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Spine in Achondroplasia

- See: Pseudoachondroplasia

- Cervical Spine:
    - stenosis of foramen magnum:
           - all patients with achrondroplasty will demonstrate some radiographic stenosis of foramen magnum, and many can be shown to
                   demonstrate either some at least some clinical symptoms or some somatosensory abnormalities;
           - may contribute to hypotonia, ventilatory insufficiency such as sleep apnea, and/or sudden death in infants;
                   - in working up stenosis of the foramen magnum recognize that respiratory abnormalities may be due to restrictive lung disease (from chest shape abnormalities);

- Spine:
    - spine is affected by progressive decrease in distance between pedicles of lumbar vertebra, which diminishes size of vertebral canal and
             may cause lower extremity paralysis and bladder dysfunction;
    - prominent lumbar lordosis is seen in achondroplasia and in many other skeletal dysplasias;
             - it generally does not respond to bracing but is not of sufficient concern to warrant surgery.
    - thoracolumbar kyphosis:
             - present in most infants, resolves in 90% of affected pts as they begin to walk;
             - some authors distiguish between supple kyphosis (most patients) and rigid kyphosis (which has a worse prognosis);
             - initial treatment is to delay sitting in infancy;
             - most flexible kyphotic curves resolve once the patient starts walking (generally delayed until age 2);
             - bracing:
                     - if flexible kyphosis persists, however, it should be treated w/ extension orthosis (generally after 3 yrs);
                     - bracing is also indicated for rigid curves with kyphosis greater than 30 deg;
                     - ref: Achondroplasia: Effectiveness of an orthosis in reducing deformity of the spine
             - indications for surgery:
                     - progressive kyphosis that occurs despite bracing requires early surgery;
                     - persistent angular thoracolumbar kyphosis w/ vertebral wedging of 40 deg or more by age 5 is aggressively treated w/ surgery;
             - surgical treatment:
                     - combined anterior strut grafts and posterior fusions should be performed, w/ anterior strut grafts & posterior fusions;
                     - anterior decompression is reserved for those pts w/ neurologic comprimise;
                     - surgical options include decompression and fusion for severe kyphosis (most will correct spontaneously but anterior decompression and
                             strut grafting & posterior fusion w/o instrumentation are indicated for kyphosis > 60 deg;
    - lumbar stenosis:
             - compared to normal pts, there is 30% decrease in cross-sectional area secondary to both abnormal endochondral ossification of posterior
                     vertebral growth centers and degenerative changes;
             - stenotic deformity in the lumbar spine of pts w/ achondroplasia tends to woresen w/ increasing age;
             - mild pre-existing thoraclumbar kyphosis further narrows the space available for the neural elements;
             - hip flexion contractures seen in these patients may cause increase lumbar lordosis and aggravate the thoracolumbar kyphosis;
             - non operative treatment should include wt loss (typically problem), bracing, and exercises (unpredictable);
                     - nonsurgical brace rx of spinal stenosis are aimed at decreasing lumbar lordosis w/ flexion, thereby "opening up" spinal canal;
             - if myelography is necessary for evaluation of neurologic deficit, it should be performed via cisternal puncture above suspected lesion
                     to avoid the technical difficulty of inserting a needle into a small canal;
             - also, removal of CSF may exacerbate neurologic symptoms in already compromised small spinal canal;
             - multilevel decompression for stenosis (recommended for inter-pedicular distances of < 20 mm at L1 and < 16 mm at L5)