In bipeds, there is a right angle between the tibial shaft and its proximal surface. In modern humans, the medial and lateral proximal articular condyles are more similar in size, more concave, and more elliptical in shape compared to quadrupeds which tend to be more spherical and more convex. The size of the lateral proximal condyle is larger in bipeds to adapt to increased weight transfer from the femur to the foot. The elliptical shape helps lock the knee in place and create a straighter forward leg movement.

The articular surface at the distal end of the tibia is oriented more inferiorly than the antero-inferior orientation seen in quadrupeds, resulting in a straighter foot path during walking.

Chimpanzees retain smaller lateral proximal condyles and the shaft lies at more of an angle to the proximal surface of the tibia. The australopith tibia has a nearly angle between the tibia’s shaft and proximal surface, and the distal end is oriented more inferiorly, as seen in modern humans.