![]() Below 50 μɛ, stress shielding is likely to occur and bone resorption takes place 1). The strain for normal remodeling of the proximal tibia should be within a physiological range of 50 to 1,500 μɛ 1). Wolff ’s Law states that bone remodels in response to applied stress and strain in the chronic phase. 6) reported the results of 22 TKAs with modular metal wedges and small tibial cemented stems: no tibial tray was considered loose at an average of 37 months of follow-up. The selection of metal augments typically mandates the use of a stem. Modular metal augments (blocks or wedges), cones, or sleeves can be used when the cortical rim or either the distal femur or proximal tibia is breached. If a stem fails to transfer the load, then the remaining cancellous bone will experience load beyond its ultimate strength, which will lead to a loss in component fixation in the initial phase 5). The knee joint bears loads that are several times the body weight. Bone grafting for large volume defects may require the use of a stem to protect the graft from excessive load. Stems should be used in revision TKA when the remaining bone stock is insufficient to support the prosthesis. In this review article, we will discuss the indications, selection of stem lengths and diameters, and fixation methods in revision TKA. Such decisions should be based on a great store of knowledge rather than on presumption. No evidence-based guidelines are available to help determine when to use a stem, which length and diameter are ideal, and whether or not to use cement fixation 4). ![]() ![]() With a stem up to 150 mm in length, marked stress shielding of the proximal tibial cortex and doubling of the strain are noted at the stem tip 3).Īlthough the need for stem to improve initial mechanical stability and ultimate component survival is well accepted, the ideal indications, proper lengths and diameters, and fixation methods remain controversial. It is known that the axial load can be reduced by 23% to 39% when a stem length reaches 70 mm 3). However, long stems may have disadvantages including end-of-stem pain and stress shielding along their length with associated reduction in bone density, a theoretical risk of subsidence, loosening, and periprosthetic fracture 1, 2). Mechanical stability can be improved by resistance to shear, reduced lift-off, and decreased micromotion 1). They improve the mechanical stability at the cost of stress shielding. Stems are required in most revision TKAs to help transfer loads from the compromised articular and metaphyseal bone to the remaining tibial cortical rim and to widely distribute the increased stress of a constrained articulation. ![]() However, it would be a more difficult task in the revision setting due to combined severe bone defects and soft tissue insufficiency. One of the primary goals of total knee arthroplasty (TKA) is to recreate a stable joint with accurate position and orientation of prostheses, mimicking the normal knee kinematics. Selection of a cementation technique should be based on thorough consideration of advantages and disadvantages of each technique. There are two traditional methods of stem fixation including the total cementation technique and the hybrid technique with a cementless press-fit stem. The stem length and diameter should be tailored according to patients’ anatomical characteristics and determined fixation strategy. The balance between overshielding and overloading the juxta-articular bone would provide excellent structural protection. ![]() Proper bone surface preparation and appropriate use of the stem based on a great store of knowledge are required to support the stemmed components effectively in revision TKA. A stem cannot be a substitute for optimal component fixation it plays an adjunctive role in transferring the loads from the compromised metaphysis to the stronger diaphysis. The use of a stem in revision TKA can protect the juxta-articular bone. The topics of the present article include the indications, selection of lengths and diameters, and fixation methods of stems in revision TKA. Although stems improve initial mechanical stability in revision total knee arthroplasty (TKA), ideal indications, proper lengths and diameters, and appropriate fixation methods remain controversial. ![]()
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