Tibial Component Designs Research Articles

Total knee arthroplasty in elderly patients: Comparison of tibial component designs

The authors examined 98 total knee arthroplasties in 73 patients who were 80 years of age or older at the time of surgery (average, 82 years; range, 80–90 years). The follow-up period averaged 4.5 years (range, 2–12 years). The patients were divided into two groups based on their tibial component design. There were 38 all-polyethylene tibial components in 28 patients and 60 metal-backed tibial components in 45 patients. There were 61 (62%) excellent, 30 (31%) good, 2 (2%) fair, and 5 (5%) poor results. Three of the five poor results required revision for septic failure. Of the knees with an all-polyethylene tibial component, 20 (53%) were rated as excellent, 15 (39%) as good, and 3 (8%) as poor. One of these knees rated as poor required revision for septic failure. The knees with a metal-backed tibial tray had 41 (68%) rated as excellent, 15 (25%) as good, 2 (3%) as fair, and 2 (3%) as poor. Both of the knees with poor results required revision for septic failure. Stratifying the results by component composition revealed 97% survival for both types of tibial trays. These results were obtained at 12 years for the all-polyethylene components and at 8 years for the metal-backed prosthesis. In conclusion, the authors believe that total knee arthroplasty is a reliable and durable procedure in the treatment of knee arthritis in the elderly. Elderly patients may represent a special case because they are generally less active than younger patients and may place less stress on their prosthesis. This may place them at less risk for mechanical failure and may make an all-polyethylene tibial component a viable option in the thin, elderly patient, who is usually less active.

Wear and contact stress studies of the Minns meniscal knee prosthesis.

This paper describes the results of wear testing and contact area studies of a Minns meniscal knee prosthesis and compares the results of previous work on wear and contact stress studies of other knee prosthesis designs. Although stresses that arise at the surface of the polyethylene meniscus components are large, after repetitive loading the contact area rises, as a consequence of plastic flow and creep, and they reduce to a fifth of the initial stress after 1 million cycles. Contact area studies show that asymmetrical loading of the meniscus give proportionally high stresses on the higher loaded meniscus and, at large values of flexion, have similar values to a more conforming but fixed polyethylene tibial component design of knee prosthesis.

Approaches to the Interface Problem in Total Joint Arthroplasty

Bone shape and composition and the configurations and interface conditions of implant components influence the stability of the joint in various ways. A stable interface depends on overall stress and microstress distribution on the bone, particularly trabecular bone. Pressure pattern studies illustrated the effect of tibial component design on overall pressure distribution. Experiments in knee joints of sheep showed that a velour layer interposed between a metallic implant and bone induces fibrous ingrowth. It was proposed that this situation could reduce peak microstresses in trabecular bone.

An analysis of tibial component design in total knee arthroplasty

An axisymmetric finite element model of the proximal tibia and cemented tibial component subject to nonaxisymmetric loading is presented. Model variations included polyethylene components and steel reinforced polyethylene components both with and without a central fixation post. Central fixation posts of 35 and 70 mm were modeled. A vertically oriented lead applied unilaterally to the tibial component was found to generally cause the largest magnitude peak stresses within the various components of the structure. The addition of steel reinforcement to tibial components without central fixation post is predicted to significantly reduce stress levels within the polymethylmethacrylate and underlying cancellous bone. Although to a lesser extent, the addition of a relatively short central fixation post to the steel reinforced tibial component further reduced these stress levels. The longer steel central fixation post can appreciably reduce proximal cement and bone stress levels. The tibial component condylar width is predicted to have little effect on polymethylmethacrylate and cancellous bone stresses, with the exception that proximal tibial cancellous bone compressive stresses are reduced with wide steel reinforced components.

A comparative evaluation of tibial component designs of total knee prostheses.

Three-dimensional finite-element stress analyses were used to compare the fixation of tibial component configurations of surface-replacement-type total knee prostheses, bases on the stresses in the cancellous bone, in the polymethylmethacrylate, and at the bone cement-bone interface. The results indicate that, in general, metal components provide lower system stresses than polyethylene components, particularly in the methacrylate and the cancellous bone, and that one-piece designs give lower bone cement-bone interface stresses compared with those with separated condylar components. Of the designs considered, a single-post, metal-backed design provided the lowest system stresses over-all. a great and confusing variety of tibial component design exists today, with more in the process of development. Short of long term clinical trials, there are few objective methods by which these designs can be evaluated and long-term performance predicted. There is evidence from clinical results that excessively high stresses in the systems can lead to loosening of the tibial component. The finite-element method provides a method for comparing prosthetic designs using system stresses a s a design criterion. On this basis, we analyzed the stress distribution for several types of tibial components and discuss the advantages and disadvantages of their designs.