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- See: Pseudoachondroplasia

- Discussion:
    - autosomal dominant disorder;
    - arises due to a point mutation for the gene encoding a fibroblast growth factor (Fibroblast growth factor receptor 3)
    - over 80% of all persons with this disorder are born to parents who are not achondroplastic, & such parents rarely have second
          achondroplastic child;
          - it is presumed in these instances that disorder is consequence of mutation and may be related to a mutation in a fibroblast
                   growth factor gene;
    - growth of endochondral bones is abnormal in achondroplasia and causes disproportionate and rhizomelic shortening of limbs;
          - since intramembranous ossification is unaffected head is relatively large and the forehead is prominent;
          - long bones are wide with flaring of the metaphyses;
    - characteristics in infancy:
          - rhizomelic short limbs and normal trunk height,
          - prominent frontal bossing & depressed nasal bridge;
          - midface hypoplasia, and relative mandibular prominence;
          - maxillary hypoplasia may lead to dental crowding and malocclusion;
          - recurrent otitis media will lead to higher incidence of conductive hearing loss in adults;

- Development & Motor Milestones:
    - patients often have a delay in reaching milestones;
    - many children do not begin to walk independently until 2-3 years;
    - hypotonic ligamentous laxity, relatively large head, & disproportionate trunk and limbs may contribute to problem;
    - obesity is common;
    - cognition:
           - intelligence is normal;
           - early speech may be difficult because of tongue thrust, but this usually resolves by school age;

- PreOperative Assessment:
    - careful preoperative assessment and postoperative monitoring of pulmonary function are necessary;
    - respiratory:
           - significant respiratory problems develop in 10% of affected individuals because of an abnormal thoracic cage configuration,
                  midfacial hypoplasia, upper airway obstruction, or spinal cord compression at the foramen magnum;
    - hydrocephalus:
           - 3% of affected individuals have hydrocephalus; detection is difficult because head size may run above 97th percentile;

- Spine in Achondroplasty:

- Upper Extremity:
    - elbow:
           - elbow extension is often diminished & posterolateral radial head dislocation may occur;
    - hands:
           - hands are short and broad;
           - trident hands (increased space between third and fourth fingers);
           - fingers are three-pronged with a space between the third and fourth digits, producing characteristic trident hand, a feature that
                     is lost late in childhood;

- Pelvis:
    - pelvis is broad and short, w/ relatively wide iliac wings & horizontal acetabular margins.

- Lower Extremity:
    - flexion contractures of the hip, and genu varum;

    - knee:
           - genu varum and varus ankle deformities are found;
           - unlike dysplasias that involve the epiphysis, DJD is rare, and prophylactic surgical correction of
                      deformities is probably not indicated;
           - bracing is not beneficial because orthosis often opens the joint medially, secondary to ligamentous laxity;
           - fibular epiphysiodesis and/or tibial osteotomies may be required for severe genum varum;

- Misc:
    - other problems include dental malocclusion, communicating hydrocephalus, arthritis, and resistant rickets.  
    - The effect of treatment on growth and deformity in hypophosphatemic vitamin D-resistant rickets.

Orthopaedic aspects of achondroplasia.

Mutations in the transmembrane domain of FGFR3 cause the most common genetic form of dwarfism, achondroplasia

Disorders of the Pediatric and Adolescent Spine.  Spinal Manifestations of Skeletal Dysplasias.