Tendons, as the name implies, are the tendinous tissues at the ends of muscles, such as the Achilles tendon at the back of the calf. The quadriceps tendon in front of the thigh. The biceps tendon in front of the upper arm, etc. Since the muscle is in the middle, it is conceivable that ligaments and muscles can be combined together to 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. However, as mentioned earlier, one can stretch and the other cannot, so two different roles are created. Tendons and muscles work together to produce extension and flexion of the joint so that we can work. The tendon is mainly to maintain the stability of the joint, like a rope twisted into several strands, but also strong and slightly elastic, 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, when a tendon is ruptured, because the end of the muscle can continue to contract, it may pull on the ruptured area during activity and cause pain, such as a partial tendon rupture due to tennis elbow. This is sometimes the case when the rotator cuff is torn, but when the tendon is ruptured, there is no contraction, so there is usually no pulling, and there is rarely any pain (of course, when there is an acute injury, that is, when it is just 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.