Biomechanical Analysis of the Use of Stems in Revision Total Knee Arthroplasty

Abstract

Adequate fixation is fundamental in revision total knee arthroplasty; consequently, surgeons must determine the correct set-up for each patient, choosing from numerous stem solutions. Several designs are currently available on the market, but there are no evidence-based quantitative biomechanical guideline yet. Therefore, several stems were designed and analyzed using a previously-validated finite-element model. The following parameters were studied: stem design characteristics (length and shape), added features (straight/bowed stem), fixation technique, and effect of slots/flutes. Bone stress and Risk of Fracture (RF) were analyzed in different regions of interest during a squat (up to 120°). For the femoral stem, the results indicated that all parameters influenced the bone stress distribution. The maximum von Mises stress and RF were always located near the tip of the stem. The long stems generated stress-shielding in the distal bone. Regarding the tibial stem, cemented stems showed lower micromotions at the bone-tibial tray interface and at the stem tip compared to press-fit stems, reducing the risk of implant loosening. The results demonstrated that anatomical shapes and slots reduce bone stress and risk of fracture, whereas flutes have the opposite effect; no relevant differences were found in this regard when alternating cemented and press-fit stem configurations. Cemented tibial stems reduce antero-posterior micromotions, preventing implant loosening.

Pre-clinical characterization of a novel flexible surface stem design for total knee replacements

“…Stems for TKR are used to reduce micromotions at the bone-implant interface: Influence of stem length and diameter as well as slots and flutes were experimentally and numerically analyzed. 14,[18][19][20] In this study, we introduced a flexible surface stem design characterized by flexible surface lamellas with the potential to reduce stress-shielding in the adjacent bone stock. The flexible surface stem specimens had either solid or open-porous structured lamellas.…”

“…14,18,19,[22][23][24][25] It is influenced by bone density, surgical technique, implant material and design, the level of press-fit, and the magnitude and direction of the physiological loads. 14,18,19,23,24,[26][27][28][29] Regarding the response of human bone cells, small micromotions at the boneimplant interface are improving cell differentiation and bone formation at the interface. 30,31 But values greater than 0.15 mm are causing fibrous tissue formation 32 increasing the risk of implant failure.…”

“…17 Biomechanical studies have shown the potential of femoral stems for revision TKR to reduce micromotions at the bone-implant interface. 14,18–20 Apart from the stem length and diameter 18–20 the surface and bulk properties of the stem are of great importance for the bone-implant interaction. 21…”

The current status of finite element analysis in the application of total knee arthroplasty and corresponding method of improvement

“…Our works successfully redefine the specific use of Finite Element Analysis in preoperative planning and propose a framework for preoperative general engineering by combining all the elements. In conjunction with the basis of existing research, we also present at the beginning a literature review on the digitization of TKA, at the CAD/CAE level as well as on parameter optimization, respectively, then we have compiled the results and gaps in the current literature [9,14]. As shown in the first figure, we combine the research carried out by Dong, Y., et al for a discussion of CAD imaging methods for tissues in a total knee model with different properties.…”

“…Multiple authors have studied the application of CAD/CAE in the area of total knee replacement researches. The existing studies have inspected the aforementioned questions from the following angles, positioning of the knee prosthetic implants and prostheses [8][9][10], static/dynamic simulation of the total knee joint [11], and optimization of the anti-wear design of the knee joint [12]. Even though the above applications can be implemented relatively well, two factors significantly affect the accuracy of computer-aided design and engineering, respectively, the poor accuracy of the datasets acquired by medical imaging technology and the wrong way of meshing during the finite element method [13].…”