A longitudinal comparison of appendicular bone growth and markers of strength through adolescence in a South African cohort using radiogrammetry and pQCT

Summary To compare growth patterns and strength of weight- and non-weight-bearing bones longitudinally. Irrespective of sex and ethnicity, metacarpal growth was similar to that of the non-weight-bearing radius but differed from that of the weight-bearing tibia. Weight- and non-weight-bearing bones have different growth and strength patterns. Introduction Functional loading modulates bone size and strength. Methods To compare growth patterns and strength of weight- and non-weight-bearing bones longitudinally, we performed manual radiogrammetry of the second metacarpal on hand-wrist radiographs and measured peripheral quantitative computed tomography images of the radius (65%) and tibia (38% and 65%), annually on 372 black and 152 white South African participants (ages 12–20 years). We aligned participants by age from peak metacarpal length velocity. We assessed bone width (BW, mm); cortical thickness (CT, mm); medullary width (MW, mm); stress-strain index (SSI, mm 3 ); and muscle cross-sectional area (MCSA, mm 2 ). Results From 12 to 20 years, the associations between metacarpal measures (BW, CT and SSI) and MCSA at the radius (males R 2 = 0.33–0.45; females R 2 = 0.12–0.20) were stronger than the tibia (males R 2 = 0.01–0.11; females R 2 = 0.007–0.04). In all groups, radial BW, CT and MW accrual rates were similar to those of the metacarpal, except in white females who had lower radial CT (0.04 mm/year) and greater radial MW (0.06 mm/year) accrual. In all groups, except for CT in white males, tibial BW and CT accrual rates were greater than at the metacarpal. Tibial MW (0.29–0.35 mm/year) increased significantly relative to metacarpal MW (− 0.07 to 0.06 mm/year) in males only. In all groups, except white females, SSI increased in each bone. Conclusion Irrespective of sex and ethnicity, metacarpal growth was similar to that of the non-weight-bearing radius but differed from that of the weight-bearing tibia. The local and systemic factors influencing site-specific differences require further investigation. Graphical abstract