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Developmental Dysplasia of Hip (DDH)

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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 90o 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°
    • > 30o indicates dysplasia
    • Significant if > 40o
  • 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
    • ~ 30o is normal
    • < 20o 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 (90o - 120o flexion and half way between full abduction and dislocation, usually about 60o 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 < 20o (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 ~10o
      • 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 < 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% 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