The Operation for Metabolic Bone Disease in Children

Patient Positioning

• Baseline IOM potentials prior to positioning: Electrophysiological monitoring (where available) should be established after induction of anesthesia and then confirmed once the patient is positioned.
• Optimize spinal alignment during positioning: Optimal reduction of any craniovertebral deformity must be achieved prior to surgery. If there is severe myelopathy or instability, then prior immobilization in a halo-body orthosis should be considered.
• Pin fixations for prone procedure involving occiput and cervical spine: Occipitocervical decompression and fixation procedures are performed in the prone position. The head should be immobilized with pin fixation.
• Check alignment after positioning: Fluoroscopy is used to confirm adequate craniovertebral alignment prior to commencing the surgery.  

Surgical Approach

Posterior midline approach

• Decompression and stabilization: For occipitocervical decompression and stabilization procedures a standard midline posterior approach is used.
• Expose facets if lateral fusion planned: If pedicle or lateral mass screws are to be placed, then the muscle reflection needs to extend more laterally to allow visualization of the line of the facet joint.
• Anticipate cartilaginous midline of C1 in young: In metabolic disorders, particularly in younger children, the posterior C1 ring is often cartilaginous and incomplete. Dissection needs to be carried out with caution to avoid inadvertent dural injury.
• Caudal extent varies with disease: The inferior extent of the approach is dictated by circumstance. Exposure from the occiput to the lower border of C2 suffices for most craniovertebral stabilization procedures. 

Transoral approach

• Decompression of craniovertebral junction: This approach is indicated for irreducible compression at the craniovertebral junction. This permits access from the lower third of the clivus to the body of C2.

Anterior cervical approach

• Ventral decompression and deformities: This approach is used for subaxial ventral compression or severe midcervical deformity unresponsive to traction.

Intervention

• Drill frequently safer for decompressive laminectomy: If bone or ligamentous thickening is causing posterior compression of the neuraxis , it is removed. A high-speed drill (cutting bur followed by diamond) under magnification is often safer than using rongeurs to remove bone and expose the dura in cases of severe compression. Ligamentous thickening is removed by sharp dissection.
• Variety of fusion techniques: A variety of internal fixation techniques at the craniovertebral junction are described (39, 42). The most commonly required are occipito-cervical fixation with autologous bone graft, occipitocervical fixation with instrumented fixation, and atlantoaxial fixation.
• Foramen Magnum decompression:

Closure

• Standard closure: Meticulous attention to wound closure and skin care is important to prevent wound-related complications and deep infection. Any metal instrumentation, particularly at the occiput, should be positioned so that there will be adequate soft tissue cover.  The wound is closed in layers.
• Drain can be used: A wound drain may be used but should remain for no longer than 24 hours to reduce the risk of infection.