First, the osteotomy easy to make mistakes on the side of the femur common mistakes 1, the femur external rotation osteotomy easy to make mistakes the so-called femur external rotation osteotomy is the knee prosthesis femoral posterior condyles designed at the same level, by Insall proposed a simplified prosthesis design and manufacturing process, and to facilitate the operation of the femur osteotomy method, that is, “Insall line external rotation osteotomy The “Insall line external rotation osteotomy” method. It operates by performing a horizontal osteotomy of the tibial plateau on a horizontal line and then bending the knee at 90° parallel to the tibial osteotomy surface to perform osteotomies of the anterior and posterior femoral condyles. This method is very scientific, but it lacks practicability, because during the osteotomy the femur is not rotated enough due to the difference between the medial and lateral tensions (medial tension is greater than the lateral tension). Westerners have studied the knee joint in Western populations and have concluded that after 3° of external rotation of the internal and external posterior condylar line of the femur, it is possible to achieve consistency with the Insall line. Therefore, many companies have designed femoral osteotomies that utilize a posterior condylar positioned rotational osteotomy, i.e., an externally rotated osteotomy with 3° of external rotation from the line of the posterior condyle of the femur. This is a kind of compromise designed for Westerners’ knee anatomy, and it is obvious that this method of osteotomy will not be suitable for all patients, and will lead to obvious deviations due to the differences in anatomical characteristics between Chinese and Westerners. We often find that after femoral osteotomy using this osteotomy method, there is often tension in the lateral patellar support band. As a result, the operator often uses a lateral patellar support band release method for re-correction of the patellar trajectory. Therefore, an externally rotated 3° osteotomy cannot always be used in femoral rotational osteotomies, and there are several other reference axes for femoral externally rotated osteotomies, such as the A-P axis, Whitesside’s axis, Clinical epicondylar axis (CEA, clinical intercondylar axis), and the Surgicalepicondylaraxis (SEA, surgical intercondylar axis). The best external rotation osteotomy should be personalized, and according to our research over the years, a relatively personalized external rotation osteotomy should refer to the femoral SEA. 2. Anterior over-rotation osteotomy This is a low-level error, but it happens occasionally even to doctors who have done a lot of TKA. There are two reasons for this: (1) the femoral osteotomy positioning rod is placed in the wrong position, the medullary positioning is backward or inserted into the medullary cavity is too shallow, and the distal end of the positioning rod is not inserted over the narrow part of the femur; (2) the femoral osteotomy plate osteotomy thickness hook is placed on the upper part of the femoral osteotomy plate, or it is not placed in the anterior-lateral ridge of the femoral condyle-trunk migration. For some “experienced” doctors, such mistakes are mostly due to the pursuit of small incisions, can not under direct vision for the femoral open marrow hole blind drilling. 3.Failure to recognize femoral deformity Whether congenital or acquired, femoral deformity is very common. It is not uncommon for TKA operations to be performed incorrectly due to femoral stem or femoral condyle deformity. Therefore, it is extremely important to take a full-length film of the lower extremity in the weight-bearing position, or at least of the femoral stem, prior to surgery. This is necessary for designing the surgical plan and minimizing osteotomy errors. Tibial side common errors 1, tibial anatomical variations through the lower limb full-length film or tibial full-length film can be taken to find the tibia congenital developmental curvature and acquired deformity. In addition to taking full-length films, extramedullary localization of the tibia is an effective way to avoid osteotomy errors. Both congenital and acquired deformities can usually be detected and corrected intra-articularly by means of extramedullary localization when the tibial stem is angulated laterally at 10° or less. When the tibial stem deformity exceeds 10° or when torsional angulation occurs, intra-articular correction is often ineffective, and extra-articular osteotomy correction is required. When the tibial deformity is corrected, TKA can be performed. 2.Low joint line and high patella this situation is mostly caused by too much tibial plateau osteotomy. When the platform bone defect occurs, the surgeon seeks a complete osteotomy surface in order to avoid bone defect after osteotomy, so the thickness of the tibial osteotomy is increased, which results in the appearance of low joint line and high patella. 3.High joint line and patellar tamponade is most commonly caused by the use of thick polyethylene spacers when the tibial osteotomy is too small. When there is a heavy flexion deformity, it is usually easy to have insufficient knee extension gap after conventional osteotomy, and the operator prefers to increase the osteotomy of the distal femur in order to obtain equal flexion and extension gaps. The removal of the osteochondral bone is followed by excessive laxity, which often requires the selection of a thicker polyethylene spacer to maintain joint stability. This solves the problem of joint stabilization, but results in joint line migration and a low patella. Low patellas often result in “patellar tamponade” when the knee is flexed beyond 90°. The way to avoid these mistakes is to perform equal osteotomies (i.e., place a polyethylene liner as thick as the bone is sawed off) regardless of whether the patient has a flexion deformity or a plateau bone defect. Errors in soft tissue balancing are traditionally understood to be the release and reconstruction of ligaments and joint capsule, especially the core meaning of soft tissue balancing is to release contractured ligaments, which is in fact an incomplete understanding of the soft tissue balancing theory of TKA surgery. It is gratifying that many scholars nowadays have recognized that the so-called soft tissue balance is not only the treatment of soft tissues, and recognized that the bone ligaments are also an important factor affecting the soft tissue balance, so many people advocate the complete removal of the ligaments when dealing with them. It is important to understand that ligaments are histologically parallel aligned fibers, and this tissue does not actively contract, but it can be “stretched”. There are two reasons why we see ligament “contractures”: 1) there is scarring around the ligament, which causes the ligament to contract; 2) there are bony encumbrances around the ligament, which support the ligament and cause it to become tense. In the former case, cleaning up the scar will get the ligament loosened. In the latter case, although we can see that the support of the osteophytes will make the ligament tense, on the other hand, the long-term support of the ligament by the osteophytes will also “stretch” the ligament. If the bony structures are surgically removed, the ligaments that have been “stretched” will become lax from their original tightness. The ligament laxity will have a new effect on the soft tissue balance, and this ligament laxity will be more difficult to deal with than its tension. Therefore, I propose the theory of limited removal of the bony ligaments. Instead of completely removing the ligaments at once, leave some of the ligaments in place (mainly on the plateau side), so that the retained ligaments will continue to support the ligaments that are already pathologic after laxity, and so that they will continue to maintain the tension needed for the surgery. Third, the prosthesis is easy to make mistakes PS and CR prosthesis differences between the two types of prosthesis due to different design concepts, so the principle of surgery will not be the same, must not be used to do the PS prosthesis surgery for CR prosthesis surgery. 1, the posterior tilt characteristics of the two prosthesis femoral components and polyethylene liner shape of the degree of difference, especially the MBCCR platform due to the high posterior lip of the polyethylene liner, and therefore require a larger platform posterior tilt, and at the same time, postoperative knee joints should be maintained in a certain degree of tension, and should never be made to the knee can not be overextended. 2, “patella-friendly” type prosthesis is not necessarily patella-friendly so-called patella-friendly prosthesis is characterized by the femoral component of the patellar surface of the “concave channel” is deeper, there is the so-called patella physiological movement track. However, this can only be effective if the patella is placed in a normal physiologic position. If the patella can not be put into its physiological position, the role of the track will force the patella can only be designed in the prosthesis track movement, it seems that the patella in the femoral prosthesis position is very good, but in fact, it is forced to accept the prosthesis track guidance, which will make the patella side of the stress doubled, which leads to patellofemoral pain. Fourth, the suture is prone to error when talking about the suture may be many people think that there is no technical content, in fact, otherwise the details of the suture will determine the postoperative effect. Flexion position suture (from the inside and outside) is a good method, this position will be easier to flexion exercise, will not affect the flexion exercise due to the pain caused by the pulling of the suture. V. Mistakes in rehabilitation 1, about the knee function exercise machine (ContinuousPassiveMotion, CPM machine) Many people like to use the CPM machine after TKA, thinking that it will help the patient to restore the mobility of the knee joint. In fact, it is inappropriate to use a CPM machine immediately after surgery because the joint trauma and surrounding tissues have not healed after surgery. The knee is not stiff after surgery, and the reason for the patient’s hypermobility is due to pain. If CPM is used at this time, bleeding and swelling will occur due to repetitive knee movement, which will seriously affect the recovery after TKA. Therefore, we recommend not to use CPM machine within 6 weeks after TKA. 2, different types of prosthesis postoperative rehabilitation methods are different, different types of prosthesis have different rehabilitation characteristics. CR prosthesis makes the joint space slightly tense due to the surgery, so we need to strengthen the knee extension exercise after the operation; while PS prosthesis makes the rotation almost no when the knee is flexed 30 times before due to the role of POST, which has a greater impact on the patellofemoral joint, so we should pay attention to the passive flexion of the knee, and should not force the knee to be flexed. If the patella is not handled properly, the “patella-friendly” type of prosthesis is more problematic in rehabilitation, as the restriction of the prosthesis on the patella can cause pain when flexing the knee. Therefore, in the early postoperative period, the patella-friendly prosthesis should not be used for strong passive knee flexion, and should not be used for “cross-legged” movements. 3, about weight-bearing squatting error many people in the rehabilitation process to make the patient do “horseback squatting crotch type” or even squatting, this kind of exercise method is not a big problem for high flexion type prosthesis, but for the conventional prosthesis is not suitable. This exercise is not a problem with high-flexion prostheses, but is not appropriate for conventional prostheses, because weight-bearing in high-flexion increases the wear on the posterior aspect of the polyethylene liner and, in the case of PS prostheses, also increases the wear on the POST. Therefore, squatting is not recommended after TKA, but it does not interfere with non-weight-bearing exercises in high flexion (which will not damage the prosthesis), and the squatting function is only a reserve function.