What constitutes the knee hinge joint?

The knee joint is primarily classified as a hinge joint, which allows for movement mainly in one plane, akin to the action of a door hinge. The correct answer highlights that the knee joint consists of the femur and tibia, which are the key bones that articulate to form this joint. This structure allows the knee to perform flexion and extension movements, which contribute to walking, running, and various other activities.

Additionally, the mention of "2 degrees of freedom" is significant because, while the knee primarily allows flexion and extension, it also has a small degree of rotational movement when in flexion, which is essential for a range of functional activities, such as pivoting. This characteristic distinguishes the knee joint from simpler hinge joints that offer only one degree of freedom.

In contrast to this, other options refer to combinations of bones that do not accurately represent the main structural components of the knee joint or miss establishing the joint's functional characteristics. For example, the fibula does not directly participate in the hinge function of the knee joint; the patella mainly serves as a stabilizing structure but does not join in the main hinge action between the femur and tibia. Overall, option B accurately encompasses both the anatomical components and the functional capabilities