Clin Biomech (Bristol, Avon). 2010 Aug 23. [Epub ahead of print]

Much is known about intervertebral disc degeneration, but little effort has been made to relate this information to the clinical problem of discogenic back pain, and how it might be treated. The authors re-interpret the scientific literature in order to provide a rationale for physical therapy treatments for discogenic back pain.

Intervertebral discs deteriorate over many years, from the nucleus outwards, to an extent that is influenced by genetic inheritance and metabolite transport. Age-related deterioration can be accelerated by physical disruption, which leads to disc “degeneration” or prolapse. Degeneration most often affects the lower lumbar discs, which are loaded most severely, and it is often painful because nerves in the peripheral anulus or vertebral endplate can be sensitised by inflammatory-like changes arising from contact with blood or displaced nucleus pulposus. Surgically-removed human discs show an active inflammatory process proceeding from the outside-in, and animal studies confirm that effective healing occurs only in the outer anulus and endplate, where cell density and metabolite transport are greatest. Healing of the disc periphery has the potential to relieve discogenic pain, by re-establishing a physical barrier between nucleus pulposus and nerves, and reducing inflammation.

Physical therapies should aim to promote healing in the disc periphery, by stimulating cells, boosting metabolite transport, and preventing adhesions and re-injury. Such an approach has the potential to accelerate pain relief in the disc periphery, even if it fails to reverse age-related degenerative changes in the nucleus.

Eur J Pain. 2010 Aug 19. [Epub ahead of print]

Back pain is common and some sufferers consult GPs, yet many sufferers develop persistent problems. Combining information on risk of persistence and prognostic indicator prevalence provides more information on potential intervention targets than risk estimates alone.

The aims of this study were to determine the proportion of primary care back pain patients with persistent problems whose outcome is related to measurable prognostic factors.

A Prospective cohort study of back pain patients (30-59years) at five general practices in Staffordshire, UK (n=389). Baseline factors (demographic; episode duration; symptom severity; pain widespreadness; anxiety; depression; catastrophising; fear-avoidance; self-rated health) were assessed for their association with disabling and limiting pain after 12-months. The proportion of those with persistent problems whose outcome was related to each factor was calculated.

Prevalence of prognostic factors ranged from 23% to 87%. Strongest predictors were unemployment and high pain intensity. The largest proportions of persistent problems were related to high pain intensity and unemployment. Combining these indicated that 85% of poor back pain outcome is related to these two factors. Poor self-rated health, functional disability, upper body pain and pain bothersomeness were related with outcome for over 40% of those with persistent problems.

Several factors increased risk of poor outcome in back pain patients, notably high pain and unemployment. These risks in combination with high prevalence of risk factors in this population distinguish factors that can help identify targets or sub-groups for intervention.

From: Eur J Pain. 2010 May;14(5):514-22

Widespread pain has negative influence on outcome in low back pain patients. Tender point examination is a standardized examination method to estimate diffuse tenderness. To assess diffuse tenderness by means of a standardized tender point examination and to analyse for associations between the number of tender points and spinal structural changes as well as psycho-social factors.

Patients sick-listed 3-16 weeks due to low back pain with or without sciatica completed a questionnaire and went through a clinical low back examination and tender point examination. Of 326 patients 111 had verified nerve root affection and 215 had non-specific low back pain with or without radiating pain. Disc height reductions were estimated on lateral X-rays.

Multivariate logistic regression analysis showed that more than 8 tender points were strongly negatively associated with disc degeneration, and verified nerve root affection and were positively associated with number of years since first episode of low back pain. Furthermore, more than 8 tender points were positively associated with widespread pain, female sex and bodily distress. With all patients included, bodily distress and the number of tender points were positively associated with the intensity of low back pain, but disc degeneration was only positively associated with low back pain in patients with less than 6 tender points.

The pain in patients with diffuse tenderness was rarely related to disc degeneration or nerve root affection, rather it may be caused by disturbed pain regulation.

BMC Musculoskelet Disord. 2010 Jul 8;11(1):155.

An estimated 80% of the population will suffer from low back pain at some point of their lives. Low back pain is the number one factor limiting activity in patients less that 45 years old, the second most frequent reason for doctor’s visits, and the third most common cause for surgical procedures. In addition to imposing upon patients’ quality of life, low back pain is of significant socioeconomic relevance because it may lead to a temporary loss of productivity, enormous medical and indirect costs, or even permanent disability.

While the management of persistent low back pain remains hotly debated, the traditional approach has been non-surgical treatment with analgesia supplemented by physiotherapy. Given the limited efficacy of these modalities, there are also a number of alternative interventions such as massage, spinal manipulation, exercises, acupuncture, back school and cognitive behavioral therapy. The two most common diseases involving chronic low back pain are discogenic low back pain, responsible for 39% of cases, and disc herniation, accounting for just less than 30% of low back pain incidence. These incidence frequencies are supported by the current data that most closely link the clinical pathology of discogenic low back pain and disc herniation to the anatomical structure of the intervertebral disc. Thus, another treatment option is motorized decompression, a technique designed to lessen pressure on the discs, vertically expand the intervertebral space, and restore disc height. However, systematic reviews to date were unable to find sufficient evidence in the literature to support the use of this modality. A subsequent chart review of 94 patients suggests that motorized non-surgical spinal decompression may be effective in reducing chronic low back pain. Furthermore, preliminary data from a prospective cohort study in patients with chronic low back pain reported a median pain score reduction from 7 to 0 (on a 11-point verbal rating scale) following a 6-week nonsurgical spinal decompression treatment protocol.

The goal of this study was therefore to determine if changes in low back pain, as measured on a verbal rating scale, before and after a 6-week treatment period with motorized non-surgical spinal decompression, correlate with changes in lumbar disc height, as measured on computed tomography scans.

Patients and their medical records were eligible for inclusion if the patient was at least 18 years of age, consented for the 6-week treatment protocol, and presented with chronic low back pain of at least 3 out of 10 on a verbal rating scale and was due to either discogenic low back pain or disc herniation according to a radiological diagnosis using standard medical definitions. Discogenic low back pain is most succinctly defined as a loss of lower back function with pain due to disc degeneration. Degenerative disc disease often emerges when abnormal stresses cause the nucleus gelatinosus to unevenly distribute weight, the annular fibrosis and end plate incur structural damage, and a destructive inflammatory response is triggered to accelerate and perpetuate the degeneration of the disc. A herniated disc (synonymous with a protruding or bulging disc) arises when the intervertebral disc degenerates and is weakened to such an extent that cartilage is pushed into the space containing the spinal cord or a nerve root and causes pain.

Initial decompression force was adjusted to patient tolerance, starting at 4.54 kg (10 lbs) less than half their body weight. If a patient described the decompression pull as strong or painful, this distraction force was decreased by 10%–25%. In subsequent treatment sessions, the distraction force was increased as tolerated to final levels of 4.54 kg to 9.07 kg (10 to 20 lbs) more than half their body weight. Patients continued to use analgesics prescribed by their physicians before enrollment, but were allowed to use additional non-steroidal pain medication should their pain increase temporarily and permitted to discontinue pain medication as needed. During the routine physical examination prior to beginning the non-surgical spinal decompression treatment session, at the first and final visits maximal pain was evaluated during a flexion-extension range of motion exam with the question How strong is your pain on a scale of 0-10 with 0 being no pain and 10 as bad as it could be?

During a two year period only 30 of those patients fulfilled the per protocol inclusion and exclusion criteria for the analysis. The 30 participants consisted of 21 female and 9 male patients with lumbar disc herniation. They had a mean age of 65 (± 15) years, a body mass index of 29 (± 5) kg/m2, and an average duration of low back pain of 12.5 (± 19) weeks with a score of 6.3 (± 2.2) on the VRS. All 30 patients had a disc prolapse and the majority (n=25) also had degenerative disc disease. The maximum force during the first treatment was on average 33.9 (± 6.8) kg and gradually increased during subsequent treatment visits to 52.4 (± 7.6) kg. Low back pain decreased from 6.2 (± 2.2) to 1.6 (± 2.3) and disc height increased from 7.5 (± 1.7) to 8.8 (± 1.7) mm. There was a statistically significant correlation between the increase in disc height and a reduction in pain, with a 1 mm increase in disc height being associated with a reduction of 1.86 on the 11-point verbal rating scale. No adverse events were reported during the treatment period.

In this cohort study we extracted data from 30 patients with discogenic low back pain and found an average reduction in pain from 6.2 to 1.6 after non-surgical spinal decompression. This level of pain relief is consistent with two previous studies using DRX9000 to decrease chronic low back pain. However, here we systematically investigated the change in disc height before and after the treatment, and were able to show that increases in disc height correlated with increased pain relief. A mechanical explanation for this correlation might be that spinal decompression reduces the pressure on the discs. This relief of stress would simultaneously promote regeneration of diseased and compressed discs and increase lumbar disc height, with the latter reducing load on the facet joints.

It is well recognized that continuous pressure on vertebral discs decreases their height. Humans are taller in the morning after the discs decompress while the body is supine overnight and shorter in the evening after the discs have borne weight during daily activity. Interestingly, this effect occurs quite rapidly so that the majority of height-loss in a day occurs within the first hour of arising. Therefore, all CT scans analyzed in this study were performed at least one hour after the subject got out of bed. The first CT scan was performed within two months before the initiation of the treatment and at least one day after or the day immediately before the final treatment session.

A clear diagnosis cannot be made in approximately 80% of cases of low back pain, and imaging techniques can only offer a partial solution to the problem of making a causal diagnosis of low back pain. One might argue that a CT scan is not as sensitive a measure of disc height as an MRI scan because it images soft tissues poorly and cannot examine internal disc morphology. However, because the primary objective was to establish an observable correlation between disc height increase and decreased low back pain, a CT scan permitting examination of the outline of the intervertebral discs at high resolution provided sufficient measurable evidence.

It has been demonstrated that low back pain can lead to muscle spasms that could directly perpetuate pain, or induce pain within the disc as nerve fibers have been described to grow into the inner part of the annulus fibrosus or nucleus pulposus. It is hypothesized that the pain-spasm-pain cycle is perpetuated by further reduction in disc height, which also simultaneously aggravates the facet joint. In either case, dampened pressure on the disc should facilitate the regeneration of the disc and assuage facet joint stress. In fact, it has been described that non-surgical spinal decompression mechanically creates negative intradiscal pressures, and it is speculated that this supports disc regeneration, though this remains controversial.

Pain measurement relies first and foremost on patient report. Taking into account the subjectivity inherent in this process, it was noted that a cut-off point, or rather the change in pain score necessary for detecting a clinically important difference in an individual patient, was needed to identify responders and non-responders to analgesia. Farrar et al reported that on average a reduction in pain intensity of at least 2 points on the NRS serves as a clinically significant change. Using this standard, in this cohort study this intervention had a success rate of over 75% (pain decreased by more than 2 out of 11 in 23 out of 30 patients). In this analysis, each millimeter of increase in disc height was associated with pain relief of roughly 2 points on the scale, a clinically important difference according to the aforementioned report.

However, not all patients responded equally. This raises the question of inter-individual variability and might be addressed by taking into account the heterogeneity of lumbar spine muscle strength acting as a counterforce to the external distraction. Even though the DRX9000 machine has an integrated sensor to detect counterforces, non-surgical spinal decompression can only work if lumbar spine muscles are relaxed. Another reason for different inter-individual response rates could be the age of the patients. However, in sub-analyses the authors did not find a correlation between age and treatment success. With regards to the elderly cohort of patients analyzed in this retrospective study, it is possible that a younger patient population might respond differently to the non-surgical spinal decompression treatment given that they would generally have less disc degeneration, be more active, and have less co-morbidity than the elderly population studied here. Yet this is a hypothesis that remains to be tested in a future prospective study investigating therapies to alleviate low back pain in younger patients. While the authors largely believe the range of muscle tone during nonsurgical spinal decompression to be the main reason for different treatment effects, other reasons for variability could be differing stages and degrees of degenerative disc disease, an assortment of activity levels, and a wide spectrum of concomitant treatments ranging from chiropractic interventions and pain medication cocktails.

Patients with chronic discogenic low back pain are usually on a wide range of analgesics, and pain and analgesic consumption is generally positively correlated. As a result, interventions that reduce pain typically lead to a reduced consumption of analgesics and thus counteract the treatment effect of the intervention (suppressor effect). The fact that a significant reduction of pain was observed even though analgesics were not controlled for corroborates the observation of pain relief through non-surgical spinal decompression.

In this study of non-surgical spinal decompression for chronic discogenic low back pain the authors were able to demonstrate an association between the restoration of disc height and pain relief. The correlation of these variables suggests that pain reduction may be mediated, at least in part, through a restoration of disc height. These results call for a randomized placebo-controlled trial to substantiate the efficacy and elucidate the mechanism of this promising treatment modality.

Spine (Phila Pa 1976). 2010 Jun 30. [Epub ahead of print]

Prospective longitudinal study to evaluate the effect of bed rest on the lumbar musculature and soft-tissues. Earlier work has suggested that the risk of low back injury is higher after overnight bed rest or spaceflight. Changes in spinal morphology and atrophy in musculature important in stabilizing the spine could be responsible for this, but there are limited data on how the lumbar musculature and vertebral structures are affected during bed rest.

Nine male subjects underwent 60 days head down tilt bed rest as part of the second Berlin Bed Rest Study. Disc volume, intervertebral spinal length, intervertebral lordosis angle, and disc height were measured on sagittal plane magnetic resonance images. Axial magnetic resonance images were used to measure cross-sectional areas of the multifidus, erector spinae, quadratus lumborum, and psoas from L1 to L5. Subjects completed low back pain questionnaires for the first 7-days after bed-rest.

Increases in disc volume, spinal length (greatest at lower lumbar spine), loss of the lower lumbar lordosis, and move to a more lordotic position at the upper lumbar spine were seen. The cross-sectional areas of all muscles changed, with the rate of atrophy greatest at L4 and L5 in multifidus and at L1 and L2 in the erector spinae. Atrophy of the quadratus lumborum was consistent throughout the muscle, but cross-sectional areas of psoas muscle increased. Subjects who reported low back pain after bed rest showed, before reambulation, greater increases in posterior disc height, and greater losses of multifidus cross-sectional areas at L4 and L5 than subjects who did not report pain. These results provide evidence that changes in the lumbar discs during bed rest and selective atrophy of the multifidus muscle may be important factors in the occurrence of low back pain after prolonged bed rest.

From: Spine J. 2010 Apr;10(4):297-305. Epub 2010 Feb 26

Sitting is associated with loss of the lumbar lordosis, intervertebral disc compression, and height loss, possibly increasing the risk of lower back pain. With a trend toward more sitting jobs worldwide, practical strategies for preventing lumbar flattening and potentially associated low back pain are important. The purpose of this study was to determine the feasibility of using upright magnetic resonance imaging (MRI) and stadiometry to measure changes in height and configuration of the lumbar spine before and after normal sitting and a sitting unloading exercise intervention.

This is a hospital-based pilot study involving pre-post assessments in a single group. The sample comprises six asymptomatic hospital employees involved in either general patient care or research writing/data collection. The outcome measures were lumbar total midsagittal cross-sectional intervertebral disc area, vertical height, lordotic angle derived from digitized MRI examinations, and seated body height measured directly with a stadiometer. Midsagittal MRI scans were performed before sitting, after 15 minutes of relaxed sitting (“postsitting”), immediately after seated unloading exercises, and approximately 7 minutes after exercise. Subsequently, seated stadiometry assessments were performed after 10 minutes of supine recumbency, 15 minutes of relaxed sitting, and every 10 seconds after seated unloading exercises until three consecutive height measurements were identical. Digitized midsagittal images were used to derive MRI based outcome measures.

After 15 minutes of sitting, mean total intervertebral disc area, lordotic angle, and vertical height of the lumbar spine decreased 18.6 mm(2), 6.2 degrees , and 12.5 mm, respectively, whereas after seated unloading exercises, these parameters increased by 87.9 mm(2), 5.0 degrees , and 21.9 mm, respectively. Similarly, mean seated height on stadiometry decreased by 6.9 mm after 15 minutes of sitting and subsequently increased by 5.7 mm after unloading exercises.

Seated upright MRI and stadiometry, as performed in this study, appear to be feasible methods for detecting compressive and decompressive spinal changes associated with normal sitting and, alternately, seated unloading exercises. Larger studies are encouraged to determine normative values of our study measurements and to determine if morphological changes induced by seated unloading predict treatment response and/or reductions in the incidence of sitting related low back pain.

These findings confirm an earlier study on the unloading sitting exercise, J Bodyw Mov Ther. 2010 Apr;14(2):119-26. Epub 2008 Jul 31. Preliminary investigation into a seated unloading movement strategy for the lumbar spine: a pilot study.

This study was a preliminary investigation into a seated unloading movement strategy for the lumbar spine using the upper extremities. With the economic burden of low back pain estimated in the billions worldwide, and also with a trend towards more jobs related to sitting, a simple distraction exercise coined chair-care is presented. An attempt to objectify using stadiometry was used to measure standing height changes after 15 min of sitting and after the exercise. The results showed significant standing height gains post-exercise when compared to post-sitting and initial standing (2.4 and 2.7 mm, respectively). No significant standing height changes were seen after 15 min of sitting. It is therefore likely that this simple seated exercise creates standing height gains of the spine. Proposed mechanisms are discussed with an emphasis on spinal hydraulics and intervertebral disc nutrition.

From: Acad Emerg Med. 2010 May;17(5):484-9.

Acute back and neck strains are very common. In addition to administering analgesics, these strains are often treated with either heat or cold packs. The objective of this study was to compare the analgesic efficacy of heat and cold in relieving pain from back and neck strains. The authors hypothesized that pain relief would not differ between hot and cold packs.

This was a randomized, controlled trial conducted at a university-based emergency department with an annual census of 90,000 visits. Emergency department patients >18 years old with acute back or neck strains were eligible for inclusion. All patients received 400 mg of ibuprofen orally and then were randomized to 30 minutes of heating pad or cold pack applied to the strained area. Outcomes of interest were pain severity before and after pack application on a validated 100-mm visual analog scale (VAS) from 0 (no pain) to 100 (worst pain), percentage of patients requiring rescue analgesia, subjective report of pain relief on a verbal rating scale (VRS), and future desire for similar packs. Outcomes were compared with t-tests and chi-square tests. A sample of 60 patients had 80% power to detect a 15-mm difference in pain scores.

Sixty patients were randomized to heat (n = 31) or cold (n = 29) therapy. Groups were similar in baseline patient and pain characteristics. There were no differences between the heat and cold groups in the severity of pain beforeor after therapy. Pain was rated better or much better in 16/31 (51.6%) and 18/29 (62.1%) patients in the heat and cold groups, respectively. There were no between-group differences in the desire for and administration of additional analgesia. Twenty-five of 31 (80.6%) patients in the heat group and 22 of 29 (75.9%) patients in the cold group would use the same therapy if injured in the future.

The addition of a 30-minute topical application of a heating pad or cold pack to ibuprofen therapy for the treatment of acute neck or back strain results in a mild yet similar improvement in the pain severity. However, it is possible that pain relief is mainly the result of ibuprofen therapy. Choice of heat or cold therapy should be based on patient and practitioner preferences and availability.

From: Disabil Rehabil. 2010 Jun 4. [Epub ahead of print]

The emotional distress caused by pain is one of the most disruptive aspects of living with the condition. This study investigates how individuals experience pain and its consequences for family life and work. Unstructured interviews, using the ‘Framework’ approach with topic guide, were recorded and transcribed. Patients were sampled for age, sex, ethnicity and occupation from new referrals with spinal pain to a rheumatology outpatient clinic. Eleven patients (five males and six females) were interviewed in English (n = 9) or their preferred language (n = 2). Interviews were read in depth twice to identify the topics. Data were extracted in phrases and sentences using thematic content analysis.

Emergent themes reported were relationships with: spouses and partners (n = 7), children/parents (n = 6), with other family and friends (n = 7) and work-related issues (n = 11). Patients valued support from family but expressed concerns about causing them worry. Work-related issues included physical and emotional efforts to keep working when in pain, fear of losing employment and financial problems. Patients expressed anxiety about how their pain affected other family members, regret at losing full work capacity and worry about financial consequences. The lived experience of chronic spinal pain has ramifications that go beyond the individual, reaching into work and social relationships.

From: Spine (Phila Pa 1976). 2010 May 25. [Epub ahead of print]

An in vivo rat-tail model was adopted to study the structural changes of degenerated intervertebral disc after different traction protocols to investigate the effects of traction with different modes and magnitudes on disc with simulated degeneration.

Traction has been commonly used in clinical practice for treating low back pain. Its effects on disc with degeneration have not been fully investigated. Forty-seven mature rats were used. Continuous static compression of 11 N was applied to the rat caudal 8-9 disc for 2 weeks to simulate disc degeneration. Tractions with different modes (static or intermittent) and magnitudes (1.4 N or 4.2 N) were applied to the degenerated disc for 3 weeks. The disc height was quantified in vivo on days 4, 18, and 39. The treated discs were then harvested for morphologic analysis.

Significant decrease in disc height with degenerative morphologic changes was observed after the application of the static compression. The changes in disc height after the application of traction were found to be magnitude dependent. Continuous decrease in disc height was observed after 4.2-N traction, whereas the disc height maintained after traction of 1.4 N. However, no obvious morphologic change was found in comparison with the degenerated discs without traction.

Although traction was not demonstrated to have restored disc with degeneration, traction with relatively low magnitude was found to have significant beneficial effect in maintaining disc height of degenerated disc, and it might be a potential intervention to slow down the process of degeneration. Future studies of the effects of low-magnitude traction on degenerated disc are recommended.

From: Spine (Phila Pa 1976). 2010 Mar 1;35(5):531-6.

Back pain is one of the most common musculoskeletal complaints of the elderly, with a point prevalence of 26.9% in the Netherlands. Van Tulder et al performed a systematic review and reported that lumbar disc degeneration could be a possible risk factor for back pain in adults. However, the review reported that the methodologic quality of most of these studies was low and the studies were difficult to compare due to difference in gender frequencies, age groups, settings, radiographic grading systems, and definitions for lumbar disc degeneration.

Lumbar disc degeneration is characterized radiologic by the presence of osteophytes, endplate sclerosis, and disc space narrowing. In 1993, Lane et al presented a reliable grading system for these individual radiographic features. In a recent review, this grading system was recommended for use in epidemiologic studies. There have been a number of recent studies that have used the classification of the individual radiographic features of disc degeneration defined by Lane et al. One of these studies described the occurrence of these separate features and their relationship with back pain in the open population, but only in a limited sample.

However, it is still unknown how to combine the individual radiographic features and how to define a clinically relevant definition for lumbar disc degeneration. Currently there is no consensus about whether the lumbosacral disc should be scored. Some studies have included the lumbosacral level in their definition of lumbar disc degeneration, while others have not. Currently within the literature, there have been no studies that have explored different definitions of lumbar disc degeneration and their association with low back pain within one study sample.

The purpose of this study was to explore the association of the different individual radiographic features, including osteophytes and disc space narrowing, with self-reported low back pain. Different definitions of lumbar disc degeneration with self-reported low back pain and disability were considered in a large open population sample. Furthermore, in order to disentangle the discrepancies in reported strength of the associations, the authors characterized the frequency of the different individual radiographic features of lumbar disc degeneration and definitions of lumbar disc degeneration, as well as their association with low back pain status, by age, gender, and vertebral level.

The authors are the first to report in one paper, multiple lumbar disc degeneration definitions and their associations with low back pain, for the separate genders and discreet age groups. In this study, disc space narrowing appeared to be more strongly associated with low back pain than osteophytes, especially in men. Disc space narrowing at 2 or more levels appeared more strongly associated with low back pain than disc space narrowing at only 1 level. The strength of the associations increased with chronic low back pain. The majority of the associations were strengthened by excluding level L5–S1.

The most frequently observed radiographic feature of lumbar disc degeneration was osteophytes, with greater frequency in men than in women. Narrowing, however, was more common in women than in men and was also shown to be more frequent at the lower disc levels. Both individual radiographic features increased in frequency with age.

Data from many studies suggest an association with lumbar disc degeneration and low back pain. The authors are not aware of data from population-based samples that have investigated the association of different definitions of lumbar disc degeneration with self-reported low back pain. MacGregor et al performed a study, using MRI scans to assess risk factors associated with severe back pain. They investigated a number of features including; disc height, signal change, disc bulge and anterior osteophytes, and made a sum score for all features together. This sum was associated with severe back pain. However, they did not state which features had the highest predictive capability. Some studies suggest an association between osteophytes and low back pain and some studies suggest an association between disc space narrowing and low back pain. The data from this study confirms the association between low back pain and disc space narrowing. In addition, the data suggest an association with osteophytes, only when a more specific definition (osteophytes) is used. However, when osteophytes and disc space narrowing were both included in the model, there was no association with osteophytes anymore. Therefore osteophytes do not have an independent association with low back pain and seem therefore an inferior derivate from disc space narrowing.

Some studies suggest that the strength of the association between low back pain and disc space narrowing grows with increasing severity of disc space narrowing. Data from this study confirm this, but only when L5–S1 is excluded. Further, the data indicate that the association between low back pain and disc space narrowing increases when a greater number of levels are affected.

The explanation for the stronger association between low back pain and disc space narrowing compared with the presence of osteophytes is unknown. It is possible that the reduction of space between the vertebrae as a consequence of the degenerative disc is more likely to lead to increased pressure on facet joints and spinal ligaments.

The explanation for the stronger association between back pain and disc space in men compared with the association in women is also unknown. It is possible that even though women reported low back pain more often, only a small proportion of the complaints are due to lumbar disc degeneration, whereas other factors determine the feeling of pain. Men and women could also report pain differently therefore effecting the association between back pain, disc space narrowing and gender. Cecchi et al showed that women presented with significantly more severe pain than men.

A possible explanation for the stronger association between low back pain and disc space narrowing, excluding level L5–S1, is the possible overrating of the narrowing grade of the lumbosacral disc. The height of the lumbosacral disc is difficult to score due to its narrowed height relative to disc L4–L5. The lumbosacral disc is also different in appearances among different individuals, independently of disease. Therefore, by using the lumbar disc definition “narrowing 1 to 4,” the inconsistency of the grading scores at this level is ruled out. Furthermore, some differences in the reported associations in the prior studies can be explained by the stratified results. Possible explanations for relatively low odds ratios previously reported could be due to the use of a young age group, the use of women only and scoring of the lumbosacral level.

Data from this study confirms the findings from recent population based radiographic surveys showing a greater frequency and severity of osteophytes in men than in women. A possible explanation for the greater frequency in men is the higher BMD in men. However, after including BMD in the model, although less explicit, men still show a greater frequency and severity of osteophytes.

Data from this study suggest a greater frequency and severity of narrowing in women than in men and confirms that the prevalence of osteophytes and disc space narrowing increases with age in both men and women.

The authors defined chronic low back pain to be present when the duration of the low back pain was more than 1 year. In this way the definition chronic low back pain included long lasting chronic complaints with long lasting impact on ones life. When they defined chronic low back pain to be present when the duration of the low back pain was more than 6 months, the OR of the associations diminished.

From this data, a useful case definition for lumbar disc degeneration can be deduced; specifically disc space narrowing at 2 or more levels from L1/2 to L4–L5. This definition shows the strongest relationship with low back pain and represents a more generalized form of lumbar disc degeneration. As a result it might be a promising clinically relevant phenotype in genetic and epidemiologic lumbar disc degeneration research.

The data provides evidence for a moderate association between disc space narrowing and low back pain. This association is only slightly less than the association of pain and radiologic knee osteoarthritis and even slightly more than the association of pain and radiologic hand osteoarthritis in the same population sample.

The most important aspect of the data are that disc space narrowing at 2 or more levels is even more related to chronic low back pain. The ability of lumbar disc degeneration in predicting low back pain at the follow-up period was unfortunately not possible to investigate, as no questions about low back pain specifically were asked at the follow-up visit.

The data provides evidence for an association between disc space narrowing and low back pain especially in men, with the association increasing, with increasing numbers of affected intervertebral disc spaces. The data highlights the frequent occurrence of individual radiographic features, as well as the increased frequency in age, of the individual radiographic features of lumbar disc degeneration in population samples of men and women.