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Bone and Soft-Tissue Disorders

Heterozygous Achondroplasia!!navigator!!

  • Prototype of rhizomelic dwarfism!
    = autosomal dominant / sporadic (80%) disease with quantitatively defective endochondral bone formation; related to advanced paternal age; epiphyseal maturation + ossification unaffected
  • Prevalence: 1÷26,000–66,000 births; M <F ◊ Most common of lethal bone dysplasias!
  • normal intelligence + motor function
  • neurologic defects
  • classically circus dwarfs
  • Skull
    • flat nasal bridge ( = hypoplastic base of skull)
    • macrocephaly + brachycephaly with enlarged bulging forehead (= nonprogressive hydrocephalus)
    • relative prognathism
    • large calvarium with frontal bossing
    • depression of nasion
    • broad mandible
    • constricted basicranium + small foramen magnum:
      • communicating hydrocephalus caused by obstruction of basal cisterns + aqueduct

Cx: apnea + sudden death ← compression of spinal cord and lower brain stem

  • Chest
    • anteroposterior narrowing of chest
    • short anteriorly flared concave ribs
    • squaring of inferior scapular margin
  • Spine
    • hypoplastic bullet- / wedge-shaped vertebra:
      • rounded anterior beaking of vertebra in upper lumbar spine (DDx: Hurler disease)
      • decreased vertebral height
    • scalloped posteriorly concave vertebral margin
    • scoliosis:
      • thoracolumbar angular kyphosis (gibbus)
      • exaggerated sacral lordosis
    • stenosis of lumbar spine:
      • narrowing of interpedicular space ← laminar thickening
      • ventrodorsal narrowing of spine ← short pedicles
      • bulging / herniation of intervertebral disks
    • wide intervertebral foramina
  • Pelvis
    • protuberant abdomen; prominent buttocks
    • rolling gait from backward tilt of pelvis and hip joints
    • square flattened iliac bones = tombstone configuration
    • “champagne glass”-shaped pelvic inlet
    • lack of flaring of iliac wings
    • horizontal acetabula (= flat acetabular angle)
    • small sacrosciatic notch
  • Extremities
    • trident hand = separation of 2nd + 3rd digit and inability to approximate 3rd + 4th finger; short stubby limbs + fingers
    • limited range of motion of elbow
    • predominantly rhizomelic micromelia of long bones (ie, femur, humerus):
      • “trumpet” appearance of long bones = shortening with disproportionate metaphyseal flaring (= actually normal width of metaphysis)
      • short femoral necks
      • limb bowing
    • “ball-in-socket” epiphysis = broad V-shaped distal femoral metaphysis in which epiphysis is incorporated
    • high position of fibular head (= disproportionately long fibula)
    • short ulna with thick proximal + slender distal end
    • brachydactyly (short tubular bones of hand + feet), especially short proximal + middle phalanges

OB-US (diagnosable >21st–27th week GA):

  • shortening of proximal long bones: femur length <99th percentile between 21 and 27 weeks MA
  • increased BPD, HC, HC÷AC ratio
  • decreased FL÷BPD ratio
  • normal mineralization, no fractures
  • normal thorax + normal cardiothoracic ratio
  • three-pronged (= trident) hand = 2nd + 3rd + 4th finger of similarly short length without completely approximating each other (= PATHOGNOMONIC)

Cx:

  1. Hydrocephalus + syringomyelia (small foramen magnum)
  2. Recurrent ear infection (poorly developed facial bones)
  3. Neurologic complications (compression of spinal cord, lower brainstem, cauda equina, nerve roots): → apnea and sudden death
  4. Crowded dentition + malocclusion

Prognosis: long life

DDx: various mucopolysaccharidoses

Homozygous Achondroplasia!!navigator!!

= hereditary autosomal dominant disease with severe features of achondroplasia (= disproportionate limb shortening, more marked proximally than distally)

Risk: marriage of two achondroplasts to each other

  • large cranium with short base + small face
  • flattened nose bridge
  • short ribs with flared ends
  • hypoplastic vertebral bodies
  • decreased interpedicular distance
  • short squared innominate bones
  • flattened acetabular roof
  • small sciatic notch
  • short limb bones with flared metaphyses
  • short, broad, widely spaced tubular bones of hand

Prognosis: often stillborn; lethal in neonatal period (← respiratory failure)

DDx: thanatophoric dysplasia

Pseudoachondroplasia!!navigator!!

= part of osteochondroplasias

Prevalence: 4÷1,000,000

Etiology: mutation of genes encoding for cartilage oligomeric matrix protein (COMP) on chromosome 19 (closely related to multiple epiphyseal dysplasia)

Age at presentation: 2–4 years

  • normal facial features and intelligence
  • mean adult height 118 (range, 82–130) cm
  • disturbance of gait; joint laxity
  • Skull: normal
  • Spine
    • persistent oval-shaped vertebral bodies
    • anterior beaking, platyspondyly, scoliosis
    • odontoid dysplasia
    • disk space widening
  • Extremities
    • short long bones with flared metaphyses
    • small irregular flared epiphyses with delayed development
    • coxa vara = medial beaking of proximal femoral neck (CHARACTERISTIC)
    • genu valgum, genu varum, genu recurvatum
    • shortening + widening of phalanges and metacarpals + metatarsals
  • Pelvis
    • widened triradiate cartilage

Cx: premature osteoarthritis

DDx:

  1. Achondroplasia (large head with prominent frontal region + depressed bridge of nose, normal epiphyses, trident hands)
  2. Multiple epiphyseal dysplasia (near normal pelvis)
  3. Spondyloepiphyseal dysplasia congenita (hip joints more affected + near normal extremities)
  4. Diastrophic dwarfism (joint contractures and scoliosis at birth / in early infancy)
  5. Metatropic dwarfism (dumbbell-shaped long bones + flattened vertebrae in infancy, less epiphyseal involvement)

Outline