Abstract
Background
Childhood obesity affects nearly one fifth of all children in the United States. Understanding the unique injury characteristics and treatment of tibia fractures in this population has become increasingly important. This study aims to explore the different injury characteristics between tibia fractures in obese and non-obese children.
Methods
215 skeletally immature children aged 2-18 who sustained tibia fractures between 2007.2019 were retrospectively reviewed. Patients were analyzed by weight group: underweight, normal weight, overweight, and obese as defined by body mass index (BMI) percentile based upon age. Analyses were performed on dichotomized groups: underweight and normal weight versus overweight and obese. Chi-square or Fisher’s exact test was used to compare differences in categorical outcome between the 2-category BMI class variables; Wilcoxon test was used to compare continuous outcomes. A multivariate logistic regression model was used to evaluate BMI associations while controlling for age, sex, race, and mechanism of injury.
Results
Distribution of BMI in the cohort included 6.5% underweight, 45.6% normal weight, 16.7% overweight and 31.2% obese. Overweight and obese children sustained fractures from low energy mechanisms at more than double the rate of normal and underweight children (20.5% versus 9.7%, p=0.028). Overweight and obese children sustained physeal fractures at a rate of 54.4% in comparison with 28.6% in their normal and underweight peers (p<0.0001, OR 2.50 (95% CI, 1.26-4.95)). Overweight and obese children sustained distal 1/3 tibia fractures at a higher rate of 56.9% compared to under and normal weight children at 33.9% (p=0.003, OR 2.24 (95% CI, 1.17-4.30)). Overweight and obese children underwent unplanned changes in treatment at a lower rate than normal and underweight children at 1% versus 8% rates of treatment change, respectively (p=0.013, OR 0.076 (95%CI, 0.009-0.655)). No significant differences were found in the rates of operative treatment, repeat reduction, post treatment complications, or physical therapy.
Conclusion
Overweight children sustain tibia fractures from low energy mechanisms at higher rates than their peers. Similarly, obese and overweight patients have higher rates of physeal injuries and higher rates of distal 1/3 tibia fractures. Complication rates are similar between obese and non-obese children undergoing treatment for tibia fractures.
Level of Evidence: III
Keywords: pediatrics, obesity, trauma, tibia fracture
Introduction
Childhood obesity is a national epidemic; the most recent CDC data demonstrates that 17.2% of all youth in the United States are classified as obese based on body mass index (BMI).1 Previous literature has reported that obese children are at increased risk of fracture, while others have not found a significant association between obesity class and fracture incidence.2-5 Several studies have reported that obese pediatric patients have different fracture patterns, more commonly require surgical treatment, and have higher rates of post-procedural complications.2,6-10 Auer et al. demonstrated that obese children had higher rates of malreduction of distal radius fractures requiring subsequent manipulation with closed reduction and casting when compared to their peers of normal BMI.11 Another study reported that obese children were significantly more likely to sustain loss of reduction in closed treatment and casting for radial and ulnar diaphyseal fractures than their normal-weight peers (44.4 vs 7.2%).6 Understanding the differences between treating obese and non-obese children is important for orthopaedic surgeons, children and their families.
There is a paucity of literature investigating the effects of obesity on lower extremity fractures. One review demonstrated that obese children were significantly more likely to sustain lower extremity injuries than upper extremity injuries.12 Obese children also tend have more severe femur and tibia fractures and higher inpatient morbidity and mortality after trauma than their normal-weight peers.7 While several studies suggest obese children have higher treatment failure in common upper extremity injuries, there are few studies evaluating the treatment outcomes for obese children sustaining tibia fractures. Pediatric tibial shaft fractures are treated nonoperatively in up to 95% of cases, though operative intervention may be increasing in prevalence.13-15
The purpose of the study is to further evaluate differences in injury characteristics, treatment algorithms, and treatment outcomes in tibia fractures in obese children versus children with normal BMI to add to a growing body of literature evaluating this topic. With increasing rates of obesity, a better understanding of potential differences in epidemiology and treatment of these populations is essential.
Methods
After obtaining approval from the Institutional Review Board, we identified all patients aged 2-18 years old who presented to our institution with a tibia fracture between January 2007 and December 2019. The initial cohort of patients included 497 patients. Patients with undocumented height or weight, incomplete follow-up or underlying bone pathology (e.g. osteogenesis imperfecta, malignancy) were excluded. Patients that were skeletally mature based on initial imaging were also excluded. After exclusions, 215 children met criteria for inclusion (Figure 1). Prospectively collected data from initial presentation, subsequent operative interventions, and clinic follow-up was retrospectively reviewed.
Figure 1.
Exclusion Criteria Chart.
Demographic information including age, gender, and body mass index was reviewed. Patients were classified into BMI categories based upon BMI for age. A BMI for age greater than 85th percentile was classified as overweight, greater than 95th percentile for obese, and less than 5th percentile for underweight based upon the guidelines from the Center for Disease Control’s expert committee on childhood obesity.16 Injury characteristics were collected including mechanism of injury, location of fracture (proximal, middle, or distal third), and Salter-Harris type, if physeal. Mechanisms of injury were further divided into high and low energy mechanisms with high energy mechanisms comprising motor vehicle collisions, pedestrian versus auto, and downhill activities (skiing, skateboarding, etc.). Low energy mechanisms included ground level falls and sporting injuries.
Patients that were seen in the emergency room underwent closed reduction by an orthopaedic surgery resident under conscious sedation if indicated based on unacceptable alignment as described by Ho and Mooney, or in the presence of clinical deformity or malrotation.14 Additional treatment including operative intervention or repeat closed reduction was under the discretion of the attending orthopaedist. A patient was deemed to have failed initial management if they had loss of reduction requiring additional intervention including cast wedging, repeat or unplanned closed reduction, or operative intervention.
Post treatment complications were reviewed including pressure injury, refracture, stiffness requiring therapy, premature closure of physes, infection and chronic pain. Additionally, total number of radiographs, need for formal physical therapy and the length of treatment or immobilization was recorded.
Median (Q1, Q3) were used to summarize continuous patient characteristics and frequencies and percentages were used to summarize categorical patient characteristics. Chi-square or Fisher’s exact test was used to compare differences in categorical outcome between the 2-category BMI class variables; Wilcoxon test was used to compare continuous outcomes.
Multivariable logistic regression was performed to evaluate associations between overweight/obese status vs normal/underweight status and outcomes controlling for the following variables: age, sex, race, and mechanism of injury. All analyses were performed in SAS 9.4 (Cary, NC). Two-sided p-values were deemed statistically significant.
Results
The median age at injury was 10 (Q1, Q3: 5, 12). The majority were male (67.4%) and approximately half were white (50.7%). Distribution of BMI categories were as follows: 6.5% underweight, 45.6% normal weight, 16.7% overweight and 31.2% obese. Demographic comparison of the two weight groups can be found in Table 1. The only significant finding was obese and overweight children sustained their fractures at an older age in comparison with their normal and underweight peers.
Table 1.
Comparison of Demographics Between Weight Groups
| Normal/ Underweight (n = 112) | Obese/ overweight (n = 103) | P | |
|---|---|---|---|
| Age (y), Median (Q1, Q3) | 7 (3, 13) | 10 (8, 12) | 0.009 |
| Sex n (%) | 0.655 | ||
| Male | 74 (66.1) | 71 (68.9) | |
| Female | 38 (33.9) | 32 (31.1) | |
| Race/Ethnicity n (%) | 0.739 | ||
| White | 58 (51.8) | 51 (49.5) | |
| Black | 23 (20.5) | 27 (26.2) | |
| Hispanic | 20 (17.9) | 21 (20.4) | |
| Other/Not Listed | 11 (9.8) | 4 (3.9) |
Significant values in bold. Table comparing demographics between the two weight groups. Values are represented as number and percentage in parentheses (%).
Low energy mechanisms of fracture were more common in the obese and overweight children. Normal and underweight children sustained high energy mechanisms at a rate of 20.5% in our cohort compared with 9.7% in overweight and obese children (p = 0.028, Table 2).
Table 2.
Comparison of Injury and Treatment Characteristics Between Weight Groups
| Normal/Underweight (n = 112) | Obese/overweight (n =103) | P | |
|---|---|---|---|
| Mechanism of Injury (%) | 0.028 | ||
| Low Energy | 89 (79.5) | 93 (90.3) | |
| High Energy | 23 (20.5) | 10 (9.7) | |
| Location of Fracture n (%) | 0.0029 | ||
| Distal | 38 (33.9) | 58 (56.9) | |
| Midshaft | 68 (60.7) | 39 (38.2) | |
| Proximal | 6 (5.4) | 5 (4.9) | |
| Physeal Injury n (%) | <0.0001 | ||
| Yes | 32 (28.6) | 56 (54.4) | |
| No | 80 (71.4) | 47 (45.6) | |
| Salter-Harris Type n (%), if Physeal | 0.7882 | ||
| SH I | 4 (12.5) | 7 (12.1) | |
| SH II | 21 (65.6) | 40 (71.4) | |
| SH III or IV | 7 (21.9) | 9 (16.1) | |
| Operative n (%) | 0.2124 | ||
| Yes | 31 (27.7) | 21 (20.4) | |
| No | 81 (72.3) | 82 (79.6) | |
| Unplanned Change in Treatment n (%) | 0.0129 | ||
| Yes | 9 (8.2) | 1 (0.97) | |
| No | 101 (91.8) | 102 (99.0) | |
| Avg number of X-rays taken , Median (Q1, Q3) | 6 (4, 9) | 7 (5, 10) | 0.137 |
| Avg length of treatment (wks) , Median (Q1, Q3) | 7 (4.5, 10) | 8 (6.5, 11) | 0.045 |
Significant values in bold. Table comparing findings of injury and treatment characteristics between the two weight groups. Values are represented as number and percentage in parentheses (%). Median (Q1, Q3) are used to summarize continuous patient characteristics.
Overweight and obese children sustained more physeal fractures than normal weight children. Overweight and obese children sustained physeal fractures at a rate of 54.4% in comparison with 28.6% of their normal and underweight peers (p<0.0001, Table 2). After adjusting for other variables, a multivariate analysis demonstrated an odds ratio of 2.50 (CI, 1.26-4.95, Table 3), indicating overweight and obese children are 2.5 times more likely to sustain a physeal fracture of their tibia (p=0.0088). Those who were overweight or obese had more distal tibia fractures compared to underweight or normal weight individuals (56.9% vs 33.9%, p=0.0029, Table 2). Again, after adjusting for other variables, overweight and obese children in our cohort were more than twice as likely to sustain a distal third tibia fracture in comparison with their normal and underweight peers (OR=2.24, (CI, 1.17-4.30), p=0.0147, Table 3). The majority of physeal fractures involved the distal physis; only 6 patients in our cohort sustained proximal tibial physeal fractures.
Table 3.
Multivariable Associations of Overweight and Obese BMI With Outcomes
| Outcome | OR (95% CI)* | P-value** |
|---|---|---|
| Distal third fracture | 2.24 (1.17, 4.30) | 0.0147 |
| Physeal Involvement | 2.50 (1.26, 4.95) | 0.0088 |
| Operative treatment | 0.60 (0.293, 1.21) | 0.1541 |
| Unplanned change in treatment | 0.076 (0.009, 0.655) | 0.0190 |
*OR = Odds Ratio, comparing odds of each outcome for Overweight/Obese compared to Normal/Underweight. **P-value calculated with multivariable logistic regression model for each outcome with predictors of BMI, age, sex, race, and mechanism of injury.
Overweight and obese children were at a significantly lower risk of undergoing an unplanned change in treatment in comparison with normal and underweight children (1% versus 8%, OR=0.076 (CI, 0.009-0.655), p=0.019). Overweight and obese children were immobilized for longer periods than their normal and underweight peers. On average, overweight children were immobilized for one additional week, averaging 8 weeks of treatment in the overweight children compared with 7 weeks in normal and underweight children (p = 0.045). There were no other significant differences in the rates of complications, failure of closed treatment or need for post-treatment physical therapy between the dichotomized groups.
Discussion
Understanding the unique challenges that arise when treating fractures in obese children has become increasingly important as the world’s obesity epidemic becomes more prevalent. There is a relative paucity of literature investigating the effect of obesity on tibia fractures in pediatric patients. Our data suggest that overweight and obese children are at a higher risk for tibia fractures sustained during everyday activities such as a ground-level falls or sporting activities. In this cohort, overweight children were two times more likely to have low energy mechanisms of tibia fracture compared to their peers.
Tibia fractures in overweight and obese children involve the physis at a higher rate. This is an important finding that adds to a growing body of literature investigating the effects of obesity on physeal development. Obesity is an established risk factor for several conditions affecting the physis including slipped capital femoral epiphysis and tibia vara.17 A prior registry study has demonstrated that obese children are at increased risk of traumatic physeal injuries, obese patients were twice as likely (risk ratio 2.20) to have lower extremity fractures involving the physis when compared to non-obese children.8 Our results corroborate this finding. The biomechanics of these differences are not understood and require further investigation. Some have suggested the physeal abnormalities in obese children may be secondary to advanced bone age or increased adiposity in the bone.8,17-19 To our knowledge, this is only the second case series evaluating the risk of physeal injury in obese children. Clinicians should be aware of this association when evaluating obese trauma patients.
There is a correlation between increasing BMI and a propensity for distal tibia fractures; with underweight patients sustaining distal third fracture at a rate of 15% and obese children at a rate of 60%. Controlling for confounding factors, a multivariate analysis demonstrated an odds ratio of 2.24 (95% CI, 1.17-4.30) for obese children sustaining a distal 1/3 fracture in comparison to normal and underweight children in our cohort. Obese children in our cohort demonstrated the highest rate of complications including pressure injury, refracture, stiffness requiring therapy, premature closure of physes, infection and chronic pain. However, the study was underpowered to demonstrate statistical significance.
Overall, 25.2% of the children in the cohort required an intervention in the operating room; either a closed reduction in the surgical suite or an open surgical procedure. Interestingly, underweight and normal weight children underwent unplanned change in treatment at a higher rate than their overweight and obese counterparts. This finding contrasts with other studies in the pediatric literature that demonstrate higher rates of treatment change in obese children due to their habitus and difficulty in controlling the fracture with immobilization alone.6,10 Overall, the number of patients with treatment failure, defined as unplanned change in treatment (n = 10), was small in this study precluding causative analysis. There is no clear etiology for this difference.
Overweight and obese children underwent, on average, one additional week of immobilization at 8 weeks (Q1, Q3: 6.5, 11) in comparison with 7 weeks (Q1, Q3: 4.5, 10) for underweight and normal weight individuals (p=0.045). Length of immobilization was at the discretion of the treating attending provider based on both provider specific algorithms and clinical evidence of healing (i.e radiographic union and the absence of pain). This finding may represent a treatment bias as providers may be more conservative in immobilizing overweight patients. Alternatively, it may be because overweight and obese children were, on average, 3 years older than their counterparts at age of injury and thus had a lower remodeling potential. Furthermore, while poorly understood, bone healing has been suggested to be slower in some obese mice models.20,21
Recognizing that obese children are at higher risk for injuries involving the physis is important when counseling the children, parents, and their other medical providers following fracture. Physeal injuries are not always evident on plain radiographs. However, knowledge that obese children are at higher risk may influence a surgeon’s decision to follow a child with serial radiographs or recommend immobilization for an extended period of time following a tibia fracture.
Limitations of our study include the retrospective nature of the data and that all patients were seen and treated at a single medical center. A large portion of patients were excluded due to incomplete documentation, which decreased the overall power of the study. Additional large, multi-center studies are needed to determine if the results of this study are generalizable to other populations. Further evaluation of factors including bone age, functional outcomes, and more precise data on time to healing would enhance our understanding of tibia fractures in this population.
In conclusion, overweight and obese children sustain tibia fractures from low energy mechanisms at double the rate of normal and underweight children. Additionally, overweight and obese children with tibia fractures have higher rates of physeal injuries, particularly of the distal physis, which adds to a growing understanding of how obesity affects the developing physis. Complication rates are similar between obese and non-obese children undergoing treatment for tibia fractures.
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