenesis
Normally, there is reciprocal developmental interaction between the acetabulum and the spherical shape of the femoral head. The femoral head originates as epiphyseal cartilage and subsequently ossifies: the epiphyseal cartilage is replaced with bone via an internal secondary ossification center. Ultimately, the femoral head is made of bone and is covered in an outer layer of articular cartilage.
In developmental dysplasia of the hip, the secondary ossification center develops in a pathological manner. Its development can be delayed, pathologically small, or aberrantly located (eccentrically). As a result, there's a pathological developmental interaction between the femoral head and the acetabulum: the femoral head is misshapen and the acetabular cartilage proliferates unchecked. This excess articular cartilage ultimately generates a shallow acetabulum that is fragile in nature.
Risk Factors
Key Risk factors for DDH include:
- Female sex (3:1 female to male ratio)
- Breech position any time during the pregnancy
- Genetic predisposition (positive family history)
- Swaddling that produces forced hip extension and adduction (so-called "traditional swaddling"). Instead the hips and knees should be slightly flexed and abducted.
Clinical Evaluation
Evaluation is performed at each well-check visit. There are various age-specific indicators for DDH. DDH is typically unilateral, so we can look for some key asymmetries. Of course when it's bilateral, these asymmetries are no longer evident.
In general, we look for the following (depending upon age):
- Hip instability
- Asymmetric leg creases
- Internal rotation of the hip
- Galeazzi test: identifies functional shortening of the femur. Despite normal leg length, the leg with the dislocated hip appears shorter because the femoral head is dislocated cranially.
- Klisic test: identifies superior displacement of the femur
- 1) Hips and knees are flexed to 90 degrees.
- 2) Adduct the hip (bring thigh to midline).
- 3) Apply posterior pressure to the knee to produce a palpable posterior hip dislocation (you will feel the hip dislocate).
- 1) Hips and knees are flexed to 90 degrees.
- 2) Abduct the hips (turn the thighs outwards)
- 3) Push the thighs anteriorly (listen for an audible clunk when the hip is reduced back into the acetabulum and feel for the reduction). A hip click is nonspecific.
- Gait abnormalities
- Trendelenburg sign: pelvic tilt
- Trendelenburg gait: lurch over the dislocated leg
- Toe-walking: compensatory toe-walking due to functional shortening of the dislocated limb.
- Hyperlordosis: in bilateral DDH
- Adduction contracture of the hip
Diagnostic Imaging
Imaging is used to confirm a clinical diagnosis of DDH
- Ultrasound provides static and dynamic imaging for children < 4 months old (the tissues are still cartilaginous at this age).
- Pelvic radiographs are used for children > 4 months old (the tissues are ossified at this age).
Management
Referral to Orthopedic surgeon.