While both the cartilage and tendon are soft tissues in the knees, they play different roles. The tendons are the very strong, fibrous tissues that attach muscles to bone. They are what allow you to move you knee back and forth - and have it stop where it should. They also help your knee maintain its stability. The cartilage joins two bones together, acting almost like a tether.
Cartilage often acts as a shock absorber in the joints and also as a stabilizer, keeping the joints steady. If a cartilage is torn, there could be friction between the joint bones and pain results. Long-term damage could be arthritis developing in the joint.