Cervical osteotomy in ankylosing spondylitis: evaluation of new developments

Abstract

Objectives: Cervical osteotomy can be performed on patients with cervical kyphosis due to ankylosing spondylitis. This study reviews the role of two new developments in cervical osteotomy surgery: internal fixation and transcranial electrical stimulated motor evoked potential monitoring (TES-MEP).

Methods: From 1999 to 2004, 16 patients underwent a C7-osteotomy with internal fixation. In 11 patients, cervical osteotomy was performed in a sitting position with halo-cast immobilization (group S), five patients underwent surgery in prone position with Mayfield clamp fixation (group P). In group P, longer fusion towards T4-T6 could be obtained that created a more stable fixation. Therefore, post-operative immobilization protocol of group P was simplified from halo-cast to cervical orthosis.

Results: Consolidation was obtained in all patients without loss of correction. Post-operative chin-brow to vertical angle measured 5 degrees (range 0-15). TES-MEP was successfully performed during all surgical procedures. In total, nine neurological events were registered. Additional surgical intervention resulted in recovery of amplitudes in six of nine events. In two patients spontaneous recovery took place. One patient showed no recovery of amplitudes despite surgical intervention and a partial C6 spinal cord lesion occurred.

Conclusion: We conclude that C7 osteotomy with internal fixation has been shown to be a reliable and stable technique. When surgery is performed the in prone position, distal fixation can be optimally obtained allowing post-operative treatment by cervical orthosis instead of a halo-cast. TES-MEP monitoring has been shown to be a reliable neuromonitoring technique with high clinical relevancy during cervical osteotomy because it allows timely intervention before occurrence of permanent cord damage in a large proportion of the patients.

Fig. 1.

a Pre-operative photograph of a patient with a cervical kyphosis due to ankylosing spondylitis. Notice an increased chin-brow to vertical angle and a horizontal gaze impairment. b Post-operative photograph of the same patient after a C7 correction osteotomy. Notice the reduction of the CBV angle and the correction of the horizontal gaze compared to the pre-operative photograph. Note the change in compensatory knee flexion and improved general balance.

Fig. 2.

a Pre-operative X-ray of the cervical spine with a rigid cervical spine due to ankylosing spondylitis. b Post-operative X-ray of the same cervical spine after a C7 osteotomy with internal fixation.

Fig. 3.

Time plots of the TES-MEP amplitudes for four bilateral muscle groups in patient 12 (Table 2). Time marks (X-axis) indicates 15 min. At each time plot, the amplitude is given as a percentage from the reference point that was set just before cervical correction (line R). Immediately after the correction (line C) a change in amplitudes is registered, with a decrease below 20% of both anterior tibial muscles and the right hand muscles. After intervention (line I) by reducing the achieved correction amplitude recovery is seen.