Tendons, as the name implies, are the tendinous tissues at the ends of muscles, commonly found, for example, in the Achilles tendon at the back of the calf, the quadriceps tendon in front of the thigh, and the biceps tendon in front of the upper arm. Because the middle is muscle, it is conceivable that ligaments and muscles combined together can produce elongation and shortening. The biggest difference in morphological structure between ligaments, and tendons is that there is no muscle, many are lamellar or rope-like, and their overall length is usually essentially fixed. Tendons and ligaments have an important feature in common, that is, both ends are basically connected to the bone, and both play a role in traction and stability. But as mentioned earlier, one can stretch and the other cannot, so there are two different roles: tendons and muscles together can make the joint stretch and flexion activities, we can work, movement; tendons are mainly to maintain the stability of the joint, like a rope twisted into several strands, and strong, there is a little elasticity, the joint ends of the bone tethered together. Because the structure and role of the two are different, of course, after the rupture of different performance: imagine, the tendon rupture, it will make the joint activity function worse, for example, the Achilles tendon rupture, the heel can not lift up (medical called ankle plantarflexion function is limited); and ligament rupture, the joint will produce the feeling of instability, for example, the anterior cruciate ligament rupture, can cause repeated sprains during sports. By the same token, after a tendon rupture, because there is a muscle end can continue to contract, it may pull the rupture site during activity, resulting in pain, such as tennis elbow caused by partial tendon rupture, rotator cuff tears sometimes pain are such; and after a tendon rupture, because there is no contraction of the problem of activity, so generally will not produce pull, and will rarely appear such symptoms as pain (of course, acute injury When there is an acute injury, that is, when the tendon has just been ruptured, there is usually pain due to innervation damage or bleeding and swelling, but when the swelling subsides, there is usually no pain). Therefore, after a period of time (usually 2-3 weeks) after an ACL rupture or patellar dislocation (medial patellofemoral ligament rupture in medical practice), there is no pain. Any pain within the knee thereafter is basically caused by problems with other intra-articular structures.