The knee joint is the most complex and functionally demanding joint in the body and the most susceptible to disease and injury. The vast majority of people will suffer from a knee injury or illness during their lifetime. To avoid, reduce or alleviate these problems, we need to start with the prevention, treatment and rehabilitation of knee injuries and diseases. First, the basic structure and function of the knee joint The human knee joint is simply composed of three bones, four sets of ligaments and two washers. The three bones are the upper thigh bone (femur), the lower leg bone (tibia), and the front knee bone (patella), all of which have a layer of cartilage on the surface that significantly reduces friction between the bones when moving. The thigh bone and calf bone constitute the femur-tibial joint, which transmits gravity when a person is standing and bearing weight. There is a groove in front of the thigh bone, and the kneecap forms the patellofemoral joint, and the kneecap moves along this groove during knee movement. The patellofemoral joint is subjected to a greater load during semi-squatting activities. The four groups of ligaments include the anterior cruciate and posterior cruciate ligaments, which form a cross in the middle of the knee joint, and the medial and lateral ligament structures located on either side of the knee joint. These four groups of ligaments connect the thigh and calf bones together and maintain the relative stability of these two bones during knee motion. Injury to any of these four groups of ligaments can cause instability in the joint and have an impact on daily activities and sports. In the joint space formed by the femur and tibia, there is a piece of cartilage on the inside and outside that acts as a gasket to protect the knee joint. This cartilage is called the meniscus because it is shaped like a crescent in most people. Second, the prevention of knee injuries and diseases Knee injuries and diseases occur either with developmental abnormalities or with improper sports or rehabilitation care. At different ages, there are different types and characteristics of the onset of the disease. Therefore, the prevention of knee injuries needs to recognize these characteristics and thus be targeted. 1, the characteristics of adolescent knee injuries and protective measures Adolescent joint cartilage, ligaments, meniscus are in the best condition, knee injuries are mainly related to improper sports. One of the most frequent is the anterior cruciate ligament injury. Compared to professional athletes, the incidence of ACL injuries is higher in the general sports population. This is mainly due to the lack of warm-up and self-protection of the average sportsperson. The stability of the human knee depends on the integrity of the ligaments and the coordination of the muscles. Inadequate warm-up, when muscles and ligaments are needed to protect the knee joint in concert, the muscles do not respond and fail to provide protection in a timely manner, which can cause injury to the ACL due to excessive stress. In addition, the lack of awareness of ACL protection and lack of understanding of protection techniques by the average sports enthusiast is also a major cause of ACL injuries. ACL injuries are most likely to occur during jump landings and sharp turns, when the foot lands first and is relatively fixed, but the upper body continues to rotate, resulting in a load that exceeds the ACL’s ability to withstand. Although ACL injuries are inevitable, research has shown that some conscious training can help reduce the incidence of ACL injuries. These include proper jump landing techniques (especially soft landing techniques with forefoot, knee and hip flexion), proprioceptive and neuromuscular training, and training to avoid extreme joint valgus during jump landings and squats. It is the nature of adolescents to enjoy sports, but there are some congenital or developmental abnormalities that make some people unsuitable for certain sports. For example, patients with unstable kneecaps are not suitable for sports that require half-squats, and patients with meniscal disc deformities are not suitable for prolonged weight-bearing exercises. Patients with congenital ligamentous laxity are not suitable for sports that require sharp stopping and turning movements. Therefore, for young people who like to play sports, it is important to go to the doctor for examination and consultation to understand the characteristics of the main structures of the knee joint and to have an idea of the appropriate and unsuitable sports or movements. 2, the characteristics of middle-aged knee injuries and protective measures people in middle age, often realize the importance of recreational sports, will consciously do some fitness exercises. However, clinically, we often encounter patients who do not exercise well, a movement of the knee joint pain instead; also often encounter deep squat training caused by medial meniscus injury, practice horse stance squat crotch caused patellar cartilage damage, a transient excessive exercise caused synovial inflammation patients. This is related to the structural state and relative overuse of the joints in middle-aged people. The articular cartilage and meniscus of the middle-aged have degenerated to some degree. The cruciate ligaments are not only degenerating, but they are also being rubbed by the adjacent areas of enlarged bone, which decreases their strength. Inappropriate training, even for recreational sports, can be counterproductive and cause injury. Middle-aged people should pay attention to the following points when training: First, do not advocate middle-aged people to carry out bodybuilding training. Bodybuilding training is for certain muscle mass training, the overall function of the limb does not help much, but will cause damage to the end of the tendon and cartilage damage. For example, resistance knee extensions, whether done on an exercise machine or at home with weights on the ankles, do increase the strength and fullness of the quadriceps, but they do cause pain behind the patella (caused by worn patellar cartilage) and pain below the patella (caused by strain on the quadriceps and patellar tendons). Simple comprehensive training such as running and appropriate bouncing can increase the overall function of the lower extremity without causing damage. Secondly, it is not advisable for middle-aged people to perform half-squats and climbing exercises. In the knee joint half squat, especially the single knee weight-bearing half squat, the patellofemoral joint to withstand three times the weight of the stress, the more half squat activities, the faster the patellofemoral joint degeneration. Sports involving half squat activities include taijiquan, mulanquan, table tennis, etc. Taijiquan, in particular, is more damaging to middle-aged and elderly joints. In addition, going up and down stairs, going up and down hills, and climbing mountains also involve bending the knee to bear or exert force, when the patellar cartilage is also subjected to excessive stress. Those who take climbing hills or stairs as a kind of training often lose more than they gain, and end up having difficulty climbing hills and stairs very early. Third, middle-aged people need to train gradually. Often people do not exercise for years, and suddenly go to practice for a few hours on a whim, resulting in joint pain for months or even years. Middle-aged people because of cartilage degeneration, the cartilage’s ability to withstand limited. Therefore, all kinds of exercise should follow the principle of gradual progress, to give the various structures of the joints a chance to adapt. In terms of training, middle-aged people are first suitable for small load training of the joint, such as sitting knee extension and flexion activities, cycling (including small load fitness bicycle), swimming, etc.; followed by running, bouncing and other holistic training. 3, the characteristics of the elderly knee injuries and protective measures The degeneration of the joints is inevitable when people grow old. This degeneration is manifested firstly in the wear and tear of the articular cartilage, secondly in the degeneration and damage of the meniscus and synovial hyperplasia. Bone growth, as previously described, is a manifestation of joint degeneration on X-rays, but bone growth in the knee joint is not the main cause of joint pain at all. Joint pain is mainly caused by the wear and tear of the cartilage and the exposed friction of the subchondral bone. The aging of the joints is a natural process that varies from person to person, but all we have to do and can do is to slow down the aging of the joints and reduce the symptoms of aging. For older knee joints, not exercising residual cartilage without nutrition will accelerate degeneration, while overtraining will accelerate wear and tear on the joint. So the key is to get the right degree. The state of joint cartilage is different for each elderly person, and so is the appropriate type and intensity of exercise. Medical examination and exercise counseling are also necessary. In terms of joint protection, the first contraindication for middle-aged people is also a contraindication for the elderly. Sitting knee extension and flexion activities, stationary bicycles and swimming are suitable for the elderly, but prolonged walking and running are not. The elderly are contraindicated to do the exercise of flexing the knee and hip back and forth and shaking the knee joint, this exercise will intensify the wear and tear of joint cartilage, causing a sudden increase in pain. 1, knee injuries, “exercise exercise on the good” When we encounter a variety of knee injuries, the most like to hear the doctor said “exercise exercise on the good”, some people will also specialize in finding “talk to the right way Some of us even go to doctors who “talk the right way”. In fact, a considerable number of patients exercise exercise not only will not be good, but will aggravate, and even cause serious consequences. Suitable for surgery and not suitable for exercise of many kinds of diseases, including the following four most typical. First is the anterior cruciate ligament injury. The ACL is the structure that maintains the stability of the knee joint during exercise. Injury to this structure can cause varying degrees of knee dislocation when we run, jump, stop, turn, or even walk quickly. This misalignment can cause falls and a sense of instability in the knee, but in some cases it is not clearly felt by the patient, while the meniscus and articular cartilage continue to sustain damage, eventually causing irreversible damage. After an ACL injury, “exercising” will not only not help, but will cause the joint to degenerate at a rate several times faster than normal. Therefore, when you have an ACL injury and cannot receive surgery in the near future for various reasons, the only “cure” is not to run, jump, or walk fast. However, with the improvement of ACL reconstruction, especially the adoption of double-bundle reconstruction with eight tendons, the success rate of ACL reconstruction has increased from 85% in the past to over 98%, and fewer doctors are advising patients to “exercise” and fewer patients are willing to “exercise”. Fewer and fewer patients are willing to “exercise”. The second is posterior cruciate ligament injury. Posterior cruciate ligament injury will cause squatting and standing, up and down the stairs, up and down the slope weakness. Targeted quadriceps functional exercise has a compensatory effect on posterior cruciate ligament insufficiency. However, for patients with posterior cruciate ligament injury causing more than two degrees of joint instability, relying on quadriceps compensation without ligament reconstruction to restore knee stability will lead to premature aging of the knee joint, resulting in more serious difficulties in squatting and standing, going up and down stairs, and going up and down slopes. In the past, patients were advised to “exercise” mainly because doctors were not sure about the success rate of posterior cruciate ligament reconstruction (early success rate was indeed less than 60%); nowadays, the success rate of posterior cruciate ligament reconstruction is comparable to that of anterior cruciate ligament reconstruction, so there is no need to delay treatment for technical reasons. Third, it is a discoid meniscus deformity. The discoid meniscus is not protective but destructive to the joint because of its abnormal shape, texture and movement in the joint. People with discoid meniscus deformity “exercise exercise” will aggravate its damage to the cartilage. It is common for patients to know that they have a discoid meniscus deformity but do not restrict movement, resulting in severe cartilage damage. Those who have a popping sound near extension of the knee are at greatest risk of cartilage damage. For a discoid meniscus, it is ideal to change the meniscus to a normal form early on through a plastic surgery, which makes the meniscus not only protective of the knee, but also less likely to damage the meniscus itself. Fourth, for patellar instability. When the patella is unstable, the patella does not move along the groove (femoral carriage) underneath the knee joint, but is on the edge of the groove, and the patella is in point contact with the cartilage of the femur below instead of face-to-face contact. Until the patella is surgically repositioned and maintained in the groove, any exercise will increase cartilage wear, exacerbate the tendency for patellar dislocation, and even cause recurrence of the dislocation. Restoring the position and stability of the patella relative to the femoral glide through comprehensive corrective and reparative surgery is imperative. In addition, the knee joint has a function called proprioceptive function. Under normal circumstances the nerve center is able to sense the extension and flexion position of the knee joint and the stresses it is subjected to through this function of the knee joint. This function facilitates the coordination of the muscles during exercise and the protection of the ligaments by the muscles. The proprioceptive function is disturbed when the knee joint has problems that cannot be solved by “exercise” as described above. Exercise before the injury is treated can exacerbate the proprioceptive disorder, thereby slowing the recovery of proprioceptive function after treatment. Like the further you go on the slanted road, the later you turn back to take the right path. 2, knee injuries, “rest and rest will be fine” On the contrary, there are some injuries without serious organic damage, but the more rest the worse. For example, soft tissue contusion of the knee, medial collateral ligament first and second degree injury, cartilage contusion, bone contusion. These injuries do not cause serious dysfunction, but resting can cause dysfunction instead. Timely functional exercise helps to soften the fibrosis, increase the compliance of the knee joint, reduce the stiffness and restore the mobility of the joint. Failure to exercise in a timely manner after a traumatic knee injury can result in a specific reaction called bone atrophy, or disuse osteoporosis. Patients with osteoporosis experience more severe pain in the knee joint when weight-bearing activities are performed, and this pain can make the patient even more reluctant to train with weight, causing further osteoporosis. The only way to break this vicious cycle is to tolerate the pain and to prevent bone atrophy is to perform functional exercises early. On the other hand, articular cartilage draws nutrients from the joint fluid during proper activity, and resting not only does not protect the cartilage, but also deprives it of nutrients and accelerates its degeneration. Therefore, when it is determined that there is no organic pathology, you cannot rely on rest to maintain the disease, otherwise the more you maintain, the heavier it becomes. The purpose of knee surgery is to repair and reconstruct the knee joint, but after the repair and reconstructive surgery, it does not mean that the joint function can be restored, but only marks the beginning of the recovery of the knee function. The ideal recovery requires overcoming physical and psychological barriers and appropriate rehabilitation. A key aspect of this is pain tolerance rehabilitation. Pain after knee surgery has its inevitability. Firstly, the primary injury will not heal immediately after surgery, and secondly, the surgery itself inevitably brings new injuries, and the post-operative pain will not go away immediately, and may even increase. For example, knee ligament reconstruction surgery. When the knee ligament is injured, other tissue structures around the joint will not be intact, and the joint capsule, synovium, articular cartilage, and bone marrow will all be disturbed by the trauma, and the diagnosis of knee ligament injury is only a primary diagnosis. When we perform repair and reconstruction surgery, we need to cut through the soft tissue (although sometimes the window is small), make holes in the bone, and pull in the new ligaments to fix them. This is bound to cause new trauma and bring new disorders. At the end of the surgery, the soft tissue and bone disorders are far from over. Some disorders may last for months, years or even a lifetime. Joint adhesions can develop after surgery, increasing pain and difficulty during exercise. So there is a potential source of pain in the knee joint after surgery. However, after the major functional structures of the knee have been repaired, it is impossible to wait until the knee is free of any pain before rehabilitating it, otherwise the joint may lose its function and the repair and reconstruction surgery would be pointless. Pain tolerance training is a basic requirement. The rehabilitation process varies from injury to injury and from surgery to surgery, and the rehabilitation plan is designed to ensure that the reconstructed structure is not damaged, so the patient can train in a step-by-step manner. Those who are able to tolerate pain and follow the rehabilitation program to the letter (without going beyond the established program) tend to have the most optimal recovery.