Non-cemented Implants Research Articles

The Current Status of Total Joint Replacement

The last two decades have witnessed tremendous strides in the evolution of acceptable and successful methods of prosthetic replacement for the arthritic joint. By and large, these techniques are predictable and durable, though not always to the complete satisfaction of the patient and surgeon. Despite the recent emphasis on alternative forms of implant fixation, cemented total joint replacements remain the standard by which all others are judged. In some settings, non-cemented implants appear to function as well as cemented ones in providing pain relief. The acetabular component in the hip and the femoral component in knee replacement are two such areas. This has resulted in the emergence of the "hybrid" joint replacement where one component is cemented while the other is not. The long-term function and durability of these non-cemented components remains to be seen. The future of joint replacement lies in the development of new "composite" materials which can more closely match the structural characteristics of the bone into which they are being implanted. Until we better understand and are able to prevent the disease processes which lead to total joint replacement, this area will continue to be the focus of intense research and development.

In vitro analysis of proximal femoral strains using PCA femoral implants and a hip-abductor muscle simulator

The strains produced in the proximal femur by noncemented and cemented PCA femoral implants have been compared to each other and to the strains in the same intact femur. The effect on the strain pattern of a hip-abductor muscle simulator was also tested. Nine embalmed femora were tested; two were used for development of the protocol, one was covered with a reflective photoelastic coating, and six were instrumented with eight strain gauge rosettes on each femur. For a given body weight on the photoelastically coated intact bone, the abductor-simulator increased the mean shear strains on both the medial (132%) and lateral (153%) aspects, with standard deviations of 13% and 20%, respectively; however, no strain-concentrated areas were observed. With an abductor simulator on the strain-gauged femurs, calcar shear strains were significantly reduced ( P < .01), from those on the intact bone, by both noncemented and cemented implants. These reductions were 74.2% and 91.8%, respectively, with no significant difference between the two techniques. Reductions in shear strain were noted at midstem on the medial side for the noncemented (20.5%) and cemented (35.9%) implants; however, only the cemented implants produced significantly less ( P < .05) strain than the intact bone at this location. At midstem on the medial aspect of the femur, there was a significant difference ( P < .05) between the data for the cemented and noncemented implants. Analysis of variance identified no other regions of significant change.

Rigidity of initial fixation with uncemented tibial knee implants

This study quantifies the in vitro motion occurring between bone and cemented and noncemented tibial components. Liquid metal strain gauges were used to measure the motion between the tibial component and bone at four locations in eight cadaver tibia at near-point cyclic loads ranging from 10 to 2,000 N. Two types of motion were observed: inducible displacement, which is reversible, followed the oscillating load and occurred in both cemented and uncemented tests, and liftoff or separation of the component and bone, which occurred only for the noncemented cases and remained even after removal of the load. For both motion types, noncemented tests exhibited significant ( P < .05) and dramatic increased interface motion compared to the cemented cases for all load types. The results suggest that the magnitudes of implant-bone interface separation at loads in the low physiologic range for noncemented implants can be sufficiently large to inhibit bony ingrowth into a prosthesis with an average pore size of 300 m.