Popliteal pain, a very common phenomenon after knee surgery, yet it is often a difficult problem to solve and causes a lot of pain to the patient. I discovered this problem in my first year of work, and over the next 3 years, I came into contact with hundreds of patients with popliteal pain symptoms. Through analyzing and treating these hundreds of cases, as well as consulting with many surgeons and rehabilitators and referring to the relevant literature, I finally summarized the problem of popliteal pain into the following 6 common conditions, and made an analysis and treatment for each of them. Most of these conditions are analyzed logically and empirically, and there is a lack of effective data support, so there is still room for improvement in terms of science. Please give your valuable opinions and exchange with each other. I. Foreign body During the surgical operation, there will inevitably be bleeding, and some microscopic magnitude of debris, and the bleeding and debris will settle near the posterior joint capsule due to gravity, causing a local inflammatory reaction, which then triggers popliteal fossa pain. The location of this pain is usually not clearly defined in one spot, but rather a widespread patch. Moreover, the pain can be relatively constant and does not vary with the flexion and extension activities of the joint. The nature of the pain is often vague. The solution is mainly through rest, physical therapy, or some medications prescribed by the doctor to reduce inflammation, and the pain will be gradually relieved when the inflammation disappears. For ACL reconstruction, the positioning of the upper and lower bony tracts is very critical. If the points are out of alignment, the ligament stabilization effect will be poor in the light cases, and in the heavy cases, the ligament may not be equally spaced and affect the joint function. In the case of the femoral tract, it is usually located at the posterior edge of the medial femoral epicondyle near the cartilage, and since the point is sometimes very close to the posterior joint capsule, it may irritate the surrounding tissues and cause popliteal fossa pain. For this type of pain, there is no particularly effective way to treat it during rehabilitation. Third, entrapment In the knee joint, due to long-term restricted movement, some normal spaces can grow other tissues, such as synovial membrane or scar, causing occupancy. The posterior joint capsule portion of the occupancy becomes squeezed and stuck during knee flexion, which then causes pain. This pain is often sharp and becomes more pronounced as the angle of flexion increases, and disappears immediately upon straightening the knee joint. In this type of condition, prevention is more significant and requires achieving the required joint angle within the prescribed time to avoid the development of an occupancy. For those who have already developed a dominant position, it is necessary to frequently do some posterior joint capsule stretching, such as passive knee extension, so that the posterior tissue elasticity gradually increases and increases the posterior space. We all know that during normal knee flexion, the tibia and femur are rolling and sliding in a complex motion. However, for the knee joint with long-term activity restriction, the soft tissue elasticity of the joint is not good, so during knee flexion, it is very easy to change to a simple rolling pattern, which directly causes a sudden increase in pressure at the back of the joint and then causes pain. This pain, although also increasing with the angle, is not sharp, but rather a dull pain, unlike the previous condition. The location of the pain is usually the entire popliteal portion and is not deviated. The solution to this type of pain is twofold. One is to increase the posterior glide of the tibia through arthrodesis techniques (mainly the posterior tibial glide technique), which coincides with the theory underlying arthrodesis, the “law of convexity and concavity”. The second is to encourage the patient to increase the strength of the posterior femoral muscles, which can also increase the posterior tibial glide. It is important to note that extra care should be taken in patients with posterior cruciate ligaments. V. Tendon Removal For many ligament reconstruction procedures, the hamstring tendon needs to be removed to reconstruct the ligament. So this also inevitably results in pain at the popliteal fossa. This type of pain has the following two distinctive features: firstly, the pain is mainly soreness and swelling, similar to the pain of muscle strain. Second, the location of the pain is the medial popliteal fossa, sometimes radiating to the mid-thigh. This type of pain usually does not last long, but should not be taken lightly because many patients feel most comfortable with the knee in a slightly flexed position, but over time, scar healing will form at the tendon extraction site, which will seriously affect the normal muscle elasticity and cause limited knee extension in the later stages, so in the early postoperative period, patients should be educated to tolerate this pain as much as possible and practice passive knee extension. Sixth, micromovement There is actually an inconspicuous joint —- upper tibiofibular joint on the lateral side of the knee against the bottom. During normal knee flexion, the upper tibiofibular joint will move slightly to match the knee movement. However, in knees with prolonged restriction of motion, the upper tibiofibular joint will gradually lose its micro-movement. Eventually, the upper tibiofibular joint does not compromise during flexion, and pain ensues. This type of pain is usually concentrated near the fibular tuberosity, and the pain is also sharp and sometimes pops. The treatment is to do a corresponding release of the upper tibiofibular joint and to do an oblique anterior-posterior sliding of the fibular tuberosity. The above six situations are a little bit of experience that I have summed up in the last few years. I hope that it will be helpful to patients and to rehabilitation practitioners, and I also hope that there will be more people and sum up more ideas.