Introduction: The use of adjunctive techniques such as electrical stimulation may improve the rate of successful anterior lumbar interbody fusion. The purpose of this study was to determine if supplemental direct current electrical stimulation of a titanium anterior spinal fusion device increases the incidence and extent of bony fusion in a nonhuman primate model.

Methods: Anterior lumbar interbody fusion was performed at the L5–L6 level in 35 adult pigtail macaque monkeys with iliac crest graft and either a titanium fusion device or a femoral allograft ring. The fusion devices of some animals received either high current (100μA) or low current (28μA) electrical stimulation using an implanted generator for the duration of the 12- or 26- week evaluation period. All animals were studied using AP and lateral radiographs, CT imaging, nondestructive mechanical testing, and qualitative and quantitative histology. Specimens were scored for presence of fusion according to a semi-quantitative scale (0 = No healing, 1 = Minimal consolidation, 2 = Consolidation, 3 = Bridging callus, 4 = Bridging callus with trabeculations, 5= Evidence of bony remodeling of callus). A similar scale was used to score the extent of fusion.

Results: As shown in Table 1, both low and high current stimulation groups had generally increased incidence of bony fusion compared to the non-stimulated and femoral allograft ring groups. At 26 weeks, the extent of bony fusion increased with the devices from 43% to 75% in a dose-dependent fashion, compared to 25% with the femoral rings. Mechanical testing also demonstrated similar increases in mechanical stiffness in a dose-dependent fashion.

Discussion: Adjunctive electrical stimulation of an anterior titanium spinal fusion device improved success rate and overall fusion quality compared to non-stimulated devices and femoral allograft rings. Stimulated devices may be particularly beneficial in patients with known risk factors for nonunion.

INTRODUCTION: The use of adjunctive techniques such as electrical stimulation may improve the rate of successful anterior lumbar interbody fusion. The purpose of this study was to determine if supplemental direct current electrical stimulation of a titanium anterior spinal fusion device increases the incidence and extent of bony fusion in a nonhuman primate model.

METHODS: Anterior lumbar interbody fusion was level in 35 adult pigtail macaque performed at the L₅–L₆ monkeys with iliac crest graft and either a titanium fusion device or a femoral allograft ring. The fusion devices of some animals received either high current (100 μA) or low current (28 μA) electrical stimulation using an implanted generator for the duration of the 12- or 26-week evaluation period. All animals were studied using AP and lateral radiographs, CT imaging, nondestructive mechanical testing, and qualitative and quantitative histology. Specimens were scored for presence of fusion according to a semi-quantitative scale (0 = No healing, 1 = Minimal consolidation, 2 = Consolidation, 3 = Bridging callus, 4 = Bridging callus with trabeculations, 5= Evidence of bony remodeling of callus). A similar scale was used to score the extent of fusion.

RESULTS: As shown in Table 1, both low and high current stimulation groups had generally increased incidence of bony fusion compared to the non-stimulated and femoral allograft ring groups. At 26 weeks, the extent of bony fusion increased with the devices from 43% to 75% in a dose-dependent fashion, compared to 25% with the femoral rings. Mechanical testing also demonstrated similar increases in mechanical stiffness in a dose-dependent fashion.

DISCUSSION: Adjunctive electrical stimulation of an anterior titanium spinal fusion device improved success rate and overall fusion quality compared to non-stimulated devices and femoral allograft rings. Stimulated devices may be particularly beneficial in patients with known risk factors for nonunion.