RESULTS

The final cohort consisted of 202 patients with 118 suffering multiple fractures which were individually evaluated. The average vitamin D level was 20 mg/ml (range, 4-78 mg/ml). Vitamin D and calcium levels are reported in Table 2. A total of 84 patients had vitamin D levels >20 ng/ml with an average of 28 ng/ml, (range, 21-78 ng/ml). Serum calcium averaged 8.7 and 8.6 in the vitamin D ≤ 20 ng/ml and >20 ng/ml groups, respectively. Rate of union for vitamin D levels >20 ng/ml was 92%, while only 81% in the group with vitamin D<20 ng/ml (p=0.07). Time to union was 7.3 months with vitamin D<20 ng/ml and 8.5 months with vitamin D>20 ng/ml (p=0.07) (Table 3). Despite a postoperative vitamin D level ≤ 20 ng/ml in 118 patients, only 15 (13%) patients were discharged with vitamin D supplementation. Among the 202 patients, bisphosphonates were not used in any patient and teriperatide was given in 2 (1%) patients postoperatively.

 DISCUSSION

Vitamin D levels significantly influence the body’s calcium balance and affect bony mineralization [3]. There is growing interest in the relationship of fracture union and vitamin D levels. Despite this interest, recommendations for therapeutic intervention following fracture fixation have not been established. To our knowledge, no study has investigated fracture union and the time to union based on the generally recommended cutoff of vitamin D levels. In patients with vitamin D levels <20 ng/ml an 11% decrease was noted in union rates without reaching statistical significance. Interestingly, faster union was noted in vitamin D-deficient patients, however, again without statistical significance. Several factors have been shown to influence vitamin D level. Such reported factors include smoking, seasonal changes, and fracture [11,13,20]. Briggs et al. reported a decrease in serum 1,25(OH)2D concentrations over a 6 week period following long bone fracture. Interestingly, they noted an increase in calcium concentration without a corresponding increase in phosphate or parathyroid hormone [11]. Additionally, Brinker et al reported that 68% of patients with a fracture nonunion were found to have a previously undiagnosed vitamin D deficiency [18]; other studies have validated this conclusion [19]. Thus, many studies have now recommended vitamin D supplementation with at least 800 IU/day in fracture patients, as supplementation has little toxicity and has an association with calcium metabolism and a link to bone healing [14,19,21]. Despite a 58% prevalence of patients with low vitamin D levels, only 13% of patients in our study were discharged home with vitamin D prescription. The role of bisphosphonate following fracture fixation remains unknown. However, its use in fracture nonunion has been reported [19]. Although over half of the patients were deemed to be vitamin D deficient, no patient was treated with bisphosphonates postoperatively. Additionally, the effect of using teriparatide, an rDNA injection, following fracture fixation in vitamin D deficient patients remains unknown. While utility has been suggested, it is impossible to draw any conclusions from this study as none of the vitamin D deficient patients who underwent fracture fixation were being treated with bisphosphonates or teriparatide. The primary objective of this investigation was post-surgical fracture union as it relates to vitamin D levels. Although not statistically significant, we demonstrate an 11% lower overall union rate amongst patients with low vitamin D levels. These results align with prior studies, which have identified a relationship between fracture healing and vitamin D levels [18,19,22,23]. We hypothesize that with a more robust sample size, this relationship may lead to statistical significance. However, studies have disputed this relationship. Despite a small sample size, Boszczyk et al. [24] compared diaphyseal non-unions to normally healing fractures in 35 patients and found no difference in the prevalence of vitamin D deficiency. Despite several publications suggesting an association between vitamin D levels and fracture union, no established guidelines exist for a reasonable and appropriate cutoff level for vitamin D therapeutic intervention. While several studies have used 20 ng/ml or less as a marker [16,17], the Institute of Medicine reported cutoffs of <30 ng/ml, arguing that at >50 ng/ml, levels are more optimal with regards to fracture patients [3]. The most sensitive and specific level has still not been identified with regards to fracture healing and merits further research. While the presence of fracture union, as it relates to vitamin D levels have been researched, the influence of such levels on time to union is unknown. In our study, vitamin D levels did not statistically influence time to union. Unexpectedly, we noted a faster time to union in vitamin D-deficient patients despite an overall lower union rate. This is in contrast to other studies, which have demonstrated a higher delayed union rate amongst vitamin D deficient patients [25]. The high incidence of polytrauma in our cohort and its effect on time to union results is unknown. It has been suggested that normalization of vitamin D levels following supplementation may reduce the incidence of delayed union [25]. Thus, it stands to reason that appropriate supplementation at the time of discharge may improve the time to union. While this was not investigated in our report, only 13% of vitamin D-deficient patients were discharged with a prescription for vitamin D. There are several limitations to this study. First, poor patient follow up may have influenced the time to union. As evident in several large trauma centers, patient follow up compliance is often challenging. Thus, the actual time to union may be falsely inflated secondary to this. This study cannot neither fully support nor oppose formerly held opinions that vitamin D is important for fracture healing and union rates given the fact that our conclusions did not reach statistical significance. Secondly, a cutoff of 20 ng/ml or less was used in this study to provide consistency with the current body of literature [16,17]. However, a different cutoff value may have influenced our findings. Further studies are needed to better establish appropriate cutoffs and subsequently examine the success of treatment methods related to inadequate vitamin D levels. Finally, the authors acknowledge that fracture healing is affected by the other variables in including fracture type, diabetes, steroid use, smoking and alcohol consumption. While these must be considered, the goal of this study was to evaluate the independent role of vitamin D in fracture healing. Subsequent studies should be performed to evaluate the effects of the aforementioned variables.

CONCLUSION

While an 11% decrease was noted in fracture union with Vitamin D deficiency, our report does not provide statistically significant data to make overarching conclusions about the influencing role of vitamin D in fracture healing or time to union following fixation. However, it was noted that Vitamin D supplementation following fracture fixation may be inappropriately deficient.  Further studies establishing the appropriate cut-off value for therapeutic intervention are needed.

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  Table 1
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  Table 2
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  Table 3