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Updated: Dec 2 2023

Osteopetrosis

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  • summary
    • Osteopetrosis is a congenital metabolic bone disease caused by defective osteoclastic resorption of immature bone that presents with increased frequency of long bone fractures, cranial nerve palsies, and low back pain. 
    • Diagnosis is made radiographically with increased cortical thickening, increased overall bone density, and loss of medullary canal diameter.
    • Treatment is multidisciplinary approach to address fracture management, and cranial nerve abnormalities.
  • Epidemiology
    • Prevalence
      • approximately 1 in 20,000 for autosomal dominant form
      • approximately 1 in 200,000 for autosomal recessive form
    • Demographics
      • genetic inheritance (3 types)
        • malignant autosomal recessive
        • intermediate autosomal recessive
        • benign autosomal dominant (most common)
      • Penetrance
        • may skip generations
        • 75% gene penetrance
  • Etiology
    • Pathophysiology
      • pathoanatomy
        • osteoclast dysfunction leads to dense bone and obliterated medullary canals
          • caused by osteoclast inability to acidify Howship's lacuna
            • due to defective carbonic anhydrase II or chloride channel dysfunction
        • 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
          • caffey disease
            • infantile cortical hyperostosis affecting mandible in addition to clavicle, ribs, and scapulae
        • 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
      • Classification of Osteopetrosis
      • 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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