Typically the instability involves the C4 – C7 spine which results in hypertrophy of the dorsal longitudinal ligament (which lies on the floor of the spinal canal) resulting in ventral spinal cord compression. A myelogram or CT will identify the ventral cord compression. When traction is placed on the cervical spine, and the myelogram/CT is repeated (“dynamic” myelogram/CT), the unstable vertebra will distract causing the dorsal longitudinal ligament to flatten. The myelogram/CT in the distracted position will then appear normal.
Surgical stabilization is the treatment of choice for the instability form of wobblers and generally carries a good to excellent prognosis. A partial ventral slot is performed in the central aspect of the two involved vertebrae and filled with cancellous bone. Intraoperative fluoroscopy is used to place 4 to 6 bone screws into the vertebral bodies. The screw heads are left protruding 1 – 1.5 cm ventral to the vertebra. Traction is applied across the affected vertebra resulting in flattening of the dorsal longitudinal ligament thereby relieving spinal cord compression. PMMA (bone cement) is placed so that it spans the two vertebrae and screw heads (Figure 2). This maintains the vertebrae in distracted position. The cancellous bone graft in the slot eventually causes the two vertebral bodies to fuse.
This procedure has been performed in hundreds of patients at the DVSC in the past 20 years with very predictable and positive results. We feel the use of intraoperative fluoroscopy greatly reduces the risks associated with surgery as well as improves the postoperative outcome.
View/download this topic in our newsletter, Cutting Edge, Fall 2007.