Yong-Chao Li,Xiao-Fei Feng,Xiao-Dong Pang,Jun Tan,Bao-Gan Peng

Yong-Chao Li,Xiao-Dong Pang,Bao-Gan Peng, Department of Spinal Surgery,The Third Medical Center of PLA General Hospital,Beijing 100039,China

Yong-Chao Li,Xiao-Fei Feng,Jun Tan,Department of Spinal Surgery,Shanghai East Hospital,Tongji University School of Medicine,Shanghai 200120,China

Jun Tan,Department of Orthopedics,Pinghu Second People's Hospital,Pinghu 314201,Zhejiang Province,China

Abstract

Key words:Disc regeneration;Dynamic stabilization system;Degenerative disc disease;Magnetic resonance imaging;BioFlex;Case report

INTRODUCTION

Degeneration of intervertebral disc is commonly accompanied by alterations of disc height,intradiscal pressure,load distribution,and motion patterns[1].Since these alterations are subsequent results following disc degeneration,it is unlikely that regeneration will occur without first restoring the physiological status of the affected spinal segment[1].Dynamic stabilization systems(DSS)are currently designed to restore physiological motion patterns and disc height and to normalize intradiscal pressure.Theoretically,they may have the potential to provide an adaptive environment for disc regeneration.Recently,both animal and clinical studies have indicated that disc distraction[2]or application of lumbar DSS[3-16]can enhance hydration in the degenerated disc and,therefore,regeneration.

This article describes a case whose lumbar disc showed rehydration in the implanted segment using the BioFlex DSS,and reviews the existing literature.

CASE PRESENTATION

Chief complaints

A 54-year-old man presented with a 10-year history of mechanical back pain,which became worse with activities and was reduced after bed rest.In the last 3 mo,his back pain had progressively increased and radiated into the left lower limb with numbness.

History of past illness

He had no relevant traumatic history.

Physical examination

Physical examination revealed a stiff lumbar spine with limited range of flexion,extension,and lateral bending.There were tenderness and percussion pain over the L4-L5 lumbar spine.Bilateral lower limb dermatomal sensation was normal,but he had decreased muscle strength(class IV)of the left hallux dorsal extensor.Lower extremity muscle tension,bilateral straight leg raising test,and strengthening test were all normal.

Laboratory examinations

Laboratory data showed no infectious or inflammatory findings.

Imaging examinations

The initial plain radiographs revealed a decrease in height of the L4-L5 disc space.No instability was noted on the dynamic radiographs of flexion and extension of the lumbar spine(Figure 1A and 1B).Magnetic resonance imaging(MRI)scans showed L3-S1 disc degeneration with associated low signal intensity and L4-L5 disc herniation(Figure 1C and 1D).

FINAL DIAGNOSIS

The final diagnosis was lumbar disc herniation(L4-L5).

TREATMENT

Before admission to our hospital,the patient had accepted various forms of conservative treatments such as physiotherapy,exercise,and drug therapy in a local clinic for 3 mo,but these therapies did not relieve his symptoms.Therefore,a posterior L4-L5 discectomy with fixation of a dynamic stabilization system(BioFlex system,Bio-Spine,Seoul,Korea)was recommended for this patient.During surgical decompression,left L4-5 laminotomy was performed with resection of the superior half of the L5 lamina and the inferior half of the L4 lamina along with preservation of left L4/5 facet joint.

OUTCOME AND FOLLOW-UP

Surgery was successful and his symptoms were clearly relieved and lumbar function was markedly improved.The visual analogue scale score of back pain,left leg pain and Oswestry disability index decreased from 6,8,and 58 preoperatively to 1,0,and 0 at 24 mo,respectively,after the procedure.Partial motion of the implanted level was noted on postoperative flexion-extension plain radiographs(Figure 2A and 2B).An increasing signal intensity in the L4-L5 disc was noted on T2-weighted MRI(Figure 2C and 2D)after 2 years of follow-up after the operation.

DISCUSSION

A degenerate intervertebral disc is associated with significant structural failure such as nucleus pulposus dehydration,endplate sclerosis,annular protrusion,internal disc disruption,and disc space narrowing[1,17].As the disc starts to degenerate,the water content of the nucleus pulposus is reduced,which is well tracked through MRI evaluation.A well-hydrated disc has bright signal intensity on T2-weighted MRI,whereas a degenerated disc appears gray to dark according to the severity of degeneration[17].

Regenerative strategies,such as transplantation of stem cells into nucleus pulposus,have been attempted to reverse disc degeneration experimentally and clinically[18].However,the lack of an appropriate microenvironment and impaired capacity of diffusion of nutrients across a calcified endplate in the degenerated disc have hampered the survival of the transplanted stem cells[17].The biomechanical concept for disc regeneration has grown popular in recent years with the improved understanding of the importance of spinal movement preservation.There is increasing evidence,however,that lumbar DSS may compensate non-physiological loads,limit pathological movement,normalize intradiscal height and pressure,and provide an adaptive microenvironment for disc regeneration[1,3,5,7,13,19].However,controversial results still exist[20,21].

Currently,two kinds of available DSS are applied clinically including pedicle screw-based DSS and interspinous process spacers.The former includes Graf ligamentoplasty(Neoligaments,Leeds,United Kingdom),and the Dynesys system(Zimmer,Inc.,Warsaw,IN,United States),FASS system(AO International,Davos,Switzerland),cosmic system(Ulrich GmbH and Co.KG,Ulm,Germany),TOPS system(Premia Spine USA,Philadelphia,PA,United States),FPSS system(Spine Vision,Paris,France),Accuflex system(Globus Medical,Inc.,Audubon,PA,United States),Safinaz(Medikon AS,Medikon,Turkey),and BioFlex system(Bio-Spine)among others.The latter includes Wallis(Abbott Spine,Bordeaux,France),DIAM(Medtronic,Memphis,TN,United States),X-Stop(St.Francis Medical Technologies,Concord,CA,United States),and Coflex(Paradigm Spine LLC,New York,NY,United States).

In this study,we showed evidence of rehydration of a degenerated disc after implantation of the BioFlex system and reviewed the relevant medical literature.PubMed,the Cochrane Library,Medline,and EMBASE were searched using the following keywords,"disc rehydration" and "dynamic stabilization system,"which identified all possible studies published up to July 2019.References from these articles were also reviewed.We found 14 original studies on this topic.The detailed clinical information and device choices of all 15 studies are shown and summarized with the current case in Table 1.A study performed by Fayet al[7]found that Dynesys may stop or reverse disc degeneration in young patients but not in older patients.Instead,Vagaet al[14]discovered that the Dynesys was able to stop and partially reverse the disc degeneration,especially in a seriously degenerated disc.However,most studies on this topic are case reports[13]or case series[3-5,7-12,15,16]with low-quality and small samples.Degenerated disc rehydration has often been found serendipitously[4-6,10-12,15].

Physiologic motion,load distribution,and intradiscal pressure are mandatory for disc viability.Because a degenerate disc cannot regenerate itself,external devices may provide preconditions for biological attempts of regeneration[1].Guehringet al[2]demonstrated that disc distraction can enhance disc rehydration of the degenerated disc and may also improve disc nutrient diffusionviathe endplates.Furthermore,the authors thought that disc rehydration after distraction was probably related to the upregulated expression of the matrix genes collagen 1,collagen 2,decorin,and biglycan and the decline of apoptosis[2].Wilke and colleagues found that changing positions are crucial to promoting fluid flow(nutrition)to the disc[22].In addition,disc loading pattern with high load,low volume,and low frequency might impart healing or regeneration of the intervertebral discs[23].DSS can not only result in disc distraction but also limit disc extension reasonably.Physiological spine motion and optimal intradiscal pressure after implantation of DSS may be maintained,which may provide optimal preconditions for disc rehydration and even further regeneration.Biological attempts of disc regeneration including stem cell,gene,and protein therapies combined with mechanical DSS may be optimal options.However,challenges still exist regarding the long-term tolerance of dynamic implants especially on the screw bone interface,and the fatigability of the composite materials[12].In addition,there may be risk of bias by industry influence in our study.At the same time,our study is a case report and more evidence is needed to support lumbar disc rehydration in the bridged segment using the BioFlex system in the future.

CONCLUSION

Rehydration of a degenerated disc occurred after implantation of the BioFlex System in an adult patient after 2 years of follow-up.

Table 1 Related research to evaluate the potential mutual relationship between dynamic stabilization systems and disc rehydration

1The present study.MRI:Magnetic resonance imaging;NA:Not available;CDS:Calibrated disc signal;ADC:Apparent diffusion coefficient;HIZ:Highintensity zone;VAS:Visual analog scale;ODI:Oswestry disability index;DSS:Dynamic stabilization system.

Figure 2 Postoperative imaging assessment.A and B:Postoperative extension-flexion radiographs revealed that partial movement was reserved in the implanted level;C and D:Magnetic resonance imaging demonstrated disc rehydration within L4-5 at the 2-yr follow-up.