Methods: Images of entire human femur cross sections were acquired by backscattered electron microscopy in the scanning electron microscope (BSE-SEM) using a Zeiss EVO 50 SEM and processed using Adobe PhotoShop CS5 to eliminate "noise" (e.g., canaliculi, cracks). Images were analyzed using Leica QWin Pro image analysis software to count osteocyte lacunae around entire cross sections.
Results: When evaluating people 1.7m and under from the sample, the correlation between osteocyte lacuna density and body height is high, positive, and significant (r = 0.78, R2 = 0.54, p = 0.037). When osteocyte lacuna density was evaluated in respect to an individual's body mass index (BMI), the relationship improves (r = 0.83, R2 = 0..62, p = 0.022). No relationship between osteocyte lacuna density was recovered in tests that included weight alone, nor were there any apparent associations with characteristics of an individual's social, economic, occupational, or medical history.
Conclusion: That our findings apply to the Malawian sample specifically below 1.7 m body height suggests that body weight variability increases dramatically in taller than average individuals in this sample, impairing the relationship between osteocyte lacuna densities and body size. That the test of a relationship between osteocyte lacuna density and BMI is improved over that of lacuna density and height alone suggests that body weight interacts with body height to generate variability in bone cell density. We conclude that within humans, smaller individuals achieve their bone and body size by growing more slowly and, in respect to their skeletons, by proliferating their bone cells less rapidly than larger individuals, leading to lower osteocyte lacuna densities.