Haversian osteons: longitudinal variation of internal structure

Area of Science:

• Bone biology
• Materials science
• Biophysics

Background:

• Osteons, the fundamental structural units of cortical bone, were previously classified into three types: light, intermediate, and dark.
• This classification was based on subjective visual assessment of their optical properties.

Purpose of the Study:

• To develop and apply a rapid, quantitative method for measuring osteon transmission.
• To investigate the optical properties of osteons in human cortical bone to determine if distinct types exist.

Main Methods:

• A novel method was developed for quantitative measurement of percent transmission of osteons in thin sections using polarized light.
• Studies were conducted on osteon segments from human cortical bone, with varying section lengths (200 and 5 micrometers).

Main Results:

• A continuous variation in percent transmission was observed across osteon populations and within serial sections.
• No correlation was found between the angulation of the osteonal segment axis and its percent transmission.
• The observed variations could not be attributed to the angle of observation relative to the osteonal segment axis.

Conclusions:

• The findings suggest that there is likely only one general type of osteon.
• The continuous variation in transmission indicates a continuous variation in collagen fiber orientation within osteons.
• This challenges the traditional classification of osteons into discrete types.