Osteon circularity and longitudinal morphology: Quantitative and qualitative three-dimensional perspectives on human Haversian systems.

ABSTRACT

OBJECTIVES: Haversian systems result from bone remodeling, and show variation in size and shape among differing ages, body weights, mechanical environments, and species. While variables such as osteon circularity (On.Cr.) are generally studied in single transverse cross-sections, little is known about On.Cr. variation along an osteon's length, investigated here, in order to strengthen our understanding of bone microstructure. MATERIALS AND METHODS: Up to 875 measurements of On.Cr. were generated for 41 osteonal segments from the proximal anterior diaphysis of femoral human cortical bone of three adult male samples (ages 46, 62, 74). We employed four hypotheses to investigate On.Cr. variability, in cross-section and longitudinally. H1 There is no difference in On.Cr. among osteons comprising single cross-sections, H2 There is no difference in On.Cr. among individuals when single cross-sections are compared, H3 There is no difference in On.Cr. among measurements taken from an osteon along the longitudinal axis, and H4 There is no discernable pattern in an osteon's deviation from circularity. RESULTS: Quantitative analysis of single cross-sections revealed relatively consistent On.Cr. measurements within individual cross-sections and among individuals, supporting both, H1 and H2. Along individual osteonal segments, substantial degrees of dispersion from central tendencies were observed in 27 out of 41 analyzed osteons (despite relatively low overall standard deviations and interquartile ranges), leading to a rejection of H3. Qualitative characterization of morphological deviation from a "typical" circularity suggests a patterned deviation, leading also to a rejection of H4. DISCUSSION: On.Cr. variation is discussed in the context of both, phenomena intrinsic to a given osteon (including repetitive, small perturbations at roughly 45 µm intervals), and extrinsic (including shared reversal sheaths, osteonal branching, transverse connections, and osteonal repathing). Interesting associations between On.Cr. and other characteristics of the local Haversian network emphasize the role of Haversian systems as integrated parts of a greater morphological complex.