Bone disease in African children with slipped capital femoral epiphysis: Histomorphometry of Iliac crest biopsies

Abstract

African teenagers with slipped capital femoral epiphysis (SCFE) not infrequently also have genu valgum (knock-knee). Because we had previously demonstrated metabolic bone disease attributable to dietary calcium deficiency in black teenagers with genu valgum, we examined 29 black teenagers (15 male, 14 female) with SCFE for metabolic bone disease. Each patient had an iliac crest bone biopsy taken (after double tetracycline labeling) for routine histomorphometry, and blood and urine samples for bone biochemistry. Spinal bone mineral density was measured in 13 patients. Compared to reported data, we found our patients to be sexually more immature, older, at least as obese, and to have more severe and more frequently bilateral hip disease. Eighty percent of the children took dairy products only once or twice a week or less frequently, and 37.9% had genu valgum. Compared with race- and age-matched South Africans, bone biopsies in our patients showed lower bone volume ( BV TV , p = 0.0003), wall thickness ( p = 0.0002), and trabecular thickness (Tb.Th, p = 0.0002), and a tendency to greater trabecular spacing (Tb.Sp, p = 0.053). Lower osteoid volume ( OV BV , p = 0.0001 ), osteoid surface ( OS BS , p = 0.0001 ), osteoid thickness (O.Th, p = 0.0002), double labeled surface ( dLS BS , p = 0.029 ), and bone formation rate ( BFR BS , p = 0.037 ) suggested poorer bone forming capacity in our patients. No evidence of hyperparathyroid bone disease or osteomalacia was found. BV TV was below the reference range (14.2%) in 65.5% of cases; these patients had lower values for Tb.Th ( p = 0.037) and Tb.N ( p = 0.0003), greater Tb.Sp ( p = 0.0002), a tendency to lower adjusted apposition rate (Aj.AR, p = 0.057), and had had less frequent intake of dairy products than those with normal BV TV ( p = 0.024). Furthermore, months since menarche correlated with histomorphometric variables BV TV ( r = 0.667, p = 0.009), Tb.Th ( r = 0.745, p = 0.002), Tb.Sp ( r = −0.549, p = 0.042), O.Th ( r = 0.784, p = 0.0009), and Aj.AR ( r = 0.549, p = 0.042). The correlation between Tb.Th and spinal bone mineral content ( r = 0.656, p = 0.015) suggests that the reduced trabecular thickness reflected a generalized bone condition. A greater than normal proportion of patients had spinal bone mineral density values below — 1 standard deviation (SD) of the mean (osteopenia) ( p = 0.0001). Patients tested for parathyroid hormone and 25-hydroxyvitamin D levels were found to have normal values. Parathyroid hormone correlated with Aj.AR ( r = 0.661, p = 0.038) and serum phosphorus ( r = −0.764, p = 0.010). We conclude that sexual immaturity and possibly past dietary calcium deficiency contributed to osteopenia, and that this, together with obesity, led to the development of more severe and more frequently bilateral SCFE in our patients than in reported series of black and white children.