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Introduction
  • A metabolic bone disease caused by defective osteoclastic resorption of immature bone 
  • Epidemiology
    • prevalence
      • approximately 1 in 3.3 million
    • demographics
      • genetic inheritance (3 types)
        • malignant autosomal recessive
        • intermediate autosomal recessive
        • benign autosomal dominant (most common)
      • penetrance
        • may skip generations
        • 75% gene penetrance
  • Pathophysiology
    • pathoanatomy
      • osteoclast dysfunction leads to dense bone and obliterated medullary canals
        • caused by osteoclast inability to acidify Howship's lacuna 
      • leads to predisposition to fracture
        • lower extremity > upper extremity > axial skeleton
        • lifelong prevalence of fracture ~ 40-50%
    • Associated conditions 
      • head
        • cranial nerve palsies
          • from overgrowth of skull foramina
          • optic n. > auditory n.  > trigeminal n. > facial n.
        • osteomyelitis
          • due to lack of marrow vascularity and impaired WBC function
      • spine
        • lower lumbar pain
          • increased prevalence of spondylolysis
      • pelvis
        • coxa vara
          • commonly due to femoral neck fracture nonunion or repeated stress fractures
          • increased risk of degenerative joint arthritis
      • extremities
        • increased tendency for long bone fractures 
          • often low energy
          • transverse
          • increased risk of delayed union and malunion 
        • carpal tunnel syndrome
Classification
 
Genetic Forms
Type

Genetic

 Clinical Presentation

Malignant Autosomal recessive  
  • proton pump or chloride channel dysfunction
  • pancytopenia, hepatosplenomegaly and infection
  • fatal at an early age without bone marrow transplant
Intermediate Autosomal recessive 
  • carbonic anhydrase II dysfunction    or chloride channel dysfunction
  • usually live into adulthood
Benign Autosomal dominant
  • chloride channel dysfunction
  • Type I does not have increased fracture risk
  • Type II is known as Albers-Schonberg disease (anemia, pathologic fractures, and premature osteoarthritis)
  • general health, life span, mental function, and physique are normal
  • most common form to be managed by orthopaedic surgeon
 
Presentation
  • Autosomal recessive forms
    • symptoms
      • frequent fractures
      • progressive deafness and blindness
      • severe anemia (caused by encroachment of bone on marrow) beginning in early infancy or in utero
        • bleeding risk 
        • frequent infections 
    • physical exam
      • macrocephaly
      • hepatosplenomegaly (caused by compensatory extramedullary hematopoiesis)
      • dental abscesses and osteomyelitis of the mandible
  • Autosomal dominant form
    • symptoms
      • usually asymptomatic 
      • fractures
        • first learn of disease after fracture
        • usually a low energy pathologic fracture to lower extremity
      • anemia (fatigue)
      • joint pain
        • lower back pain common
        • early hip osteoarthritis 
    • physical exam
      • general
        • normal height and appearance
        • generalized osteosclerosis
      • range of motion
        • usually normal unless underlying osteoarthritis
      • head and neck
        • high risk of cranial nerve palsy
Imaging
  • Radiographs
    • recommended views
      • AP and lateral of bone of interest
    • general findings
      • increased cortical thickening
      • increased overall bone density
      • loss of medullary canal diameter
        • bone-in-bone appearance
    • additional findings
      • "erlenmeyer flask" proximal humerus and distal femur
      • "rugger jersey spine" with very dense bone 
      • block femoral metaphysis 
      • coxa vara
Studies
  • Histology
    • histology shows defective osteoclasts  
      • lack ruffled border and clear zone
      • islands of calcified cartilage within mature trabeculae
    • empty lacunae and plugging of the haversian canals also seen
  • Laboratory studies
    • autosomal recessive
      • increases acid phosphatase
      • may have increased PTH +/- calcium
    • autosomal dominant
      • usually normal
Treatment
  • Medical management
    • bone marrow transplant
      • indications
        • autosomal recessive (infantile-malignant) form
    • high dose calcitriol (1,25 dihydroxy vitamin D), bone marrow transplant
      • indications
        • autosomal recessive (infantile-malignant) form
    • interferon gamma-1beta
      • indications
        • autosomal dominant form
  • Cranial nerve impingment
    • Neurosurgical decompression
  • Fracture management
    • nonoperative
      • indications
        • diaphyseal long bone fractures
        • upper extremity fractures
      • techniques
        • prolonged casting and non-weight bearing
        • acceptable bone alignment, rotation and length 
      • outcomes
        • healing may be delayed
        • fracture remodeling limited
          • increased risk of malunion and refracture
    • operative
      • indications
        • proximal femur fractures
      • techniques
        • plate and screws
          • avoid intramedullary devices
          • slow steady drilling
          • constant cooling and change of drill bit
      • outcomes
        • increased risk of hardware failure
        • higher union rates and lower malunion rates compared to non-operative management
          • decreased risk of coxa vara
  • Degenerative joint disease
    • total hip arthroplasty
      • indication
        • end stage osteoarthritis
      • techniques
        • femur
          • cannulated reamers under fluoroscopy
          • short stemmed implants
          • usually uncemented components are used
        • acetabulum
          • small, sharp reamers
          • irrigation
          • multiple screws 
    • total knee arthroplasty indication
      • indications
        • end stage osteoarthritis
      • technique
        • consider navigation
Complications
  • Refracture
    • caused by
      • hard brittle bones
      • hardware failure
  • Infection
    • increased risk due to reduced tissue vascularity
  • Malunion
  • Non-union
 

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Questions (8)
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(OBQ06.123) What is the cellular mechanism responsible for osteopetrosis (Albers-Schönberg Disease)? Review Topic

QID: 309
1

Inactive osteoclast Gs alpha subunit of the G-protein coupled receptor

11%

(118/1055)

2

Inactive osteoclast carbonic anhydrase

83%

(872/1055)

3

Inactive osteoclast mitochondria

2%

(16/1055)

4

Overactive osteoblast ruffled border

2%

(22/1055)

5

Overactive osteoblast RunX2

2%

(25/1055)

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

(OBQ07.260) A 5-year-old boy has sustained multiple fractures since birth. A pelvis radiograph taken 4 years ago is shown in Figure A. A current spine radiograph is shown in Figure B. Which of the following describes the mode of inheritance of this disease? Review Topic

QID: 921
FIGURES:
1

Autosomal dominant

47%

(499/1066)

2

Autosomal recessive

43%

(460/1066)

3

X-linked dominant

3%

(35/1066)

4

X-linked recessive

6%

(63/1066)

5

Trinucleotide repeat

0%

(3/1066)

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

(OBQ12.58) Which of the following most accurately describes the cause of osteopetrosis? Review Topic

QID: 4418
1

Decreased expression of type I collagen

2%

(102/4161)

2

Decreased mineralization of osteoid matrix

6%

(238/4161)

3

Loss-of-function of GS alpha protein gene

7%

(281/4161)

4

Loss-of-function of carbonic anhydrase II gene

81%

(3360/4161)

5

Mutation of FGFR3

4%

(153/4161)

Select Answer to see Preferred Response

PREFERRED RESPONSE 4

(OBQ11.139) An enzymatic mutation leading to abnormal carbonic anhydrase function in osteoclasts would lead to a condition best illustrated by which of the following radiographs in Figures A thru E. Review Topic

QID: 3562
FIGURES:
1

Figure A

62%

(1630/2644)

2

Figure B

29%

(763/2644)

3

Figure C

8%

(204/2644)

4

Figure D

1%

(26/2644)

5

Figure E

0%

(11/2644)

Select Answer to see Preferred Response

PREFERRED RESPONSE 1

(OBQ08.110) A 22-year-old male sustained a distal radius fracture following a fall down the stairs. The emergency room physician noticed abnormal bone appearance on the radiographs and referred him for skeletal survey and further orthopaedic evaluation. Pelvis and spine radiographs are provided in Figures A and B. Which of the following best describe the etiology of the bony disease? Review Topic

QID: 496
FIGURES:
1

Defect in renal 25-(OH)-vitamin D1 alpha-hydroxylase

4%

(63/1521)

2

Defective osteoclast function

88%

(1337/1521)

3

Autosomal dominant inheritance of altered fibroblast growth factor receptor 3 (FGFR3)

3%

(41/1521)

4

Alteration in osteoblast differentiation

2%

(29/1521)

5

Inability of proximal tubules to reabsorb phosphate

3%

(42/1521)

Select Answer to see Preferred Response

PREFERRED RESPONSE 2
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