Images in spine surgery: atlantoaxial instability in Down syndrome.

A 6 year old boy with Down syndrome, presented with a 6 month history of neck pain. The pain was located in the suboccipital region with referral to the posterior part of the occiput, rostrally. His family had noticed that he had difficulty in walking and had unsteadiness of gait for a few months, which had led to a few falls. This was progressively getting worse. He did not report any loss of motor strength, sensory disturbance or bladder/ bowel incontinence. Examination showed that his neck pain was accentuated with flexion and extension. He had mildly increased tone in all extremities. His motor strength and sensory examination was within normal limits. He demonstrated hyper-reflexia in all four extremities and had a positive Babinski sign bilaterally. Sustained left sided clonus was also noted. On the flexion X-rays of his cervical spine an increased ADI (Atlanto-Dens interval) of 11 mm was noted. His CT scan confirmed this finding and also demonstrated an associated Dystropic Os Odontoideum. MRI examination showed an extensive area of high signal intensity at the cervico-medullary junction. The patient had application of a halo ring under fluoroscopic guidance and an awake intubation. He was placed in a halo vest for positioning prone. The prone positioning was performed under neuromonitoring with SSEP (Somatosensory evoked potentials) and MEP (Motor evoked potentials). This patient underwent a posterior occipitocervical instrumentation and fusion in the reduced position. He was instrumented using sublaminar wires as the anatomy of the Axis was deemed inappropriate for screw fixation. His Postoperative C-spine x-rays showed a reduced ADI and on flexion/extension views there was no sign of Atlanto-Axial instability. Post operatively he remained in a halo vest for 3 months. Resolution of patient's symptoms was noted on periodic follow-up exams with complete restoration to a stable gait.