Vitamin D Deficiency and Secondary Hyperparathyroidism as Potential Causes of Idiopathic Knee Angular Deformity: A Prospective Cross-Sectional Comparative Study.

BACKGROUND

Genu valgum and genu varum have various causes; however, the cause in some children remains unknown, leading to a diagnosis of idiopathic angular deformity. In this study, we investigated whether vitamin D deficiency could lead to idiopathic knee angular deformity in the absence of typical radiographic findings of rickets by examining serum markers in affected children and controls.

METHODS

In this prospective cross-sectional comparative study, we evaluated 38 children aged 7 to 14 years with genu valgum or varum without medical conditions or radiographic findings affecting lower limb alignment and 29 controls. Laboratory parameters and the prevalence of vitamin D deficiency (serum 25-hydroxyvitamin D level <20 ng/mL) or hyperparathyroidism [serum parathyroid hormone (PTH) level >60 pg/mL] were compared between the 2 groups. The prevalence of angular deformities was compared among the groups based on the presence of vitamin D deficiency and hyperparathyroidism. Binary logistic regression analysis was used to calculate the odds ratios (ORs) for angular deformities based on vitamin D deficiency and hyperparathyroidism.

RESULTS

The mean serum 25-hydroxyvitamin D levels did not significantly differ between the angular deformity (16.7±6.1 ng/mL) and control groups (19.9±7.1 ng/mL) ( P =0.055). However, vitamin D deficiency was more prevalent in the angular deformity group than in the control group (79% vs. 48%, P =0.009). Angular deformities were more prevalent in children with both vitamin D deficiency and hyperparathyroidism than in those without these conditions [11/13 (85%) vs. 5/18 (28%), P =0.012]. The logistic regression analysis-adjusted for age, sex, and weight-showed a higher risk of angular deformity in children with both vitamin D deficiency and hyperparathyroidism (OR: 9.86, 95% CI: 1.36-71.47, P =0.024), but not in children with vitamin D deficiency alone.

CONCLUSIONS

Isolated vitamin D deficiency without other laboratory abnormalities or radiographic findings of rickets did not lead to knee angular deformity. However, in cases in which vitamin D deficiency elevates PTH levels, idiopathic genu valgum or genu varum might be observed.

LEVEL OF EVIDENCE: Level III-prognostic study.