Elsevier

World Neurosurgery

Volume 82, Issue 6, December 2014, Pages 1388-1393
World Neurosurgery

Peer-Review Report
Biomechanical Analysis of Disc Pressure and Facet Contact Force After Simulated Two-Level Cervical Surgeries (Fusion and Arthroplasty) and Hybrid Surgery

https://doi.org/10.1016/j.wneu.2014.06.013Get rights and content

Objective

The objective of this study was designed to compare 2-level cervical disc surgery (2-level anterior cervical discectomy and fusion [ACDF] or disc arthroplasty) and hybrid surgery (ACDF/arthroplasty) in terms of postoperative adjacent-level intradiscal pressure (IDP) and facet contact force (FCF).

Methods

Twenty-four cadaveric cervical spines (C3-T2) were tested in various modes, including extension, flexion, and bilateral axial rotation, to compare adjacent-level IDP and FCF after specified treatments as follows: 1) C5−C6 arthroplasty using ProDisc-C (Synthes Spine, West Chester, Pennsylvania, USA) and C6−C7 ACDF, 2) C5−C6 ACDF and C6−C7 arthroplasty using ProDisc-C, 3) 2-level C5−C6/C6−C7 disc arthroplasties, and 4) 2-level C5−C6/C6−C7 ACDF. IDPs were recorded at anterior, central, and posterior disc portions.

Results

After 2-level cervical arthrodesis (ACDF), IDP increased significantly at the anterior annulus of distal adjacent-level disc during flexion and axial rotation and at the center of proximal adjacent-level disc during flexion. In contrast, after cervical specified treatments, including disc arthroplasty (2-level disc arthroplasties and hybrid surgery), IDP decreased significantly at the anterior annulus of distal adjacent-level disc during flexion and extension and was unchanged at the center of proximal adjacent-level disc during flexion. Two-level cervical arthrodesis also tended to adversely impact facet loads, increasing distal rather than proximal adjacent-level FCF.

Conclusion

Both hybrid surgery and 2-level arthroplasties seem to offer significant advantages over 2-level arthrodesis by reducing IDP at adjacent levels and approximating FCF of an intact spine. These findings suggest that cervical arthroplasties and hybrid surgery are an alternative to reduce IDP and facet loads at adjacent levels.

Introduction

Adjacent-segment degeneration (ASD) is a long-term complication of cervical fusion procedures that requires additional surgical intervention with time 8, 9. Great effort has been devoted to preventing this type of progressive deterioration, including the development of artificial cervical discs and the introduction of hybrid surgical techniques involving single-level treatments (anterior cervical discectomy and fusion [ACDF] plus arthroplasty) as opposed to 2-level ACDF. A number of biomechanical studies, including our preliminary reports (2, 3, 4), also have documented the changes that range of motion (ROM) spinal movements exact at the adjacent vertebral level after spinal fusion, hybrid surgery, or cervical arthroplasty. Unfortunately, these investigations do not fully explain the degenerative disc changes that ensue.

According to recent speculation, altered spinal biomechanics may create pressure changes within adjacent discs after surgery. Although Nachemson (13) was first to use intradiscal pressure (IDP) for estimating in vivo load, others have examined the effects of spinal fusion on IDP in various postures 5, 6, and some have suggested that assessing the load transmitted by facet joints (facet contact force [FCF]) is another critical component in biomechanical evaluation of the spine 11, 15.

We subsequently sought to stratify adjacent-level IDP and FCF in vivo according to type of surgery performed: 2-level cervical fusion, 2-level disc arthroplasty, or single-level hybrids thereof. Using cadaveric simulations of these procedures, we sought to gauge the potential for later development of ASD.

Section snippets

In Vitro Cadaveric Testing

Twenty-four cadaveric human cervical spines (C3-T2) were selected for study, excluding those with bony deformity by fluoroscopic radiographs (anteroposterior and lateral views) and low bone mineral density by dual-energy X-ray absorptiometry scan (Discovery QDR Series; Hologic, Inc, Bedford, Massachusetts, USA), equating osteoporosis with a T score < −2.5. The specimens were thawed overnight at room temperature and were meticulously stripped of muscles, with careful preservation of spinal

Results

All cadaveric specimens selected were free of osteoporosis (T score >2.5 by dual-energy X-ray absorptiometry scan), corresponding with a bone mineral density of 0.56–0.83 g/cm2. There were no instrument-related fractures during placement of cervical screws and artificial disc prosthetics.

Discussion

Compared with ACDF, a number of authors have reported that cervical disc replacement is more likely to maintain physiologic segmental motion after implantation and therefore improve clinical outcomes 7, 10, 12, 14, 18. However, others have insisted that single-level hybrid (ACDF/arthroplasty) procedures and single-level arthroplasty may be reasonable alternative treatments because 2-level arthroplasty may allow excessive motion at treated levels 16, 19. We previously reported that full C4−T1

Conclusions

The present study demonstrates that adjacent-level IDP and FCF in vivo differ, depending upon the nature of spinal surgery performed (2-level fusion, 2-level arthroplasty, or hybrid surgery). On the basis of our simulations, IDP increased at the anterior annulus of distal adjacent-level disc during flexion and axial rotation and at the center of proximal adjacent-level disc during flexion following 2-level cervical arthrodesis. It was also evident that cervical fusion surgeries tend to

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Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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