Multifidus Muscle Atrophy Not Observed Following Two-segment Anterior Interbody Fusion: A Rabbit Model Study With a 12-Month Follow-up.

Study Design. Experimental study evaluated magnetic resonance imaging (MRI) and histologic changes in the multifidus muscle after anterior spinal fusion. Objective. To determine the effect of spinal fusion on the multifidus muscle in an anterior rabbit model through the use of MRI and histologic evaluation. Summary of Background Data. Retraction and splitting approach are known to be important factors in postoperative injury and atrophy of the multifidus muscle. The effect and possible mechanism of spinal fusion as an independent factor remains unknown. Methods. Thirty-six New Zealand white rabbits were divided into two groups. Animals in the fusion group underwent twolevel anterior spinal fusion whereas those in the control group underwent similar surgery without spinal fusion. The status of the multifidus muscle was evaluated with MRI and histological analysis at preoperative, 3 weeks, 6 weeks, 3 months, 6 months, and 12 months postoperatively. Results. All rabbits in the fusion group achieved solid fusion. The mean T1-weighted and T2-weighted signal intensity ratios of gross multifidus to psoas muscles were all approximately 1.0 postoperatively, with no remarkable difference between the groups. The mean lesser diameter of myofibrils in either group did not significantly differ between the preoperative and postoperative specimens. There was no significant fibrotic change or fatty degeneration for either group. Decrease in acetylcholine activity or granular degeneration of the neuromuscular junction were not observed, and normal shape and size were found in nearly all samples at all time points in both groups (P>0.05). Conclusion. After two-segment anterior spinal fusion, multifidus atrophy was not observed throughout a 12-month follow up. The rabbit model of anterior fusion is better suited to study the effect of fusion alone on the status of the multifidus muscle.