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https://upload.orthobullets.com/topic/4094/images/Clinical photo - colorado_moved.jpg
https://upload.orthobullets.com/topic/4094/images/histology and zone structure of the physis.jpg
https://upload.orthobullets.com/topic/4094/images/zone structure of the physis.jpg
https://upload.orthobullets.com/topic/4094/images/achondroplasia clinical features.jpg
https://upload.orthobullets.com/topic/4094/images/achondroplasia trident hand clinical photograph.jpg
https://upload.orthobullets.com/topic/4094/images/ap and lateral spine radiographs in achondroplasia.jpg
Introduction
  • Epidemiology
    • most common skeletal dysplasia
  • Genetics
    • autosomal dominant (AD) 
    • a sporadic mutation in >80% 
      • risk increases with advanced paternal age
    • caused by G380 mutation of FGFR3 (fibroblast growth factor receptor 3, on chromosome 4P)      
      • gain of function mutation that increases inhibition of chondrocyte proliferation in the proliferative zone of the physis  
      • results in defect in endochondral bone formation
      • a quantitative cartilage defect
  • Associated conditions
    • medical conditions
      • weight control problems
      • hearing loss
      • tonsillar hypertrophy
      • frequent otitis media
    • spinal manifestations
      • lumbar stenosis
        • patients at risk due to short pedicles, thick facets and ligamentum flavum
        • most likely to cause disability 
      • thoracolumbar kyphosis 
      • foramen magnum stenosis
        • may cause periods of apnea or suddent death in infants
Presentation 
  • Symptoms
    • history
      • normal intelligence 
      • delayed motor milestones
    • symptoms of spinal stenosis
      • pseudoclaudication and standing discomfort
      • numbness and paresthesias
      • subjective weakness
  • Physical exam
    • rhizomelic dwarfism  
      • humerus shorter than forearm and femur shorter than tibia
      • normal trunk
      • adult height ~ 50 inches
    • facial features
      • frontal bossing
    • extremities
      • trident hands (fingers same length with divergent ring and middle fingers)  
      • genu varum
      • radial head subluxation
      • muscular hypotonia in infancy
    • spine
      • thoracolumbar kyphosis 
      • excessive lordosis 
Imaging
  • Radiographs  
    • lumbar spine findings
      • shortened pedicles 
      • decreased interpedicular distance from L1-S1 (pathognomonic)
      • vertebral wedging in thoracolumbar kyphosis
      • posterior vertebral scalloping  
    • pelvis and extremities
      • recommended views
        • AP pelvis and weight-bearing hip-to-ankle AP  
      • findings
        • champagne glass pelvis (pelvis is wider than deep) 
        • Squared iliac wings
        • Inverted V in distal femur physis
  • MRI
    • indications
      • to evaluate spinal stenosis  
      • adjunct to sleep study for screening foramen magnum stenosis in infants   
Treatment - Spine Conditions
  • Thoracolumbar kyphosis
    • nonoperative
      • observation 
        • 90% improve 
      • bracing
        • if persitent vertebral wedging after age 3 years
        • may be poorly tolerated
    • operative
      • anterior strut corpectomy with posterior fusion or isolated posterior fusion
        • indications
          • bracing has failed
          • kyphosis of > 45-60° 
  • Lumbar stenosis
    • nonoperative
      • weight loss, physical therapy, corticosteroid injections
        • indications
          • first line of treatment and frequently effective
    • operative
      • multilevel laminectomy and fusion
        • indications
          • spinal stenosis with severe symptoms
          • nonoperative management has failed
  • Lumbar hyperlordosis
    • nonoperative
      • observation
        • treatment typically not required
  • Foramen magnum stenosis
    • operative
      • surgical decompression of foramen magnum
        • indications
          • sleep apnea or cord compression 
Treatment - Extremity Conditions
  • Genu varum
    • operative
      • tibial +/- femur osteotomies (based on CORA)
        • indications
          • pain or fibular thrust
          • progressive deformity
  • Short stature
    • operative
      • lower limb lengthening 
        • indications (very controversial)
          • feasible due to soft tissue redundancy
      • upper extremity lengthening
        • indications
          • upper extremity lengthening required to maintain ADL's
Complications
 
 

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Questions (17)
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(OBQ12.82) Which of the following radiographs represents the condition associated with the genetic mutation G380R in the transmembrane domain of fibroblast growth factor receptor 3 (FGFR3)? Review Topic

QID: 4442
FIGURES:
1

Figure A

5%

(203/3947)

2

Figure B

7%

(257/3947)

3

Figure C

74%

(2936/3947)

4

Figure D

10%

(401/3947)

5

Figure E

2%

(91/3947)

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(OBQ06.139) A 7-year-old presents to your office for general orthopedic evaluation at the request of his primary care physician. A clinical picture of the patient with his taller sibling is shown in Figure A. What physeal zone is affected by the mutation leading to this patient's condition? Review Topic

QID: 325
FIGURES:
1

Zone of hypertrophy

25%

(688/2743)

2

Reserve zone

1%

(38/2743)

3

Zone of proliferation

72%

(1971/2743)

4

Primary spongiosa

1%

(25/2743)

5

Secondary spongiosa

0%

(6/2743)

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(OBQ09.10) Which of the following conditions is associated with a mutation in fibroblast growth factor receptor-3 (FGFR3)? Review Topic

QID: 2823
1

Marfan syndrome

2%

(24/1141)

2

Gaucher's disease

0%

(1/1141)

3

Fibrous dysplasia

4%

(49/1141)

4

Achondroplasia

92%

(1045/1141)

5

Diastrophic dysplasia

2%

(22/1141)

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(OBQ10.161) Dwarfism caused by a defect of fibroblast growth factor receptor-3 (FGFR3) is associated with all of the following traits EXCEPT: Review Topic

QID: 3254
1

Rhizomelic limb shortening

8%

(209/2737)

2

Normal intelligence

4%

(103/2737)

3

Frontal bossing

4%

(105/2737)

4

Cervical spine instability

75%

(2057/2737)

5

Spinal stenosis

10%

(261/2737)

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PREFERRED RESPONSE 4

(OBQ06.226) Achondroplasia results from abnormal chondrocyte function in the physis. What receptor is defective and what region of the physis is affected? Review Topic

QID: 237
1

FGFR-3, zone of proliferation

78%

(791/1013)

2

FGFR-2, zone of proliferation

5%

(49/1013)

3

FGFR-3, zone of hypertrophy

15%

(151/1013)

4

FGFR-2, zone of hypertrophy

2%

(18/1013)

5

COMP, zone of hypertrophy

0%

(2/1013)

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