(From the May 2015 Issue of PediatricsOnline)
In adults, obesity and abnormal knee alignment are recognized as risk factors for the onset and progression of knee osteoarthritis. However, that link has yet to be confirmed in children and adolescents. Now, a study published in the Journal of Rheumatology moves one step closer to supporting the idea that risk factors for knee osteoarthritis may be occurring as early as adolescence. According to the study, in puberty, obese children have greater valgus alignment than non-obese children.
“This means that mechanical abnormalities are present in obese children, especially around and after puberty. However, the clinical significance of this finding is not yet known: whether these children have more pain, whether obese children with valgus knee alignment have an increased incidence of knee osteoarthritis,” says Sharon Bout-Tabaku, MD, MSCE, pediatric rheumatologist in the Section of Rheumatology at Nationwide Children’s Hospital and lead author on the study.
When comparing obese and non-obese knee alignment without considering pubertal stage or sex, no association was found between variations in knee alignment and obesity. However, when groups were separated based on pubertal stage and sex, two findings became apparent: obesity is associated with greater valgus, or knock-kneed, alignment in late adolescence, and higher body mass index (BMI) values are associated with greater variation in alignment in females.
“Younger children, 3- to 5-year-olds, often naturally have a mild knock-kneed appearance, regardless of body habitus, that typically resolves as they get older to a normal adult alignment," says Daniel Ruggles, DO, orthopedic surgeon in the Department of Orthopaedics at Nationwide Children’s. "In our clinical experience, however, it is more common to see persistent knee valgus that does not resolve in overweight children and adolescents.”
Dr. Bout-Tabaku and her team performed a cross-sectional study using existing dual-energy X-ray absorptiometry (DXA) results and patient data collected as part of other research studies and clinical care. The metaphyseal-diaphyseal angle (MDA) was measured using the DXA image and used to assess the knee alignment.
“At this point, we still have not collected enough data on whether malalignment, as seen in our study, is related to pain or function or whether it gets worse,” Dr. Bout-Tabaku says. “However, our study indicates that practitioners who take care of obese children should assess their alignment, their musculoskeletal pain and their function.”
Dr. Ruggles reinforces the importance of monitoring lower limb alignment for changes over time. “Children who are suspected to have knee alignment problems should be referred to an orthopedic specialist so that the diagnosis can be confirmed and the progression of the alignment problems can be tracked,” explains Dr. Ruggles.
Dr. Bout-Tabaku also recommends that practitioners seeing obese patients provide education and aggressive treatment regarding weight loss, including working with a physical therapist to develop a tailored and safe program that will allow maximal exercise and not stress the joints excessively.
“We have to be vocal advocates for healthy weight programs for our orthopedic patients,” agrees Dr. Ruggles, who is also clinical assistant professor of Orthopaedic Surgery at The Ohio State University. “I can surgically make a child’s limbs straight again, but if they are obese, the alignment problems could come back.”
Dr. Bout-Tabaku further explains that the relationship between obesity and joint damage occurs silently and along a continuum just like hypertension and diabetes. These changes may be occurring even in adolescents who are obese. “In the long term, childhood obesity may be related to abnormal alignment, injuries to the joints and, ultimately, osteoarthritis,” Dr. Bout-Tabaku says.
To further establish the links among knee alignment problems, obesity and risk for osteoarthritis, more research is needed.
“I, along with collaborators and other researchers, am trying to gather more data to show that obesity not only affects the daily function of children but also affects the joint function and structure,” Dr. Bout-Tabaku says. “I also believe that reversal of weight loss during childhood and adolescence might provide a window of opportunity to reverse any significant joint dysfunction.”
“We need to define the degrees of deformity that are putting these patients at risk for developing osteoarthritis later in life,” Dr. Ruggles says. “Then, we can consider when to use surgical interventions to mitigate that risk.”
Dr. Bout-Tabaku is currently working with the Teen Longitudinal Assessment of Bariatric Surgery study (TeenLABS) consortium, looking at musculoskeletal pain and function in obese children before and after undergoing bariatric surgery. The baseline data was released online April 27, 2015, in JAMA Pediatrics. She is also working on a pilot study comparing alignment and performance measures, such as strength and gait, in obese and non-obese children.
Bout-Tabaku S, Shults J, Zemel BS, Leonard MB, Berkowitz RI, Stettler N, Burnham JM. Obesity is associated with greater valgus knee alignment in pubertal children, and higher body mass index is associated with greater variability in knee alignment in girls. Journal of Rheumatology. 2015, 42:126-133.