Change in Lordosis at the Occipitocervical Junction Following Posterior Occipitocervical Fusion in Skeletally Immature Children

Background: Occipitocervical fusion is indicated in children who develop instability of the upper cervical spine from trauma, congenital anomalies and syndromes, following decompression surgery, and from infectious or inflammatory conditions. A posterior approach using autograft and instrumentation is the most common approach to fusion. Theoretically, this approach halts the growth of the posterior spinal elements, but allows the anterior spinal column to continue to grow. Increasing lordosis at the occipitocervical junction has been shown to occur during growth in a small series of five very young children followed through skeletal maturity (1).

Purpose: To evaluate the change in occipitocervical angle during growth in children treated with occipitocervical fusion who were expected to have a minimum of two years spinal growth remaining.

Methods: Between 1985-2003, 47 children underwent occipitocervical fusion. Nineteen of these patients were less than 11 years of age at time of surgery (1.9-10.9) and were followed radiographically for an average of 5.9 years (2.3-11.8). The occipitocervical angle was measured using a variation of McRae’s line and a line from the anteroinferior aspect of the lowest fused vertebral body to the occipital wire (1). Post-operative neutral radiographs were compared to those at most recent follow-up. Data was analyzed using Student’s t-test.

Results: Six patients each were fused from occiput (O) to C2, C3, and C4. One patient was fused from occiput to C5. Average change in occipitocervical angle was 4.4 degrees (-7 to 26). Average change in angle per vertebral level per year was 0.2 degrees (-0.7 to 1.1). There was a significant difference in the change in angle between patients fused from O-C2 and those fused from O-C3 or greater (P<0 .01). There was no significant change in occipitocervical angle between groups older or younger than any age (3yo to 8yo, all P>0.10). There was no significant change in angle in patients who underwent decompression surgery prior to fusion versus those who did not (P=0.18).

Conclusions: An increasing lordosis occurs at the occipitocervical junction following fusion in skeletally immature children. The extent of involvement of the cervical spine in the fusion is the most important indicator in the severity of increased lordosis. Decompression surgery prior to fusion does not effect the development of increasing occipitocervical angle lordosis. Surprisingly, younger age at time of fusion was not significant in the development of increased lordosis. If occipitocervical fusion is indicated in a skeletally immature child, fusion in slight flexion or neutral position to account for expected anterior spinal column growth should be considered.

1. Rodgers WB, Coran DL, Kharrazi FD, Hall JE, Emans JB. Increasing lordosis of the occipitocervical junction after arthrodesis in young children: the occipitocervical crankshaft phenomenon. J Pediatr Orthop. 1997 Nov-Dec;17(6):762-5.