Focusing on the delayed complications of fusing occipital squama to cervical spine for stabilization of congenital atlantoaxial dislocation and basilar invagination

Objectives Occipito-cervical(OC) fusion is often practiced for congenital atlanto-axial dislocation (CAAD) and basilar invagination (BI) with claims of good long term outcome. Little has been discussed about the delayed complications following fusing occipital squama to cervical spine (OC fusion). We have described and analyzed delayed complications with OC fusion in our patients that helps us understand the underlying dynamics and biomechanics. Patients and methods Twenty seven patients of CAAD and BI underwent OC fusion (between 2008 and 11) after transoral odontoidectomy or direct posterior reduction with OC distraction. OC fusion was achieved using either sublaminar wiring or with precurved rods and screws or contoured loop. One patient was referred after OC fusion with contoured loop and wires with additional C1 laminectomy. The outcome (> 12 months) and delayed complications in these patients were analyzed. Results Five types of delayed complications were noticed in 6 of the 28 patients who underwent OC fusion. Five of 6 patients were adults. Vertical redislocation with posterior midline fusion (n = 2), adjacent level angular listhesis (n = 1) and swan neck deformity (n = 1) was seen in cases of OC fusion with sublaminar wires alone. Progressive C1 dislocation was seen in the lone patient who was referred after OC fusion with loop and wires. Vertical and angular dislocation was seen in 1 patient of OC fusion with precurved rod and screws. Conclusion Progressive redislocation and adjacent level dislocation are delayed complications seen after OC2 fusion. These complications are more often seen in adults, especially with sublaminar wiring/semi rigid OC fixation.