Indications

Our preferred technique for mobile atlantoaxial dislocation is Goel and Laheri’s technique of lateral mass plate and screw fixation, as discussed.2–6 In our experience, we have observed that in select cases, placement of the bone graft and titanium spacers by themselves made the region stable, and the need for additional plate and screw fixation could be avoided. Patients with atlantoaxial dislocation following trauma and those having only subtle or moderate recent-onset abnormal mobility of the joint and “normal taut” ligamentous assembly were more suitable for the described technique. The excessive mobility of the atlantoaxial joint and the laxity of ligaments in cases with congenital and long-standing dislocation probably make them unsuitable for the described technique in isolation, but it can still be employed in combination with most other methods of fixation. Direct operative observation of the nature of the facets and the joint and the stability of the impacted spacer within the joint space also determine if any additional fixation device is necessary.

Surgical Technique

The basic surgical steps in exposure of the region have been described in our articles on the subject.2–8 Cervical traction is given prior to induction of anesthesia, and the weights are progressively increased to ~4 to 5 kg, or one-eighth of the patient’s total body weight. The patient is placed prone with the head end of the table elevated to ~35°. The atlantoaxial facet joints are widely exposed on both sides after either sectioning or elevating superiorly the large C2 ganglion. The joint capsule is excised, and the end-plate articular cartilage is widely removed using a microdrill. The facets are distracted with the help of varying sizes of osteotomes, which are introduced in the joint with their sharp edge and then turned 90° to effect distraction. The joint space is assessed, and a specially designed spiked titanium spacer suitable for the region is impacted, or “jammed,” into the joint space using suitable instruments. The average size of the spacers used measures 12 mm in length, 10 mm in breadth, and 6 mm in height. Customized titanium spacers have multiple small holes and are tapered on one side for easier insertion during placement in the joint space ( Figs. 14.1, 14.2, 14.3, and 14.4 ). The base of the spacer has a transverse slot that assists in placement and stabilization of the instrument used for its impaction into the joint cavity. Introduction of the bone graft pieces within the joint cavity provides stability to the implant and additional opportunity for bone fusion. Multiholed titanium spacers allow bone incorporation and fusion across the distracted joint space. Corticocancellous bone graft pieces harvested from the iliac crest are stuffed into the space available around the spacers. Additional bone graft is placed over the posterior elements of C1 and C2 after decorticating the host bone area with a burr. Postoperatively, the traction is discontinued, and the patient is placed in a four-post hard cervical collar for 3 months; all physical activities involving the neck are restricted during this period. However, sitting and standing are encouraged, as during these maneuvers, the weight of the head helps in further impaction of the spacers and stability of the joint.

Although the biomechanical properties need to be evaluated further, the technique of facet distraction as described here simulates several successfully employed and evaluated interbody fixation techniques used for the subaxial spine. From our experience, it appears that distraction of the facets increases stability, as multiple ligamentous structures and axial loading of the spine contribute to stability. The extent of the stability achieved is significantly enhanced by the use of specially designed spiked spacers. The release of distraction after introduction of the spacers and bone graft assists in further impaction of the spikes of the spacers into the facets and stabilization. The distraction of the facets and impaction of the spacer and bone graft can be technically challenging, but they are c ertainly less complicated than interarticular and transarticular screw fixation methods. Because no screws are implanted, the problem of vertebral artery injury is avoided.

Between January 2003 and January 2007, six patients underwent the discussed method of fixation.1 All six patients had posttraumatic mobile and reducible atlantoaxial dislocation. The mean follow-up period was 16 months (range 5–47 months). Successful atlantoaxial stabilization and ultimate bone fusion were achieved in all patients and were documented with dynamic radiography. There were no neurological, vascular, or infective complications. During the follow-up period, all patients showed neurological recovery, and there was no indication of implant migration or failure, suggesting the effectiveness of the operation.

Because no wire, screws, plates, or rods were used for fixation, as is the norm in other fixation procedures, the extent of stability provided by the implant will have to be assessed by a larger series done over a longer period of time. The issues of the most appropriate size and type of spacer and the extent of optimum distraction necessary also will have to be evaluated further.