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 ~10^o
  • 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 < 20^o 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