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 flex, so we can work and move; tendons are mainly to maintain the stability of the joint, like a rope twisted into several strands, and strong, with a little elasticity, the bones at both ends of the joint tethered together. Because the structure and role of the two are different, of course, after the rupture of different performance: imagine, after the tendon rupture, it will make the joint function worse, for example, after 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, after the anterior cruciate ligament rupture, it can cause repeated sprains during sports. By the same token, after a tendon rupture, because the end of the muscle can continue to contract, it may pull on the rupture site during activity, resulting in pain, such as tennis elbow, which causes partial tendon rupture, and rotator cuff tears, which sometimes cause pain; while after a tendon rupture, because there is no problem of contraction activity, so there is generally no pull, and there will rarely be such symptoms as pain (of course, acute injury When the tendon is ruptured, that is, when it 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), a ruptured ACL or patellar dislocation (medial patellofemoral ligament, in medical terms), there is no pain. Any pain within the knee thereafter is basically caused by problems with other intra-articular structures.