Obesity is a rapidly expanding health problem in children and adolescents and is the most prevalent nutritional problem for children in the United States. Some believe that obesity has become a major epidemic in American children, with the prevalence having more than doubled since 1980. This epidemic has led to a near-doubling in hospitalizations with a diagnosis of obesity between 1999 and 2005 and an increase in costs from $125.9 million to $237.6 million between 2001 and 2005. This article describes some of the orthopaedic conditions commonly encountered in overweight/obese children and adolescents, classically infantile and adolescent tibia vara and slipped capital femoral epiphysis. Also discussed are genu valgum, which has been associated with obesity, and other difficulties encountered in providing orthopaedic care to obese children.
Obesity is a rapidly expanding health problem in children and adolescents, and is the most prevalent nutritional problem for children in the United States. In addition to poor nutrition, sedentary activity is a significant contributor to childhood obesity. The many reasons for lower physical activity levels in today’s youth include time spent watching television or at a computer, not walking or riding to school, cutting back on school physical education programs, and increasing use of labor-saving mechanical devices. Some believe that obesity has become a major epidemic in American children, with the prevalence having more than doubled since 1980. The combination of genetic and environmental factors contributing to increasing levels of obese children and the roles of insulin excess and leptin resistance are nicely reviewed in articles by Lustig and colleagues. As in adults, Body Mass Index (BMI) has been used to screen for overweight and obese patients. BMI is defined as kilograms per meter squared, representing a function of body weight and height. It is adjusted for age and gender and is subdivided into BMI percentiles. In children and adolescents, a BMI in the 85th to 95th percentile or a BMI of 25–30 kg/m 2 is considered overweight, whereas a child above the 95th percentile or with a BMI greater than 30 kg/m 2 is considered obese. This epidemic has led to a near-doubling in hospitalizations with a diagnosis of obesity between 1999 and 2005 and an increase in costs from $125.9 million to 237.6 million between 2001 and 2005.
Childhood obesity has a well-documented association with multiple medical comorbidities. Additionally, children that are overweight are more likely to become overweight adults than their normal-weight peers. Obesity in adulthood has been linked to many diseases, including cardiovascular disease, type 2 diabetes mellitus, osteoarthritis, chronic back pain, and obstructive sleep apnea.
This article describes some of the orthopaedic conditions commonly encountered in overweight/obese children and adolescents, classically infantile and adolescent tibia vara and slipped capital femoral epiphysis (SCFE). Also discussed are genu valgum, which has also been associated with obesity, and other difficulties encountered in providing orthopaedic care to obese children.
Musculoskeletal trauma in obese pediatric patients
Pediatric patients most commonly seek orthopaedic care for musculoskeletal trauma, and most fractures in childhood are treated with closed methods. Maintaining correct alignment and positioning using splints or casts relies on the principles of 3-point contact and proper molding. The large soft-tissue envelope of obese children can make safe and secure casting difficult, potentially leading to skin complications, to loss of fracture reduction, and to a decision to treat injuries operatively rather than with casting. When surgery is planned, the greater loads across the fracture in obese patients may require more rigid fixation than is typically used in pediatric patients.
In the adult population, obesity has been found to be an independent risk factor of trauma-related morbidity, although there is a decreased risk of fractures. However, a chart review and questionnaire study performed by Taylor and colleagues noted that overweight children had a higher incidence of fractures. They also found a higher incidence of musculoskeletal pain, specifically knee pain. Skaggs and colleagues found that girls who sustained forearm fractures from a low-energy mechanism were more likely to be obese, with a radius that had a decreased cross-sectional area when compared with matched controls without forearm fractures. It was proposed that the smaller cross-sectional diameter combined with increased body mass and minor trauma created a predisposition to fracture in these patients.
Others studies have questioned the reasons for increased numbers of fractures in the obese adolescent population. Leonard and colleagues and Taylor and colleagues found increased bone mineral density in obese adolescents, although the relationship of bone mass to obesity is controversial and often conflicting. These findings have led some to propose that the increased risk of fracture is due to the inactivity that contributes to obesity. Inactivity may lead to decreased proprioception and poor balance, leading to an increased risk of falling.
When fractures do occur in the obese, complications are increased. Rana and colleagues examined the effect of obesity on numerous outcome measures at their level 1 trauma center. They found that obese children had an increased incidence of extremity fractures, fractures necessitating operative intervention, decubitus ulcers, and deep venous thrombosis (DVT). The findings of increased DVT were confirmed in a study by Vu and colleagues examining the risk factors of DVT in hospitalized children, which found that obesity was a risk factor with a prevalence ratio of 2.1. Literature on adults suggests that obesity may be a risk factor of venous thromboembolic disease (VTED). VTED is fortunately rare in children who do not have coagulopathies, and this rarity leads to controversy about the appropriateness of chemoprophylaxis in pediatric patients, especially in adolescents approaching skeletal maturity/adulthood. Not enough data is available to make recommendations about the value or efficacy of VTED prophylaxis in obese adolescents.
Leet and colleagues found that obese children (BMI >95th percentile) and extremely heavy children (BMI between the 90th and 94th percentile) with operatively treated femur fractures had a significantly increased incidence of complications. The complications included: refracture, pin-site infection requiring debridement, loss of alignment in frame, wound infection, malunion, osteomyelitis, wound dehiscence, compartment syndrome, broken rod, and broken pin. Fracture stabilization must be augmented in the obese patient, because of the known limitations and increased incidence of implant failure. Recent studies of titanium elastic nails used for pediatric femur fractures has found an increased incidence of malunion in children weighing more than 45 kg. Several studies have found that weight was an independent risk factor of malunion. Some have suggested that patients weighing more than 45.36 kg should undergo intramedullary nail fixation using small diameter nails with interlocking screws. The key with any of these devices is to enter the femur though the trochanter, not the piriformis fossa, and not to cross the distal femoral epiphysis with the implant. Another fixation option that is more rigid than elastic nailing is plate fixation, with open or submuscular approaches.
If operative treatment is chosen, obesity can alter physiologic responses to surgical procedures. Studies indicate that obese adults undergoing surgical procedures have an increased risk of complications, and the actual procedures are technically more challenging because of their body mass. The senior author’s experience is that musculoskeletal procedures to stabilize fractures or perform osteotomies in obese pediatric patients are technically more difficult, involving positioning challenges, difficulties obtaining adequate intraoperative imaging, larger incisions, longer operative times, and more complications.
Few studies are available to evaluate the impact of childhood obesity on surgical procedures. A retrospective review of pediatric surgical patients over a 4-year period found increased preoperative diagnoses of medical comorbidities and prolonged recovery room stays in obese children compared with normal-weight children. Davies and Yanchar found that obese children undergoing appendectomies had problems before, during, and after surgery that were similar to those experienced by obese adults. An increased use of sophisticated scanning suggested that appendicitis is difficult to diagnose in obese children. Additionally, they found that childhood obesity led to increased surgical times, increased risk of wound infections, and increased time to ambulation.
The difficulties noted earlier also translate to orthopaedic practice. Obese children presenting for orthopaedic evaluation may prove more difficult to manage, because physical examinations to identify joint effusions, joint laxity, and soft tissue masses are more difficult when the extremities have a thick layer of subcutaneous fat. Operative procedures on the lower extremities in obese children can substantially impair mobility, because the children often do not have sufficient upper extremity strength to ambulate safely with crutches or a walker. Postoperative respiratory difficulties may be exacerbated by poor mobilization.
Similar to adults, obstructive sleep apnea (OSA) is a comorbidity that warrants consideration in children, because it can increase the risks of anesthesia during a surgical procedure. OSA can lead to nocturnal snoring, hypoxia, and hypercarbia and has a prevalence of 2% in children. OSA has been associated with increased perioperative anesthetic complications, including difficulty with intubation and acute respiratory failure during the induction of anesthesia. Additionally, postoperative complications have been reported, including hypoxia, airway edema, obstruction of the upper airway, pulmonary edema, and respiratory failure. Gordon and colleagues reported that 11 of 18 patients with Blount disease who were older than 9 years had been diagnosed with sleep apnea and required noninvasive positive-pressure ventilation. The orthopaedic surgeon should ask obese adolescents about snoring as a risk factor of OSA and take appropriate supportive measures before, during, and after surgery.
Effects of obesity on the growing skeleton
Several common orthopaedic clinical situations in overweight children are created by increased mechanical load on growing bones. Bone is a dynamic tissue that responds to the mechanical stresses and loads placed on it. The differentiating factor in pediatric orthopaedics is that the bones are growing, and the growth plate is a specialized organ that is also sensitive to the surrounding mechanical environment. Two laws or principles have long been offered to explain the effects of mechanical loading on the longitudinal growth of bone. The Hueter-Volkmann law states that bone growth is suppressed by an additional compressive loading through the immature growth plate, and growth is accelerated by reduced loading. Similarly, the Delpech law states that increasing tension across the growth plate leads to increased growth. These laws describe complex physiologic relationships, the mechanisms of which have been studied but are not completely understood.
The Hueter-Volkmann and Delpech laws can explain some of the pathologic conditions related to the increased loading of growth plates in the overweight child. Several basic science experiments have found that static, sustained loads affect growth plates in different animals, with increased compression leading to reduced longitudinal growth. Similarly, although not as well defined, when tension was applied across the growth plate in lambs, they experienced an increase in growth. Applying the Hueter-Volkmann theory to overweight children, the additional weight on their growth plates could lead to an increased load or compression, creating a decrease in growth, especially on the concavity of a malaligned joint (example medial knee joint in genu varum). Conversely, if there is malalignment of a load-bearing joint leading to tensile forces across the convexity of the joint (eg,the lateral knee joint in genu varum), those distraction forces may lead to less pressure across the physis and accelerated growth (Delpech law). Thus a vicious cycle is established, in which malalignment leads to abnormal mechanical forces creating abnormal physeal growth, causing worsening malalignment. Biopsy studies of the 3 pediatric orthopaedic conditions (infantile tibia vara, adolescent tibia vara, and SCFE), commonly believed to be related to obesity and resultant mechanical overload of the physis, have demonstrated histopathology findings supportive of this hypothesis. Abnormal forces are thought to disrupt physeal growth and suppress endochondral ossification, leading to deformities. Others have noted that similar pathophysiology may be involved in genu valgum and scoliosis deformities.
The knee is the most common site of musculoskeletal pain in overweight children. The knee’s position and overall alignment are critical when assessing the effects of increased weight on an overweight child. Two conditions, genu varum and genu valgum, involving the knee joint in children have been linked to obesity, with higher overall incidences in the overweight population.
Blount Disease or Tibia Vara
Blount disease is a developmental disorder involving abnormal growth from the medial part of the proximal tibial physis. It was first described by Blount in 1937 as only a frontal plane deformity(tibia vara), but subsequently, other authors have noted that multiplanar deformities are commonly seen. Abnormal, asymmetric growth results in a 3-dimensional deformity of the tibia with primarily varus, procurvatum, and internal rotation ( Fig. 1 ).
These deformities have been shown to lead to progressive deformity, with gait deviations, limb-length discrepancy, and premature arthritis of the knee. There are 2 clinically distinct forms of Blount disease, infantile and adolescent, which are based on whether the limb deformity develops before or after age 4 years. The exact cause of both forms of Blount disease has yet to be fully determined. Many have suggested a mechanical basis for the disease, based on the observations that the disease occurs more frequently in children who start walking at an early age and those who are overweight. Blount disease has long been associated with increased weight and obesity.
The deformity to the proximal tibia is thought to be due to excessive medial compressive forces causing growth inhibition (Heuter-Volkman law). In a child with genu varum, obesity has been shown to substantially increase the compressive forces created on the medial compartment of the knee. Cook and colleagues assessed the load distribution in the proximal tibia as a function of varus or valgus alignment, and they estimated physeal growth inhibition by applied compression forces. They determined that 20° of varus deformity in an obese 2-year-old and 10° of varus deformity in an obese 5-year-old could generate enough compressive force to retard growth of the medial tibial physis. In another study, Dietz and colleagues looked at the relationship between the percentage of ideal body weight and the tibiofemoral shaft angles. They found a significant correlation ( r = 0.75) with a mixture of obese and nonobese patients; however, they found a stronger correlation ( r = 0.90) among the obese only. The effect of childhood obesity on 3-dimensional knee biomechanics was studied by Gushue and colleagues using gait analysis. Overweight children showed substantially higher peak internal knee abduction moments during early stance with increased loading of the medial compartment of the knee joint compared with children of normal weight, potentially contributing to development of varus alignment.
Infantile Blount disease affects children before age 4 years. Bilateral involvement is common and more likely to occur in the infantile form. The infantile form affects girls and boys equally; however, African American children are affected more commonly than other children. Infantile Blount disease develops between the ages of 2 and 4 years, when normal physiologic varus seen in infants progresses to physiologic valgus, and it must be distinguished from physiologic bowing. Scott and colleagues compared children with physiologic bowing and those diagnosed with infantile Blount disease and found a significantly increased BMI in those with infantile Blount disease. Sabharwal and colleagues found that the infantile form had more severe varus and procurvatum deformities of the proximal tibia than did those with the adolescent form. They also found that the magnitude of deformity strongly correlated with increased weight in those with the early form of the disease and that the correlation with deformity was stronger in extremely obese individuals (BMI >40) ( Fig. 2 ). The authors of one paper thought that the greater deformity in the younger patients was due to the differences in the epiphyses due to aging. They proposed that there was increased pliability in the unossified epiphyses of younger patients, leading to more growth inhibition than in adolescents. These findings support the development of the deformity being attributed to abnormal loading of the proximal tibial physis.
Adolescent Blount disease is less common than the infantile form, and the incidence is higher in the male sex; yet, African Americans who are morbidly obese comprise more than 90% of the reported cases. One study found the prevalence of adolescent Blount disease to be 2.5% in obese male adolescents. There were theories that the adolescent form was due to massive weight gain during adolescence in individuals with underlying varus alignment that could lead to excessive medial compartment loading and altered physeal growth ( Fig. 3 A). However, one observational study found no correlation between varus static alignment and development of the adolescent form. Along these lines, Davids and colleagues examined the gait deviations related to the increased thigh girth associated with adolescent obesity. Their hypothesis was that obese children with larger thighs would have difficulty adequately adducting their hips and this could result in “fat-thigh” gait. They concluded that a fat-thigh gait could produce a varus moment at the knee, leading to increased compressive forces at the medial part of the proximal tibial physis sufficient to retard physeal growth ( Fig. 4 ). Although data suggest that obesity may lead to excessive loading of the proximal medial tibial physis, it is unlikely that this is the sole cause of the deformity.
For both forms of Blount disease, the treatment is customized based on the child’s age, the magnitude of the deformity, the limb-length discrepancy, the psychosocial factors, and the surgeon’s experience. Nonoperative modalities for infantile Blount disease include orthoses or surgical management. Once Blount disease is diagnosed, progressive deformity is expected and observation is not recommended. The natural history of significant varus malalignment of the knee is early medial compartment osteoarthrosis, leading pediatric orthopaedic surgeons to attempt to normalize coronal plane alignment with orthotic or surgical treatment. The guiding treatment principle is to decrease the compressive forces acting on the medial physeal region, to allow the reversal of pathologic processes and restore normal growth. Surgical treatment options include various types of realignment osteotomies, guided growth, gradual asymmetrical physeal distraction, resection of a physeal bar, and elevation of the medial tibial plateau. The indications and descriptions of these techniques are beyond the scope of this article; however, the specific literature related to surgery and overweight patients is reviewed.
Pirpiris and colleagues observed children requiring surgery for the treatment of infantile and late-onset Blount disease and found a clear relationship of increased surgery with increased BMI. For the adolescent form of Blount disease, there are no effective nonoperative treatments for substantial degrees of adolescent tibia vara. If the patient has substantial growth remaining, a guided growth strategy can be effective and can avoid the potential morbidity of osteotomies. McIntosh and colleagues found that BMI of more than 45 kg/m 2 was a risk factor of failure of lateral hemiepiphysiodesis in the treatment of adolescent tibia vara. One of the guided growth techniques uses a tension band plate on the convex side of the growth plate (see Fig. 3 B). The implant chosen for this method of correction might require consideration of the patient’s weight and body habitus. Schroerlucke and colleagues reported 8 failures out of 31 patients with their use of 8-plate tension band device treatment of angular deformities. All 8 failures were in patients with Blount disease, with an unacceptable failure rate of 44%. They concluded that stronger plates need to be used in Blount disease. Some have recommended 2 adjacent plates in the heavier adolescents to decrease implant failure. Stanitski and colleagues reported on the use of the Ilizarov circular external fixator, with gradual correction of 17 obese patients with adolescent tibia vara. The only complications were one delayed union and one premature consolidation; however, all achieved alignment within 5° of normal. They concluded that in this high risk surgical patient population, circular external fixation was an excellent treatment method. Others have noted substantial difficulty in achieving surgical alignment goals using unilateral external fixation, with frequent complications. Complications including wound healing problems, infections, pin tract sepsis, nerve palsies, and compartment syndrome have been reported.
Obesity may also predispose the knee to the development of a valgus deformity. Genu valgum is most commonly physiologic and requires no surgical intervention. Pathologic causes of genu valgum have been described after fractures with certain hereditary disorders and associated with infectious and metabolic disorders. Although limited data link obesity to genu valgum, the theory is that in children and adolescents who have valgus alignment at the knee, increased weight leads to greater compression on the lateral distal femoral physis (Hueter-Volkmann law), leading to diminished lateral growth and progressive valgus deformity ( Fig. 5 ). Zhang and colleagues described 2 cases of overweight girls without a history of prior injury or medical condition who developed progressive genu valgum. They proposed that obesity led to repetitive microtrauma at the distal femoral physis, contributing to the deformity. Stevens and colleagues also found a correlation of obesity and valgus deformity of the knee in a gait analysis study. Of the 16 patients studied, six (37.5%) were obese, showing a correlation of increased weight or BMI to genu valgum. Their study showed that genu valgum could predispose to abnormal knee joint kinetics, including increased knee valgus, increased hip abduction, and frontal plane knee moments. Finally, they suggested that early recognition of potentially progressive valgus deformity of the knee may allow for earlier correction and restoration of lower extremity biomechanics.