Pain on either sides of the knee is usually related to meniscal tears,
injuries to the collateral ligaments, and even to arthritis.
Ligament injury causes pain to worsen on walking, bending and stretching the knee. Meniscii too if torn or injured cause pain worsening on walking and result in joint instability—that is you are not confident the knee joint will take your weight. Often the person feels a popping sensation on moving the joint.