Artificial knee arthroplasty is a technically demanding surgical procedure that requires the pursuit of perfection in detail, otherwise complications are more frequent and require careful design before surgery.
I. Pre-operative diagnosis
Artificial joint replacement surgery results vary from disease to disease. Pre-operative knowledge of the primary disease helps to determine the improvement of post-operative pain, function and deformity; total knee replacement for rheumatoid arthritis has a higher chance of complications than osteoarthritis; severe joint deformity may require the preparation of a special prosthesis.
II. Reading X-rays
High-quality x-rays are valuable for preoperative measurements and should be taken in a neutral position to avoid internal or external rotation of the femur, preferably with pre-marked magnification, a function not available with the digital x-ray machines now commonly used. If the femur is significantly bowed, it may be due to external rotation, and the osteotomy angle of the distal femur will become larger. Excessive external rotation osteotomy should be avoided and can be reviewed by extramedullary positioning. The articular marginal bones will affect the balance of the medial and lateral ligaments and will also affect the size of the osteotomy surface. Posterior joint capsule free bodies will affect postoperative knee extension function and deep flexion.
III. X-ray measurement and template measurement
Full-length radiographs of the lower extremity in the weight-bearing position are helpful in determining abnormal lower extremity force lines, but many hospitals are not equipped to perform this examination. The measurements include the mechanical axis of the femur, the anatomical axis of the femur, and the angle between the mechanical and anatomical axes to determine the intraoperative angle between the osteotomy plate and the intramedullary positioning rod, and the osteotomy surface of the tibial plateau should be perpendicular to the mechanical axis. The medullary entry point is located in the middle of the intercondylar fossa, 5 mm above the posterior cruciate ligament stop. The medial and lateral offset will lead to deviation of the osteotomy surface inward and outward, which is more likely to occur when the medullary cavity is too wide.
IV. Selection of knee prosthesis type
It is important to have a good understanding of the design features and applicability of different prostheses. Knee prosthesis can be divided into surface replacement prosthesis and restrictive prosthesis, cemented prosthesis and non-cemented prosthesis, fixed platform prosthesis and rotating platform prosthesis, normal flexion prosthesis and high flexion prosthesis, posterior cruciate ligament preservation and posterior stabilization prosthesis according to different classification methods. The price of different prostheses varies greatly.
Five, choose the fixation method
Bone cement type fixed bone-prosthesis interface between the mild mismatch can be eliminated by bone cement, non-cement type requires osteotomy nearly perfect. The initial results of the two are similar, the domestic general use of bone cement fixation.
VI. Bone defect treatment plan
A common form of defect in primary replacement is a posterior medial tibial plateau bone defect, often with severe internal knee valgus, while femoral defects are uncommon and severe knee valgus may have a bone defect or hypoplasia of the femoral epicondyle. The management of bone defects depends on the extent and location of the defect and includes cement filling, autologous bone grafting, allograft bone grafting, and assembled metal wedges.
Bone cement filling is suitable for small bone defects up to 5 mm in depth, inclusive defects, and elderly patients, but the biomechanical properties of bone cement are relatively poor and should not be used for large segmental bone defects, especially in young patients, because it cannot restore bone volume.
Autologous bone grafting is suitable for defect depths greater than 5 mm, invasion of more than 50% of the tibial plateau on one side and in young patients. The advantages of autologous bone grafting are easy integration, reliable healing, stability and durability, but limited material extraction.
Allograft bone grafting is suitable for large inclusive or segmental bone defects, without autologous bone or with insufficient autologous bone, but the long-term success of allograft bone fusion with the host bone is uncertain.
Indications for assembled metal wedges include moderate bone defects, elderly and revision patients, but they do not restore bone volume and are expensive.
VII. Type and degree of deformity
Severe valgus deformity and/or joint instability can be treated with a restrictive prosthesis. With improvements in surgical techniques, non-restrictive prostheses are becoming more widely available. Rotating hinge knee prosthesis can be the last choice, which itself has good alignment and intrinsic stability and is relatively simple to operate, but has a high incidence of prosthesis loosening and late infection. Special cases may require some special surgical instruments, which also need to be prepared in advance.
VIII. Functional requirements
Surgical design varies from person to person, and preoperative consideration should be given to both the functional needs of the patient and the realistic and reasonable and economic affordability. A high flexion knee prosthesis is a better choice for patients who frequently squat, kneel, or meditate; a smaller valgus angle of the distal femoral osteotomy is preferable for fat people compared to thin people; for most patients, restoring a painless, mobile, and stable knee joint to achieve self-care is the most basic and realistic requirement.
IX. Patellofemoral plasty and patellar replacement
The available data suggest that patellar replacement and patellarplasty have similar results and are not affected by the degree of patellar degeneration, and that patellar replacement depends on the surgeon’s preference, but patellar replacement is not indicated in the following cases.
the patellofemoral articular surface is essentially normal
Obese patients with a high incidence of patellofemoral pain and complications
Thin patella (less than 18 mm) or severe wear
Young active patients with high risk of loosening
X. Surgery sequence
Bilateral knee replacement surgery can be completed in two separate surgeries, one hospitalization in one separate surgery, or one hospitalization in one phase, depending on the specific situation; for some special cases with simultaneous replacement of the same hip and knee, hip replacement is performed first and then knee replacement.