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Relationship between lumbar disc degeneration and bone mineral density in middle-aged and elderly population with non-specific low back pain

Xihan Xiang¹, Junrong Chen², and Huilou Liang³
¹Chengdu Sport University, Chengdu, China, ²Sichuan Province Orthopedic Hospital, Chengdu, China, ³GE HealthCare MR Research, Beijing, China

Synopsis

Keywords: Other Musculoskeletal, Degenerative

Motivation: Lumbar disc degeneration (LDD) is a major cause of lower back pain, but the relationship of LDD and adjacent structures, especially bone mineral density (BMD), is unclear, which confuses clinicians in estimating condition.

Goal(s): To investigate the relationship between LDD and BMD in a non-specific low back pain (NSLBP) population.

Approach: We assessed the relationship between the extent of LDD, obtained from MRI, and BMD of vertebral bodies, measured using quantitative CT, in NSLBP patients.

Results: Our results showed that LDD was negatively correlated with vertebra BMD in NSLBP patients, with L2/3 disc degeneration serving as an independent influencing factor for vBMD.

Impact: L2/3 intervertebral disc degeneration is an independent influencing factor for vBMD. Further investigation can explore if the degree of L2/3 intervertebral disc degeneration through MRI can predict OP, thereby reducing the occurrence of complications such as osteoporotic fractures.

Introduction

Nonspecific low back pain (NSLBP) refers to LBP of unknown origin that is not attributed to specific spinal diseases or radicular pain. It accounts for approximately 90% of patients with LBP and significantly affects people's lives. Age-related lumbar disc degeneration (LDD) and osteoporosis (OP) are both causes of low back pain¹. LDD is characterized by biomechanical and structural changes in intervertebral discs, including annular rupture and protrusion of the nucleus pulposus, which can compress the spinal cord and nerve roots, leading to LBP. OP is characterized by low bone mass and microstructural deterioration, making individuals susceptible to low-energy fragility fractures. Both conditions impose a significant health burden on society and individuals. Bone mineral density (BMD) is a reliable and precise surrogate measure for bone strength, commonly utilized to assess the risk of fractures². However, the relationship between LDD and BMD remains controversial³, and LDD patients may have a higher risk of osteoporotic fractures⁴. Therefore, studying the relationship between LDD and BMD is of great significance and can provide valuable insights for the clinical prevention and treatment of osteoporotic fractures. Compared to traditional X-ray and CT, magnetic resonance imaging (MRI) is radiation-free and more sensitive in assessing LDD. We selected NSLBP patients from middle-aged and elderly population as the study subjects and investigated the relationship between LDD and OP using MRI and quantitative CT (QCT).

Methods

Patients: After IRB-approved written informed consent was obtained, patients with NSLBP were scanned on 3.0 T MRI (SIGNA Architect, GE Healthcare) and CT (Siemens Somatom Definition AS+) to measure the grade of LDD and vBMD, respectively. 308 subjects were enrolled in study.
Imaging parameters: The MR scan included axial T2 FSE (0.5×0.8×3.0 mm3, TR=3224 ms, TE=120 ms).
Data processing: The degree of intervertebral disc degeneration at L1/2-L5/S1 was evaluated using the modified 8-grade Pfirrmann classification standard⁵ on MRI T2W images (Figure 1A). CT Data were transmitted to QCT Pro workstation to measure the mean vBMD of three vertebral bodies at T12, L1, and L2 levels (Figure 1B).The patients were divided into three groups based on the measured BMD values⁶: 1) bone mass normal group with an absolute BMD value >120 mg/cm³; 2) bone mass reduction group with an absolute BMD value of 80-120 mg/cm³; 3) osteoporosis group with an absolute BMD value <80 mg/cm³.
Statistical analysis: All analyses were performed using SPSS 26.0 software. One-way analysis of variance (ANOVA) was used to compare age, weight, height, BMI among the three groups. Chi-square test was used to compare gender distribution. Kruskal-Wallis H test was used to compare the differences in degeneration grades of intervertebral discs from L1/L2 to L5/S1 and the average intervertebral disc. Spearman's rank correlation was used to evaluate the correlation between LDD and vBMD. Multiple regression analysis was conducted to assess the relationship between vBMD and age, body mass index, and lumbar intervertebral disc degeneration.

Results

As shown in Table 1 and Figure 2, there were statistically significant differences in age, height, and L1/2-L4/5 intervertebral disc degeneration degree among three groups (P<0.05). Note that OP group showed significantly higher Pfirrmann grade than the other two groups. As shown in Table 2, except for BMI and L5/S1 intervertebral disc, age, and the degree of intervertebral disc degeneration in other segments were negatively correlated with vBMD (P<0.05). As shown in Table 3, in the multiple linear regression analysis, only L2/3 intervertebral disc was an independent influencing factor for vBMD (β= -0.369, P=0.001).

Discussion

Our results indicated a negative correlation between LDD and vBMD in middle-aged and elderly NSLBP patients, with L2/3 being an independent influencing factor for vBMD. The possible reason for the negative correlation between LDD and vBMD is that vBMD decrease may lead to vertebral instability, microcirculation disorders, and endplate degeneration, resulting in uneven stress and restricted nutrient absorption in the intervertebral disc, which promotes disc degeneration⁷. In clinical practice, L1/L2-L3/L4 intervertebral disc degeneration is mostly physiological and less affected by structural and load factors compared to L5/S1, making it more reflective of the physiological degeneration of the spine⁸ and more closely related to OP. MRI has the advantage of being radiation-free, and our study reveals the potential of using L2/3 intervertebral disc degeneration on MRI to predict the occurrence of OP, which can help prevent osteoporotic fractures from occurring in advance.

Conclusions

LDD and vBMD are negatively correlated in the NSLBP population, with L2/3 intervertebral disc being an independent influencing factor for vBMD. This provides important evidence for using MRI to assess the degree of intervertebral disc degeneration in patients and predict the risk of OP.

Acknowledgements

No acknowledgement found.

References

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Figures

Figure 1. A 57-year-old woman with L2/3 disc degeneration and an average lumbar vBMD of 77.4 m g/cm3 assigned to the osteoporosis group. On T2W images, lumbar intervertebral disc degeneration was graded according to the modified 8-level Pfirrmann grading system. The L2/3 intervertebral disc was graded as level 5, while the L1/2, L3/4, and L5/S1 intervertebral discs were graded as level 3, and the L4/5 intervertebral disc was graded as level 4. Regions of interest (ROIs) were drawn at the center of the T12, L1, and L2 vertebral bodies in QCT pro workstation, avoiding cortical bones (B).

Figure 2. Histograms showing the Pfirrmann grade at L1/2-L5/S1 disc (left) and L2/3 disc (right) in 3 groups respectively. Error bars represent standard deviation.

Table 1. Participant’s characteristics for the three BMD group. The p values < 0.05 were considered statistically significant. ^achi-squared test, ^bone-way variance analysis (ANOVA), ^cKruskal–Wallis H test.

Table 2. Spearman's rank correlation coefficients used to evaluate the correlation between LDD and vBMD. between LDD grade and lumbar vertebral vBMD (volumetric bone mineral density). Single asterisk (*) indicates p < 0.05.

Table 3. Results of multiple regression analysis for assessing the effect of LDD in adjacent discs on the mean (L1–L3) vertebral vBMD. The p values < 0.05 were considered statistically significant.

Proc. Intl. Soc. Mag. Reson. Med. 32 (2024)

1561

DOI: https://doi.org/10.58530/2024/1561