Biochemical observations in Blount's disease (infantile tibia vara)

Blount's disease or congenital tibia vara is a clinical entity characterized by tibia bowing, tibia torsion, and beaking of the medial tibia metaphysis on plain radiograph. In our environment, burnt-out rickets patients with biochemical and radiological diagnosis of rickets who after treatment still have residual bone changes despite normal bone biochemistry) can also present with similar clinical and radiological features as Blount's disease. However, certain biochemical variations, including antioxidants, may serve as a basis for differentiation between these two disorders. The serum levels of calcium, inorganic phosphate, zinc, copper, and alkaline phosphatase in 15 patients (10 females and five males) aged between two- and five years (mean 3.8 +/- 1.1 (SD)) with clinical and radiological features of Blount's disease were determined. The mean weight of the patients with Blount's disease was 14.0 +/- 2.4 kg (range: 11.5-16.3 kg). Fifteen subjects (nine females and six males) matched for age and sex without clinical features of any metabolic bone and/or nutritional diseases who were attending the surgical outpatient clinic served as control subjects. The serum concentrations of inorganic phosphate and calcium, though lower in patients with Blount's disease compared with controls, did not reach statistical significance. Alkaline phosphatase activity was increased in the serum of all patients with Blount's disease. In addition, there was an observed significant reduction in serum concentration of zinc (P < 0.03) compared to the control subjects. As for calcium level, the concentration of serum copper in Blount's patients was reduced, but this was not statistically significant. These biochemical observations, especially those of the antioxidant micronuent zinc, may serve as a basis for the differentiaion of the sometimes clinically inseparable disorders of Blount's and rckets and may aid in early differential diagnosis, appropriate treatment as well as prevention of complications.