The linea aspera: a virtual case study testing emergence of form and function.

The linea aspera (LA) forms a characteristic ridge along the posterior aspect of the human femur. Absent in youth, the LA emerges during early puberty and becomes more prominent with advancing age. Pauwels, a pioneer of mechanobiology, hypothesized that the LA forms in the precise location where axial intracortical stresses are greatest, effectively "stiffening" the femur in bending. This study reassesses the mechanical role of the LA in virtual models of human femora, accounting for increasing prominence of the LA at juvenile, young adult and aged stages. Using finite element analysis, peak stresses and the relationship between the LA, neutral axis and centroidal axes (CAs) are evaluated for cross-sections along the mid-diaphysis of the virtual femora. Additionally, the relationship between LA and CAs is studied in anatomical cross-sections from Pauwels' manuscript as well as aged cadaveric donors, indicating that his conclusion may have been stymied by lack of modern computational methods. The results of the current study do not support a mechanical role of the LA as its emergence results in less than a 3% decrease in peak stress, while increasing prominence of the LA also serves to rotate CAs away from calculated stress field, implicating a less "bone centric" view of form and function.