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Abstract

  1. Top of page
  2. Abstract
  3. SUBJECTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. REFERENCES

Objective

Osteoporotic Fractures in Men (Hong Kong) and Osteoporotic Fractures in Women (Hong Kong) represent the first large-scale prospective population-based studies on bone health in elderly (age ≥65 years) Chinese men (n = 2,000) and women (n = 2,000). We undertook the current study to investigate the prevalence of lumbar disc space narrowing in these subjects, and to identify the potential relationship between disc space narrowing and sex, bone mineral density (BMD), and other demographic and clinical data.

Methods

On lumbar lateral radiographs, L1/L2–L4/L5 disc space was classified into 4 categories: 0 = normal; 1 = mild narrowing; 2 = moderate narrowing; 3 = severe narrowing. We compared demographic and clinical data between subjects with and those without total disc space narrowing scores ≥3.

Results

Disc space narrowing was more common in elderly women than in elderly men. The mean ± SD disc space narrowing score for the 4 discs was 2.71 ± 2.21 for men and 3.08 ± 2.50 for women (P < 0.0001). For the 3 age groups of 65–69 years, 70–79 years, and ≥80 years, the average disc space narrowing score increased with increasing age in both men and women, and to a greater degree in women than in men. The average disc space narrowing score differences between women and men were 0.12, 0.40, and 0.90, respectively, in the 3 age groups. For both men and women, a disc space narrowing score ≥3 was associated with older age, higher spine and hip BMD, low back pain, and restricted leg mobility.

Conclusion

The prevalence and severity of disc space narrowing are higher in elderly women than in elderly men. With increasing age, disc space narrowing progresses at a greater rate in women than in men. A disc space narrowing score ≥3 is associated with higher spine and hip BMD.

Intervertebral disc degeneration is a common musculoskeletal condition. It can progress to disc herniation, spinal canal stenosis, and, in conjunction with facet joint arthrosis, degenerative spondylolisthesis. The factors initiating and influencing the progression of disc degeneration remain unclear. Nevertheless, there is general agreement that spinal mechanical stress accelerates the progression of disc degeneration. Young men are more susceptible to disc degeneration than are young women, most likely due to increased mechanical stress and physical injury. Disc degeneration becomes apparent in men in the second decade of life, almost a decade earlier than in women (1, 2). The severity of age-matched disc degeneration is also generally greater in young and middle-aged men (1, 2). In a recent magnetic resonance imaging (MRI)–based survey of young adults ages 20–22 years, lumbar disc degeneration was significantly more frequent in men (3).

While young and middle-aged men are more likely to have lumbar disc degeneration than women, 2 recent population-based studies indicated that this trend is reversed in elderly subjects, with women tending to have more severe lumbar disc degeneration than men. In a radiographic study of subjects age ≥55 years, De Schepper et al (4) found that disc space narrowing was more prevalent in women than in men. Using an MRI-based disc degeneration grading system, Griffith et al and Wang et al showed that elderly female subjects had more severe disc degeneration than elderly male subjects at all lumbar levels (5, 6). It has been postulated that a decrease in estrogen level may be important with regard to accelerated disc degeneration in postmenopausal women (7).

Osteoporotic Fractures in Men (Mr. OS) (Hong Kong) and Osteoporotic Fractures in Women (Ms OS) (Hong Kong) represent the first large-scale prospective cohort studies ever conducted on bone health in Asian men and women. Two thousand elderly Chinese men and 2,000 elderly Chinese women were studied to determine the relationship of anthropometric, lifestyle, medical, and other factors with bone mineral density (BMD) at the hip and spine. The purpose of the current study was 4-fold: 1) to determine the prevalence of radiographic lumbar disc space narrowing in elderly Chinese men and women; 2) to confirm whether disc space narrowing is more prevalent in elderly Chinese women than men and how this changes among different age groups; 3) to investigate the relationship between disc space narrowing and BMD; and 4) to identify potential risk factors for lumbar disc space narrowing in the Chinese population. Radiographic disc space narrowing is a manifestation of late-stage disc degeneration.

SUBJECTS AND METHODS

  1. Top of page
  2. Abstract
  3. SUBJECTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. REFERENCES

Two thousand Chinese men and 2,000 Chinese women age ≥65 years were recruited from local communities by advertisements placed in housing estates and community centers for elderly people for a prospective cohort study from August 2001 to March 2003. The project was designed primarily to examine the BMD of older Chinese adults prospectively for 4 years. All subjects were community dwelling, able to walk without assistance, without bilateral hip replacement, and with the potential to survive the duration of the primary study as judged by their preexisting medical status. Subjects were invited to the research center for interviews and physical examination. The study protocol was approved by the Chinese University of Hong Kong Ethics Committee. Written informed consent was obtained from all subjects. Data from the baseline evaluation were analyzed and are reported herein.

The participants were interviewed using a structured standardized questionnaire. This questionnaire included demographic information, socioeconomic status, medical history related to osteoporosis, history of fracture, current medications (verified by direct inspection or medical record), and alcohol and tobacco consumption. Dietary intake was recorded using a modified Block Food Frequency questionnaire based on the data from the Hong Kong Adult Dietary Survey in 1995 (8). Physical activity was measured by the Physical Activity Scale for the Elderly (PASE) questionnaire (9) modified for use in older Chinese in Hong Kong (10). Height and weight were measured with the subjects wearing indoor clothing without shoes. Height was measured using the Holtain Harpenden stadiometer. Body weight was measured using the Physician Beam Balance Scale (Healthometer). Both readings were recorded to 1 decimal place. Grip strength in both hands was measured with a Preston Grip Dynamometer. Three tests on each hand were performed. The average result of the second and third tests on each hand was used. Body mass index (BMI) was calculated in weight (kg)/height (m2). BMD (gm/cm2) at the total hip and spine (L1–L4) was measured by Hologic QDR 4,500 W densitometers. The in vivo coefficients of variation of the system were 0.9% and 0.7% at the lumbar spine and at the total hip, respectively.

Left lateral thoracic and lumbar spine radiographs were obtained by adjusting exposure parameters according to participants' body weight and height. Hard copies of lumbar spine radiographs were analyzed in this study. The readers were blinded to clinical characteristics of the participants. Intervertebral disc space height changes were classified into 4 categories: 0 = normal; 1 = mild narrowing (<30% reduction in disc height); 2 = moderate narrowing (30–60% reduction in disc height); 3 = severe narrowing (>60% reduction in disc height) (4, 11–13). Reader 1 (X-JZ) was a senior radiologist with >10 years of experience in reading radiographs. Reader 2 (MD) was a junior radiologist with 5 years of experience in reading radiographs. Before the formal grading started, 1 week was given to allow these 2 readers to familiarize themselves with the grading system by comparing lateral lumbar spine radiographs from the Mr. OS (Hong Kong) and Ms OS (Hong Kong) studies as well as by comparing normal lumbar radiographs stored at our institution. Reader 1 read all 4,000 lumbar spine radiographs, while reader 2 read 1,000 lumbar spine radiographs selected sequentially such that 1 of every 4 radiographs (from 500 men and 500 women) was read. To minimize intrareader bias (14), radiographs of male subjects and female subjects were mixed together, and the reading of all radiographs was completed in 2 months. Disc space narrowing at L5/S1 was not included, as assessment of disc narrowing at this level is known to be less reliable (4).

For discs L1/L2–L4/L5, the intrareader reproducibility of reader 1 had a kappa value for grade 1 of 0.81, for grade 2 of 0.912, and for grade 3 of 1, with an overall kappa value of 0.872. The interreader reproducibility between reader 1 and reader 2 had a kappa value of 0.72, also indicating good agreement. In this study the results for reader 1 were analyzed further. The results for reader 2, which were similar to those for reader 1 in trend, are available at http://www.diir.cuhk.edu.hk/web/supplementary/.

Twenty-five variables were analyzed with regard to their relationship to disc space narrowing, including age, weight, height, BMI, spine BMD, hip BMD, PASE score, average of left/right grip strength, dietary calcium intake, hypertension, diabetes, history of fracture after age 50 years, osteoarthritis, smoking history, fall in past 12 months, longest occupation involving physical labor, number of children borne, low back pain, weakness of lower limbs, clumsiness in walking, difficulty bending forward, difficulty lifting a 10-pound object, difficulty putting on socks, difficulty getting in or out of the front seat of a car, and difficulty in standing for 2 hours. Disc space narrowing of the lumbar spine was defined as positive for this analysis when the sum of the disc space narrowing scores for discs L1/L2–L4/L5 was ≥3.

Statistical analyses were performed using SAS software, version 9.1.3 (SAS Institute). Characteristics of participants with or without disc space narrowing scores ≥3 were compared for both sexes. Two-sample independent t-tests were used for continuous variables, while chi-square tests were used for categorical variables. Logistic regression analysis was performed for significant factors. All statistical tests were 2-sided. P values less than 0.05 were considered significant.

RESULTS

  1. Top of page
  2. Abstract
  3. SUBJECTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. REFERENCES

The study subjects included 2,000 Chinese men (mean age 72.4 years [range 65–92 years]) and 2,000 Chinese women (mean age 72.6 years [range 65–98 years]). There was no age difference between men and women (P = 0.254). Seven lumbar radiographs in men and 2 radiographs in women were judged suboptimal in quality, and disc space assessment was not performed for these subjects. In addition, 3 discs in men and 4 discs in women were judged to have been sites of prior infection and were excluded from analysis. For discs L1/L2–L4/L5, 48.0% of those for men had grade ≥1 disc space narrowing and 15.9% had grade ≥2 disc space narrowing, while 51.0% of those for women had grade ≥1 disc space narrowing and 20.9% had grade ≥2 disc space narrowing. The prevalence of grade 1 disc space narrowing was slightly greater in men (32.2% versus 30.0%; P < 0.005), while the prevalence of grade ≥2 disc space narrowing was greater in women (20.9% versus 15.9%; P < 0.0001). The overall grade ≥1 disc space narrowing was more common in women (51.0% versus 48.0%; P < 0.0001). The mean ± SD disc space narrowing scores for discs L1/L2–L4/L5 were 2.71 ± 2.21 for men and 3.08 ± 2.50 for women (P < 0.0001). Details of disc space narrowing prevalence at each level for men and women are shown in Table 1 (the results for reader 2, which showed a trend similar to those for reader 1, are available at http://www.diir.cuhk.edu.hk/web/supplementary/).

Table 1. Prevalence of disc space narrowing (DSN) at each disc level in men and women*
Sex, DSN gradeL1/L2L2/L3L3/L4L4/L5∑L1–L4
  • *

    Values are the number (%) of disc spaces. The numbers of disc spaces in men measured at the 4 disc levels (L1/L2, L2/L3, L3/L4, and L4/L5) were 1,996, 1,998, 1,997, and 1,998, respectively, yielding a total of 7,989 measured at levels L1/L2–L4/L5 (∑L1–L4). The number of disc spaces in women measured at each of the 4 disc levels was 1,992, yielding a total of 7,968 measured at levels L1/L2–L4/L5. See Subjects and Methods for definitions of grades.

Men     
 1476 (24)614 (31)718 (36)764 (38)2,572 (32)
 294 (5)156 (8)187 (9)520 (26)957 (12)
 319 (1)52 (3)71 (4)166 (8)308 (4)
 ∑1–3589 (30)822 (41)976 (49)1,450 (73)3,837 (48)
 ∑2–3113 (6)208 (10)258 (13)686 (34)1,265 (16)
Women     
 1447 (22)612 (31)673 (34)655 (33)2,387 (30)
 2118 (6)252 (13)281 (14)589 (30)1,240 (16)
 350 (3)88 (4)96 (5)192 (10)426 (5)
 ∑1–3615 (31)952 (48)1,050 (53)1,436 (72)4,053 (51)
 ∑2–3168 (8)340 (17)377 (19)781 (39)1,666 (21)

The disc space narrowing scores for the 3 age groups 65–69 years, 70–79 years, and ≥80 years are shown in Table 2. Disc space narrowing severity throughout the lumbar spine increased with increasing age in both men and women (P < 0.001). The differences in disc space narrowing score between men and women also increased with increasing age, being 0.12, 0.40, and 0.90, respectively, in the 3 different age groups (this same trend was also shown by the results for reader 2, available at http://www.diir.cuhk.edu.hk/web/supplementary/). Further analysis demonstrated more grade ≥2 disc space narrowing as age increased, while grade 1 disc space narrowing remained similar across the 3 age groups (Table 3) (further information is available at http://www.diir.cuhk.edu.hk/web/supplementary/).

Table 2. Disc space narrowing score in 3 age groups*
 Age 65–69 yearsAge 70–79 yearsAge ≥80 yearsP for trend
  • *

    Values are the mean ± SD of discs L1/L2–L4/L5. The numbers of men ages 65–69 years, 70–79 years, and ≥80 years were 662, 1,151, and 184, respectively. The numbers of women ages 65–69 years, 70–79 years, and ≥80 years were 668, 1,112, and 216, respectively.

Male2.358 ± 2.0282.787 ± 2.2143.516 ± 2.543<0.001
Female2.478 ± 2.0523.188 ± 2.5314.417 ± 2.990<0.001
Male/female difference (P)0.12 (0.286)0.401 (<0.001)0.901 (<0.001)
Table 3. Prevalence of disc space narrowing (DSN) in 3 age groups in men and women*
Sex, DSN gradeAge 65–69 yearsAge 70–79 yearsAge ≥80 years
  • *

    Values are the number (%) of disc spaces with each grade of narrowing. Each value reflects the sum of discs L1/L2–L4/L5. The numbers of disc spaces in men ages 65–69 years, 70–79 years, and ≥80 years were 2,648, 4,607, and 736, respectively. The numbers of disc spaces in women ages 65–69 years, 70–79 years, and ≥80 years were 2,672, 4,451, and 864, respectively. See Subjects and Methods for definitions of grades.

Men   
 1832 (31.4)1,488 (32.3)252 (34.2)
 2270 (10.2)573 (12.4)115 (15.6)
 363 (2.4)192 (4.2)55 (7.5)
 ∑1–31,165 (44.0)2,253 (48.9)422 (57.3)
 ∑2–3333 (12.6)765 (16.6)170 (23.1)
Women   
 1798 (29.9)1,320 (29.7)269 (31.1)
 2331 (12.4)733 (16.5)176 (20.4)
 365 (2.4)254 (5.7)111 (12.8)
 ∑1–31,194 (44.7)2,307 (51.8)556 (64.4)
 ∑2–3396 (14.8)987 (22.2)287 (33.2)

Potential risk factors and their relationship with disc space narrowing (sum score ≥3) are shown in Table 4. For both men and women, a disc space narrowing score ≥3 was associated with older age, higher spine and hip BMD, low back pain, restricted leg mobility including difficulty in lifting a 10-pound object, and difficulty standing for 2 hours. For men, a disc space narrowing score ≥3 was also associated with a lower PASE score; for women, a disc space narrowing score ≥3 was also associated with lower grip strength and higher BMI. This study did not show a significant association between a disc space narrowing score ≥3 and weight, height, dietary calcium intake, hypertension, diabetes, history of fracture after age 50 years, osteoarthritis, smoking history, or longest occupation involving physical labor (Table 4). Further logistic analysis showed that older age, high spine and hip BMD, low back pain, and difficulty standing for 2 hours were significant predictors of a disc space narrowing score ≥3 in both sexes. BMI, grip strength, and number of children borne were not significant predictors of a disc space narrowing score ≥3 (Table 5).

Table 4. Comparison of demographic and clinical data between the subjects with and those without disc space narrowing (DSN)*
 MenWomen
Total DSN score ≥3 (n = 937)Total DSN score <3 (n = 1,061)χ2 or tPTotal DSN score ≥3 (n = 962)Total DSN score <3 (n = 1,035)χ2 or tP
  • *

    Except where indicated otherwise, values are the mean ± SD. Disc space narrowing of the lumbar spine was defined as positive when the sum of the disc space narrowing scores for discs L1/L2–L4/L5 was ≥3. BMI = body mass index; BMD = bone mineral density; PASE = Physical Activity Scale for the Elderly. See Subjects and Methods for definitions of grades.

  • By t-test.

  • By chi-square test.

Age, years73.19 ± 5.1271.69 ± 4.80−6.74<0.000173.43 ± 5.6071.66 ± 4.92−7.51<0.0001
Weight, kg62.65 ± 9.5762.27 ± 9.21−0.890.373254.84 ± 8.6254.20 ± 8.36−1.680.0926
Height, m1.63 ± 0.061.63 ± 0.05−0.690.49271.51 ± 0.051.51 ± 0.051.280.2021
BMI, kg/m223.50 ± 3.2023.41 ± 3.07−0.650.517024.11 ± 3.4823.74 ± 3.40−2.400.0163
Spine BMD, gm/cm20.987 ± 0.1790.919 ± 0.176−8.51<0.00010.788 ± 0.1500.716 ± 0.137−10.99<0.0001
Hip BMD, gm/cm20.875 ± 0.1310.854 ± 0.125−3.560.00040.719 ± 0.1170.699 ± 0.116−3.99<0.0001
PASE score, 0–40093.88 ± 47.73100.21 ± 52.302.820.004884.26 ± 32.0386.61 ± 34.321.580.1154
Average of left/right grip strength, kg30.91 ± 6.6431.46 ± 6.281.900.057219.95 ± 4.2120.56 ± 4.173.250.0012
Dietary calcium intake, mg/day632.14 ± 296.14625.19 ± 299.16−0.520.6029571.30 ± 269.63568.70 ± 264.44−0.220.8283
Hypertension, no. (%)397 (42.4)438 (41.3)0.240.6228468 (45.2)402 (41.8)2.390.1225
Diabetes, no. (%)138 (14.7)155 (14.6)0.010.9402143 (13.8)142 (14.8)0.360.5466
History of fracture after age 50 years, no. (%)61 (6.5)71 (6.7)0.030.8704171 (16.5)163 (16.9)0.060.8006
Osteoarthritis, no. (%)67 (7.2)56 (5.3)3.020.0823110 (10.6)98 (10.2)0.100.7472
Smoking, no. (%)112 (12.0)126 (11.9)0.000.957518 (1.7)19 (2.0)0.150.6961
Fall in past 12 months, no. (%)138 (14.7)169 (15.9)0.550.4577252 (24.4)230 (23.9)0.050.8187
Longest occupation involving physical labor, no. (%)77 (8.2)100 (9.4)0.910.339935 (3.5)26 (2.8)0.710.3988
Children borne3.44 ± 2.153.65 ± 2.112.160.0308
Low back pain, no. (%)316 (33.7)296 (27.9)7.950.0048578 (55.9)485 (50.4)5.900.0151
Weakness of lower limbs, no. (%)55 (5.9)33 (3.1)9.000.002784 (8.1)72 (7.5)0.280.5993
Clumsiness in walking, no. (%)208 (22.2)185 (17.4)7.140.0075347 (33.5)288 (29.9)2.960.0853
Difficulty bending forward, no. (%)85 (9.1)63 (5.9)7.120.0076111 (10.7)95 (9.9)0.390.5329
Difficulty lifting 10-pound object, no. (%)87 (9.3)73 (6.9)3.910.0481283 (27.3)222 (23.1)4.800.0284
Difficulty putting socks on foot, no. (%)49 (5.2)55 (5.2)0.000.963450 (4.8)24 (2.5)7.630.0058
Difficulty getting in/out of front car seat, no. (%)67 (7.2)50 (4.7)5.360.0206143 (13.8)108 (11.2)3.040.0811
Difficulty standing for 2 hours, no. (%)292 (31.2)272 (25.6)7.500.0062627 (60.6)530 (55.1)6.160.0131
Table 5. Logistic regression of total disc space narrowing score ≥3*
 MenWomen
UnitModel 1: hip BMD, OR (95% CI)Model 2: spine BMD, OR (95% CI)UnitModel 1: hip BMD, OR (95% CI)Model 2: spine BMD, OR (95% CI)
  • *

    Unit = SD of the variable except for number of children borne; OR = odds ratio; 95% CI = 95% confidence interval; AUC = area under the curve (see Table 4 for other definitions). See Subjects and Methods for definitions of grades.

  • P < 0.05.

  • Hip BMD for model 1 and spine BMD for model 2.

Age, years5.01.38 (1.26–1.52)1.32 (1.20–1.45)5.01.47 (1.34–1.62)1.40 (1.27–1.54)
BMI, kg/m23.451.03 (0.93–1.15)0.94 (0.85–1.05)
BMD, gm/cm20.131.26 (1.14–1.38)1.33 (1.24–1.42)0.121.39 (1.24–1.55)1.64 (1.50–1.80)
PASE score, 0–400−50.31.08 (0.99–1.19)1.07 (0.98–1.18)
Average of left/right grip strength, kg−4.21.09 (0.99–1.20)1.12 (1.01–1.24)
Children borne, no.10.95 (0.91–0.99)0.95 (0.91–0.99)
Low back painYes/no1.30 (1.07–1.58)1.31 (1.07–1.60)Yes/no1.19 (0.99–1.44)1.23 (1.02–1.50)
Difficulty standing for 2 hoursYes/no1.17 (0.95–1.43)1.13 (0.92–1.40)Yes/no1.15 (0.95–1.39)1.15 (0.95–1.41)
AUC0.6150.6460.6340.681

DISCUSSION

  1. Top of page
  2. Abstract
  3. SUBJECTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. REFERENCES

The current study represents the largest study on radiographic disc space narrowing in community-dwelling elderly men and women in China. A particular strength of this study is that both men and women from the same community-based population were investigated with lateral lumbar spine radiographs being obtained, thereby enabling men and women to be directly compared. Similar to recent reports, our data showed a high prevalence of disc space narrowing in elderly subjects, with its severity being higher in women than in men (4, 6). Also similar to previous reports, disc space narrowing was most common at the L4/L5 level (4). However, our results show that mild disc space narrowing (grade 1) is more common in men (32.2%) than in women (30.0%). Although grade 1 disc space narrowing is more subjective, independent scoring by reader 2 showed a similar trend, indicating that this result is likely to be reliable (further information is available at http://www.diir.cuhk.edu.hk/web/supplementary/).

One interesting finding of the current study is that the male/female difference in disc space narrowing severity increased as age increased (Table 2). Recent evidence suggests that estrogen, through a variety of potential biologic effects, also seems to affect disc degeneration (7). It has been suggested that relative estrogen deficiency may be contributing to the accelerated disc degeneration seen in postmenopausal women, either through a direct effect on disc cells or through an indirect effect on blood perfusion of the spine. Hormone replacement treatment seems to have a beneficial effect on lumbar intervertebral disc height in postmenopausal women (15). There is estrogen receptor β gene expression in human intervertebral disc cells such that estrogen can enhance cell proliferation in annulus cell cultures (16). Impaired disc nutrition is also considered a major factor in disc degeneration (17–19). In animal studies, vertebral marrow perfusion decreased after ovariectomy in animal studies (20). Estrogen has a positive effect on vascular smooth muscle and endothelial cells. Estrogen promotes vasodilatation, is known to prevent neointimal thickening after catheter balloon injury, and also ameliorates atherosclerotic lesions (21). Since the disc nucleus obtains a considerable supply of nutrients via diffusion from the end plate, it is feasible that decreased vertebral perfusion in postmenopausal women contributes to the decreased diffusion and nutrient supply of the intervertebral disc nucleus (22). Intradisc diffusion of an MRI-based contrast agent also decreases after ovariectomy in female rats (23).

The observation that as age increases, disc space narrowing progresses more rapidly in women than in men, would support the notion that sex hormones do influence disc degeneration. Other potential factors that tend to be more common in women should be further explored, such as thoracic scoliosis, weak postural muscle, and more heavy lifting (relative to their strength), including shopping.

The relationship between osteoporosis and degenerative changes has been studied mainly in the hip joint and the wrist, where high BMD is usually associated with increased degenerative change (24). The correlation between osteoporosis and intervertebral disc degeneration in the spine is less clear. Some studies suggested that disc degeneration was associated with higher lumbar spine BMD (24–29). In contrast, a few studies showed that many patients with osteoporosis have severe disc degeneration (30, 31). It has been proposed that osteoporosis may be an etiologic factor in the development of lumbar disc degeneration by inducing loss of vertebral height, leading to instability, facet arthrosis, and disc degeneration (31). The present study confirmed our previous finding that disc degeneration was associated with higher lumbar spine BMD (6).

Reduced BMD leads to end plate weakening and loss of vertebral body height, a process that allows the disc to push into the end plates and expand. This possibly facilitates dissipation of forces applied to the disc and thus helps reduce disc damage. The increased contact surface area may also decrease pressure (32). In a previous smaller MRI-based cohort study (33), no significant relationship was observed between total hip T score status and severity of disc degeneration. The current study demonstrated that hip BMD is a significant predictor of disc space narrowing for both men and women (Table 4). However, the spine BMD difference in the subjects with and without disc space narrowing (0.068 for men, 0.072 for women) was larger than the hip BMD difference (0.021 for men, 0.020 for women) (Table 4). Disc space narrowing, marginal osteophytosis, facet joint arthrosis, and age-related loss of vertebral height are all known to result in dual x-ray absorptiometry (DXA)–measured BMD being artificially higher (34). To solve this confounding effect of degenerative disease leading to increased BMD as measured by DXA, quantitative computed tomography (CT) is a better technique. With a small cohort of subjects with spine BMD measured with quantitative CT, it was shown that lumbar disc spaces were more likely to be narrowed when spine BMD was higher (6).

In this study, we defined disc space narrowing of the lumbar spine as positive when the sum of the disc space narrowing scores for discs L1/L2–L4/L5 was ≥3. This is broadly similar to the method of De Schepper et al (4). De Schepper et al defined disc space narrowing as positive when there was grade ≥1 narrowing at ≥2 levels; disc space narrowing positivity was related to chronic low back pain, and the associations were strengthened by excluding level L5/S1 (4). Our study also confirmed that disc space narrowing can be associated with low back pain and restricted lower limb activity (Table 4). A disc space narrowing score ≥3 is associated with older age for both men and women, with lower physical activity for men, and with lower grip strength and higher BMI for women. Dietary calcium intake, hypertension, diabetes, and smoking did not show significant associations with a disc space narrowing score ≥3 in this study. Although increased disc space narrowing was associated with a reduced concurrent physical activity level (PASE score) in men, it was not found to be associated with prior occupational physical activity.

A limitation of the current study was that only relatively healthy subjects without any hip replacement and with the likelihood of surviving the study duration were enrolled. This could have led to a selection bias in favor of relatively healthy participants. However, this may be an inevitable feature of medium- to long-term prospective cohort studies. There is also a possibility that a single-sided disc space narrowing might have been overlooked, as a frontal lumbar radiograph was not obtained. However, this circumstance is very unusual and would apply equally to men and women. The study questionnaire was designed with a view to determining risk factors for osteoporosis and was not specifically designed to characterize risk factors for disc space narrowing. Therefore, the variables associated with disc space narrowing could not be explored in greater depth.

In conclusion, this large-scale population-based study shows that the prevalence and severity of disc space narrowing is higher in elderly women than in elderly men. As age increases, disc space narrowing progresses more rapidly in women than in men. More severe disc space narrowing is associated with higher spine and hip BMD, back pain, and restricted leg mobility.

AUTHOR CONTRIBUTIONS

  1. Top of page
  2. Abstract
  3. SUBJECTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. REFERENCES

All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be published. Dr. Wang had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study conception and design. Wang, Griffith, T. Kwok, P. C. Leung.

Acquisition of data. Wang, A. W. L. Kwok, J. C. S. Leung, T. Kwok, P. C. Leung.

Analysis and interpretation of data. Wang, Griffith, Zeng, Deng, Ahuja.

REFERENCES

  1. Top of page
  2. Abstract
  3. SUBJECTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. REFERENCES
  • 1
    Miller JA, Schmatz C, Schultz AB. Lumbar disc degeneration: correlation with age, sex, and spine level in 600 autopsy specimens. Spine 1988; 13: 1738.
  • 2
    Lebkowski WJ. Autopsy evaluation of the extent of degeneration of the lumbar intervertebral discs. Pol Merkur Lekarski 2002; 13: 18890. In Polish.
  • 3
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