Why do long bones such as the femur have thick compact outer layers?

Long bones, such as the femur, have thick compact outer layers because they are subject to prominent bending, shear, and torsional forces. While bones that primarily experience compressive or tensile forces often rely on internal trabecular structures for rigidity, the tubular configuration and thick cortex of long bones provide the necessary strength and rigidity to support weight and function as lever arms.12

This dense compact bone forms a protective shell around the interior cancellous bone, offering greater structural integrity where it is most needed. By utilizing this thick-walled, tubular design, long bones achieve maximal structural support while maintaining a relatively lightweight composition compared to other materials with similar strength, such as steel or aluminum.213