Atlas of pathophysiology, 2 Edition

Part II - Disorders

Musculoskeletal disorders

Developmental dysplasia of the hip

Developmental dysplasia of the hip (DDH) is an abnormal development or dislocation of the hip joint present from birth.

Age Alert

DDH is the most common disorder affecting the hip joints of children younger than age 3. About 85% of affected infants are females.

DDH can be unilateral or bilateral. It affects the left hip more often (67%) than the right. This abnormality occurs in three degrees of severity:

·   dislocatable—hip positioned normally but manipulation can cause dislocation

·   subluxatable—femoral head rides on edge of acetabulum

·   dislocated—femoral head totally outside the acetabulum.

Causes

Unknown, but genetic factors may play a role.

Risk factors

·   Breech delivery (malposition in utero; DDH 10 times more common than after cephalic delivery)

·   Elevated maternal relaxin

·   Large neonates and twins (more common)

Pathophysiology

DDH may be related to trauma during birth, malposition in utero, or maternal hormonal factors. For example, the hormone relaxin, secreted by the corpus luteum during pregnancy, causes relaxation of pubic symphysis and cervical dilation; excessive levels may promote relaxation of the joint ligaments, predisposing the infant to DDH. Also, excessive or abnormal movement of the joint during a traumatic birth may cause dislocation. Displacement of the bones within the joint may damage joint structures, including articulating surfaces, blood vessels, tendons, ligaments, and nerves. This may lead to ischemic necrosis because of the disruption of blood flow to the joint.

Signs and symptoms

·   In neonates: no gross deformity or pain

·   Complete dysplasia: hip rides above the acetabulum, causing the level of the knees to be uneven

·   Limited abduction on the dislocated side as the growing child begins to walk

·   Swaying from side to side (“duck waddle”)

·   Limp

·   Asymmetry of the thigh fat folds

·   Positive Ortolani's sign

·   Positive Trendelenburg's sign

Clinical Tip

A positive Ortolani's or Trendelenburg's sign confirms DDH.

Eliciting Ortolani's sign

·   Place infant on his back, with hip flexed and in abduction. Adduct the hip while pressing the femur downward. This will dislocate the hip.

·   Then, abduct the hip while moving the femur upward. A click or a jerk (produced by the femoral head moving over the acetabular rim) indicates subluxation in a neonate younger than 1 month. The sign indicates subluxation or complete dislocation in an older infant.

Eliciting Trendelenburg's sign

·   When the child rests his weight on the side of the dislocation and lifts his other knee, the pelvis drops on the normal side because abductor muscles in the affected hip are weak.

·   However, when the child stands with his weight on the normal side and lifts the other knee, the pelvis remains horizontal.

Diagnostic test results

·   X-rays show the location of the femur head and a shallow acetabulum (also to monitor disease or treatment progress).

·   Sonography and magnetic resonance imaging assess reduction.

Treatment

Infants younger than age 3 months

·   Reduce dislocation—gentle manipulation

·   Maintain reduction—splint-brace or harness worn for 2 to 3 months to hold the hips in flexed and abducted position

·   Tighten and stabilize joint capsule in correct alignment—night splint for another month

Beginning at ages 3 months to 2 years

·   Try to reduce dislocation—gradual abduction of the hips with bilateral skin traction (in infant); or skeletal traction (in child who is walking)

·   Maintain immobilization—Bryant's traction or divarication traction for 2 to 3 weeks (with both extremities in traction, even if only one is affected); for children weighing less than 35 lb (16 kg)

·   If traction fails—gentle closed reduction under general anesthesia to further abduct the hips, followed by spica cast for 4 to 6 months

·   If closed treatment fails—open reduction and immobilization in spica cast for an average of 6 months or surgical division and realignment of bone (osteotomy)

Beginning at ages 2 to 5

·   Skeletal traction and subcutaneous adductor tenotomy (surgical cutting of the tendon)

·   Osteotomy

Delayed until after age 5

·   Restoration of satisfactory hip function is rare

P.219

HIP DISPLACEMENT

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Signs of DDH

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