metabolic bone disease

The patients studied had infantile tibia vara (Blount’s disease), with none presenting in the adolescent stage (since none of the children was over six years of age). The clinical symptoms, which included gradual but progressive bowing, internal rotation, or internal tibia torsion and recurvatum, reported to occur before the age of one in all patients, were consistent with the classical features described by Blount. The gender distribution of the patients showed a female preponderance, a finding similar to the earlier report of Bateson. However, in the present study, none of the patients had a BMI greater than 30, suggesting that none of the patients was obese, a finding which is at variance with some studies. These revealed a higher prevalence of infantile Blount’s disease among obese female children who started walking at an early age (one to three).

The absence of strict obesity among our patients may suggest that obesity may not be a key risk factor in the etiology of Blount’s disease in our environment where malnutrition is still prevalent.

The biochemical results obtained in the present study, showed a modest hypocalcemia and hypophosphatemia in patients with Blount’s disease with a concomitant significant increase (P<0.05) in serum alkaline phosphatase activity. Although radiological-ly, the features of Blount’s disease are distinct from those of rickets, the pattern of changes in , phosphate, and alkaline phosphatase activity appear to resemble those in secondary hyperparathyroidism and rickets. The lack of statistical significance in the serum concentrations of calcium and inorganic phosphate may be due to the small sample size. In Nigeria, as in most developing countries, it takes a long time to accumulate sufficient data due to low referral rate to the hospitals.

In rickets, an increase in the activity of serum alkaline phosphatase is one of the consistent biochemical findings. The increased serum alkaline phosphatase activity arises from increased activity in the osteoblasts. Using the upper limit of reference values for ALP activity as a cut-off point, 100% of the patients suffering from Blount’s disease in this series exhibited higher than upper limit of reference values. It is known that the activity of this bone isoenzyme (ALP) increases up to five times the upper limit in normal children during the pubertal bone growth spurt. Alkaline phosphatase is a zinc-dependent enzyme and acts probably by releasing phosphate from pyrophosphate for osteogenesis.

The overall modest hypocalcemia, hypophosphatemia, and elevated serum ALP activity in the patients in this study—although consistent with the biochemical finding in rickets—differ from the earlier report of Bathfield and Beighton, who found normal concentrations of calcium canadian, phosphorus and ALP activity in their patients with Blount’s disease in South Africa. Geographical, cultural, genetic, and nutritional or other environmental factors may account for the discrepancy between these studies.

The mean concentrations of serum copper and zinc in patients with Blount’s disease were reduced by about 32% and 48%, respectively, of the mean concentrations of serum copper and zinc in control subjects. Though no significant differences were observed between male and female subjects, the levels of copper (PO.05), inorganic phosphate (P<0.05), and zinc (PO.005) were all significantly higher in male controls than in male Blount’s patients (Table 3). The significance of this is uncertain, as it is not clear if this contributes to the gender bias for Blount’s disease, or it may suggest that the disease is more severe in the male subjects compared to their female counterparts.

The decreases observed in serum copper and zinc concentration may be an indication of copper and zinc deficiency in patients suffering from Blount’s disease. This is consistent with an earlier observation that infants with copper deficiency may develop an osteoporotic fracture. A similar observation of zinc deficiency resulting in skeletal abnormalities in growth in birds has been reported, and an osteopathy—similar to that observed in scurvy—was observed in infants with copper deficiency. The development of skeletal abnormalities in copper deficiency may be due to impaired activity of the copper dependent enzyme lysyl oxidase, which results in defective cross-linking of collagen and, thus, increasing vulnerability to bony deformation under physiological loading.

In addition to all the other metabolic roles, copper and zinc also play a vital role in bone formation and maintenance of bone strength. The observed slight decrease in serum copper in patients with Blount’s disease may be significant, if a larger population is considered. Thus, it is possible that the levels of copper and zinc may serve as a basis of differential diagnosis of Blount’s disease.

CONCLUSION

Based on the information obtained from this limited study, reduction of serum copper (which has been shown to be associated with some form of osteopathy) and zinc concentration in Blount’s disease may aid in the definitive diagnosis of the disease.