Paediatrics: Hip disorders: developmental dysplasia of the hip

Hip disorders: developmental dysplasia of the hip

Previously known as ‘congenital dislocation of the hip’. Disorder of hip joint development resulting in hip instability/subluxation/dislocation 9 ac-etabular dysplasia.

•   Incidence: 2:1000 (but up to 20:1000 newborn hips are unstable; 90% spontaneously stabilize by 9wks).

•   Risk factors: family history (1:5), female > male (5:1), Left > right (1.5:1), racial predilection, breech presentation.

•   Aetiology: capsular laxity (increased type III collagen, maternal oestrogens), decreased intrauterine volume (breech position, first born, oligohydramnios).

•   Associations: other ‘packaging’ disorders: torticollis (20%), metatarsus adductus (10%), talipes calcaneovalgus, teratologic dislocation, Down’s syndrome.

·  Teratologic dislocation: a distinct form of hip dislocation associated with neuromuscular syndromes (e.g. myelodysplasia, arthrogryposis, chromosomal abnormalities, lumbosacral agenesis, diastrophic dwarfism). The hip is dislocated before birth. It is more difficult to treat.

Disease progression

Capsular laxity + shallow acetabulum l instability/subluxation/dislocation l muscle contracture l progressive acetabular dysplasia with a fibro-fatty substance filling the acetabulum (pulvinar); femoral head becomes hypoplastic.

History 

Usually uneventful pregnancy; parents may notice delayed walk-ing, painless limp, prone to falls. DDH may be incidental finding.

Examination

All newborn infants should be screened for DDH before discharge and then again at 6wks. High-risk infants are selected for ultrasound screening. Still controversy over selective v universal screening program.

Neonate

•   Is hip dislocated? If so, is it reducible? Ortolani’s test (O for out). Gently elevate (anteriorly) and abduct the dislocated hip to reduce it (clunk of reduction).

•   If not dislocated, can I dislocate it (i.e. dislocatable)? Barlow’s test. Gently adduct and depress (posteriorly) femur; vulnerable hip dislocates.

These 2 provocation manoeuvres become unreliable after age 6–8wks.

•   Infant: asymmetric gluteal folds, limited abduction, leg length discrepancy. Galeazzi sign—flex knees with feet together; +ve sign = affected femur appears short due to dislocated hip joint. (Note. Also +ve if femur is congenitally short; –ve with bilateral DDH).

• Older child: may walk with limp; positive Trendelenburg test. With bilateral dislocations, the only sign may be an exaggerated lumbar lordosis and limited hip abduction.

Investigations

• Age <6mths: hip US (before ossification; operator-dependent).

·>6mths: AP pelvis radiograph. A shallow acetabulum with increased acetabular index, and hypoplastic femoral head in superolateral position is demonstrated. Shenton’s line broken.

Treatment

Depends on age of child. An urgent referral to a paedi-atric orthopaedic surgeon is needed in order to start treatment as soon as possible. The aim is to achieve and maintain concentric hip reduction to encourage early acetabular development to reduce the risk of future degenerative joint disease.

Complications

• Early: inadequate reduction and redislocation.

• Intermediate: residual acetabular dysplasia; avascular necrosis.

• Late: early osteoarthritic changes.

Prognosis

Any residual acetabular dysplasia may be treated with a pelvic osteotomy as a secondary procedure. Long-term acetabular dysplasia is likely to lead to early degenerative changes in the hip.