- Used when bone cannot accommodate fixation devices: In the young child (less than 3 years of age) or in the context of some bone dysplasias where the bone quality is poor (e.g., mucopolysaccharidoses), rigid fixation to bone may not be possible. Onlay bone graft techniques supplemented by wires or cables are then indicated.
Bone graft sources
- Rib: Rib is easy to harvest and readily available. In bone dysplasias rib quality may be poor and graft resorption can occur.
- Fibula/tibia: Harvesting a graft from the fibula or tibia requires orthopedic expertise. Taking a graft from these bones may impair return to mobility after surgery.
- Calvarial bone: Calvarial bone is easily harvested via a separate occipital incision. Calvarial bone readily regrows, and a full thickness graft can be used. The natural curve of the calvarium is suited to the occipitocervical lordosis.
- Cables join occiput to cervical laminae: The bone graft is secured to the occiput and the cervical laminae with cables. Drill holes are placed in the occiput for passage of the cables. Care needs to be taken in passing sublaminar cables. A loop of suture can be passed beneath the lamina and the loop then used to pull through the cable. A single cable should not be passed under more than one lamina.