INTRODUCTION

Background

Vitamin D plays a key role in maintaining bone health and calcium homeostasis, yet upwards of 97% of the general orthopedic trauma population have been shown to have low levels of vitamin D at the time of injury [1]. Inadequate levels of vitamin D may result in a higher fracture risk and osteomalacia [1,2]. Multiple studies have supported vitamin D supplementation for preventing hip fractures, attenuating the sequelae of falls, and promoting better overall bone health [3–5]. Moreover, prolonged low levels of vitamin D, particularly below 20 ng/mL, make supplementation especially beneficial for older adults in reducing fracture risk and improving bone mineral density (BMD) [6–10]. A cross-sectional study was designed to examine the relationship between vitamin D levels and bone quality at the time of injury. The objective of the study was to measure the rate of vitamin D deficiency in the young orthopedic trauma patient population and determine if it had an impact on BMD measured on computed tomography (CT) imaging of the lumbar spine [11,12]. CT imaging has been shown to be an accurate tool for measuring bone mineral density and a viable alternative to dual-energy x-ray absorptiometry (DEXA). Hounsfield unit (HU) measurement has been shown to be a simple and rapid way to assess bone quality with threshold values of 110 HU for detecting osteoporosis and 135 HU for detecting osteopenia being 90% specific [13]. Studies show that values of less than 100 HU were consistent with a BMD T-score of –2.5, which is indicative of osteoporosis [14,15].

Objectives

We hypothesized that there would be a large proportion of vitamin D–deficient young orthopedic trauma patients and that there would not be many patients with osteoporosis or osteopenia in this younger population. We did not expect a correlation between BMD and vitamin D levels in the younger orthopedic trauma population aged 18 to 50 years.

METHODS

Ethics statement

This study was approved by the Institutional Review Board of West Virginia University (No. 2112491699). Written informed consent was not required in accordance with the Institutional Review Board regulations. However, a cover letter was provided to each potential subject in which the study was explained; the patients could verbally decline to participate.

Study design and setting

This study was a prospective cross-sectional analysis recording the vitamin D levels and BMD of the lumbar spine in orthopedic trauma patients at a level I trauma center. The data were collected over 1 year and included patients aged 18 to 50 years who sustained a non-fragility fracture and had a CT scan of the abdomen and pelvis upon presentation. A fragility fracture is defined as a pathological fracture that results from minimal trauma (e.g., a fall from standing height) or no identifiable trauma at all [16]. The patients were de-identified under password encryption once their measurements had been recorded and entered into Microsoft Excel (Microsoft Corp) for data collection and statistical analysis. Enrollment was consecutive and consisted of all trauma patients that presented to our level I trauma center who met the inclusion and exclusion criteria and agreed to participate.

Participants

Patients were excluded if they were not in the correct age range, did not receive a CT scan as deemed appropriate, suffered from a fragility fracture, had a history of previous lumbar surgery precluding HU measurement, or had a history of lumbar bony or metastatic lesions.

Data collection

Vitamin D levels were obtained for all trauma patients as is standard of care at our facility, and CT scans were taken as indicated based on the initial trauma workup. Levels of 25-hydroxyvitamin D in serum were typically collected within the first few days of admission; fasting status has not been shown to significantly impact transient levels (about 1 ng/mL variability), and overall serum levels can take several weeks to change even with supplementation [17,18]. Upon completion of the CT scans, two radiologists measured the HUs of the lumbar spine to determine BMD. BMD was assessed by drawing a circular region of interest centered on the individual L1, L2, and L3 vertebral bodies on CT images in the sagittal plane to obtain a HU value at each level. The circular region of interest was centered at the mid-body on the sagittal plane, with the radius tangential to the superior and inferior endplates excluding the cortical bone. The mean was then calculated and used as the representative BMD for each patient. All CT images were generated from scanners that underwent rigorous phantom based quality assurance standardization and calibration protocols. Patients were recruited over the course of 2022 with injury dates ranging from February to October 2022; the study was concluded when 100 patients who met the inclusion criteria with appropriate follow-up were enrolled.

The HU measurement was compared to the initial vitamin D level upon presentation, and the correlation coefficient was calculated to determine if there was a relationship between the two variables. If the patient was found to have a low vitamin D level, they were given 50,000 units once a week for 8 weeks. In addition, patients who were found to have low BMD based on CT HU measurements were referred for follow-up with our metabolic bone team to evaluate for further workup and possible treatment of osteopenia or osteoporosis.

Statistical analysis

We recorded the vitamin D deficiency rate and osteoporosis/osteopenia rate among young orthopedic trauma patients presenting with traumatic fracture injuries. We defined vitamin D deficiency as below 30 ng/mL as specified by our institution. We defined osteoporosis as a value below 110 HU and osteopenia as a value below 135 HU. These values were determined from prior studies comparing DEXA scans to CT HU measurements [12]. Finally, we used a linear regression model to assess trends between vitamin D levels and BMD on CT scans.

RESULTS

In total, 100 patients were enrolled in this study of vitamin D deficiency rates and osteoporosis/osteopenia rates in the young orthopedic trauma population. The mean vitamin D level in our patient population was 25.1±12.4 ng/mL (range, <7–76 ng/mL; 95% confidence interval, 65–82 ng/mL). The mean patient’s Hounsfield unit value was 215±43 HU (range, 116–328 HU) (Table 1). Out of the 100 patients, 75 (75%) were vitamin D–deficient and none (0%) had osteoporosis. Five of the patients had osteopenia, with BMD <135 HU but >110 HU. We performed a linear regression analysis comparing vitamin D levels to BMD in the patient population (Fig. 1). The regression model showed an inverse correlation between vitamin D levels at the time of injury and HU measurements in patients with normal vitamin D levels at presentation; this finding was statistically significant (P=0.025). A higher Hounsfield unit measurement of the lumbar spine correlated with a lower vitamin D level at the time of presentation in the patients who presented without a deficiency.

DISCUSSION

In previous longitudinal studies in older patients, vitamin D deficiency was associated with low BMD and increased fracture risk [6]. Zaidi et al. [13] did not show a significant difference in BMD from the ages of 20 to 50 years. Our study showed that there was a high proportion of younger fracture patients who were vitamin D–deficient at the time of injury (75%). There was an inverse relationship between vitamin D levels on arrival and BMD values as measured by HUs on CT of the lumbar spine in patients with clinically normal vitamin D levels (>30 ng/mL) at time of injury. There were no patients who were found to have osteoporosis and a small percentage that had osteopenia (5%).

The 25-hydryoxyvitamin D levels in this study are similar to previously published studies in the geographic area. McConda et al. [19] reported an average 25-hydroxyvitamin D level for resident physicians (average, 29 years) in West Virginia, USA, was 29 ng/mL. Manickam et al. [20] also reported similar vitamin D levels in young physicians in Chicago (IL, USA) with an average age of 28 years and an average 25-hydoxyvitamin D level of 22 ng/mL. Their prevalence of vitamin D deficiency mirrored that of our cohort at 77%, further demonstrating the high rate of vitamin D deficiency in the younger population and the need for further studies on its effect on BMD.

Schreiber et al. [12] established a correlation between Hounsfield unit density calculated on CT scans and BMD. Our hypothesis was that there would not be a direct correlation between BMD and vitamin D levels in this patient population. However, we did not predict an inverse relationship between vitamin D levels and BMD. Adequate levels of vitamin D have an important effect on calcium metabolism, osteoblastic activity, matrix ossification, and bone remodeling, hence a theoretically lower BMD with lower levels of vitamin D [21]. As seen in previous studies, prolonged low levels of vitamin D, particularly below 20 ng/mL, make supplementation especially beneficial for older adults in reducing fracture risk and improving BMD [6–9].

Within younger patient populations, studies have reported mixed results when looking at BMD related to vitamin D levels [20,22]. Manickam et al. [20] found a high prevalence of low BMD (37.5%) within their cohort and even had four subjects with osteoporosis as measured on DEXA scans. However, even with a higher incidence of osteoporosis and osteopenia, they did not find a statistically significant relationship between serum vitamin D levels and BMD. Many studies have shown a strong relationship between these two variables in the older population, specifically postmenopausal women. The discrepancies within this study’s patient population solidify the importance and need for further studies to elucidate which factors drive BMD within younger patients and if these factors put patients at greater risk for fragility fractures.

Specific to this study, further investigation is required to confirm and explore the inverse relationship between vitamin D and BMD in the younger orthopedic trauma patient. There is also limited evidence on how HU measurements relate to the ability to heal fractures [23].

Limitations

One limitation of the study was the lack of diversity in the patient population, as the study population represented patients from a rural level I trauma center in Appalachia. This study likely would have been more representative of the general population with a larger and more diverse patient population. Additionally, we did not consider the time of year or evaluate the impact of temporal exposure to sunlight and its impact on vitamin D levels. Another limitation is that there may have been bias by excluding patients who did not have a CT scan of the abdomen and pelvis as part of the initial workup. This exclusion criterion may have biased the study population to those patients with higher energy mechanisms, and therefore excluded patients with lower energy mechanisms who sustained significant musculoskeletal injury. This group may have had a lower BMD than the study group. Furthermore, we did not use DEXA scans to evaluate bone mineral density, which has been accepted as the gold standard for BMD evaluation. Finally, the results may have been limited by the number of patients enrolled in the study.

Conclusions

This prospective study was conducted to determine if the young orthopedic trauma patient population had a high rate of vitamin D deficiency. We also aimed to determine the prevalence of osteoporosis in this population by using a newer measurement of BMD values. Finally, the goal was to determine if there was a correlation between the initial vitamin D level at presentation and BMD values. This study showed a high rate of vitamin D deficiency in this young population of patients. There were no patients with osteoporosis and a small percentage with osteopenia (5%). There was also an inverse relationship between vitamin D levels and BMD in patients who had normal vitamin D levels at presentation. Future research could include follow-up regarding replacement of vitamin D deficiency, and its possible interaction on fracture union.

ARTICLE INFORMATION

Author contributions

Conceptualization: MAB, CW; Data curation: EK, MB, KS, LM, EB; Formal analysis: MAB, CW; Investigation: MB, KS, EK, LM, EB; Methodology: MAB, CW; Project administration: MAB, CW, EB; Supervision: MAB, CW, EB; Validation: MAB, KS, MB, CW; Visualization: MB, EK; Writing–original draft: MB, KS; Writing–review & editing: all authors. All authors read and approved the final manuscript.

Conflicts of interest

The authors have no conflicts of interest to declare.

Funding

The authors received no financial support for this study.

Acknowledgments

The authors thank Gerald Hobbs, PhD (Department of Statistics, West Virginia University Morgantown, WV, USA) for assistance with statistical analysis and Suzanne Danley (Department of Orthopaedics, West Virginia University, Morgantown, WV, USA) for manuscript formatting and editing.

Data availability

Data analyzed in this study are available from the corresponding author upon reasonable request.

Fig. 1.

Bivariate analysis of vitamin D levels and Hounsfield unit values at the time of injury (in patients with a normal level of vitamin D >30 ng/mL) show an inverse relationship between vitamin D levels and Hounsfield unit values.

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Figure & Data

References

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