TIBIAL GLIDE IS CAUSED BY LIGAMENTOUS FORCES.
A first semester student needs to predict arthrokinematics based on the rules of concavity and convexity. The reasons that joint surfaces move the way they do goes beyond our first semester objectives. Those who want to know anyway can consider the fact that joint structure (whether a surface is concave or convex) does not directly produce arthrokinematics. Only forces produce movement.
A previous edition of your text (Smith, Weiss, & Lehmkuhl, 1983, p.55) explains:
- during knee flexion:
- tibia rolls posteriorly, elongating ACL.
- ACL's pull on tibia causes it to glide posteriorly.
- during knee extension:
- tibia rolls anteriorly, elongating PCL.
- PCL's pull on tibia causes it to glide anteriorly.
Source:
Smith, L.K., Weiss, E.L., & Lehmkuhl, L.D. (1983). Brunnstrom's Clinical Kinesiology. (4th ed.). Philadelphia: F.A. Davis.