Developmental Dysplasia of Hip (DDH)

Developmental dysplasia of the hip refers to a broad spectrum of conditions characterised by instability of the hip with subluxation or dislocation due to acetabular or femoral dysplasia.

Incidence

• 6.4 per 1000 births in Australia
• 7.4 per 1000 births in South America 
• Females more than Males
  • 80% of all dislocations are females
  • Breech female has 1 in 35 chance of DDH
• 60% of DDH are the first born child
• Siblings of affected children have 10 times increased risk of DDH
• Left hip more than Right hip
  • 60% left
  • 20% right
  • 20% bilateral

Aetiology

• Genetic predisposition
• Joint laxity (dominant inheritance)
• Acetabular dysplasia (polygenic inheritance)
• 41% concordance with monozygotic twins, 2.8% with dizygotic
• Associated with :
  • Torticollis
  • Metatarsus adductus
  • Calcaneovalgus feet
  • Congenital recurvatum or dislocated knee
• Racial
  • Aborigines, Lapps, Navajo and Italians of South Tyrol have increased incidence (may be due to swaddling in extension)
• Environmental
• Hormonal influence 
  • Joint laxity more in females
  • Lower incidence in boys, as male hormones reduce effect
    • Hormonal effect lasts about 10 days
    • Estrogens inhibit collagen cross linking and may contribute to laxity
• Intra-uterine malposition
  • 10 fold increased risk with breech
  • Associated with oligohydramnios
  • Increased incidence among first born children
• Teratologic
  • Arthrogryposis
  • Chromosomal abnormalities
  • Sacral agenesis
• Acquired
  • Sepsis : The head and neck of the femur may be destroyed leading to pathological dislocation
    • TB 
    • Pyogenic
  • Traumatic
  • Unbalanced paralysis, particularly adductor spasm
    • CP
    • Spina bifida
    • Polio

Pathology

• Acetabulum and femoral head develop from primitive mesenchymal cells 
• At 7 weeks gestation a cleft develops in pre-cartilaginous cells
• The normal development of the acetabulum is dependant on the presence of the femoral head
• There is little remodelling capacity of the acetabulum after the age of 7 - 8 years 
• If the head is not contained in the developing acetabulum, false acetabulum develops
• Femoral neck is usually short and excessively anteverted
• Capsule remains intact and may develop hour glass restriction, due to indentation by psoas tendon
• Cartilaginous labrum is often large and may be folded into the joint
• Ligamentum teres is often unduly thick and may limit reduction
• Muscles arising from pelvis gain adaptive shortening
• Rate of growth in first year is rapid, if hip dislocates during this time neither develop normally
• Transverse acetabular ligament is displaced superiorly resulting in possible block to reduction
• Subluxation of the hip will result in more rapid degeneration of the hip and earlier development of OA than frank dislocation
• Blocks to reduction :
  • Inverted limbus
  • Hour-glass constriction of capsule (psoas tendon over acetabular inlet) 
  • Capsular adhesions
  • Deformation of head or neck of femur
  • Thick ligamentum teres 
  • Hypertrophy of transverse ligament
  • Acetabular floor filled with fibro-fatty tissue (the pulvinar)
  • Tight adductors or psoas

Clinically

• Neonatal history important (breach, assisted delivery, etc.)
• Hips may be asymptomatic
• Clicky hips may be evident 
• Limitation of abduction on nappy changes
• Asymmetrical skin creases
• Leg may be slightly short and externally rotated
• Delayed walking not usually a feature
• Limp or asymmetry evident after walking commences, but bilateral dislocation may be less apparent
• Bilateral dislocation
  • No asymmetry
  • Abnormally wide perineal gap
• Decreased abduction, esp. in flexion
• Ortolanis' test
  • Tests hip reducibility by manoeuvre
  • Gentle abduction + anterior translation
• Barlows' test
  • Hip flexed to 90°, slight abduction
    • Pressure over greater trochanter may reduce a dislocated hip
    • Pressure over lesser trochanter may dislocate an unstable hip
  • Is a two stage test :
    • Is the hip dislocated ?
    • Is the hip dislocatable ?
      • 60% of unstable hips at birth are stable at 1 week
      • 88% stable at 3 months
      • Only 12% remain unstable
• Galleazzi sign : The affected limb is short in the thigh when the knee is flexed to 90^o with the hips flexed to 45° and the heels at the same level
• Even with screening, a significant number are presenting late

X-Rays

• Earliest X-Rays of value at 6 weeks to 3 months
• Associated with delayed appearance of the epiphysis
• Hilgenreiners line is a horizontal line through triradiate cartilage 
• Perkins vertical line is drawn from outer edge of acetabulum
• Should see head medial to vertical line and below horizontal line
• Acetabular angle (index) is the angle between Hilgenreiners line and a line drawn from upper outer acetabular edge toward triradiate cartilage
  • Normal is < 27.5°
  • > 30^o indicates dysplasia
  • Significant if > 40^o
• Von Rosen's line : with hips abducted 45° and 25° internally rotated, line drawn up the shaft of the femur should intersect acetabulum and not ilium above it
• Shentons line should be continuous
• Centre edge angle (Wiberg) is the angle between a vertical line passing through femoral head center and a line drawn from femoral head center toward upper outer edge of acetabulum
  • ~ 30^o is normal
  • < 20^o indicates dysplasia

Other Investigations

 
U/S

• Valuable in the very young, with 90% sensitivity
• Reliable up to the age of 1 year
• Graf pioneered using static measurements taken from coronal scans, described 4 types of hip based on 3 lines and 2 angles:
  • Lines
    1. Baseline : line along outer ilium to the point where perichondrium unites the with the ilium
    2. Inclination line : from the point where the perichondrium unites with the ilium to the acetabular labrum
    3. Acetabular roof line : from the lower edge of the ilium at the triradiate cartilage to the point where perichondrium unites with ilium
  • Angles
    • ? : between 1 and 2 above 
    • ? : between 1 and 3 above

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

CT Scan

May need CT to

• Delineate bony anatomy 
• Femoral anteversion 
• Location of uncovered femoral head
• Assist in planning osteotomy

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

Before weigh bearing

• Splint in the safe zone (90^o - 120^o flexion and half way between full abduction and dislocation, usually about 60^o abduction)
• Reassess every six weeks 
• Continue splint to three months at which time do X-Ray
• Duration of splinting is related to the age at diagnosis, development of the acetabulum and stability of the hip
  • Rough guide : splint for twice the age of the patient when splint applied
  • If only a dysplastic hip and no frank dislocation six weeks may be enough
• Unreducible hips may need pre-operative traction (Pughs) 

After weight bearing (crawling)

• Principle is to reduce and hold the hip in the joint until it is stable
• Traction may be required to restore normal station of the hip prior to surgery to reduce the risk of AVN
  • The majority of orthopaedist would use traction and continue for an average of three weeks, but the efficacy of pre-operative traction remains questionable
  • In children older than 3 years, traction before open reduction has been reported to produce poorer results than femoral shortening 
• Continuation of attempts at closed reduction for more than four weeks is very unlikely to succeed and will only accentuate the pathological process
• Closed reduction alone leads to high incidence of AVN
• 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
• More than 2 years : need open reduction
• More than 4 years : need open reduction and femoral shortening
• More than 8 years
  • No scope for femoral or acetabular remodelling 
  • Perform salvage procedures

Treatment after Age limit

• Treatment of the dislocation is unwise over a certain age as complications of treatment outweigh the benefits at this point
• Age limit for bilateral dislocation is 4 years (lower as the risk of intervention is doubled and partial failure leads to asymmetry)
• For unilateral dislocation possibly 6 years and definitely 8 years is the upper limit, after which salvage procedures are the choice
• Trochanteric advancement may improve gait and partially restore function
• Treatment should be completed by the age of 5 years

Acetabular dysplasia

• 1 year old and under : Splint as for DDH 
• After 1 year : Operation if head remains uncovered

Indications for open reduction

• Failure to achieve reduction
• Femoral head persistently above triradiate cartilage 
• Femoral head will not enter acetabulum
• Position required to maintain reduction is extreme
• If arc of reduction and re-dislocation is < 20^o (small safe zone)
• Failed previous reduction
• Age : Children> 3 years old generally accepted in association with femoral shortening
• Inverted limbus

Reconstruction procedures if

• Continued subluxation or instability
• Failure of adequate acetabular development

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
• Reconstruction procedures
  • All redirect acetabulum (except Pemberton) 
    • Medialise : Chiari, Sutherland
    • Lateralise : Steele (also decreases abductor distance)
  • Sutherland 
    • Like Salter
    • Also osteotomise through pubic body, which brings freedom of movement at medial point of rotation
  • 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
  • Salter
    • 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
  • Dial
    • Periarticular acetabular osteotomy, osteotomise outside capsule
    • Risks : vascular damage, sciatic nerve damage
  • Steele
    • Great latitude in correction
• 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 medialisation
  • Shelf (Wilson + Staheli)
    • Allows coverage with congruity, leaves hip lateral
  • Trochanteric Transfer
  • Contralateral epiphyseodesis

Complications

• Pavlic 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%

Prognosis

• 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% sucess 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

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