1 Introduction

The obesity rate in the US and globally, particularly among children aged 6–19, has tripled since the 1970s.^1,2 Obesity, through metabolic syndrome, causes dysregulation of the endocrine axis and alters bone physiology through various pathways.³ The primary contributors include increased inflammatory cytokines, insulin resistance, altered leptin production, and vitamin D deficiency.⁴ Central obesity induces insulin resistance, which impairs the function of osteoblasts and osteoclasts by affecting leptin concentrations.^3,5 Increased leptin levels reduce bone growth and speed up bone resorption.⁶ Additionally, abdominal obesity increases systemic inflammation and pro-inflammatory cytokines, contributing to osteoporosis.⁷ Leptin receptors in skeletal growth centers act as skeletal growth factors, leading obese adolescents to grow taller and reach their full height at younger ages.⁷

Obesity influences the pattern and severity of orthopedic injuries.⁸ Children with high BMI are more prone to distal lower limb fractures compared to upper limb fractures.^2,9 Furthermore, complex fracture patterns, nerve palsies, and postoperative complications—especially in cases of supracondylar humeral fractures—are more common in obese children.¹⁰ Obesity also poses challenges in fracture care, as traditional casting depends on the cast's ability to stabilize the injured bone. Studies have shown that obese children are at greater risk for fracture displacement following cast treatment, leading to an increased need for re-reduction in cases such as distal radius fractures.^11–13

Considering the increasing incidence of childhood obesity and evidence linking obesity to unique injury patterns and more severe trauma outcomes, this study aims to investigate the relationship between weight and injury patterns, as well as the morbidity and mortality rates of lower limb fractures in two groups: obese children and children with normal weight.

2 Material and methods

This retrospective, cross-sectional study examined all patients aged 1–18 years who visited the emergency department or orthopedic clinic of our tertiary Hospital between 2014 and 2016. Demographic information, summaries of medical records, and therapeutic procedures performed were analyzed. The inclusion and exclusion criteria were as follows.

3 Results

A total of 247 patients were included in the study, comprising 178 males (72.1 %) and 69 females (27.9 %). The average age of the participants was 68.01 ± 38.91 months, with a range from 13.4 months to 161.7 months consists of 94 (38.1 %) toddler (age between 1 and 4 years), 62 (25.1 %) preschool (4–7 years), and 91 (36.8 %) school age (7–13 years). The anthropometric data of the patients are as follows: height is 106.33 ± 17.19 cm, and weight is 68.01 ± 38.91 kg. The mean BMI of the patients was 17.45 ± 2.30 kg/m², with BMI percentile of 65.28 ± 31.96 %, ranging from 1.0 to 99.9 percent.

As depicted in the bar chart (Fig. 1), the BMI classifications were as follows.-Underweight: 21 patients (8.5 %)-Normal weight: 118 patients (47.8 %)-Overweight: 63 patients (25.5 %)-Obese: 45 patients (18.2 %)

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Fig. 1 Bar chart of BMI categories.

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Table 1 and Fig. 2 illustrate the distribution of fractures across different regions of the lower limbs. The frequencies were as follows.-Femur fractures: 94 cases (38.1 %)-Tibia fractures: 80 cases (32.4 %)-Foot fractures: 42 cases (17 %)-Pelvic fractures: 18 cases (7.3 %)-Knee fractures: 8 cases (3.2 %)-Ankle fractures: 5 cases (2 %)

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Fig. 2 Bar chart of facture sites according to BMI categories.

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The average length of hospital stay was 8.04 ± 4.89 days. Table 2 summarizes the frequency and percentage of referral types, discharge statuses, and complications. Adverse effects were observed in 11 patients, with detailed information provided in Table 2.

Table 3 compares gender, fracture location, type of referral, and discharge status among the four BMI groups. A statistically significant difference was observed only in the complications section, where 11 out of 13 cases (84.61 %) occurred in the overweight and obese groups. The majority of malunion cases were also found in these groups, and these differences were statistically significant.

Table 4 presents a comparison of age and length of hospital stay across the four BMI groups. Significant differences were noted for both age (p = 0.046) and length of stay (p < 0.001). Additionally, a Pearson correlation test revealed a significant positive correlation between BMI and the length of hospital stay (correlation coefficient = 0.728; p < 0.001).

4 Discussion

Our research aimed to evaluate the impact of a child's BMI on the progression of lower limb fractures. The findings revealed no significant differences in the incidence of fractures across different body regions among the BMI categories. However, tibial fractures were less frequent in the obese group compared to others. This trend may be attributed to the greater amount of adipose tissue surrounding the calves in obese individuals, which could offer some protective effect. Aside from these observations, there were no statistically significant differences between BMI groups regarding discharge status or the mode of admission (emergency vs. outpatient). Nonetheless, the overweight and obese groups exhibited a markedly higher prevalence of complications and longer hospital stays compared to other BMI groups. Among these complications, malunion was the most reported issue.

A study conducted over a 10-year period and published in 2022 by Heath et al.¹⁴ analyzed the time to union in fractures among obese and non-obese children. The study included 147 children with an average age of 11.8 years. Of these, 5 children (3.4 %) were underweighted, 28 (19 %) were obese, 33 (22.4 %) were overweight, and 81 (55.1 %) had a normal weight. The findings revealed that children with a higher BMI experienced significantly longer times to union after fractures compared to children with lower BMI. Similarly, our study indicated that malunion issues were notably more prevalent among obese children.

In another study conducted by McGregor et al.¹⁵ in 2022, 215 children aged 2–18 years with tibial fractures were evaluated. The average age of participants was 10 years, with boys comprising 67.4 % of the sample. Regarding BMI distribution, 6.5 % of the children were underweight, 45.6 % had normal weight, 16.7 % were overweight, and 31.2 % were obese. The findings of McGregor et al. did not demonstrate significant differences in surgical treatment rates, recurrence of fracture reduction, post-treatment complications, or the need for physical therapy between the obese/overweight group and the underweight/normal weight group. These results differ from our findings, where complications were significantly more frequent in the overweight and obese groups. One possible reason for this discrepancy may be that our study examined all lower limb fractures, while the study by McGregor et al. focused specifically on tibial fractures.¹⁵

In a 2019 study, Li et al.^16,17 examined the impact of BMI on the outcomes of fractures in the upper and lower extremities. Their extensive study included 202,286 children admitted to the hospital with upper or lower limb fractures. The findings highlighted a link between obesity and the need for open reduction procedures. Moreover, obese patients had significantly longer hospital stays and incurred higher healthcare costs compared to non-obese patients. Additionally, age was identified as another significant factor, with the severity and complexity of complications increasing as the child aged. The study also examined the broader consequences of the disease, including infections, nerve and vessel damage, and other complications. Their findings showed that obese children had a markedly higher rate of postoperative complications compared to the general population. Our study aligns with the results of Li et al. study,^16,17 as we also observed that patients with higher BMI experienced significantly longer hospital stays and more complications.

In 2016, Burrus et al.¹⁸ conducted a study evaluating 14,638 children with tibial shaft fractures. Among these patients, 820 (5.6 %) were morbidly obese, and 1091 (7.4 %) were obese. The findings indicated that obese and morbidly obese patients experienced a significantly higher incidence of complications compared to other patients. These complications included infection, nonunion, thrombosis, and surgical implant removal. The results of our study align with these findings, as we observed that overweight and obese patients had a significantly higher incidence of complications such as malunion compared to other groups.

The impact of obesity on pediatric fractures extends beyond mechanical pressure on the fracture site. While tension at the fracture site may lead to displacement of the union line and issues with internal implant movement, biological factors also play a role. Research on upper limb fracture nonunion has demonstrated that obesity can activate inflammatory pathways, which restrict proper tissue regeneration. This suggests that obesity may biologically influence the healing process in pediatric limb fractures.¹⁹

The findings of this study have dual applicability. From a research perspective, they contribute to understanding the role of BMI in bone fractures and provide a methodological framework for future studies. From a clinical perspective, these results, alongside other research, can assist orthopedic specialists in managing fractures in overweight and obese children. It is evident that orthopedic surgeons should implement additional measures when treating these patients to mitigate the risk of complications following fracture treatment.

Our study has several limitations. Firstly, although the sample size was adequate, we were unable to include a larger number of patients due to resource constraints. Additionally, while obesity may contribute to upper limb fractures through factors other than mechanical stress, our investigation was limited to lower limb fractures. However, one of the strengths of our study is that it is one of the few focusing on this topic, particularly among the Iranian population. To strengthen the findings, future research with a larger sample size and consideration of upper limb fractures in diverse demographics is recommended.

5 Conclusion

The results of our study demonstrated that although BMI did not influence the distribution of fractures across different body regions, the patient's condition at discharge, or the method of admission, it was significantly associated with outcomes and results. Specifically, the rate of complications and the duration of hospitalization were notably higher in the obese and overweight groups compared to the other BMI groups. Among these complications, malunion was particularly prominent. Our study was limited to cases of lower limb fractures, and further research examining upper limb fractures is recommended.

CRediT authorship contribution statement

Mohammad Ghorbani: All authors had full access to the data in the study and took responsibility for the integrity of the data and the accuracy of the data analysis. Morteza Behjat: Methodology, Writing – review & editing. Mohammad Hallaj Moghaddam: Conceptualization, Writing – review & editing, Supervision. Sajjad Abrishami Moghaddam: Formal analysis, Visualization. Saeid Esmaeilian: Investigation, Formal analysis, Writing – original draft. Seyed Ali Moshtaghioon: Formal analysis, Writing – original draft. Ali Parsa: Conceptualization, Methodology, Resources, Writing – original draft, Writing – review & editing, Supervision. Elham Rahmanipour: Methodology, Writing – original draft.

Declaration of ethical approval for study

In the review of the cases, confidentiality and other ethical principles were upheld, and the examination of the cases was conducted with written permission from the university's ethics committee. All stages of this study were conducted in accordance with the Helsinki ethical principles and have been approved by the Ethics Committee of Mashhad University of Medical Sciences. This research was presented on September 01, 2016 to the organizational ethics committee of the Mashhad University of Medical Sciences under the title " The Effect of Obesity on Pediatric Lower Limb Fractures and Their Treatment Outcomes" and was approved with the code IR. MUMS.REC.1395.134.

Declaration of informed consent

There is no information (names, initials, hospital identification numbers, or photographs) in the submitted manuscript that can be used to identify patients.

Authorship declaration

All authors listed meet the authorship criteria according to the latest guidelines of the International Committee of Medical Journal Editors.

Data availability

The data supporting this study's findings are available upon reasonable request from the corresponding author.

Funding

No sources funded this research.