Introduction

In molecular biology, a common way to test the function of a protein or other cellular component is by "knocking it out." Cells are somehow blocked from producing the protein and the resulting phenotype gives you an indication as to what the function of that protein is. For example, if the cell has membrane abnormalities, you have a clue that the protein may help to form the cell membrane. This is the traditional "Knockout" experiment: an abnormal result gives you a clue about the normal function.

In this activity, you'll apply this same principle to determine the function of each of the knee ligaments. Why is it important to know the functions of the knee ligaments? A ligament's function istells directly related toyou both itshow potentialit forcan injurybe injured and the effectloss of function that results from its injury. For example, if a ligament functions to limit the range of rotation at a joint, rotating the joint beyond that limit will injure that ligament in the form of a strain or tear. And once that ligament is strained or torn, it can no longer function properly to limit that rotation, causing either pain, instability, or both. So, to understand  the cause and consequence of, say, an ACL injury, you need to first understand the function of the ACL.

A ligament's function tells you both how it can be injured and the loss of function that results from its injury.