PubMed · 10608971
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P A Setness, D Hoel. 1999. Knee replacement.. https://doi.org/10.3810/pgm.1999.12.818
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Total knee replacements using intercondylar cams, such as posterior stabilized types, have been in use for many years. In a previous study, software was written to analyze an alternative shape of the intercondylar cams. The goal of the current study was to investigate in a more general way the potential of intercondylar cams, or guide surfaces, for reproducing the anterior-posterior motion of the natural knee throughout the flexion range. Typical sagittal outlines for the femoral and tibial bearing surfaces were defined, and a parametrized shape for the femoral guide surface was defined to produce a wide range of shapes. Software was written in which the femoral component was flexed in increments, with the posterior translation defined as a function of the flexion angle. The shape of the tibial guide surface was derived from the locus of the femoral guide surface at its multiple flexion positions. By iterating methodically through possible shapes of femoral guide surfaces, several types of total knee replacement components in common use today were identified, as well as other configurations of potential interest. For quantification of a given design, the software calculated the anterior and posterior laxity at each flexion angle. Laxity was defined as the motion before the femoral guide surface impacted the tibial guide surface or until the contact point of the bearing surfaces reached a specified slope. Convex femoral and concave saddle-shaped tibial guide surfaces produced small laxities in both directions over most of the flexion range. A saddle design with small laxities in the first half of flexion, combined with a posterior stabilized feature, was an interesting combination. Potential improvements to the currently used designs were shown in this study, and new shapes of intercondylar guide surfaces were derived that could be considered for application.
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A new method is presented which allows the construction and implantation of highly precise custom-made endoprostheses for knee joints. The procedure is based on a computer-aided subtraction process of three-dimensional CT data. Using the differences of the CT scans, the endprosthetic components are modelled by means of a newly developed software package. The implants are manufactured by CNC machines and stereolithography. The method enables the surgeon to reduce bone resections and ensures an exact profile of the bone-implant interface. Incorrect positioning will be avoided and the implantation process can be performed more easily while the size of the operative approach will be minimized. Better postoperative kinematics and reduction of shearing effects will lead to better results in the long run. The procedure offers a series of new possibilities to optimize monocondylar and bicondylar knee joint endoprostheses.