Load-sharing through elastic micro-motion accelerates bone formation and interbody fusion

Abstract

Background context: Achieving a successful spinal fusion requires the proper biological and biomechanical environment. Optimizing load-sharing in the interbody space can enhance bone formation. For anterior cervical discectomy and fusion (ACDF), loading and motion are largely dictated by the stiffness of the plate, which can facilitate a balance between stability and load-sharing. The advantages of load-sharing may be substantial for patients with comorbidities and in multilevel procedures where pseudarthrosis rates are significant.

Purpose: We aimed to evaluate the efficacy of a novel elastically deformable, continuously load-sharing anterior cervical spinal plate for promotion of bone formation and interbody fusion relative to a translationally dynamic plate.

Study design/setting: An in vivo animal model was used to evaluate the effects of an elastically deformable spinal plate on bone formation and spine fusion.

Methods: Fourteen goats underwent an ACDF and received either a translationally dynamic or elastically deformable plate. Animals were followed up until 18 weeks and were evaluated by plain x-ray, computed tomography scan, and undecalcified histology to evaluate the rate and quality of bone formation and interbody fusion.

Results: Animals treated with the elastically deformable plate demonstrated statistically significantly superior early bone formation relative to the translationally dynamic plate. Trends in the data from 8 to 18 weeks postoperatively suggest that the elastically deformable implant enhanced bony bridging and fusion, but these enhancements were not statistically significant.

Conclusions: Load-sharing through elastic micro-motion accelerates bone formation in the challenging goat ACDF model. The elastically deformable implant used in this study may promote early bony bridging and increased rates of fusion, but future studies will be necessary to comprehensively characterize the advantages of load-sharing through micro-motion.

Keywords: Anterior; Cervical; Fusion; Load-sharing; Micro-motion; Plate.

Figure 1

The one-level 24 mm elastically deformable plates used in this study were fabricated from titanium alloy and were designed to allow controlled micro-motion during physiologic loading.

Figure 2

Single level 24 mm elastically deformable plates (left) and dynamic plates (right) were placed using standard ACDF techniques with a PEEK interbody cage filled with local autograft.

Figure 3

Mid-sagittal sections were used to quantify the volume of bone filling the PEEK interbody cage (C). The fraction of bone filling the cage was compared between the elastically deformable plate (E) group (left) (Animal 108) and the dynamic plate (D) group (right) (Animal 106). Sections are stained with Stevenel’s Blue and Van Gieson Picro Fuchsin.

Figure 4

To quantify bone formation in the interbody space, a region of interest was selected within the interbody cage (left and center). Bone tissue was selectively thresholded (right), quantified, and expressed as a fraction of the total area of the region of interest.

Figure 5

Lateral plain x-rays were taken post-operatively and at 2 and 6 weeks post-operatively of elastically deformable plate treated motion segments (left) and dynamic plate treated motion segments (right).

Figure 6

Based on CT scan, extent of bone formation and bridging was variable among animals and treatment groups ranging from robust bridging bone (left) (Animal 310 at 12 weeks) to some bone formation without bridging (right) (Animal 301 at 12 weeks).

Figure 7

Based on CT scans at 8 weeks and 12 weeks, treated levels were classified as definitely fused, probably fused, possibly fused, possibly not fused, probably not fused, or definitely not fused.

Figure 8

Bridging bone was assessed from CT scans at 8 weeks and 12 weeks. Treated levels were assessed for bridging in the anterior, posterior, left lateral, right lateral, within, and peripheral zones.