The Effect of Anterior Spinal Fusion on Spinal Canal Development in an Immature Porcine Model

Study Design. Experimental study. Objective. To investigate whether anterior spine fusion in the immature porcine spine has an adverse effect on the development of spinal canal. Summary of Background Data. Neurocentral cartilage (NCC) is located in the posterior vertebral body and responsible for the development of posterior aspect of the spinal canal. Injury to the NCC interferes with the development of the spinal canal. Methods. Twelve 8-week-old domestic pigs were used to develop an anterior fusion model. A standard procedure as L3-L4, L4-L5 discectomy, and L3-L5 anterior instrumented spine fusion was performed. To evaluate the development of the spinal canal, all subjects had computed tomography scans before the procedure and at the final follow-up. The spinal canal area was measured at the control level (CL) (L2), arthrodesis level (AL) (L4), superior (L3), and inferior (L5) instrumented level (SIL and IIL). Percent change in spinal canal area from before surgery to final follow-up was also calculated. Results. Eleven subjects were available for the study. All subjects developed local kyphosis over the fused segments. The average area of L2 (CL) was 0.56 +/- 0.06 cm(2) before surgery. The average areas of the L3 (SIL), L4 (AL), and L5 (IIL) were 0.62, 0.70, and 0.77 cm(2), respectively. At the final follow-up the average area of L2 was 1.20 cm(2). The average areas of the SIL, AL, and IIL were 1.16, 1.19, and 1.33 cm(2), respectively. The percent increase in spinal canal area at the CL was 116.6% whereas it was 85.8%, 71.0%, and 71.2% at SIL, AL, and IIL, respectively. Conclusion. Anterior spinal arthrodesis in the immature porcine spine results in iatrogenic retardation on spinal canal growth. This effect is most likely related to the tethering effect of the interbody fusion over the NCC. Although, it is difficult to directly extrapolate these findings to clinical practice, the spine surgeons operating on pediatric patients should be aware of this possibility.