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Developmental Dysplasia of Hip (DDH)

Introduction

Developmental dysplasia of the hip (DDH) encompasses a subset of disorders:

  • congenital dysplasia or dislocation of the hip
  • disorders associated with:
    • neurologic disorders (eg myelomeningocele, cerebral palsy) "neuromuscular dysplasia"
    • connective tissue disorders
    • myopathic disorders (eg arthrogryposis)
    • syndromic conditions (eg Larsen syndrome)
  • The stimulus for the acetabulum to develop a concave shape is the presence of a concentric, spherical femoral head
  • Deformities of the acetabulum and femoral head increase with increased time of dislocation/subluxation of the femoral head
  • Dysplasia may involve the femoral head, acetabulum or both
  • The most common findings include a shallow acetabulum and persistent femoral anteversion
  • Hip may be subluxatable or dislocated (reducible or irreducible)
    • a dysplastic hip does not necessarily need to be subluxated
    • a subluxated hip is dysplastic by definition
  • Subluxation invariably leads to degenerative joint disease

Pathophysiology

  • Multifactorial; genetic and adverse intrauterine environment ("a packaging disorder")
  • Risk Factors:
    • Breech 17-23% of children with DDH are born breech (10x risk)
    • Family history poses a 10x risk
    • 80-85%% of patients are female
    • First born children affected twice as often as siblings
      • "unstretched" uterus
  • Other associated factors:
    • Postural deformities
    • Oligohydramnios
    • Joint laxity
  • Right vs. Left:
    • Left hip affected in 60-67%%
      • adducted against mother's lumbosacral spine in the most common in utero position
    • Right hip affected in 20%
    • Both hips affected in 20%
  • Associated with:
    • Torticollis
    • Metatarsus adductus

Epidemiology

  • 1/1000 children born with dislocated hip
  • 10/1000 children born with hip dysplasia or hip subuxation
  • Most common in Native Americans, Laplanders
    • swaddling with hips in extension implicated
    • Extremely rare in Africans

Anatomy

  • Soft tissue deformities (i.e. obstacles to reduction)
    • neolimbus
      • Most common pathologic change
      • Described by Ortolani
      • Ridge of hypertrophied acetabular cartilage involving the superior, posterior, and inferior aspects of the acetabulum. 
      • Femoral head subluxates over this ridge with a palpable sensation known as the Ortolani sign
    • labrum
      • may be inverted and hypertrophied, blocking reduction of the hip
      • closed reduction with inverted labrum is associated with increased incidence of osteonecrosis
    • limbus
      • as head migrates superiorly, capsular tissue becomes interposed between the labrum and acetabular outer wall. Fibrous tissue forms secondary to mechanical stimulation and becomes known as the limbus.
      • prevents concentric reduction of hip
      • Lovell and Winter also describe a limbus as a true inverted labrum (or hypertrophied labrum)
    • ligamentum teres
      • with prolonged dislocation the ligamentum teres hypertrophies and may block reduction
    • pulvinar
      • fibrofatty tissue that may preclude reduction
    • transverse acetabular ligament
      • contracts and becomes obstacle to reduction
    • iliopsoas tendon
      • hip shortening causes tendon to become contracted
    • hip capsule
      • iliopsoas tendon impinges on elongated capsule, causing it to assume an hourglass shape
  •  Accessory centers of acetabular ossification
    • seen in 2-3% of normal hips
    • may be present in up to 60% of hips in pts with DDH
    • likely a secondary abnormality caused by pressure damage from the subluxed femoral head/neck

Natural History

  • 1/60 infants has a positive Barlow test in one or both hips
    • >60% stabilize within first week of life
    • 88% stabilize within first two months of life
    • 12% become a true congenital dislocation
  • Degree of subluxation loosely correlates with incidence and timing of the development of OA
  • Adults with bilateral complete dislocation:
    • a false acetabulum is more likely to have poor outcomes
    • back pain secondary to increased lordosis is common
  • Adults with complete unilateral dislocation
    • flexion and adduction contractures about the hip cause genu valgum and osteoarthritis of the knee

Patient History and Physical Findings

History:
  • Ask about risk factors as above
Associated Physical Findings:
  • torticollis
  • metatarsus adductus
Early Physical Findings of DDH:
  • Barlow maneuver:provocative test. hip flexed, adducted. Posterior force applied to leg. In a positive test the femoral hed is palpated as is subluxates/dislocates posterior
    • 60% of unstable hips at birth are stable at 1 week
    • 88% stable at 3 months
  • Ortolani maneuver: "click of entry". hip is abducted and anterior force is applied to trochanter.
  • Ortolani sign: palpation of femoral head gliding in and out of the acetabulum over the neolimbus.
Late Physical Findings of DDH:
  • Galeazzi sign: apparent femoral shortening
  • Asymmetry of gluteal, thigh or labial folds
  • Asymmetric abduction
  • Patients with bilateral involvement:
    • Asymmetry signs above may be absent
    • May have hyperlordosis and a waddling gait.

Imaging and Diagnostic Studies

Ultrasound:

  • Static vs. Dynamic Exam
    • Dynamic exam reveals subluxation during ROM
  • Applications
    • visual confirmation/quantification of disease in children with abnormal physical exams
    • monitoring efficacy of Pavlik harness treatment (every 7-10 days)
    • routine screening
      • used commonly in Europe
      • not cost effective
  • Morphological assessment
    • alpha angle - quantifies slope of superior aspect of acetabulum
      • 0-12 wks: >50 degrees is normal
      • 6-12 wks: > 60 degrees is normal
    • beta angle - quantifies cartilaginous aspect of acetabulum; not extremely useful
    • normal coverage: ~50%

Radiography:

  • Plain radiographs should be used to confirm diagnosis at 4-6 weeks of age
  • proximal femoral ossific center appears at 4-7 months
  • radiographic lines
    • Hilgenreiner's line
    • Perkin's line
      • medial metaphyseal beak and secondary ossification center should be located in inferior, medial quadrant of intersection of Perkin's line and Hilgenreiner's line
    • Acetabular Index
      • Useful in children 8 y/o or younger
    • Acetabular angle of Sharp
      • used after triradiate cartilage is closed
    • Shentons line - should be intact on all views in patients older than 3-4 years of age
    • Lateral center edge angle (of Wiberg)
      • useful in children 5 y/o and older
    • Anterior center edge angle (of Lequesne)
    • For adult radiographic measurements, see the Hip Dysplasia page
  • Other radiographic findings:
    • absence of teardrop
    • delayed appearance of femoral head ossification center or small ossification center
  • Look for accessory centers of ossification in the acetabulum as the patient ages. Present in as many as 60% of DDH hips. They  are likely stimulated by abnormal forces between the femoral head and acetabulum and contribure to the development of a more normal, deeper acetabulum.

    MRI
  • Need for anesthesia limits utility

Arthrogram

  • Arthrogram and EUA  are used for delayed or resistant cases
  • Can help todefine optimal position for correction of femoral or acetabular parts
  • Indicate sphericity of femoral head and congruency with the joint

Classification

  • Type 1
    • Developmental 
    • Occurs in the perinatal period and respond well
  • Type 2
    • Acquired 
    • Neuromuscular / infective origin
  • Type 3
    • Teratologic disorders

Based on Presentation

  • Early
  • Late

Classification by degree

  • Type 1: Hip stable
  • Type 2: Hip subluxable
  • Type 3: Hip dislocatable
  • Type 4: Hip dislocated

Radiological (Tonnis)

  • Type 1: Femoral capital epiphysis medial to Perkins line and below Hilgenreiners line
  • Type 2: Epiphysis below Hilgenreiners line but lateral to Perkins
  • Type 3: Epiphysis lateral to Perkins line at the level of the acetabular margin
  • Type 4: Epiphysis lateral to Perkins line and above the acetabular rim

Classification of AVN in DDH (Kalamchi)

  • Grade 1
    • Involvement of the femoral capital ossific nucleus 
    • Due to a transient deficiency of the blood supply 
    • Normal head or slight loss of height
  • Grade 2
    • Epiphysis and lateral physis involved 
    • Head in valgus with short lateral portion of neck 
    • Lateral growth plate may close prematurely
  • Grade 3
    • Epiphysis and central physis involved
  • Grade 4
    • Epiphysis and all of physis involved 
    • Coxa breva or coxa vara 
    • Trochanteric overgrowth

Differential Diagnosis (Painless limp)

  • Infantile coxa vara
  • Pathological dislocation
  • Poliomyelitis with evidence of paralysis

Treatment

Fundamental goals are the same for all ages: obtain and maintain reduction of the hip. This is achieved more easily at a young age and provides the optimal physical environment for the development of a normal femoral head and acetabulum.
Nonoperative treatment:
  • 0-6 months: Pavlik harness
    • Maintains reduction and provides stabilization by preventing hip extension and adduction
    • for the unstable hip: if worn full-time for 6 weeks, instability resolves in 95% of cases
    • for the subluxated or dislocated hip: 85% success rate for using the harness to guide the reduction
    • harness should be worn for 6-12 weeks after clinical stability is achieved
    • x-rays are not indicated until 3 months after stability is achieved
    • after 6 months of age failure rate is >50% for treatment with Pavlik Harness
    • contraindicated in patients with muscle imbalance (cerebral palsy, myelodysplasia), contractures (arthrogryposis), abnormal connective tissue laxity (Ehlers-Danlos Syndrome)
    • Application:
      • chest strap at nipple line
      • hip flexion at 100-110 degrees
      • hip abduction kept in "safe zone" (between redislocation point and maximum comfortable abduction)
      • the brace should be checked ever 7 -10 days for necessary adjustments
    • Complications:
      • excessive hip flexion may lead to:
        • inferior dislocation
        • femoral nerve compression neuropathy that resolves with brace removal
      • damage to cartilaginous femoral head and proximal femoral physeal plate secondary to forced abduction  or persistent use of harness despite the failure of reduction in a patient with complete dislocation
      • knee subluxation
      • brachial plexus palsy
      • skin breakdown in groin and popliteal fossa
  • 6months to 18 - 24  months of age: Closed vs. Open Reduction
    • Examine under anaesthesia 
      • Perform arthrogram
      • May need adductor release
      • If reduced, spica for 6 -12 weeks and follow with X-Rays
      • If concentric reduction not achieved or "unsafe", perform open reduction
        • May need derotation femoral osteotomy
        • +/- femoral shortening
        • +/- acetabular procedure
  • Older than 2 years: Open reduction
  • Older than 4 years need open reduction and femoral shortening
  • Older than 8 years
    • Minimal potential for femoral or acetabular remodeling;
    • Perform salvage procedures
Operative treatment:

Procedures:

  • Varus rotation osteotomy best done before age of 4 years, because of the limited ability of the acetabulum to remodel after this age
  • After the age of 4 years, acetabular procedures are thought to be more effective than femoral
Reshaping (Incomplete) Osteotomies
  • Dega
    • Osteotomy through outer table only
    • Hinge on open triradiate cartilage
  • Pemberton 
    • Changes direction/shape of acetabular roof at triradiate cartilage
    • Must be done in young child, so that acetabulum can remodel
    • May cause stiffness, as distortion of acetabular roof increases acetabular pressure 
    • Increases volume of acetabulum with greater correction, esp. for those with true acetabular dysplasia
Redirectional (Complete) Osteotomies
  • Salter (Single Innominate Osteotomy)
    • Covers by rotation of acetabulum on symphysis pubis
    • Improves acetabular index by ~10o
    • Lengthens by ~ 1 cm, may need to shorten as well as do varus/derotation
  • Sutherland
    • Like Salter
    • Also osteotomy through pubic body, which brings freedom of movement at medial point of rotation
  • Dial
    • Periarticular acetabular osteotomy, osteotomy outside capsule
    • Risks : vascular damage, sciatic nerve damage
  • Steele
    • Great latitude in correction
  • Ganz (aka "Bernese") Periacetabular osteotomy
    • Technically difficult
    • Must be done after skeletal maturity
    • Posterior column is left intact
    • Most freedom of correction
    • No post op immobilization is required. Crutch weight bearing encouraged.
    • Pelvic shape is maintained (permits normal vaginal delivery)
Salvage procedures
  • Chiari
    • Described 1955 for acetabular dysplasia associated with DDH
    • Osteotomy just above joint capsule angled 10° up and inward, displace at least 50% of pelvic thickness
    • Complications : cut too high or too low, sciatic nerve injury
    • 15 year follow up
      • Good result 75%
      • Fair 9%
      • Poor 16%
      • Better result if patient less than 4 years old at operation and adequate medialization
  • Shelf (Wilson + Staheli)
    • Allows coverage with congruity, leaves hip lateral
  • Trochanteric Transfer
  • Contralateral epiphyseodesis

Pearls and Pitfalls

Tips and problems to avoid

Postoperative Care

Include immediate postoperative care and rehabilitation

Outcome

  • Dysplastic acetabulum with CE angle < 20o has tendency for hip to subluxate and restricted abduction and flexion
  • Estimated that 20 - 50% of degenerative OA is secondary to subluxation of the hip or dysplasia, as measured by a reduction in the CE angle
  • Pavlik harness has 98% success for acetabular dysplasia and 85% success in the treatment of DDH
ref: Malvitz and Weinstein JBJS 76A 1777-1792, 1994. 152 dislocated hips in 119 patients, average follow up 30 years, treated with closed reduction:
  • Hips reduced younger do best
  • AVN with growth disturbance occurred in 60%, in some not obvious for many years
  • The young infant who does get AVN tends to get a more severe form of it; however, the younger infants have a much less chance of AVN
  • 65 hips (43%) had X-Ray evidence of OA
  • 17 hips had THR, with patient average age of 36 years
  • Function tended to decrease with time, so prognosis is guarded for these patients

Complications

  • PavliK harness fails to reduce the hip in as many as 8% of cases
  • AVN occurs in as many as 2.4% of cases splinted in the safe zone
  • AVN incidence increases in open procedures with an incidence of 
    • 8% for antero-lateral approaches
    • 10% for inguinal approaches
    • 17% for the Ludloff (medial) approach 
    • 5% when shortening femoral osteotomy was combined with open reduction
  • Salter indicators of AVN
    • Failure of appearance of the ossific nucleus 1 year after reduction
    • Failure of growth of an existing nucleus 1 year after reduction
    • Broadening of femoral neck 1 year after reduction
    • Increased radiographic density of the femoral head followed by radiographic appearance of fragmentation
    • Residual deformity of head and neck when re-ossification is complete
      • Coxa vara
      • Coxa magna
      • Coxa plana 
      • Coxa breva (short broad femoral neck)
    • Pre-reduction traction and adductor tenotomy did not decrease the incidence of AVN 
      • Abduction into the frog position was the incriminating factor, causing compression of vessels of the trochanteric anastomosis and retinacular vessels
      • Long term growth defect occurred in 0.7%

References

 

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