Updated: 6/16/2021

Achondroplasia

0%
Topic
Review Topic
0
0
N/A
N/A
Questions
18
0
0
100%
0%
Evidence
11
0
0
100%
0%
Videos / Pods
1
Topic
Images
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
  • summary
    • Achondroplasia is a common congenital skeletal dysplasia caused by an autosomal dominant mutation in the fibroblast growth factor receptor 3 gene. Patients present with rhizomelic dwarfism with characteristic features such as lumbar and foramen magnum stenosis, frontal bossing and normal intelligence. 
    • Diagnosis is made based on family history associated with typical clinical and radiographic features.
    • Treatment involves observation and physical therapy for majority of spinal anomalies. Surgical spinal instrumentation and fusion are indicated in patients with progressive spinal stenosis associated with neurological deficits. 
  • Epidemiology
    • Incidence
      • most common skeletal dysplasia
  • Etiology
    • Genetics
      • a sporadic mutation initially in >80%, then AD
        • 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
Questions (18)
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK

(OBQ14.21) A 13-month-old child is found to have the abnormal spine imaging shown in Figure A. The deformity resolves spontaneously when he begins to walk. What is the most common form of inheritance for the gene defect associated with his underlying condition?

QID: 5431
FIGURES:
1

Autosomal dominant

55%

(1329/2416)

2

Autosomal recessive

26%

(622/2416)

3

X-linked dominant

6%

(135/2416)

4

X-linked recessive

10%

(244/2416)

5

Mitochondrial

2%

(60/2416)

L 4 B

Select Answer to see Preferred Response

Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK

(SBQ13PE.99.1) Which of the following is associated with achondroplasia?

QID: 214243
1

Atlanto-axial instability

35%

(449/1293)

2

Central sleep apnea

36%

(464/1293)

3

Dural ectasia

13%

(168/1293)

4

Genu valgum

12%

(157/1293)

5

Cauliflower ear

4%

(50/1293)

L 4 C

Select Answer to see Preferred Response

(SBQ13PE.62) A 13-year-old girl presents with her mother for evaluation of left knee pain. Her mother also has short stature and is followed in the orthopaedic spine clinic. Both patients have frontal bossing. What is the genetic defect responsible for this condition?

QID: 5155
FIGURES:
1

Cartilage oligomeric matrix protein (COMP) on chromosome 17

6%

(147/2334)

2

Cartilage oligomeric matrix protein (COMP) on chromosome 19

6%

(149/2334)

3

Fibroblast growth factor receptor 3 (FGFR-3)

84%

(1962/2334)

4

Runt-related transcription factor 2 (RUNX2)

2%

(37/2334)

5

Core-binding factor subunit alpha-1 (CBF-alpha-1)

1%

(15/2334)

L 2 A

Select Answer to see Preferred Response

Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK

(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)?

QID: 4442
FIGURES:
1

Figure A

5%

(242/5209)

2

Figure B

7%

(339/5209)

3

Figure C

76%

(3946/5209)

4

Figure D

9%

(490/5209)

5

Figure E

2%

(127/5209)

L 2 A

Select Answer to see Preferred Response

Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK

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

QID: 3254
1

Rhizomelic limb shortening

7%

(243/3281)

2

Normal intelligence

4%

(120/3281)

3

Frontal bossing

4%

(126/3281)

4

Cervical spine instability

75%

(2462/3281)

5

Spinal stenosis

10%

(326/3281)

L 2 C

Select Answer to see Preferred Response

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

QID: 2823
1

Marfan syndrome

3%

(42/1510)

2

Gaucher's disease

0%

(4/1510)

3

Fibrous dysplasia

5%

(69/1510)

4

Achondroplasia

91%

(1370/1510)

5

Diastrophic dysplasia

2%

(23/1510)

L 1 A

Select Answer to see Preferred Response

(SAE07PE.11) Where is the underlying defect in a rhizomelic dwarf with the findings shown in Figure 5?

QID: 6071
FIGURES:
1

Type I collagen

5%

(14/305)

2

Type II collagen

3%

(10/305)

3

Collagen oligomeric protein (COMP)

11%

(34/305)

4

Sulfate transport

9%

(27/305)

5

Fibroblast growth factor receptor 3

71%

(217/305)

L 3 E

Select Answer to see Preferred Response

(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?

QID: 325
FIGURES:
1

Zone of hypertrophy

24%

(777/3234)

2

Reserve zone

2%

(51/3234)

3

Zone of proliferation

72%

(2341/3234)

4

Primary spongiosa

1%

(36/3234)

5

Secondary spongiosa

0%

(10/3234)

L 2 A

Select Answer to see Preferred Response

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

QID: 237
1

FGFR-3, zone of proliferation

77%

(1031/1345)

2

FGFR-2, zone of proliferation

5%

(69/1345)

3

FGFR-3, zone of hypertrophy

15%

(206/1345)

4

FGFR-2, zone of hypertrophy

3%

(34/1345)

5

COMP, zone of hypertrophy

0%

(2/1345)

L 2 B

Select Answer to see Preferred Response

Evidence (11)
VIDEOS & PODCASTS (3)
EXPERT COMMENTS (7)
Private Note