Bone includes many structural and chemical components which provide both flexibility and strength. One such structure is the cement line, a 1-5 μm-thin structure located primarily in compact bone. Past research has correlated the pathological condition of “shin splints” with the micro-damage of bone, which often follows cement lines. It has been suggested that cement lines have rather paradoxical properties. Upon fatigue fracture of bone, microcracks often travel along cement lines and become trapped. This trapping and subsequent dispersion of energy have been hypothesized to prevent a complete fracture from occurring, extending bone life. Cement lines have been implicated in a variety of areas concerning bone strength, including energy absorption, fracture and fatigue processes, and elastic function.

The regional distribution of cement lines in cadaveric tibiae was quantified and correlated with the mechanical properties of bone, allowing the investigation of bone as a structure and as a material. In Part I, tibiae were mechanically loaded, and slices subsequently processed for image processing which quantified cement line length/unit area. The results indicate that the average load necessary to completely fracture female tibiae (4.17 kN) was significantly less (p<​0.05) than for male tibiae (7.92 kN). Furthermore, anterior quadrant cement line quantity was significantly greater (p<​0.05) than the other quadrants, and mean cement line quantity in males (0.0099 μm/μm²) was significantly greater (p<​0.05) than in females (0.0092 μm/μm²). Correlation analysis revealed a positive relationship (r = 0.5160) between cement line quantity and the maximum breaking load.

In Part II, standardized cores of compact bone were tested under a bending load. The distribution of cement line quantity with respect to quadrant and gender revealed values similar to those obtained from Part I. Correlation analysis revealed that cement line quantity was again correlated with the breaking load (r = 0.8208), but also with breaking stress (r = 0.8640) and breaking energy (r = 0.5598).

These data suggest that the anterior quadrant of human tibiae may experience increased remodeling than the other quadrants, and that male tibiae may remodel more than female tibiae. Finally, the correlation data strengthens existing hypotheses that cement lines are important structures affecting bone strength.