Patterns of strain in the macaque tibia during functional activity

The strain environment of the tibial midshaft of two female macaques was ev aluated through in vivo bone strain experiments using three rosette gauges around the circumference of the bones. Strains were collected for a total o f 123 walking and galloping steps as well as several climbing cycles. Princ ipal strains and the angle of the maximum (tensile) principal strain with t he long axis of the bone were calculated for each gauge site. In addition, the normal strain distribution throughout the cross section was determined from the longitudinal normal strains (strains in the direction of the long axis of the bone) at each of the three gauge sites, and at the correspondin g cross-sectional geometry of the bone. This strain distribution was compar ed with the cross-sectional properties (area moments) of the midshaft. For both animals, the predominant loading regime was found to be bending about an oblique axis running from anterolateral to posteromedial. The anterior a nd Part of the medial cortex are in tension; the posterior and part of the lateral cortex are in compression. The axis of bending does not coincide wi th the maximum principal axis of the cross section, which runs mediolateral ly. The bones are not especially buttressed in the plane of bending, but of fer the greatest strength anteroposteriorly. The cross-sectional geometry t herefore does not minimize strain or bone tissue. Peak tibial strains are s lightly higher than the peak ulnar strains reported earlier for the same an imals (Demes et al. [1998] Am J Phys Anthropol 106:87-100). Peak strains fo r both the tibia and the ulna are moderate in comparison to strains recorde d during walking and galloping activities in nonprimate mammals. (C) 2001 W iley-Liss, Inc.