The Open Orthopaedics Journal




ISSN: 1874-3250 ― Volume 13, 2019

Disc Height and Sagittal Alignment in Operated and Non-Operated Levels in the Lumbar Spine at Long-Term Follow-Up: A Case-Control Study



Anne Froholdt*, 1, 2, Jens Ivar Brox1, Olav Reikerås1, Gunnar Leivseth3
1 Division of Orthopaedic Surgery, Oslo University Hospital, Rikshospitalet, Norway
2 Department of Physical Medicine and Rehabilitation, Drammen Hospital, Vestre Viken Trust, Norway
3 Department of Clinical Medicine, Neuromuscular Diseases and Research Group, University of North Norway, Tromsø, Norway

Abstract

Purpose:

To compare lumbar disc degeneration at 9-year follow-up in patients with chronic low back pain who had instrumented lumbar fusion or no fusion.

Material and methodology:

The main outcomes were disc height and sagittal alignment measured by Distortion Compensated Roentgen Analysis (DCRA). Secondary outcome included the Oswestry Disability Index and VAS back pain.

Results:

Forty-eight patients with baseline and 9-year radiographs from L2- S1 were included. Twenty-three had lumbar fusion and 25 had no fusion. Disc height was reduced at all levels independent of fusion. No difference in disc height and sagittal alignment was observed between patients fused and not fused. There were weak correlations, ranging from 0.04 to 0.36, between clinical and radiological parameters.

Conclusion:

Lumbar disc degeneration increased at all measured levels independent of fusion and correlated poorly with clinical outcome.

Keywords: : Chronic low back pain, cognitive, disc degeneration, exercise, fusion, long term..


Article Information


Identifiers and Pagination:

Year: 2013
Volume: 7
First Page: 258
Last Page: 263
Publisher Id: TOORTHJ-7-258
DOI: 10.2174/1874325001307010258

Article History:

Received Date: 11/1/2013
Revision Received Date: 21/2/2013
Acceptance Date: 21/4/2013
Electronic publication date: 28/6/2013
Collection year: 2013

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© Froholdt et al.; Licensee Bentham Open.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.5/) which permits unrestrictive use, distribution, and reproduction in any medium, provided the original work is properly cited.


* Address correspondence to this author at the Department of Orthopaedic Surgery, Oslo University Hospital, Rikshospitalet, 0027 Oslo, Norway; Tel: (+47) 90196984; E-mail: annefroholdt@hotmail.no




INTRODUCTION

Degeneration of the lumbar spine is a common and age-related finding in the normal population [1Kanayama M, Togawa D, Takahashi C, Terai T, Hashimoto T. Cross-sectional magnetic resonance imaging study of lumbar disc degeneration in 200 healthy individuals J Neurosurg Spine 2009; 11(4): 501-7.]. Both genetic and behavioral factors contribute to disc degeneration [2Battie MC, Videman T, Parent E. Lumbar disc degeneration: epidemiology and genetic influences Spine (Phila Pa 1976 ) 2004; 29(23): 2679-90.]. Intervertebral disc degeneration is reported to start in the second decade of life and progress slowly in some patients and more rapidly in others. The reason for the different progression is not clear, but twin studies suggest that up to 70% of the variation is hereditable [3Sambrook PN, Macgregor AJ, Spector TD. Genetic influences on cervical and lumbar disc degeneration: a magnetic resonance imaging study in twins Arthritis Rheum 1999; 42(2): 366-72.].

The impact of disc degeneration on chronic low back pain (CLBP) is debated [4Peterson CK, Bolton JE, Wood AR. A cross-sectional study correlating lumbar spine degeneration with disability and pain Spine (Phila Pa 1976) 2000; 25(2): 218-3.]. Livshits et al. [5Livshits G, Popham M, Malkin I, et al. Lumbar disc degeneration and genetic factors are the main risk factors for low back pain in women: the UK Twin Spine Study Ann Rheum Dis 2011; 70(10): 1740-5.] reported that individuals with severe lumbar disc degeneration had more back pain compared to those with minor degeneration, while Carragee et al. [6Carragee EJ, Alamin TF, Miller JL, Carragee JM. Discographic, MRI and psychosocial determinants of low back pain disability and remission: a prospective study in subjects with benign persistent back pain Spine J 2005; 5(1): 24-35.] reported weak associations between structural changes on magnetic resonance imaging (MRI) and back pain and disability.

The number of lumbar fusion operations performed for CLBP and disc degeneration has increased rapidly in the past two decades, but the effectiveness of lumbar fusion surgery has been questioned after the publication of three randomised trials [7Brox JI, Sorensen R, Friis A, et al. Randomized clinical trial of lumbar instrumented fusion and cognitive intervention and exercises in patients with chronic low back pain and disc degeneration Spine (Phila Pa 1976 ) 2003; 28(17): 1913-21.-9Fairbank J, Frost H, Wilson-MacDonald J, Yu LM, Barker K, Collins R. Randomised controlled trial to compare surgical stabilisation of the lumbar spine with an intensive rehabilitation programme for patients with chronic low back pain: the MRC spine stabilisation trial BMJ 2005; 330(7502): 1233.], two of these concluding that lumbar fusion is no more effective than cognitive behavioral intervention.

Patients fused for disc degeneration and CLBP may be more prone to further degeneration than the rest of the population. The level cranial or caudal to the fusion level is considered to be more susceptible to subsequent degeneration because the adjacent level is suggested to be exposed to higher mechanical stress compared to the other levels. It is believed that this may accelerate the degenerative process and result in new symptoms from the unfused adjacent segment. However, conflicting results exist and several studies have demonstrated degenerative changes at multiple levels above a previous fusion, not limited to the first adjacent segment [10Lund T, Oxland TR. Adjacent level disk disease--is it really a fusion disease? Orthop Clin North Am 2011; 42(4): 529-41., 11Pellise F, Hernandez A, Vidal X, Minguell J, Martinez C, Villanueva C. Radiologic assessment of all unfused lumbar segments 7.5 years after instrumented posterior spinal fusion Spine (Phila Pa 1976 ) 2007; 32(5): 574-9.]. Thus, we expect that disc degeneration will worsen over time in all lumbar segments independent of fusion, although fusion and genetic factors may accelerate this process [12Levin DA, Hale JJ, Bendo JA. Adjacent segment degeneration following spinal fusion for degenerative disc disease Bull NYU Hosp Jt Dis 2007; 65(1): 29-36.-14Weiler C, Schietzsch M, Kirchner T, Nerlich AG, Boos N, Wuertz K. Age-related changes in human cervical, thoracal and lumbar intervertebral disc exhibit a strong intra-individual correlation Eur Spine J 2011; 21(Suppl 6): S810-8.].

The clinical implication of observed degeneration of the adjacent segment to fusion is uncertain. Several authors have reported poor correlation between radiological adjacent segment degeneration and clinical symptoms [15Kumar MN, Jacquot F, Hall H. Long-term follow-up of functional outcomes and radiographic changes at adjacent levels following lumbar spine fusion for degenerative disc disease Eur Spine J 2001; 10(4): 309-13.-17Schulte TL, Leistra F, Bullmann V, et al. Disc height reduction in adjacent segments and clinical outcome 10 years after lumbar 360 degrees fusion Eur Spine J 2007; 16(12): 2152-8.]. Valid methods for assessment of symptoms from the adjacent segment are lacking and decisions for eventual elongation of the fusion are made from clinical judgment. Thus, empirical results about the association between adjacent segment degeneration and clinical symptoms in the long-term are of interest.

Animal studies have demonstrated increased degeneration of articular cartilage and connective tissue after immobilization [18Lee S, Sakurai T, Ohsako M, Saura R, Hatta H, Atomi Y. Tissue stiffness induced by prolonged immobilization of the rat knee joint and relevance of AGEs (pentosidine) Connect Tissue Res 2010; 51(6): 467-77., 19Stokes IA, Iatridis JC. Mechanical conditions that accelerate intervertebral disc degeneration: overload versus immobilization Spine (Phila Pa 1976 ) 2004; 29(23): 2724-32.]. Lack of mobilisation of the intervertebral discs may alter intracellular properties and predispose the disc to degeneration [19Stokes IA, Iatridis JC. Mechanical conditions that accelerate intervertebral disc degeneration: overload versus immobilization Spine (Phila Pa 1976 ) 2004; 29(23): 2724-32.]. The main technical goal of lumbar fusion is to achieve rigidity and intersegmental fusion. It may be hypothesized that disc degeneration will continue within the fused segments, but to our knowledge this hypothesis has not been examined.

The main objective of the current study was to compare disc height and intervertebral sagittal alignment in operated and non-operated levels in the lumbar spine at long-term follow-up after instrumented lumbar fusion and compare these results with those of non-operated patients. The secondary aim was to examine the association between clinical outcome (pain and disability) and disc degeneration at long-term follow-up.

MATERIAL AND METHODOLOGY

Patients

A flow-chart of the included patients is demonstrated in Fig. (1). Forty-eight patients previously included in a randomized study to compare lumbar fusion with cognitive behavioural treatment [7Brox JI, Sorensen R, Friis A, et al. Randomized clinical trial of lumbar instrumented fusion and cognitive intervention and exercises in patients with chronic low back pain and disc degeneration Spine (Phila Pa 1976 ) 2003; 28(17): 1913-21., 8Brox JI, Reikeras O, Nygaard O, et al. Lumbar instrumented fusion compared with cognitive intervention and exercises in patients with chronic back pain after previous surgery for disc herniation: a prospective randomized controlled study Pain 2006; 122(1-2): 145-55., 20Brox JI, Nygaard OP, Holm I, Keller A, Ingebrigtsen T, Reikeras O. Four-year follow-up of surgical versus non-surgical therapy for chronic low back pain Ann Rheum Dis 2010; 69(9): 1643-8.] were available for participation in the present case-control study. Of these, 23 had undergone lumbar fusion and 25 had no fusion. There were no significant differences in baseline characteristics between the patients included in the present study and all patients included in the original clinical trial (Table 1).

Table 1

Baseline Characteristics of All Patients Randomised in the Clinical and Patients as Treated in the Present Study. Means ± SD or Number of Patients (%) are Given




Fig. (1)

Flow chart of patients included in the present study.



Eight of 23 fused patients had re-operation because of persistent pain. Implants were removed in five of the eight patients and three had an extended fusion. Ten of 23 patients had a single level fusion at L5/S1, and 13 patients had a two-level fusion from L4 to S1. At baseline, 12 of 25 non-operated patients were considered candidates for having a L5/S1 fusion, and 13 patients considered candidates for having a L4 to S1 fusion.

The Ethics Committee for Medical Research in Health Region South-East of Norway approved the study.

Treatments

The lumbar fusion consisted of posterolateral autologous bone transplantation and transpedicular screw fixation of the L4/L5 and/or L5/S1 segments and postoperative physiotherapy prescribed by the surgeon. The cognitive intervention and exercises programme was conducted over a 3-week period [7Brox JI, Sorensen R, Friis A, et al. Randomized clinical trial of lumbar instrumented fusion and cognitive intervention and exercises in patients with chronic low back pain and disc degeneration Spine (Phila Pa 1976 ) 2003; 28(17): 1913-21., 8Brox JI, Reikeras O, Nygaard O, et al. Lumbar instrumented fusion compared with cognitive intervention and exercises in patients with chronic back pain after previous surgery for disc herniation: a prospective randomized controlled study Pain 2006; 122(1-2): 145-55.]. The goal was to make the patients confident in participating in daily activities previously labelled as not recommended.

Radiographic Outcome Measures

Lateral radiographs were obtained both at inclusion (i.e., before treatment) and at long-term follow-up. Radiographs were obtained from levels L1 to S1, but L1/L2 level images were excluded because of poor quality. Consequently, we included the two fused levels (L4/L5 and L5/S1) and two non-fused levels (L2/L3 and L3/L4) in the analyses.

All evaluations of disc height and sagittal alignment were performed by an independent reviewer who measured disc height and sagittal alignment (e.g., the position of the cranial vertebra in relation to the caudal vertebra) by Distortion Compensated Roentgen Analysis (DCRA) [21Frobin W, Brinckmann P, Biggemann M, Tillotson M, Burton K. Precision measurement of disc height, vertebral height and sagittal plane displacement from lateral radiographic views of the lumbar spine Clin Biomech (Bristol, Avon ) 1997; 12(Suppl 1): S1-S63.]. This computer-assisted method, based on measurements from plain lateral radiographic views, has been validated previously by comparison with Roentgen Stereophotogrammetric Analysis (RSA) [22Leivseth G, Brinckmann P, Frobin W, Johnsson R, Stromqvist B. Assessment of sagittal plane segmental motion in the lumbar spine. A comparison between distortion-compensated and stereophotogrammetric roentgen analysis Spine 1998; 23(23): 2648-55.]. Fig. (2) illustrates the DCRA method and summarizes the definitions of the parameters used. The DCRA protocol [21Frobin W, Brinckmann P, Biggemann M, Tillotson M, Burton K. Precision measurement of disc height, vertebral height and sagittal plane displacement from lateral radiographic views of the lumbar spine Clin Biomech (Bristol, Avon ) 1997; 12(Suppl 1): S1-S63.] compensates for distortion caused by axial rotation, lateral tilt, and off-centre positioning of the spine. This permits processing of radiographs taken in normal clinical settings; knowledge of the exposure geometry is not required. All motion segments imaged on a lateral radiograph can be evaluated.

Fig. (2)

Definition of parameters defined by DCRA.

DCRA Definition
Mean vertebral depth Mean of distances of corners 1 and 2 and corners 3 and 4
Sagittal plane angel Angle between vertebral midplanes, which is defined as the line running through midpoints between corners 1 and 3 and 2 and 4, respectively.
Disc height Sum of the distances from the corners 2 and 4 from the bisectrix between midplanes, divided by the mean depth of the cranial vertebra. As disc height depends linearly on sagittal plane angle, a correction is applied in order to permit comparisons among radiographs taken in different postures of the lumbar spine.
Sagittal translation or postero-anterior (dorso-ventral) displacement Distance between the projections of the centre points (geometric center of corners 1-4) of the vertebrae onto the bisectrix, divided by the mean depth of the cranial vertebra. Displacement is counted positive if the cranial vertebra is displaced in anterior direction with respect to the caudal vertebra. Similar to disc height a correction is applied in order to permit comparisons among radiographs taken in different postures of the lumbar spine.

Printed with permission from G. Leivseth



Sagittal alignment and disc height are given as the standard deviation from the gender-, age-, and level-appropriate normal values [21Frobin W, Brinckmann P, Biggemann M, Tillotson M, Burton K. Precision measurement of disc height, vertebral height and sagittal plane displacement from lateral radiographic views of the lumbar spine Clin Biomech (Bristol, Avon ) 1997; 12(Suppl 1): S1-S63.]. By example, a value of minus 1.0 denotes that the respective parameter is one standard deviation below normal.

In the present study heights of the vertebrae, measured from the radiographs, taken pre- treatment and at follow-up, agreed on average within an error of 2% of the vertebral depth. Assuming that mean vertebral depth is 35 mm, this corresponds to a measurement error in disc height in the order of 0.7 mm. A previous methodological study reported that the error in sagittal plane displacement amounts to 0.015 (measured in units of mean vertebral depth); e.g., for a vertebral depth of 35 mm, this corresponds to an error of 0.5 mm [21Frobin W, Brinckmann P, Biggemann M, Tillotson M, Burton K. Precision measurement of disc height, vertebral height and sagittal plane displacement from lateral radiographic views of the lumbar spine Clin Biomech (Bristol, Avon ) 1997; 12(Suppl 1): S1-S63.].

Clinical Outcome Measures

The Norwegian version 1.0 of the Oswestry disability index (ODI) [23Fairbank JC, Couper J, Davies JB, O'Brien JP. The Oswestry low back pain disability questionnaire Physiotherapy 1980; 66(8): 271-3.] was used to evaluate condition-specific disability and pain. This score has 10 questions about pain and disability and ranges from 0% (no pain and disability) to 100% (worst possible pain and disability).

Back pain was rated on vertical visual analogue scales from 0 to 100 (worst pain imaginable). Maximum pain and minimum pain during the last week and current pain were scored on three different scales. The mean of these scores provides the pain index for back pain [24Fritzell P, Hagg O, Wessberg P, Nordwall A. 2001 Volvo Award Winner in Clinical Studies: Lumbar fusion versus nonsurgical treatment for chronic low back pain: a multicenter randomized controlled trial from the Swedish Lumbar Spine Study Group Spine (Phila Pa 1976 ) 2001; 26(23): 2521-32.].

Statistical Methods

Data were checked for normal distribution. Results in cases (fused patients) and controls (non-operated patients) were compared using differences in standard deviation from the gender-, age- and level-appropriate normal values. In addition, paired samples t-tests were used to compare changes in disc height and alignment from baseline to long-term follow-up within groups. Analysis of covariance (ANCOVA) was used to compare differences in change between cases and controls at long-term follow-up with adjustments for previous surgery, disc herniation, and baseline measures in disc height and alignment. We did not adjust for re-operation.

The Spearman R correlation coefficient was used to examine the association between disc height, sagittal alignment, ODI, and back pain at the 9-year follow-up. Analyses were performed with the Statistical Package for the studies of Social Sciences, version 18 (SPSS, Inc., Chicago, IL).

RESULTS

At the 9-year follow-up, disc height was significantly reduced from baseline at levels L3/L4 and L4/L5, but not at L2/L3 and L5/S1 in both cases and controls (p<0.05) (Table 2).

Table 2

Values are Disc Heights Given as the Difference in Standard Deviations from an Age and Gender Adjusted Normal Population. Mean ±SD at Baseline and 9-Years Follow-Up in Fused and Non-Fused Patients and the Mean Difference (95% CI) Between Groups are Given




Sagittal alignment was significantly increased at level L2/L3 in cases and controls (p<0.001), and in addition at level L5/S1 in controls (p<0.05). We observed no difference in the other investigated levels (Table 3). There was no difference between cases and controls at any level (Table 3).

Table 3

Values are Sagittal Alignment Given as the Difference in Standard Deviation from an Age and Gender Adjusted Normal Population. Mean ±SD at Baseline and 9-Years Follow-Up in Fused and Non-Fused Patients and the Mean Difference (95% CI) Between Groups are Given




There were weak correlations between clinical and radiological parameters ranging from r = 0.04 (p = 0.79) to r = 0.36 (p = 0.01). This means that from zero to 13 % of the variation in clinical parameters were explained by variation in radiological parameters.

There were weak correlations between lumbar levels for disc height and sagittal alignment (Table 4).

Table 4

Correlations Between Lumbar Levels for Disc Height and Sagittal Alignment




DISCUSSION

We found increased degeneration of the lumbar discs in both cases and controls at long-term follow-up. There were no difference between cases and controls and no association with changes in pain and disability.

Disc degeneration is a normal feature of ageing [25Williams FM, Popham M, Sambrook PN, Jones AF, Spector TD, Macgregor AJ. Progression of lumbar disc degeneration over a decade: a heritability study Ann Rheum Dis 2011; 70(7): 1203-7.], and it is unclear how fusion influence on this. In the present study, reduction of lumbar disc height was independent of whether the level was fused or not. Reductions in disc height at the fused levels L4/L5 and L5/S1 were similar to reductions in disc height at non-fused levels, and to the identical levels in non-operated patients. Results are in agreement with previous studies, but these earlier studies did not include a control group of non-operated patients [10Lund T, Oxland TR. Adjacent level disk disease--is it really a fusion disease? Orthop Clin North Am 2011; 42(4): 529-41., 11Pellise F, Hernandez A, Vidal X, Minguell J, Martinez C, Villanueva C. Radiologic assessment of all unfused lumbar segments 7.5 years after instrumented posterior spinal fusion Spine (Phila Pa 1976 ) 2007; 32(5): 574-9.].

In agreement with previous studies, we found weak associations between changes in pain and disability and changes in disc height [26Berg S, Tropp HT, Leivseth G. Disc height and motion patterns in the lumbar spine in patients operated with total disc replacement or fusion for discogenic back pain. Results from a randomized controlled trial Spine J 2011; 11(11): 991-8.]. The observed correlations in the present study ranged from 0.04 to 0.36, which means that only 0- 13% of the observed variation in disability and pain could be explained by radiological changes. Berg et al. [26Berg S, Tropp HT, Leivseth G. Disc height and motion patterns in the lumbar spine in patients operated with total disc replacement or fusion for discogenic back pain. Results from a randomized controlled trial Spine J 2011; 11(11): 991-8.] reported that despite fulfillment of surgical goals for either the lumbar fusion or disc prosthesis group, there was poor correlation between disc degeneration and clinical outcome at 2-years follow-up.

Spine surgeons often use radiological signs of disc degeneration in decision-making, with respect to eventual re-operation at adjacent levels. However, the observed weak associations reported between radiological and clinical outcomes do not support this strategy.

Sagittal alignment describes the position of a vertebra in relation to an adjacent vertebra. We found small changes within groups and no differences between groups at long-term follow-up. Unfavourable sagittal alignment has been proposed as a risk factor for development of degenerative changes at the adjacent level, but this remains controversial [10Lund T, Oxland TR. Adjacent level disk disease--is it really a fusion disease? Orthop Clin North Am 2011; 42(4): 529-41.]. In agreement with Pellisé et al. [11Pellise F, Hernandez A, Vidal X, Minguell J, Martinez C, Villanueva C. Radiologic assessment of all unfused lumbar segments 7.5 years after instrumented posterior spinal fusion Spine (Phila Pa 1976 ) 2007; 32(5): 574-9.] we found increased sagittal alignment in the second adjacent level cephalad to the fusion. This tendency was observed both in fusion cases and in non-fusion patients, and we believe that this observation raises questions regarding the influence of fusion on sagittal alignment.

There were weak correlations between disc degeneration in neighboring segments in both patient groups [11Pellise F, Hernandez A, Vidal X, Minguell J, Martinez C, Villanueva C. Radiologic assessment of all unfused lumbar segments 7.5 years after instrumented posterior spinal fusion Spine (Phila Pa 1976 ) 2007; 32(5): 574-9., 14Weiler C, Schietzsch M, Kirchner T, Nerlich AG, Boos N, Wuertz K. Age-related changes in human cervical, thoracal and lumbar intervertebral disc exhibit a strong intra-individual correlation Eur Spine J 2011; 21(Suppl 6): S810-8.] and weak correlations between sagittal alignment in neighboring levels. This finding suggests that factors other than fusion (for example, genetic factors and ageing) are important factors contributing to disc degeneration [2Battie MC, Videman T, Parent E. Lumbar disc degeneration: epidemiology and genetic influences Spine (Phila Pa 1976 ) 2004; 29(23): 2679-90., 25Williams FM, Popham M, Sambrook PN, Jones AF, Spector TD, Macgregor AJ. Progression of lumbar disc degeneration over a decade: a heritability study Ann Rheum Dis 2011; 70(7): 1203-7.].

The extent and severity of reported disc degeneration vary widely from study to study and are influenced by the technology used to examine the disc [2Battie MC, Videman T, Parent E. Lumbar disc degeneration: epidemiology and genetic influences Spine (Phila Pa 1976 ) 2004; 29(23): 2679-90.]. Both magnetic resonance imaging (MRI) and radiographs correlate with the morphological degree of degeneration [27Benneker LM, Heini PF, Anderson SE, Alini M, Ito K. Correlation of radiographic and MRI parameters to morphological and biochemical assessment of intervertebral disc degeneration Eur Spine J 2005; 14(1): 27-35.]. MRI is considered to be the gold standard modality for imaging spinal structures in vivo, and signs of degeneration (i.e., altered T2 signal intensity, annular tears, and Modic changes) are seen at an earlier stage on MRI compared to plain radiography [28Tertti M, Paajanen H, Laato M, Aho H, Komu M, Kormano M. Disc degeneration in magnetic resonance imaging. A comparative biochemical, histologic, and radiologic study in cadaver spines Spine (Phila Pa 1976 ) 1991; 16(6): 629-34.]. However, interpretation of MRI images is difficult because of artifacts in patients who have steel implants. The fused patients in the present study had steel implants; therefore we used plain radiography and applied the validated DCRA method to obtain indicators of disc degeneration such as disc height and sagittal alignment [22Leivseth G, Brinckmann P, Frobin W, Johnsson R, Stromqvist B. Assessment of sagittal plane segmental motion in the lumbar spine. A comparison between distortion-compensated and stereophotogrammetric roentgen analysis Spine 1998; 23(23): 2648-55.].

The strengths of the present study are the application of the DCRA method, the inclusion of both fused and non-fused patients, the long observation time and the use of age- and gender-adjusted values from a large database of approximately 3,000 healthy individuals to calculate results in SD from population values.

An important limitation of our study is the lack of randomization and the small number of patients. The DCRA method is resource intensive (and precise) and corresponding patient samples are reported in previous studies using this method [11Pellise F, Hernandez A, Vidal X, Minguell J, Martinez C, Villanueva C. Radiologic assessment of all unfused lumbar segments 7.5 years after instrumented posterior spinal fusion Spine (Phila Pa 1976 ) 2007; 32(5): 574-9., 29Kolstad F, Nygaard OP, Leivseth G. Segmental motion adjacent to anterior cervical arthrodesis: a prospective study Spine (Phila Pa 1976 ) 2007; 32(5): 512-7.]. The estimates of mean differences and their corresponding confidence intervals reflect both the inter-individual differences and the sample size. Differences between cases and controls were much smaller than the observed variation between patients. By example, with the standard deviation of 1.3 and the observed group difference of 0.34 at the L3-4 segment, 205 patients are required in each group to detect 0.05 % significance with 80 % power. The lack of correlation between clinical and radiological parameters suggests that the observed difference has no clinical significance.

We conclude that disc degeneration at long-term is not associated with lumbar fusion or other clinical parameters. This finding opposes the commonly held belief that lumbar spine fusion leads to increased adjacent level degeneration that may require re-operation. Our findings need to be validated in future, larger studies.

CONFLICT OF INTEREST

The authors declare that they have no conflict of interest.

AKNOWLEDGEMENTS

We thank the Research Council of Norway and Vestre Viken Hospital Trust for providing the financial support for this study.

REFERENCES

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[17] Schulte TL, Leistra F, Bullmann V, et al. Disc height reduction in adjacent segments and clinical outcome 10 years after lumbar 360 degrees fusion Eur Spine J 2007; 16(12): 2152-8.
[18] Lee S, Sakurai T, Ohsako M, Saura R, Hatta H, Atomi Y. Tissue stiffness induced by prolonged immobilization of the rat knee joint and relevance of AGEs (pentosidine) Connect Tissue Res 2010; 51(6): 467-77.
[19] Stokes IA, Iatridis JC. Mechanical conditions that accelerate intervertebral disc degeneration: overload versus immobilization Spine (Phila Pa 1976 ) 2004; 29(23): 2724-32.
[20] Brox JI, Nygaard OP, Holm I, Keller A, Ingebrigtsen T, Reikeras O. Four-year follow-up of surgical versus non-surgical therapy for chronic low back pain Ann Rheum Dis 2010; 69(9): 1643-8.
[21] Frobin W, Brinckmann P, Biggemann M, Tillotson M, Burton K. Precision measurement of disc height, vertebral height and sagittal plane displacement from lateral radiographic views of the lumbar spine Clin Biomech (Bristol, Avon ) 1997; 12(Suppl 1): S1-S63.
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Endorsements



"Open access will revolutionize 21st century knowledge work and accelerate the diffusion of ideas and evidence that support just in time learning and the evolution of thinking in a number of disciplines."


Daniel Pesut
(Indiana University School of Nursing, USA)

"It is important that students and researchers from all over the world can have easy access to relevant, high-standard and timely scientific information. This is exactly what Open Access Journals provide and this is the reason why I support this endeavor."


Jacques Descotes
(Centre Antipoison-Centre de Pharmacovigilance, France)

"Publishing research articles is the key for future scientific progress. Open Access publishing is therefore of utmost importance for wider dissemination of information, and will help serving the best interest of the scientific community."


Patrice Talaga
(UCB S.A., Belgium)

"Open access journals are a novel concept in the medical literature. They offer accessible information to a wide variety of individuals, including physicians, medical students, clinical investigators, and the general public. They are an outstanding source of medical and scientific information."


Jeffrey M. Weinberg
(St. Luke's-Roosevelt Hospital Center, USA)

"Open access journals are extremely useful for graduate students, investigators and all other interested persons to read important scientific articles and subscribe scientific journals. Indeed, the research articles span a wide range of area and of high quality. This is specially a must for researchers belonging to institutions with limited library facility and funding to subscribe scientific journals."


Debomoy K. Lahiri
(Indiana University School of Medicine, USA)

"Open access journals represent a major break-through in publishing. They provide easy access to the latest research on a wide variety of issues. Relevant and timely articles are made available in a fraction of the time taken by more conventional publishers. Articles are of uniformly high quality and written by the world's leading authorities."


Robert Looney
(Naval Postgraduate School, USA)

"Open access journals have transformed the way scientific data is published and disseminated: particularly, whilst ensuring a high quality standard and transparency in the editorial process, they have increased the access to the scientific literature by those researchers that have limited library support or that are working on small budgets."


Richard Reithinger
(Westat, USA)

"Not only do open access journals greatly improve the access to high quality information for scientists in the developing world, it also provides extra exposure for our papers."


J. Ferwerda
(University of Oxford, UK)

"Open Access 'Chemistry' Journals allow the dissemination of knowledge at your finger tips without paying for the scientific content."


Sean L. Kitson
(Almac Sciences, Northern Ireland)

"In principle, all scientific journals should have open access, as should be science itself. Open access journals are very helpful for students, researchers and the general public including people from institutions which do not have library or cannot afford to subscribe scientific journals. The articles are high standard and cover a wide area."


Hubert Wolterbeek
(Delft University of Technology, The Netherlands)

"The widest possible diffusion of information is critical for the advancement of science. In this perspective, open access journals are instrumental in fostering researches and achievements."


Alessandro Laviano
(Sapienza - University of Rome, Italy)

"Open access journals are very useful for all scientists as they can have quick information in the different fields of science."


Philippe Hernigou
(Paris University, France)

"There are many scientists who can not afford the rather expensive subscriptions to scientific journals. Open access journals offer a good alternative for free access to good quality scientific information."


Fidel Toldrá
(Instituto de Agroquimica y Tecnologia de Alimentos, Spain)

"Open access journals have become a fundamental tool for students, researchers, patients and the general public. Many people from institutions which do not have library or cannot afford to subscribe scientific journals benefit of them on a daily basis. The articles are among the best and cover most scientific areas."


M. Bendandi
(University Clinic of Navarre, Spain)

"These journals provide researchers with a platform for rapid, open access scientific communication. The articles are of high quality and broad scope."


Peter Chiba
(University of Vienna, Austria)

"Open access journals are probably one of the most important contributions to promote and diffuse science worldwide."


Jaime Sampaio
(University of Trás-os-Montes e Alto Douro, Portugal)

"Open access journals make up a new and rather revolutionary way to scientific publication. This option opens several quite interesting possibilities to disseminate openly and freely new knowledge and even to facilitate interpersonal communication among scientists."


Eduardo A. Castro
(INIFTA, Argentina)

"Open access journals are freely available online throughout the world, for you to read, download, copy, distribute, and use. The articles published in the open access journals are high quality and cover a wide range of fields."


Kenji Hashimoto
(Chiba University, Japan)

"Open Access journals offer an innovative and efficient way of publication for academics and professionals in a wide range of disciplines. The papers published are of high quality after rigorous peer review and they are Indexed in: major international databases. I read Open Access journals to keep abreast of the recent development in my field of study."


Daniel Shek
(Chinese University of Hong Kong, Hong Kong)

"It is a modern trend for publishers to establish open access journals. Researchers, faculty members, and students will be greatly benefited by the new journals of Bentham Science Publishers Ltd. in this category."


Jih Ru Hwu
(National Central University, Taiwan)


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