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VOL. 95-B, No. 8, AUGUST 2013 1127

SPINE: RESEARCH

Do intervertebral discs degenerate before they herniate, or after?

P. Lama,C. L. Le Maitre,P. Dolan,J. F. Tarlton,I. J. Harding,M. A. Adams

From University of Bristol, Bristol, United Kingdom

P. Lama, BSc, MS(Medical Anatomy), PhD Candidate P. Dolan, BSc, PhD, Reader M. A. Adams, BSc, PhD, ProfessorUniversity of Bristol, Centre for Comparative and Clinical Anatomy, Bristol BS2 8EJ, UK.

C. L. Le Maitre, BSc, PgCert(HE), PhD, Senior LecturerSheffield Hallam University, Biomedical Research Centre, City Campus, Howard Street, Sheffield S1 1WB, UK.

J. F. Tarlton, BSc, PhD, Senior Research FellowUniversity of Bristol, Matrix Biology, School of Veterinary Science, Langford, Bristol BS40 5DU, UK.

I. J. Harding, BA, FRCS(Orth), Consultant Orthopaedic SurgeonUniversity of Bristol, Department of Orthopaedics, Southmead Hospital, Southmead Road, Bristol BS10 5NB, UK.

Correspondence should be sent to Professor M. A. Adams;e-mail: [email protected]

©2013 The British Editorial Society of Bone & Joint Surgerydoi:10.1302/0301-620X.95B8. 31660 $2.00

Bone Joint J 2013;95-B:1127–33.Received 24 January 2013; Accepted after revision 15 March 2013

The belief that an intervertebral disc must degenerate before it can herniate has clinical and medicolegal significance, but lacks scientific validity. We hypothesised that tissue changes in herniated discs differ from those in discs that degenerate without herniation. Tissues were obtained at surgery from 21 herniated discs and 11 non-herniated discs of similar degeneration as assessed by the Pfirrmann grade. Thin sections were graded histologically, and certain features were quantified using immunofluorescence combined with confocal microscopy and image analysis. Herniated and degenerated tissues were compared separately for each tissue type: nucleus, inner annulus and outer annulus.

Herniated tissues showed significantly greater proteoglycan loss (outer annulus), neovascularisation (annulus), innervation (annulus), cellularity/inflammation (annulus) and expression of matrix-degrading enzymes (inner annulus) than degenerated discs. No significant differences were seen in the nucleus tissue from herniated and degenerated discs. Degenerative changes start in the nucleus, so it seems unlikely that advanced degeneration caused herniation in 21 of these 32 discs. On the contrary, specific changes in the annulus can be interpreted as the consequences of herniation, when disruption allows local swelling, proteoglycan loss, and the ingrowth of blood vessels, nerves and inflammatory cells.

In conclusion, it should not be assumed that degenerative changes always precede disc herniation.

Cite this article: Bone Joint J 2013;95-B:1127–33.

Herniated disc tissue removed at surgery usu-ally appears abnormal, suggesting that degen-erative changes precede, or even cause,herniation.1 But some degenerative changesappear to follow herniation.2-4 The question ofwhich comes first is important, as patients witha symptomatic disc herniation can, forinstance, be denied personal injury compensa-tion on the grounds that the herniated discmust already have been degenerated andwould have herniated in any event even if theinjury had not occurred.

Herniated disc tissue mostly comprisesnucleus pulposus, with variable amounts ofannulus fibrosus, endplate cartilage andbone.5,6 As the nucleus pulposus contains a highconcentration of hydrophilic proteoglycan, her-niated tissue in vitro swells by between two- andthree-fold within hours of escaping from thepressurised confines of the disc.2 Swellingallows fragmented proteoglycan to be lost, andthe herniated tissue becomes a collagen-rich andproteoglycan-poor mass of ‘crabmeat’.2 In thisway, the characteristic degenerative changes indisc tissue could occur after herniation.

Nor is there any need to assume that a disc mustbe degenerated before it can herniate. Herniationcan be created in cadaveric tissues, either as a sud-den injury7,8 or by a wear-and-tear (‘fatigue’) pro-cess,9 suggesting that herniation can be a physicalprocess driven by excessive mechanical loading.However, the fact that many patients report noinjury before the onset of sciatica suggests thatsome discs are more susceptible to herniation thanothers, probably on account of the weakeningeffects of middle age10 or genetic factors.11

Degeneration, therefore, need not always pre-cede herniation, and some degenerative changescan follow herniation. In this study we comparedherniated disc tissue removed at surgery with disctissue that had reached a similar stage of degener-ation without herniating. We hypothesised thatchanges in herniated discs differ from those foundin degenerated discs, and are consistent with beinga consequence rather than the cause of herniation.

Materials and MethodsThe study was approved by the NReS ethicscommittee, Frenchay Hospital, Bristol, UnitedKingdom. Specimens of herniated disc material

1128 P. LAMA, C. L. LE MAITRE, P. DOLAN, J. F. TARLTON, I. J. HARDING, M. A. ADAMS

THE BONE & JOINT JOURNAL

removed at operation were compared with specimens fromdiscs that had degenerated in situ, without herniation. Sep-arate comparisons were made for the three types of tissue:nucleus pulposus (NP), inner annulus fibrosus (IAF) andouter annulus fibrosus (OAF). These can reliably be distin-guished histologically.

Specimens were from the posterior or posterolateralregions of the lumbar intervertebral discs of 32 patients;21 with a herniated (extruded) disc, and 11 with otherdiagnoses including spondylolisthesis and ‘discogenic pain’,but with no herniation. An anonymous clinical data sheetwas obtained for each patient, and the Pfirrmann grade12 ofdisc degeneration was recorded from MRI scans. Details ofthe groups are shown in Table I. After excision, disc sam-ples were blotted on tissue paper to remove blood, andstored in small airtight containers. Within 20 minutes ofsurgery, samples were snap-frozen by immersing in chilledisopentane, and stored at -70°C until sectioning.Histology. The specimens were moved from the freezer to acryostat maintained at -20°C and embedded in optimal cut-ting tissue (OCT) medium. Sections 5 μm thick wereobtained using a Leica CM1900 cryostat (Heidelberger,Nussloch, Germany) and fixed in 10% neutral buffered for-malin. Sections were stained with Ehrlich’s haematoxylinand eosin (H&E) to reveal details of the cells and matrix orwith toluidine blue to assess proteoglycan loss. Regions ofthe NP, IAF and OAF were identified according to theshape and number of cells, and the appearance of collagenfibres and lamellae under polarised light. As far as possible,three fields of view representing each type of tissue wereanalysed in each thin section. Using criteria that have pre-viously been described13 the following histological featureswere graded on ordinal scales: degree of cell clustering (0 to5), number of inflammatory cells (0 to 3), proteoglycan loss(0 to 3), severity of tears/fissures in the matrix (0 to 3) andthe presence of blood vessels (0 to 3). In each case, ‘0’ refersto ‘absence’ of the feature and the higher bound refers to‘abundance’. Scores were averaged across fields of view,and then across specimen groups.

Immunohistochemistry. Labelled antibodies were used todetect cells producing the matrix-degrading metallopro-teases (MMPs). The 5 μm OCT-embedded sections werefixed in ice-cold acetone for 10 minutes and rinsed in phos-phate-buffered saline (PBS). They were then treated withrabbit serum (Dako, Ely, United Kingdom) at 1:5 dilutionsin PBS for 60 minutes to block non-specific binding of sec-ondary rabbit antibody. The sections were treated with pri-mary mouse monoclonal antibodies to the matrix-degradingenzymes MMP-1 (Abcam, Cambridge, United Kingdom),MMP-2 (Novus Biologicals, Cambridge, United Kingdom)and MMP-3 (Millipore, Watford, United Kingdom) at 1:25dilutions in PBS, and incubated at 4°C overnight. Secondaryantibodies (biotinylated rabbit anti-mouse IgG; Dako),diluted 1:200 in PBS, were applied for 60 minutes, and theantigen–antibody signal was amplified using extra avidin–alkaline phosphatase conjugate (Sigma-Aldrich, Poole,United Kingdom), diluted 1:100. Fast red (Sigma-Aldrich)was applied for 10 minutes. In the controls the primary anti-bodies were omitted during incubation. Sections weremounted with Faramount medium (Dako) and examinedusing a Leica DMRB light microscope. Three fields of viewper section were taken from the NP, IAF and OAF regions,whenever present. Images were captured with a computer-linked Olympus DP72 camera (12.8 megapixels). Immuno-positive cells were counted and analysed using ‘Volocity’software (Perkin Elmer, Cambridge, United Kingdom). Immunofluorescence with laser confocal microscopy. Thiscombination of techniques facilitated the detection andquantification of small nerves and blood vessels in largevolumes of dense tissue. Specimens were sectioned at 30 μmon a Leica CM1900 cryostat before being fixed in ice-coldacetone for 10 minutes and rinsed in PBS. Sections werethen blocked with 20% donkey serum (Sigma Aldrich) inPBS for 60 minutes at 4°C, washed with three changes ofsaline, and treated with mouse monoclonal primary anti-bodies. Dilutions were 1:25 for PGP 9.5 (general cytoplas-mic neuronal marker; ABD Sorotec, Kidlington, UnitedKingdom), 1:500 for Substance P (sensory nerve marker;

Table I. Details of the two groups of intervertebral disc specimens

Herniated discs (HD) Degenerated in situ discs (DD)

Discs (n) 21 11Mean age (yrs) (range) 53 (35 to 74) 53 (39 to 72)Spinal level (n)

L2/3 1 1L3/4 2 0L4/5 4 6L5/S1 14 4

Gender (n)Male 8 6Female 13 5

Mean Pfirrman grade (range) 3.6 (3 to 4) 3.0 (2 to 4)Mean duration of pain (mths) (range) 14 (2 to 60) 18 (4 to 60)

DO INTERVERTEBRAL DISCS DEGENERATE BEFORE THEY HERNIATE, OR AFTER? 1129

VOL. 95-B, No. 8, AUGUST 2013

Abcam, Cambridge, United Kingdom) and 1:20 dilutionfor CD 31 (endothelial cell marker; Dako, Cambridgesh-ire, United Kingdom). Immunofluorescence was achievedusing conjugated Alexa Fluor donkey anti-mouse second-ary antibody (Invitrogen, Paisley, United Kingdom) at1:200 dilution in PBS. In order to diminish autofluores-cence, sections were immersed in 0.01% Sudan black Bfor 5 minutes. DAPI (4',6-diamidino-2-phenylindole; Vec-tor Laboratories, Peterborough, United Kingdom) wasused to stain nuclei dark blue. For the secondary antibody,excitation was at 520 nm and emission at 594 nm. ForDAPI, excitation was at 405 nm and emission at 488 nm.Controls were included in each staining process. Fourthick sections were examined from each specimen and,depending on the section, up to three fields of view weretaken of each of the three types of tissue (NP, IAF andOAF). All the sections were sequentially scanned to pre-vent cross-talk between different fluorophores. Digitalimages were captured with a Leica DM IRBE argon laserconfocal inverted microscope. ‘Volocity’ image analysissoftware was used to: a) count the number of discretestained features (blood vessels or nerves) and b) calculatethe total area of each stained feature in each of three fieldsof view, in each tissue type, in each section.Statistical analysis. Mann-Whitney U tests were used tocompare mean values between herniated and non-herniatedin situ tissues in the NP, IAF and OAF regions. Spearman’srank correlation was used to examine associations betweenhistological variables assessed on ordinal scales. All testswere performed using SPSS software v16 (SPSS Inc., Chi-cago, Illinois). A p-value < 0.05 was considered to indicatestatistical significance.

ResultsEach specimen of herniated disc (HD) was fully extrudedthrough the posterior annulus at operation. Ten had lostcontinuity with the rest of the disc (sequestrations), and

11 were in contact with a nerve root. Specimens of degen-erated disc (DD) were removed from discs that were neitherherniated nor bulging, and so were in structural continuitywith the rest of the disc.Histology. OAF tissue was characterised by arrays ofcrimped type I collagen fibres, organised into narrow andapproximately parallel lamellae with alternating fibreangles, and with elongated fibroblast-like cells. NP tissuehad no crimped collagen, and contained rounded chondro-cyte-like cells. Intermediate IAF tissue had irregular colla-gen fibres in wide and disorganised lamellae, with cells thatwere more rounded than elongated, and frequentlyappeared in clusters.

The histology scores are summarised in Table II (rows 1to 5). Tears and fissures in the extracellular matrix weremore abundant in HD specimens (Fig. 1). Artefactual tearsarising from tissue processing could often be distinguishedby a lack of cells on the free surfaces, and were not includedin the scoring system. Loss of proteoglycan was wide-spread, especially in HD tissue (Fig. 1a and 1c). Cell clus-tering (Fig. 1c) was most common in IAF tissue, especiallynear the boundary with the nucleus, but was rare in OAFtissue. Inflammatory cells were not observed in NP tissue,and in the annulus were much more abundant in HD thanin DD specimens (Fig. 1a and 1d). Inflammatory cells wereparticularly abundant around fissured areas of annulus thatalso showed marked loss of proteoglycans (Fig. 1d), andscores for inflammation were highly correlated with scoresfor proteoglycan loss (r2 = 0.80; p < 0.001). Blood vesselsmanifested as single-layer endothelial cell capillaries, andwere observed only in the annulus (Fig. 1b). They weremore common in HD than DD specimens, and oftenaccompanied inflammatory cells near matrix fissures andon free surfaces (Fig. 1b and 1d), although overall correla-tion between scores for inflammation and fissuring wasnon-significant. Blood vessels were observed in only twoDD specimens, and both had well-developed radial fissures

Table II. Summary of results comparing herniated discs (HD) with degenerated discs (DD). Each of the three tissue types (nucleus, inner annulusand outer annulus) is considered separately, and ‘n’ values reflect the absence of some tissue types from some disc samples

Nucleus Inner annulus Outer annulus

Mean (SD) variable* HD (n = 17) DD (n = 8) p-value HD (n = 21) DD (n = 11) p-value HD (n = 12) DD (n = 8) p-value

Tears/fissures (0 to 3) 1.8 (1.5) 1.5 (1.0) 0.350 2.2 (1.5) 1.5 (0.7) 0.005 2.2 (0.7) 1.3 (0.9) 0.039PG loss (0 to 3) 1.4 (0.8) 0.9 (0.7) 0.136 2.1 (0.4) 1.8 (0.9) 0.584 1.8 (1.0) 1.0 (0.4) 0.048Cell clusters (0 to 5) 1.4 (0.8) 1.2 (1.0) 0.742 2.5 (1.0) 2.4 (1.2) 0.685 0 0.2 (0.3) 0.008Inflammation (0 to 3) 0 0 - 1.0 (0.9) 0.0 (0.1) 0.001 1.4 (1.2) 0.4 (0.8) 0.051Blood vessels (0 to 3) 0 0 - 1.3 (1.1) 0.2 (0.5) 0.012 1.3 (0.9) 0.4 (0.8) 0.028Blood vessels (CD 31 area μm2)

0 0 - 10 564 (13 015) 1597 (5221) 0.046 18 433 (22 184) 4788 (13 993) 0.050

Nerves (count/mm2)Sub P 0 0 - 0.55 (0.76) 0.09 (0.30) 0.051 1.27 (1.22) 0.29 (0.49) 0.042PGP 9.5 0 0 - 0.68 (0.89) 0.18 (0.40) 0.054 1.38 (1.20) 0.43 (0.79) 0.048

Mean MMP count (cells/mm2)MMP-1 41.7 (52.4) 35.7 (49.1) 0.938 99.8 (71.5) 55.4 (47.3) 0.031 60.9 (72.7) 20.9 (37.5) 0.052MMP-2 21.1 (23.7) 13.0 (15.4) 0.876 33.3 (26.7) 25.5 (21.9) 0.434 15.8 (19.5) 7.4 (10.8) 0.046MMP-3 31.1 (28.5) 26.4 (22.0) 0.785 84.5 (79.1) 28.6 (29.0) 0.050 21.8 (47.4) 12.0 (22.6) 0.052

* PG, proteoglycan; CD 31, cell differentiation factor 31 (endothelial cell marker); PGP 9.5, protein gene product 9.5 (neuronal marker); Sub P, Substance P (nociceptive neuronal marker); MMP, matrix metalloproteinases)



in the annulus (Fig. 1e). Figure 2 compares all histologicalvariables between HD and DD annulus.Immunohistochemistry. Cells staining positive for thematrix-degrading enzymes MMP1, MMP2 and MMP3

(Fig. 3) were more common in HD than DD specimens(Table II), although the differences only reached signifi-cance in the annulus. MMP-2 staining usually affectedfibroblasts, solitary chondrocytes and medium-sized cell

Histological images. Figure 1a – Proteoglycan depletion of the matrixis indicated by weak toluidine blue staining. Elongated nuclei of outerannulus cells contrast with those of more rounded inflammatory cellson the free surface (outer annulus, herniated disc). Figure 1b – Fissureswere co-localised with blood vessels (arrows) and inflammatory cells(outer annulus, herniated disc, haematoxylin & eosin (H&E) staining).Figure 1c – Extensive cell clustering (arrows) was associated with fis-suring (inner annulus, herniated disc, H&E staining). Figure 1d – Exten-sive inflammatory cell invasion was associated with blood vessels(arrows) and fissures (outer annulus, herniated disc, H&E staining).Figure 1e – Blood vessels were associated with fissures (inner annulus,degenerated disc, H&E staining). In all cases, bar = 50 μm.

Fig. 1a Fig. 1b

Fig. 1c Fig. 1d

Fig. 1e



clusters, whereas MMP-1 and -3 staining was observed onsingle, paired, clustered and fibroblastic cells, sometimes inassociation with inflammatory cells and blood vessels.Immunofluorescence with laser confocal microscopy. Thicksections and fluorescent staining made it easier to detectsmall blood vessels and nerves (Fig. 4). Values in rows 6 to8 of Table II refer to the absolute area of CD-31 staining(μm2), and to the mean number of discrete structures (permm2) staining positive for PGP 9.5 and Substance P. Bloodvessels were much more common in HD than in DD speci-mens. The same was true of nerves that were positive forPGP 9.5 or Substance P, and that tended to associate withblood vessels. No blood vessels or nerves were found in NPtissue, and seven HD specimens that showed no immuno-positivity to CD-31, Substance P or PGP 9.5 in confocalmicroscopy contained only NP tissue.

DiscussionThis is the first direct comparison between herniatedintervertebral disc tissues and tissues that have reached asimilar (Pfirrman) grade of degeneration without herniat-ing. We found that herniation involved distinct tissuechanges compared to degeneration, and differences wereusually most pronounced in OAF tissue and least in NP tis-sue, where no differences were statistically significant. Age-related degeneration is usually most advanced in the NP,14

so the similarities in NP tissue suggest that herniation did

not represent an advanced or accelerated stage of normaldisc degeneration in 21 of the 32 discs in the present study.

The strengths of the study included the use of the sametechniques and reagents on both samples of discs, and theuse of laser confocal microscopy to examine multiple thicksections of tissue reduced the sampling problems inherentin conventional histological assessment. A third strengthwas the use of automatic quantitative image analysis tominimise the risk of subjective bias.

Although herniated and degenerated discs have not pre-viously been compared, Carreon et al15 compared ‘trau-matic cervical disc herniation’ with ‘degenerated discherniation’ and reported that proteoglycan loss, MMPactivity and inflammation were similar in both. This con-trasts with our findings for annulus tissues (Fig. 2), but

2.50

2.00

1.50

1.00

0.50

0.00

Patient GroupHerniatedDegenerated-in-situ

Mea

n s

core

s

Blood vesselsInflammatory cellsTearsPG lossCell clusters

Histological variables

Fig. 2

Bar charts comparing the mean histological scores for degenerated andherniated discs. Scores were averaged for the inner and outer annulus.The following features differed significantly between the two groups:PG loss (p = 0.028), tears (p < 0.001), inflammatory cells (p < 0.001), andblood vessels (p < 0.001). Error bars denote the standard error of themean (SEM).

Fig. 3b

Immunohistochemical images. Figure 3a – Inflammatory cellsstaining positive (red) for matrix metalloproteinases (MMP)-1(inner annulus, herniated disc). Figure 3b – Two cells showingcytoplasmic staining for MMP-1 (inner annulus, degenerated disc).In both images Ehrlich’s haematoxylin was used to counterstaincell nuclei blue. Bar = 50 μm.

Fig. 3a



there may be no conflict because the previous study did notdistinguish between types of tissue. A comparison between‘protruded’ and ‘extruded’ discs reported fewer inflamma-tory cells in the former,16 which is consistent with our results.

Many previous studies have examined herniated ordegenerated discs without comparing them. Herniateddiscs often show inflammatory changes, which are attrib-uted to neovascularisation and healing following injury.17

This inference is supported by an increased expression ofgrowth factors in herniated discs compared with macro-scopically normal discs in patients of similar age.18 Vigor-ous inflammatory and healing processes evident inherniated disc tissue probably explain why they can ‘reab-sorb’ over time.19 Other reported changes in herniated discsinclude nerve terminals positive for Substance P,20 invasionby macrophages and lymphocytes,21 increased expressionof MMPs and prostaglandins,22 and increased apoptosis,23

which is itself associated with tissue injury24 and swelling.25

In contrast, discs that degenerate without herniatingshow slowly progressive and widespread changes that can-not easily be distinguished from normal ageing, and whichare more advanced in the NP.14,26 Proteoglycans becomefragmented and are lost from the tissue,27 leading toreduced hydration28 and loss of pressure within thenucleus.29,30 Increased cell senescence31 and apoptosis23

reduce the population of viable cells. Cell clusteringincreases,32 particularly in the IAF and NP,33 and manyclustered cells increase the production of matrix-degradingenzymes such as the MMPs.26 Nutrient transportproblems34 probably do not initiate these changes, becausetransport across the endplate increases with age and degen-eration,35 but there can be little doubt that poor transport ofnutrients impairs healing, especially in the centre of the disc.

Differences between herniated and degenerated discs canbe explained as follows. Herniated tissue that escapes the

pressurised confines of the disc swells and loses proteogly-cans, and these changes, which occur in only a few days invitro,2 facilitate the invasion of inflammatory cells and theingrowth of blood vessels and nerves.36 Swelling could alsodisturb cell–matrix interactions and promote apoptosis andcell proliferation. Neovascularisation can follow loss of pro-teoglycans, because they inhibit the ingrowth of blood ves-sels and nerves in vitro.37,38 This ingrowth would also befacilitated by the proximity of herniated tissue to blood ves-sels in the posterior longitudinal ligament and nerve roots.The lack of differences between herniated and degeneratedNP tissue suggests that herniation is not a normal progres-sion from degeneration. Rather, it appears to involve addi-tional processes that affect the annulus most, and so mayoccur from the outside in, after herniation has occurred. Ani-mal models of disc injury and healing support this concept: astab or slash in the peripheral annulus provokes a vigoroushealing response in OAF tissues only,39,40 where the densityof cells is highest.33 Discs that degenerate in situ can have asimilar MRI appearance to herniated discs, because MRIchanges primarily reflect loss of proteoglycans and water, asindicated by the T2 relaxation time. However, the structuralcohesion of an intact annulus, which acts in tension torestrain the pressure of swelling in the NP, prevents gross tis-sue swelling and its sequelae. The confined pressurised envi-ronment within an intact disc also prohibits the ingrowth ofblood vessels and nerves, except where there is a gross radialfissure to facilitate their entry,41,42 as was found in twodegenerated discs in this study.

Distinctions between disc herniation and degenerationare important clinically. Discs that degenerate in situ oftencause no major symptoms,43 whereas many herniated discsgive rise to sciatica and may become the focus of medico-legal litigation. Some herniated discs may possibly herniatebecause of constitutional degenerative changes and genetic

Fig. 4b

Images from immunofluorescence and confocal microscopy. Figure 4a – Blood vessels immunostained red for CD31 (outer annulus, herniateddisc). Figure 4b – Small nerve immunostained red for PGP 9.5 (outer annulus, herniated disc). In both images cell nuclei are counterstained bluewith DAPI (4',6-diamidino-2-phenylindole). Bar = 50 μm.

Fig. 4a



factors,11 and this would explain why degenerative changesare sometimes seen at levels adjacent to a herniated disc.However, the results of this study support the epidemiolog-ical evidence that some discs herniate for other reasons,including injury,44-46 and that some degenerative changesevident at surgery are the consequences rather than causesof herniation. Indeed, herniation is a known risk factor forfurther disc degeneration.47

In conclusion, degenerative changes in herniated discscan be the consequence rather than the cause of herniation.It should not be assumed that degenerative changes alwaysprecede (or cause) disc herniation.

This work was funded in the United Kingdom by BackCare, and by a scholarshipfrom the State Government of Sikkim, India.

No benefits in any form have been received or will be received from a com-mercial party related directly or indirectly to the subject of this article.

This article was primary edited by J. Butler and first-proof edited by J. Scott.

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