BMI, Bowed Legs Correlate With Impaired Gait in XLH Children, Study Finds

Most children with X‐linked hypophosphatemia (XLH) have complex deformities in their lower limbs that cause significant gait abnormalities, a study has found.

Notably, a distinctive gait problem called “waddling gait” — moving the trunk sideways while walking — is a major mechanism to compensate for bowed legs, and appears to increase with greater body mass index (BMI). Since a large proportion of children with XLH are overweight, diet and exercise that reduce BMI may help these children maintain regular gait patterns.

The study, “Disease-specific gait deviations in pediatric patients with X-linked hypophosphatemia,” was published in the journal Gait and Posture.

XLH is characterized by the inability of the kidneys to reabsorb phosphate, leading to chronic low blood levels of phosphate, as well as rickets and weaker bones. Patients also experience gait problems, such as waddling gait, but little is known about the bone or physical alterations leading to such impairments.

In the study, researchers in Vienna, Austria, set out to examine the bone deformities and gait deviations in children with XLH, which could potentially identify risk factors and measures to prevent gait problems.

The study involved 12 children and adolescents with XLH, mean age 8.8 years, who underwent gait and movement analysis at the Orthopaedic Hospital Speising, but had not received any bone procedures or guided growth approaches.

At the time of their gait analysis, 10 patients were receiving conventional phosphate and vitamin D medication, one was receiving antibody treatment with Crysvita (burosumab), and one had not received any form of therapy.

A group of 18 healthy children (12 girls and six boys), mean age 7.8 years, were included as controls. Data from these individuals were obtained from the hospital’s gait laboratory database.

Compared to the controls, patients had a greater step width, meaning that their feet were farther apart laterally.

Overall, the range of motion of the hip throughout a gait cycle was significantly smaller in patients than in controls, as were the extension and flexion of the knee and ankle.

XLH patients also had a greater lateral trunk lean during gait, which means that they leaned sideways while walking. This waddling gait was seen in five patients, and correlated with having varus knee deformity, or inward bowed legs.

“The association of commonly occurring gait deviations such as increased lateral trunk lean with knee deformities points to a role of minimal invasive guided growth surgery to correct frontal axis deviations [and] improve gait abnormalities,” the researchers wrote.

A greater waddling also correlated with higher BMI, which might “indicate obesity as a risk factor for the development of this specific gait impairment,” they added. “Given that one third of pediatric patients with XLH have been reported to be overweight, metabolic control could be of high importance for maintaining regular gait patterns.”

An analysis of the lower limbs and wrist also found rickets in all patients.

The gait deviation index (GDI) is a tool that examines several features to determine gait quality in patients compared with normally developing children. The lower the GDI score, the greater the gait deficiencies.

Results showed that children with XLH had significantly reduced gait quality, and that this measure was also correlated with BMI scores, again supporting lifestyle interventions as a means to reduce weight to improve gait in these patients.

“Given the association of metabolic control and gait quality, this study underlines the necessity of a multidisciplinary approach in the treatment and follow up of children with XLH,” the scientists wrote.

Overall, this was the first study to describe gait deviations and bone deformities in children and adolescents with XLH, demonstrating complex deformities of the lower limbs.

The researchers suggested that these measures should be routinely implemented to determine the effectiveness of surgical approaches at improving gait quality.

“The characterization of abnormal gait in patients with XLH and identification of associated factors may aid to specifically address gait impairments in intervention studies and to target and improve mobility restrictions at earliest possible time points in multidisciplinary care,” they concluded.