Assessment of Pfirrmann lumbar disc degeneration with body mass index using 3T magnetic resonance imaging: A cross-sectional study

INTRODUCTION

One of the primary causes of disability worldwide is low back pain (LBP), and it is more common in adults and older individuals.^[1] It is widely acknowledged that LBP is largely caused by lumbar intervertebral disc degeneration, and that the degree of disc degeneration is generally correlated with the severity of chronic lower back symptoms.^[2] Among the numerous factors that affect musculoskeletal health, body mass index (BMI) has become a crucial but intricate element. It is a simple yet valuable screening tool commonly used to assess and categorize body weight. It also serves as a quick and cost-effective method to identify potential weight-related health risks.

The spinous processes, size, shape, and structure of the vertebral body are some of their distinguishing characteristics.^[3] The lumbar vertebrae are separated by intervertebral discs, which are articulating, fibrocartilaginous, cylindrical structures connecting the vertebral bodies. They can be microscopically split into an outer annulus fibrosus that surrounds a central nucleus pulposus (NP).^[4] The most commonly used imaging technique for diagnosing degenerative disc disease (DDD) is magnetic resonance imaging (MRI).^[5] A grading system for disc degeneration was developed by Pfirrmann et al. (2001), based on the appearance of discs on sagittal T2-weighted MRI scans.^[6] Pfirrmann disc degeneration grading estimates the water content on a grade from I to V.^[7]

Intervertebral disc degeneration is characterized by morphological changes, including reduced disc height, bulging of the intervertebral disc, annular tears, and the formation of osteophytes.^[8] Although they are suitable for qualitative review, they are challenging to apply for quantitative analysis. At an early stage, NP signal strength changes enable easier quantitative evaluation.^[9] The NP and annulus fibers in normal intervertebral discs produce a strong signal on T2-weighted MR imaging. Disc degeneration is characterized by a decrease in signal from the inner fibers of the annulus and NP.^[10] Quantitative measures of disc degeneration on MRI have been developed and utilized to overcome some of the limitations of the Pfirrmann 5-grade classification system. Quantitative Pfirrmann disc degeneration involves measuring the signal intensity of the NP, disc membrane, ligaments, fat, and air.^[5] Compared to conventional subjective scales, quantitative assessments are more sensitive to change and are generally reported to have excellent reliability.^[11]

Intervertebral discs are prone to degenerative modifications, and the occurrence of these is closely linked to aging, high BMI, smoking, hereditary factors, mechanical factors, and misuse.^[12] Previous studies highlight the use of lower-field MRIs or qualitative assessments for disc degeneration. While some literature discusses disc degeneration longitudinally, few studies have made a direct connection between BMI and disc degeneration at different stages of life. The current study expands existing knowledge by providing useful information that directly links BMI to disc degeneration parameters at a specific point in time. The present study, with this background, aimed to assess the association between BMI and disc degeneration in the lumbar spine using 3T MRI.

MATERIALS AND METHODS

Procedure

Before the MRI scan, the participant’s BMI was calculated by obtaining their sex, age, height, and weight. To assess the Pfirrmann disc degeneration, a region of interest was placed at the NP of all the disc levels (L1–L5) on the T2-weighted image, and for fat only at the degenerated level and is depicted in Figure 1,^[12] as BMI and disc degeneration are correlated. The mean and standard deviation of the NP and fat were measured. The World Health Organization (WHO) classification of weight status was used to categorize BMI, i.e., underweight (<18.5 kg/m²), normal range (18.5–24.9 kg/m²), overweight (25.0–29.9 kg/m²), and obese (≥30 kg/m²). It was correlated with the Pfirrmann disc degeneration scale.^[13] The Pfirrmann grading system, based on T2-weighted images, was applied to all disc levels, specifically L1–L2, L2–L3, L3– L4, L4–L5, and L5–S1. BMI was associated with Pfirrmann grades III, IV, and V at L4–L5 and L5–S1 levels.

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Figure 1:

Depicts the region of interest (ROI) measurement of the nucleus pulposa (NP) and fat. (a) Depicts ROI measurement of NP at degenerated disc level L4 and (b) depicts ROI measurement of fat adjust to degenerated disc level L5.

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RESULTS

The present cross-sectional study, conducted between May 2024 and January 2025, included 58 participants (37 males and 21 females), who met the requirements for inclusion and exclusion criteria.

Using descriptive statistics, the mean values for age, height, weight, and BMI were calculated. Table 2 shows that the participants’ ages ranged from 30 to 66 years, with a mean of 48.64 ± 10.55 years. Height ranged from 142 to 177 cm, with a mean of 161.76 ± 7.98 cm, and weight ranged from 45 to 110 kg, with a mean of 68.72 ± 13.32 Kg. The BMI ranged from 16.1 to 54.6 Kg/m², with a mean of 26.28 ± 6.09 Kg/m². This reflects the diverse characteristics of the population.

An independent “t-test” was used to compare the signal intensity of fat between the males and females. At the L1 level, the comparison of signal intensity of fat among males and females was (P = 0.697). Similarly, at L2 (P = 0.641) and L3 (P = 0.261), significant differences were observed in L4 (P = 0.014) and L5 (P = 0.013), where females showed higher fat content than males.

Table 3 depicts the frequency and percentage analysis revealing a clear trend from lower to higher grades across the groups L1–L2, L2–L3, L3–L4, L4-L5, and L5–S1. L1–L2 is primarily composed of lower grades, with grades I and II accounting for over 80%. In contrast, L5–S1 is dominated by higher grades, with 67.2% in grade V. Intermediate groups (L2–L3, L3–L4 and L4–L5) show a gradual shift, with increasing frequencies in grades III to V. This pattern suggests a progression toward more advanced grades from L1–L2 to L5–S1.

BMI was categorized according to the WHO classification of weight status, i.e., underweight (<18.5 kg/m²), normal range (18.5–24.9 kg/m²), overweight (25.0–29.9 kg/m²), and obese (≥030 kg/m²) (1). Figure 2 shows that out of 58 participants, 6.9% (4) were underweight, 36.2% (21) were in the normal ra7ge, 37.9% (22) were overweight, and 19% (11) were obese. This distribution highlights the study’s inclusivity in representing patients across all BMI categories and reflects the diversity of the population.

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Figure 2:

Body mass index (BMI) categorization among the study participants.

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Table 4 and Figures 3 and 4 explore the association between BMI and disc degeneration at L4–L5 and L5–S1 levels for Pfirrmann grades III, IV, and V using the Fisher-Freeman-Halton-Exact Test. Among 58 patients, no significant association was found (P = 0.6498 and P = 0.6233), indicating that BMI does not significantly affect the severity of disc degeneration at this level.

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Figure 3:

Association between body mass index (BMI) categories and disc degeneration grade at the L4–L5 level.

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Figure 4:

Association between body mass index categories and disc degeneration grade at the L5–S1 level.

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Comparison based on BMI and signal intensity of NP across all lumbar levels. At NP L1 (P = 0.778) across different BMI ranges that are <18.5 kg/m², 18.5–24.9 kg/m², 25–29.9 kg/m², and >30 kg/m². Similarly, at NP L2 (P = 0.628), at L3 (P = 0.221), at L4 (P = 0.785) and L5 (P = 0.0587). Oneway ANOVA test was used, which suggests no statistically significant differences in NP levels (L1–L5) across different BMI categories [Figure 5].

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Figure 5:

Depicts the relationship between body mass index and signal intensity of the nucleus pulposa across all lumbar levels.

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The relationship between BMI and signal intensity of fat across different lumbar levels [Figure 6]. The findings reveal that fat at the L1 was P = 0.98 across different BMI ranges, that is, <18.5 kg/m², 18.5–24.9 kg/m², 25–29.9 kg/m², and >30 kg/m². Similarly, fat at L2 was P = 0.961, at L3 P = 0.807, at L4 P = 0.297, and at L5 P = 0.553. One-way ANOVA test also showed no significant differences in fat levels (L1–L5) across BMI categories.

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Figure 6:

Depicts the relationship between body mass index and signal intensity of fat across all lumbar levels.

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DISCUSSION

The current study focuses on BMI, age, and sex. The findings indicate that females have significantly higher fat deposits at the vertebrae level L4 (P = 0.014) and L5 (P = 0.013) compared to males. Similar findings were observed in a study conducted by Vardhan et al., which revealed that disc degeneration was more prevalent in males.^[14] In contrast, females had higher fat deposition at the L4 and L5 vertebrae levels.^[14]

The current study assessed Pfirrmann grades at all disc levels and found that grades IV and V were more prevalent in the L4–L5 and L5–S1 levels. At L4–L5, among 58 participants, grade IV accounted for 74.1% and grade V for 8.6% of the cases. Whereas at L5–S1, grade IV was 25.9% and grade V was 67.2%, indicating advanced degenerative changes in lower lumbar levels were significantly greater at L5-S1 compared to the upper level. According to a study by Oh et al., Pfirrmann grades III and IV were more prevalent in the lower lumbar levels, specifically L4–L5 and L5–S1 levels, compared to other lumbar disc levels.^[15] At the L4–L5 level, grades IV and V were 46.2% and 10.3%, respectively. At the L5–S1 level, grade IV was 47.9% and grade V was 10.4%.^[15]

In the present study, Pfirrmann grading was applied across all lumbar levels. In contrast, Yu et al. implemented both the Pfirrmann grading system and a modified Pfirrmann grading system to assess pathological conditions such as spondylolisthesis, lumbar spinal stenosis, and lumbar disc herniation.^[16]

The current study demonstrated an association between BMI categories and disc degeneration at the L4–L5 and L5–S1 levels. The results showed no significant association between disc degeneration and BMI categories, with P = 0.6498 at the L4–L5 level and P = 0.6233 at the L5–S1 level, indicating that BMI does not significantly affect disc degeneration severity at the L4–L5 and L5–S1 levels. A study conducted by Samartzis et al. found that multilevel disc degeneration was noted in 41.4% of individuals with normal weight, 24.6% of those with underweight, 54.9% of those with overweight, and 65.2% of those with obesity.^[17] DDD score pairwise comparisons revealed a significant difference between normal and overweight subjects (P < 0.001) and between underweight and normal subjects (P < 0.001), but there was no significant difference between obese and overweight subjects (P = 0.092).^[17]

The current study shows no significant correlation between BMI and lumbar disc degeneration. Segar et al. found that age showed a strong correlation (r = 2.04) with disc degeneration, while BMI had a weaker association (r = 1.01), suggesting that age is a more significant factor in disc degeneration than BMI.^[18] Another study reported that higher BMI was associated with lumbar spine stenosis and not with lumbar disc herniation or degenerative spondylolisthesis, indicating that increased BMI may not be a significant predictor for all types of lumbar disc diseases.^[19] Videman et al. suggested that increased BMI may have a protective effect on intervertebral discs rather than contributing to degeneration. These studies indicate that factors such as age and body composition play a more critical role in spinal health.^[20]

Although the present study found no significant association between BMI and disc degeneration, various studies have reported a significant association between higher BMI and lumbar disc degeneration. According to a study conducted by Vardhan et al., individuals with sedentary lifestyles had a higher prevalence of degenerative changes, especially at the L5-S1 level.^[14] In addition, a higher BMI was associated with more disc degeneration, particularly among those aged 61–70. This finding contrasts with the present study, which shows no significant correlation between BMI and lumbar disc degeneration.^[14]

Liuke et al. revealed that a BMI over 25 kg/m² increases the risk of disc degeneration, and that the effect of high BMI is greater in youth and middle age.^[21] This result contradicts the findings of the present study, which show no significant correlation between BMI and lumbar disc degeneration.^[21] Salo et al. found a significant association between occupational physical loading and severe lumbar disc degeneration, specifically at the L5–S1 level, in post-menopausal women.^[22] In addition, the study suggests that confounding factors such as smoking, age, and higher BMI are significantly associated with severe lumbar disc degeneration, which contrasts with the present study’s findings, which show no significant correlation between BMI and lumbar disc degeneration.^[22]

The current study recommends that, instead of focusing solely on BMI as a risk factor, future research should investigate more specific markers, such as muscle mass, fat composition, and mechanical stress loading patterns, to examine the relationship between body mass and disc degeneration. Advanced imaging methods such as quantitative MRI (T2 mapping or T1r imaging) can provide more detailed and objective assessments of disc degeneration.

The limitations of the current study include its single-center design, which may limit the external validity of the findings, and the relatively small sample size, which may restrict the generalizability of the results to broader populations. The exclusion of participants with factors such as aging, smoking, and hereditary factors might also have a major impact on disc degeneration and can be considered in future research.

CONCLUSION

Using the Pfirrmann grading system on 3T MRI, the present study examined the correlation between BMI and lumbar disc degeneration. The findings indicate that there was no significant association between disc degeneration and BMI, despite disc degeneration being evident across several BMI groups. Thus, the study concludes that other factors, such as age and body composition, also play a significant role in triggering disc degeneration, in addition to BMI alone. The study also noted gender variations in fat content, with females accumulating more fat at L4–L5 than males. In light of these results, additional research is required to investigate the association between disc degeneration and BMI using a larger sample size, additional risk factors, and advanced imaging techniques.