If a tibial extension is used during the primary knee arthroplasty, then, during the revision surgery, it will have to be removed and replaced with a new extension. The need for reoperation, or revision surgery, is about 14–15%, and almost 44% of them may require more than two supplementary interventions. This can further weaken the implant’s fixation, requiring the implantation of a new prosthesis. The presence and configuration of the tibial extension (size and mode of fixation) can determine a phenomenon known as stress shielding, leading to bone loss in the areas where it is higher. Moreover, a good alignment helps to balance the forces transferred to the soft tissues, which are essential for proper joint mobility. This can reduce both the mechanical stress forces on the bearing surfaces and the shear forces at the bone–cement and bone–prosthesis levels. It is crucial for the survivorship of the implant to achieve a very good alignment of the femur, tibia, and patellar components of the implant during the total knee replacement surgery. Moreover, there is the case of some unexpected intraoperative events that may require additional implant fixation. Medical practice reveals the following situations of a complicated primary TKA where a stem can be effective: when the bones have altered physical properties created by various diseases (osteoporosis, osteoarthritis, and rheumatoid arthritis), when the patients have extreme varus–valgus deformities, when there is a pre-existing proximal tibial defect, when there is a previously performed corrective osteotomy, when there is a large proximal tibial defect or necrosis, when the bones have malunited fractures, and in the situation when the patients’ particularities such as age or lifestyle overexert the implant. Tibial extensions have different lengths and widths and can be fixed in different ways, either by full cementation, only proximal cementation, or press-fit, without cement. The role of a tibial stem in the primary TKA is to enhance the stability of the implant in complicated cases this is achieved by reducing micromotions at the bone–implant interface and, as a result, the risk of aseptic loosening, which is one of the main causes of failure. The most common problems that appear after total knee replacement surgery are wear of the polyethylene insert and loosening of the femoral and tibial components, or even their breakage. Knee arthroplasty: ( A) Tibial bone with prosthesis, laboratory model, ( B) Postoperative radiograph ((1) femoral metal implant, (2) polyethylene spacer, (3) tibial metal implant, and (4) tibial stem extension). Conclusions: It was concluded that, if the bone is healthy and has good structural properties, it is not necessary to use the tibial extension in the primary operation and if the bone has diminished physical properties, it is necessary to use the tibial extension at the primary operation, enhancing the stability, fixation, and implant lifespan. Dynamic compression showed slightly better results with the tibial stem in both healthy and degraded bone. Compression fatigue was reduced to almost half in the case of altered bone when adding a stem. Results: The maximum stress and displacement values in the static compression regime show that adding a stem is only beneficial to structurally altered bone. Using finite elements (FEs), the virtual model of the tibial bone was connected to that of the prosthetic implant, with and without a stem, and its behavior was analyzed during static and dynamic stresses, both in the situation in which the bone had normal physical properties, as well as in the case in which the bone had diminished physical properties. The following question arises: which situation requires the use of a standard configuration implant (without a stem) and which situation requires using the extension? Materials and Methods: The opportunity to use the tibial extension in the primary TKA was analyzed in correlation to the tibial bone structural properties. This is important because it is not a common practice to use the extension in a primary TKA, a standard configuration offering sufficient stability and good long-term survivorship. Background and Objectives: This study’s purpose was to examine the benefit of using a tibial extension in the primary operation of total knee arthroplasty (TKA).
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