Fatty Infiltration of Multifidus Muscles: An Easily Overlooked Risk Factor for the Severity of Osteoporotic Vertebral Fractures

Abstract

Objectives

Osteoporotic vertebral fractures (OVFs) are a critical public health concern requiring urgent attention, and severe OVFs impose substantial health and economic burdens on patients and society. Analysis of the risk factors for severe OVF is imperative to actively prevent the occurrence of this degenerative disorder. This study aimed to investigate the risk factors associated with the severity of OVF, with a specific focus on changes in the paraspinal muscles.

Methods

A total of 281 patients with a first‐time single‐level acute OVF between January 2016 and January 2023 were enrolled in the study. Clinical and radiological data were collected and analyzed. The cross‐sectional area (CSA) and degree of fatty infiltration (FI) of the paraspinal muscles, including the multifidus muscles (MFMs), erector spinae muscles (ESMs), and psoas major muscles (PSMs), were measured by magnetic resonance imaging (MRI) of the L4/5 intervertebral discs. According to the classification system of osteoporotic fractures (OF classification) and recommended treatment plan, OVFs were divided into a low‐grade OF group and a high‐grade OF group. Univariate and multivariate logistic regression analyse s were performed to identify risk factors associated with the severity of OVF.

Results

Ninety‐eight patients were included in the low‐grade OF group, and 183 patients were included in the high‐grade OF group. Univariate analysis revealed a significantly higher incidence of a high degree of FI of MFMs (OR = 1.71, p = 0.002) and ESMs (OR = 1.56, p = 0.021) in the high‐grade OF group. Further multivariate logistic regression analysis demonstrated that a high degree of FI of the MFMs (OR = 1.71, p = 0.002) is an independent risk factor for the severity of OVF.

Conclusion

A high degree of FI of the MFMs was identified as an independent risk factor for the severity of OVF. Decreasing the degree of FI in the MFMs might lower the incidence of the severity of OVF, potentially reducing the necessity for surgical intervention in OVF patients.

The detailed process of paraspinal muscle parameter calculation. (A) Original image. (B) Image after the region of interest is delineated. (C) Selection of fat area in regions of interest.

Introduction

Osteoporotic vertebral fractures (OVFs) are one of the most common complications of osteoporosis (OP), mainly manifested by collapsed and deformed vertebrae. ¹ , ² Research reports indicate that OVF accounts for nearly half the approximately 10,000 cases of osteoporotic fractures that occur annually in the United States. ³ OVF not only causes severe pain and kyphosis but can also lead to disability and even death, seriously affecting the quality of life of patients. ⁴ , ⁵ , ⁶ Despite the implementation of various preventive measures, the incidence rate of OVF has not significantly declined among individuals aged 50 years and above. ⁷ Therefore, proactive prevention and treatment of OVF is of utmost importance.

Currently, the primary treatment options for OVF include conservative treatment and vertebral augmentation surgery. However, in cases of OVF with severe complications such as spinal cord compression, vertebral collapse, and spinal deformity, open surgery, including surgical stabilization and decompression, might be necessary, which can give rise to a variety of more serious complications. ⁸ Identifying relevant risk factors and reducing the incidence of severe OVF holds significant clinical importance. However, current research predominantly focuses on risk factors associated with OVF, including age, history of fragility fractures, blood tests, serum biochemical indicators, bone turnover markers (BTMs), corticosteroid use, bone mineral density (BMD), and body mass index (BMI), while there have been limited studies reporting the risk factors associated specifically with the severity of OVF. ⁹ , ¹⁰ , ¹¹

The paraspinal muscles, comprised mainly of the psoas muscles (PSMs) anteriorly and the multifidus muscles (MFMs) and erector spinae muscles (ESMs) posteriorly, are intimately associated with the spine, providing essential support for its proper function and structure. Moreover, the paraspinal muscles play an indispensable role in maintaining the dynamic equilibrium and movement of the spine. ¹² Paraspinal muscle degeneration, characterized by a decline in the muscle cross‐sectional area (CSA), diminished muscle strength, and an escalation in fatty infiltration (FI), has been reported to be strongly linked to the onset and progression of conditions such as disc herniation, spinal stenosis, and scoliosis. ¹³ , ¹⁴ , ¹⁵ Additionally, paraspinal muscle degeneration serves as a crucial risk factor for OVF, and has become an important predictor of low back pain. ¹⁶ , ¹⁷ FI, representing a crucial aspect of paraspinal muscle degeneration, might contribute to diminished muscle strength and endurance. Notably, among patients with OVF, fatty infiltration has emerged as a predictive factor associated with the progression of vertebral body collapse. ¹⁶ , ¹⁸ Considering the above, it is reasonable to suspect a connection between the paraspinal muscle degeneration and the severity of OVF. Therefore, this retrospective study aimed to: (i) compare the differences in the demographic data and paraspinal muscle degeneration between patients with low‐grade OF and high‐grade OF groups; and (ii) identify the risk factors correlated with the severity of OVF, with a specific focus on changes in the paraspinal muscles.

Materials and Methods

Study Population

This study was approved by the Institutional Review Board of Guangzhou Red Cross Hospital (No. 2022108‐01), which waived the informed consent requirement due to the retrospective nature of the study. From January 2016 to January 2023, a total of 486 consecutive patients diagnosed with acute OVF were included as participants in this study. The inclusion criteria for this study were as follows: (i) patients who were diagnosed with acute OVF by MRI; (ii) patients with a first‐time acute single‐segment OVF at the level of T10–L5; (iii) patients with available lumbar X‐ray images from the time of the initial diagnosis of acute OVF and with no clear history of trauma; and (iv) patients with complete clinical information. The exclusion criteria were as follows: (i) patients with a history of spinal surgery, including vertebroplasty, discectomy, spinal decompression, or fusion surgery (n = 65); (ii) patients with pathological fractures due to multiple myeloma, spinal metastasis, or infection (n = 43); (iii) patients with a history of OVF (n = 82); and (iv) patients with Parkinson's disease, amyotrophic lateral sclerosis, or other neuromuscular disorders (n = 15). Ultimately, a total of 281 patients were enrolled in our study.

Based on the OF classification, ¹⁹ compressive fractures were categorized into five types: OF 1, no vertebral deformation, vertebral body oedema present only on MRI‐STIR images; OF 2, deformation with no or only slight involvement of the posterior wall (<1/5); OF 3, deformation with significant involvement of the posterior wall (>1/5); OF 4, loss of vertebral body frame integrity or crush fracture; and OF 5, injuries with distraction or rotation. According to the “Osteoporotic Fractures” working group of the Spine Section of the German Society for Orthopedics and Trauma (DGOU‐OF), conservative treatment is recommended for types OF 1 and OF 2. Fracture types OF 3, OF 4, and OF 5 might require surgical treatment. According to the treatment method and the severity of OVF, the patients were divided into a low‐grade OF group (OF 1 + 2) and a high‐grade OF group (OF 3 + 4 + 5).

Image Acquisition

MRI and radiographic images of the lumbar spine were obtained using a 1.5 T scanner and digital X‐ray system, respectively. MR examinations were performed with a 1.5‐T (Siemens Avanto) imager with the following sequences: a sagittal T1‐weighted spin‐echo sequence (TR, 535 ms; TE, 11 ms), a sagittal T2‐weighted spin echo sequence (TR, 3500 ms; TE, 90 ms), and a spectral attenuated inversion recovery (SPAIR) sequence (TR, 3500 ms; TE, 90 ms). A Discovery XR650 machine (General Electric) was used for all digital X‐ray imaging, and radiological parameters were measured in the standing lateral position.

Data Collection and Image Analysis

Clinical Information

We extracted data on potential risk factors for compression fractures from medical records, which included sex, age, medical history of diabetes and hypertension, BMD, history of other fractures (nonvertebral fractures), and nutritional status. BMD was assessed through dual‐energy X‐ray absorptiometry (DXA) scanning, which covered the femoral regions and the lumbar spine (L1–L5) for evaluation. Nutritional status was determined by four key indicators: albumin, prealbumin, transferrin, and hemoglobin.

Radiographic and MRI Image Analysis

A standing lateral lumbar plain radiograph was obtained during the acute compression fracture. The radiographs were evaluated for several imaging parameters, including spondylolisthesis, sacral slope (SS), and fracture location. Spondylolisthesis was defined as the slippage of one vertebral body relative to an adjacent vertebral body. ²⁰ The sacral slope (SS) is the angle between the line to the superior endplate of the sacrum 1 vertebra and the horizontal. ²¹ The location of compression vertebral fractures was divided into thoracolumbar fractures and non‐thoracolumbar fractures.

Several parameters were evaluated using MRI images, including the degree of intervertebral disc degeneration, the thickness of subcutaneous fat, the cross‐sectional area (CSA) of the paraspinal muscles, fatty infiltration (FI) of the paraspinal muscles, and OF staging. The degeneration of the intervertebral discs was graded using Pfirrmann's method ²² to grade the degeneration of the two adjacent intervertebral discs of the compressed vertebral body, calculate the sum of the degeneration grades, and classify them into mild degeneration (grades 1–5) and severe degeneration (grades 6–10) groups according to the sum of degeneration. The thickness of subcutaneous fat was defined as the thickness of the fat at the spinous process at the level of the L4/5 intervertebral disc (IVD). According to the measurement method of Chen et al. (2022), ²³ the CSA and degree of FI of the paraspinal muscles were measured on T2WI at the level of the L4/5 IVD using the open‐source software ImageJ (version 1.53; National Institutes of Health, Bethesda, MD, USA). In the first step, ImageJ software was used to manually outline the paraspinal muscles, including the multifidus muscles (MFMs), erector spinae muscles (ESMs), and psoas major muscles (PSMs), and the corresponding vertebral bodies. In the second step, the fat area of the paraspinal muscles was selected using the threshold function of ImageJ software. As a final step, the relative total CSA (rTCSA), relative function area (rFCSA), and degree of FI of the paraspinal muscles were calculated. The detailed parameter calculation method is shown in Figure 1. To assess intraexaminer reproducibility, images from 50 patients were randomly selected, and parameters were measured repeatedly after 2‐week intervals. All measurements were performed by two experienced musculoskeletal radiologists with 7 and 11 years of experience (YC.X and F.X), whereby kappa and alpha intrarater and interrater reliability measurements were noted as excellent (κ = 0.81–1.00). OF staging was evaluated blindly and individually by two experienced radiologists with 7 and 11 years of experience in reading lumbar spine MR images (YC.X and F.X, respectively), and if there was disagreement between the two radiologists, another senior musculoskeletal radiologist with 20 years of experience (XW. Z) determined the OF stage.

FIGURE 1.

The detailed process of paraspinal muscle parameter calculation: (A) original image, (B) image after the region of interest (ROI) is delineated and (C) selection of fat area in ROIs.

Statistical Analyzes

All statistical analyses were performed using SPSS (version 23.0, Armonk, NY, USA). p < 0.05 indicated a statistically significant difference. The mean and standard deviation was calculated for all continuous variables. The normality of the data was assessed using the Shapiro–Wilk test and plotting histograms of the measurement distributions. Means of continuous variables were compared between the low‐grade OF group and the high‐grade OF group using an unpaired t‐test, and the χ²‐test or Fisher's exact probability test was used to investigate whether there were differences between categorical variables.

Univariate logistic regression analysis was performed to select potential candidate risk factors. Those with statistical significance (p < 0.05) were further included in the multiple logistic regression. Multiple regression analysis was performed using a step‐forward approach to assess odds ratios (ORs) and 95% confidence intervals (CIs) for all potential risk factors.

Results

Patient Characteristics

A total of 281 patients with OVF were included in the current study, including 98 patients in the low‐grade OF group and 183 patients in the high‐grade OF group. The mean age of the patients included in the study was 78.42 ± 5.0 years (range 65–97 years). Fifty‐eight patients were male, and 223 patients were female. The degree of FI in the ESMs (0.52 vs. 0.49, p = 0.028) and MFMs (0.54 vs. 0.51, p = 0.047) was significantly higher in patients with high‐grade OF compared to those with lower‐grade OF. No statistically significant differences in gender, age, medical history of diabetes and hypertension, BMD, history of other fractures, fracture level, sacral slope, spondylolisthesis, degeneration of intervertebral discs, nutritional status, subcutaneous fat thickness, rFCSA and rCSA of ESMs, MFMs, and PSMs, and FI of PSMs were observed between the groups (Table 1).

TABLE 1.

Clinical characteristics of the patients in this study

Characteristics	Overall (N = 281)	Low‐grade OF group (N = 98)	High‐grade OF group (N = 183)	Statisticalvalue	p‐value
Gender				0.735	0.391
Female	223 (79.4)	75 (76.5)	148 (80.9)
Male	58 (20.6)	23 (23.5)	35 (19.1)
Age (years)	78.42 ± 8.62	77.96 ± 8.42	78.67 ± 8.746	−0.655	0.604
Diabetes				0.24	0.624
Absent	219 (77.9)	78 (79.6)	141 (77.0)
Present	62 (22.1)	20 (20.4)	42 (23.0)
Hypertension
Absent	102 (36.3)	36 (36.7)	66 (36.1)	0.012	0.911
Present	179 (63.9)	62 (63.3)	117 (63.9)
History of other fractures
Absent	254 (90.4)	89 (90.8)	165 (90.2)	0.031	0.860
Present	27 (9.6)	9 (9.2)	18 (9.8)
Fracture level				0.488	0.486
Thoracolumbar	40 (14.2)	12 (12.2)	28 (15.3)
Non‐thoracolumbar	241 (85.8)	86 (87.8)	155 (84.7)
Sacral slope	36.75 ± 8.03	35.79 ± 8.32	37.27 ± 7.84	−1.478	0.141
BMD (kg/m2)	0.70 ± 0.13	0.69 ± 0.12	0.70 ± 0.14	−0.885	0.117
Spondylolisthesis				1.186	0.276
Absent	216 (76.9)	79 (80.6)	137 (74.9)
Present	65 (23.1)	19 (19.4)	46 (25.1)
Degeneration				0.062	0.814
Mild	154 (54.1)	54 (55.1)	98 (53.6)
Severe	129 (45.9)	44 (44.9)	85 (46.4)
Nutritional status
ALB (g/L)	36.69 ± 3.74	36.27 ± 3.70	36.91 ± 3.75	−1.362	0.174
PAB (mg/L)	232.09 ± 63.63	228.51 ± 64.60	234.00 ± 63.20	−0.69	0.491
TRF (g/L)	1.92 ± 0.36	1.93 ± 0.36	1.92 ± 0.36	0.301	0.763
Hb (g/L)	123.3 ± 15.38	124.61 ± 14.84	122.60 ± 15.66	1.045	0.297
Subcutaneous fat thickness	30.83 ± 9.71	30.65 ± 8.52	30.93 ± 10.32	−0.229	0.819
rFCSA of ESMs	0.83 ± 0.31	0.82 ± 0.31	0.83 ± 0.31	−0.169	0.866
rCSA of ESMs	1.22 ± 0.36	1.18 ± 0.36	1.25 ± 0.36	−1.503	0.134
FI of ESMs	0.51 ± 0.13	0.49 ± 0.13	0.52 ± 0.12	−2.207	0.028
rFCSA of MFMs	0.45 ± 0.18	0.45 ± 0.17	0.45 ± 0.19	0.073	0.942
rCSA of MFMs	1.59 ± 0.72	0.70 ± 0.21	0.74 ± 0.22	−1.355	0.177
FI of MFMs	0.53 ± 0.14	0.51 ± 0.14	0.54 ± 0.14	−1.999	0.047
rFCSA of PSMs	0.82 ± 0.26	0.80 ± 0.25	0.83 ± 0.26	−1.177	0.240
rCSA of PSMs	0.86 ± 0.26	0.84 ± 0.25	0.88 ± 0.26	−1.065	0.288
FI of PSMs	0.22 ± 0.65	0.22 ± 0.07	0.22 ± 0.06	0.017	0.987

Abbreviations: ALB, albumin; BMD, bone density; CSA, cross‐sectional area; ESMs, erector spinae muscles; FI, fatty infiltration; Hb, hemoglobin; MFMs, multifidus muscles; OF, osteoporotic fractures; PAB, prealbumin; PSMs, psoas major muscles; TRF, transferrin.

Univariate and Multivariable Regression Analysis

The results of the univariate and multivariate logistic regression analyses are shown in Tables 2 and 3. Univariate analysis revealed that FI of MFMs and ESMs were significant factors for the severity of OVF. Furthermore, subsequent multivariable analysis showed that a high degree of FI in the MFMs (OR 1.71 95% CI 1.22–2.39) is a risk factor for high‐grade OF.

TABLE 2.

Univariate logistic regression analyzing the risk factors for the severity of OVF

Variable	Odds ratio	95% CI	p‐value
Gender	0.77	0.43–1.40	0.392
Age	1.10	0.83–1.44	0.531
Diabetes	1.16	0.64–2.12	0.624
Hypertension	1.03	0.62–1.71	0.911
History of other fractures	1.08	0.47–2.50	0.860
Fracture level	0.77	0.37–1.60	0.486
Sacral slope	0.85	0.64–1.14	0.279
BMD	0.95	0.67–1.36	0.795
Spondylolisthesis	1.40	0.76–2.55	0.277
Degeneration	1.02	0.84–1.25	0.814
Subcutaneous fat thickness	1.07	0.83–1.38	0.611
rFCSA of ESMs	0.86	0.60–1.23	0.409
rCSA of ESMs	1.13	0.92–1.38	0.237
FI of ESMs	1.56	1.07–2.27	0.021
rFCSA of MFMs	1.06	0.82–1.38	0.652
rCSA of MFMs	1.17	0.92–1.49	0.207
FI of MFMs	1.71	1.22–2.39	0.002
rFCSA of PSMs	0.88	0.68–1.13	0.315
rCSA of PSMs	1.15	0.90–1.47	0.263
FI of PSMs	0.92	0.65–1.30	0.634

Abbreviations: BMD, bone mineral density; CI, confidence interval; CSA, cross‐sectional area; ESMs, erector spinae muscles; FI, fatty infiltration; MFMs, multifidus muscles; OVF, osteoporotic vertebral fracture; PSMs, psoas major muscles.

TABLE 3.

Multivariate logistic regression analyzing the risk factors for the severity of OVF

Variable	Odds ratio	95% CI	p‐value
FI of ESMs	1.17	0.748–1.823	0.495
FI of MFMs	1.71	1.22–2.39	0.002

Abbreviations: CI, confidence interval; ESMs, erector spinae muscles; MFMs, multifidus muscles; OVF, osteoporotic vertebral fracture.

Representative cases are shown in Figures 2 and 3. Due to compromised vertebral body frame integrity, the fracture depicted in Figure 2 corresponds to OF 4, accompanied by severe FI in the MFMs. In contrast, the fracture type in Figure 3 is OF 2, indicating only slight involvement of the posterior vertebral wall, with a relatively mild FI in the MFMs.

FIGURE 2.

Female, 79 years old. The fracture type is osteoporotic fractures (OF) 4. (A) Sagittal T2 fat suppression. (B) Sagittal T2WI. (C) Transverse T2WI. (D) The fat area image outlined on the transverse T2WI indicates severe fatty infiltration (FI) of the multifidus muscles (MFMs).

FIGURE 3.

Female, 65 years old. The fracture type is osteoporotic fractures (OF) 2. (A) Sagittal T2 fat suppression. (B) Sagittal T2WI. (C) Transverse T2WI. (D) The fat area image outlined on the transverse T2WI indicates mild fatty infiltration (FI) of the multifidus muscles (MFMs).

Discussion

This study demonstrates an association between the severity of OVF and FI in the paraspinal muscles, such that a higher level of paraspinal muscle fatty infiltration is linked to increased OVF severity. A high degree of FI of the MFMs was a risk factor for severe OVF. These results provide valuable guidance for the prevention and rehabilitation of severe OVF. To our knowledge, this study is the first to investigate the correlation between the paraspinal muscles and the severity of OVF across all age groups.

Correlation Between the Fatty Infiltration of the Paraspinal Muscles and Osteoporotic Vertebral Fractures

Previous studies have demonstrated a correlation between the CSA and degree of FI of the paraspinal muscles with spinal stability and alignment. ²⁴ Degenerative changes in the paraspinal muscles can affect spinal sagittal balance and overall alignment. A direct consequence of this degeneration is a reduction in muscle strength, which ultimately results in an increased load on the anterior vertebral bodies, consequently increasing the risk of OVF. ²⁵ Fatty infiltration is a significant pathophysiological alteration associated with muscle degeneration and dysfunction. Huang et al. reported that FI in L3/4 was a predictive factor for severe OVF in postmenopausal women. ²⁶ In contrast to our current study, which encompassed a broad age range, their research specifically focused on postmenopausal women aged over 50 years. Their categorization of OVF severity was based on the fractured vertebral compression sagittal cross‐sectional area (RCSA). Nevertheless, assessing the severity of fractures solely by the extent of vertebral height reduction might not provide a completely accurate representation. Lee et al. categorized their cohort of 120 patients into three groups: they first classified the recruited people into a control group and a fracture group according to the presence or absence of OVF, and the fracture group was further differentiated into an osteoporotic BMD and an osteopenia BMD group based on the BMD T‐score of −2.5. Their investigation revealed that the high percentage of fatty infiltration of the multifidus muscle increased the risk of spinal fracture, even when the BMD T‐score suggested osteopenia. This is consistent to some extent with our findings. Similarly, it is noteworthy that their study solely encompassed female participants, a factor that might have had a bearing on the results. ²⁷ Jeon et al. examined 55 consecutive patients with OVF who were treated conservatively in a single spine center. Their study ascertained that fatty degeneration of the paraspinal muscles was a predictor of progressive vertebral collapse. ¹⁶ Habibi et al. conducted a multicenter prospective cohort study in which they revealed that with the poor prognosis of conservatively treated OVF patients, only FI% of paraspinal muscles was significantly associated with new OVF in the thoracolumbar region and residual lower back pain in the lumbar region. ²⁸ Their studies consistently identified an association between paraspinal muscle degeneration and unfavorable prognoses in OVF patients undergoing conservative treatment. In fact, we contend that heightened consideration should be directed toward the paraspinal muscle degeneration in all OVF patients, regardless of the specific treatment modality administered.

Independent Risk Factors for Osteoporotic Vertebral Fracture Severity and Their Underlying Mechanisms

In our study, according to the latest DGOU‐OF staging and treatment guidelines, ¹⁹ the data of patients were divided into low‐grade OF and high‐grade OF. This classification system provides valuable guidance for treatment strategies and interventions. Our study revealed that a high degree of fatty infiltration of the multifidus muscles is a risk factor for severe OVF, whereas there is no correlation between the relative functional cross‐sectional area of the multifidus muscles and the severity of OVF. Furthermore, neither the rFCSA nor the degree of FI of the erector spinae and psoas major muscles were found to be risk factors for severe OVF.

The paraspinal muscles, consisting primarily of the MFMs, ESMs, and PSMs, play a vital role in upholding spinal stability, serving as integral components of the musculature of the human trunk. Similar to riggings on a mast, the ESMs serve as a crucial stabilizer, playing a significant role in maintaining sagittal alignment. ¹² The PSMs are the sole paraspinal muscles that directly link the spine to the lower limbs, contributing to the maintenance of postural equilibrium. ²⁹ In our current study, we discovered that only the MFMs were significantly correlated with severe OVF. This is probably because the MFMs are situated deep in the spinal region, which is composed of numerous small muscle units that are separated by fascial planes. Symmetrically distributed on both sides of the spine, the paraspinal muscles have the largest attachment area. ³⁰ The significance of muscular stabilization within the “neutral zone” range of motion in the lumbar region has been emphasized. The MFMs play a vital role as stabilizers in this neutral zone, and impairments in these muscles are strongly linked to low back pain (LBP). ³¹ These findings not only suggest that MFM atrophy (leading to a decrease in the attachment area, CSA, and fiber length) might contribute to spinal instability but also offer a potential mechanism for the development of severe OVF. To mitigate the influence of body size on muscle parameters, we calculated the relative CSA, which expresses the ratio of the muscle CSA to the IVD CSA at the corresponding level. ³² However, the rFCSA is not associated with the severity of OVF in all paraspinal muscles. Additionally, Shahidi et al. found no significant change in the CSA with age in both sexes. However, they observed an age‐related increase in the fat signal fraction in the ESMs and MFMs in both sexes. ³³ FI can occur independently of changes in total muscle size, wherein muscle fibers are replaced by adipose tissue, serving as a meaningful indicator of muscle quality and functional status. When FI of the paraspinal muscles has occurred, their ability to stabilize the spinal column is compromised, leading to the development of severe OVF. The association between FI and severe OVF might be due to the accumulation of adipocytes in muscle tissue, which promotes the secretion of proinflammatory cytokines. Consequently, this process can increase muscle protein catabolism, reduce myofibril synthesis and ultimately lead to a decrease in muscle strength. ³⁴ Moreover, the accumulation of fat in muscle tissue can negatively affect the contractile strength of the muscles that stabilize the spine. As a consequence, this can result in segmental instability and sagittal plane imbalance, leading to an abnormal distribution of loading on the vertebrae and an elevated risk of severe OVF. ³⁵

Clinical Significance of Knowing Risk Factors for Osteoporotic Vertebral Fracture Severity and Their Intervention Measures

We contend that risk factors are meaningful only if they can be modified by evidence‐based interventions. Fortunately, the degeneration of the MFMs can be modified through the implementation of functional exercise. Hides et al. demonstrated that targeted stabilization training effectively mitigated MFM atrophy in athletes and relieved their low back pain. ³⁶ Furthermore, research has consistently demonstrated the effectiveness of aerobic exercise (e.g., walking, jogging and cycling) alone or in combination with resistance exercise (e.g., strength training using free weights, kettlebells, or gym equipment) in reducing FI, especially among adults with chronic illnesses. ³⁷ Marcus found that aging is accompanied by an increase in muscle fatty infiltration and that this fatty infiltration is amenable to change after 12 weeks of thrice‐weekly resistance training in older individuals. ³⁸ Therefore, we believe that implementing a long‐term, comprehensive exercise regimen targeting postural stability, mobility, and mechanical efficiency is critical for older individuals exhibiting a concurrent high degree of FI in the L4/5 MFMs.

Limitations and Strengths

This study investigated the correlation between the paraspinal muscles and the severity of OVF across all age groups. These results have valuable implications for the development of targeted prevention and intervention strategies tailored for severe OVF. However, this study also has some limitations. First, this retrospective study was conducted at a single center with a small sample size, which introduces a certain degree of bias, and lacks long‐term follow‐up data. As a result, the generalizability of the research findings is limited. Second, we solely employed a quantitative analysis to assess the paraspinal muscles, while qualitative aspects such as paraspinal muscle strength were not evaluated. Nevertheless, we addressed this limitation by quantifying the fatty infiltration of the paraspinal muscles, and our primary focus was on discerning radiologically observable variations in paraspinal muscle quality among patients with mild or severe OVF. Finally, we focused our analysis on the L4/5 segment exclusively to assess paraspinal muscle degeneration, although this specific segment is widely recognized as the most representative in terms of overall paraspinal muscle degeneration.

Conclusion

In conclusion, we have shown that the FI of the MFMs is recognized as a risk factor for severe OVF. Simply put, a higher degree of fat infiltration in the L4/5 multifidus muscles likely contributes to the occurrence of severe OVF. This study's clinical relevance lies in its findings serving as guidance for healthcare professionals from different disciplines to make early treatment and prevention decisions for severe OVF patients based on the detection of a high degree of multifidus fatty infiltration on L4/5 MRI scans, thus helping prevent the occurrence of severe OVF. In future studies, we will further increase the sample size, adopt a multi‐center design, collect prospective data, and impose stricter controls on variables to assess the efficacy of our research findings. These studies have the potential to offer more effective and precise guidance for clinical decision‐making.

Conflict of Interest Statement

The authors have no conflicts of interest to declare.

Ethical Statement

This study was approved by the Institutional Review Board of Guangzhou Red Cross Hospital (No. 2022108‐01)

Author Contributions

Wuyan Xu and Xiaowen Liu were involved in drafting and revising the manuscript. Yuchao Xiong was the guarantor of the integrity of the entire study. Fan Xu handled the manuscript review. Xuwen Zeng carried out the study concepts; Siming Li carried out the study design. Li Wu, Shaohua Liang, Ye Zhang, and Junbing Huang carried out the data acquisition and data analysis. All authors read and approved the final manuscript.

Funding Information

This study has received funding from the Guangzhou Planned Project of Science and Technology, China (grant number: 202102010102) (Xuwen Zeng), the Guangzhou Science and Technology Project of Health, China (grant number: 20231A011021) (Yuchao Xiong), and the Guangzhou Science and Technology Project of Health, China (grant number: 20211A010019) (Fan Xu).

Data Availability Statement

The datasets generated or analyzed during the study are available from the corresponding author upon reasonable request.