Phase transformation of a new generation yttria-stabilized zirconia femoral head after total hip arthroplasty

In vivo wear performance of highly cross-linked polyethylene vs. yttria stabilized zirconia and alumina stabilized zirconia at a mean seven-year follow-up

Background

Zirconia was introduced as an alternative to alumina for use in the femoral head. The yttria stabilized zirconia material was improved by adding alumina. We evaluated highly cross-linked polyethylene wear performance of zirconia in total hip arthroplasty. The hypothesis was that alumina stabilized zirconia could decrease highly cross-linked polyethylene wear.

Methods

Highly cross-linked polyethylene wear was measured with a computerized method (PolyWare) in 91 hips. The steady-state wear rates were measured based on the radiographs from the first year postoperatively to the final follow-up and were compared between hips with yttria stabilized zirconia and alumina stabilized zirconia.

Results

The steady-state wear rate of highly cross-linked polyethylene against zirconia was 0.02 mm/year at a mean follow-up of 7 years. No significant difference was observed between groups with yttria stabilized zirconia and alumina stabilized zirconia.

Conclusions

Addition of alumina to the zirconia material failed to show further reduction of highly cross-linked polyethylene wear and our hypothesis was not verified.

Orthopedic applications of silicon nitride ceramics

Silicon nitride (Si(3)N(4)) is a ceramic material developed for industrial applications that demand high strength and fracture resistance under extreme operating conditions. Recently, Si(3)N(4) has been used as an orthopedic biomaterial, to promote bone fusion in spinal surgery and to develop bearings that can improve the wear and longevity of prosthetic hip and knee joints. Si(3)N(4) has been implanted in human patients for over 3 years now, and clinical trials with Si(3)N(4) femoral heads in prosthetic hip replacement are contemplated. This review will provide background information and data relating to Si(3)N(4) ceramics that will be of interest to engineering and medical professionals.

State of the art in hard-on-hard bearings: how did we get here and what have we achieved?

Total hip arthroplasty has shown excellent results in decreasing pain and improving function in patients with degenerative disease of the hip. Improvements in prosthetic materials, designs and implant fixation have now resulted in wear of the bearing surface being the limitation of this technology, and a number of hard-on-hard couples have been introduced to address this concern. The purpose of this article is to review the origins, development, survival rates and potential advantages and disadvantages of the following hard-on-hard bearings for total hip arthroplasty: metal-on-metal standard total hip arthroplasty; metal-on-metal hip resurfacing arthroplasty, ceramic-on-ceramic total hip arthroplasty; and ceramic-on-metal bearings. Improvements in the manufacturing of metal-on-metal bearings over the past 50 years have resulted in implants that provide low wear rates and allow for the use of large femoral heads. However, concerns remain regarding elevated serum metal ion levels, potential teratogenic effects and potentially devastating adverse local tissue reactions, whose incidence and pathogenesis remains unclear. Modern total hip resurfacing has shown excellent outcomes over 10 years in the hands of experienced surgeons. Current ceramic-on-ceramic bearings have demonstrated excellent survival with exceptionally low wear rates and virtually no local adverse effects. Concerns remain for insertional chipping, in vivo fracture and the variable incidence of squeaking. Contemporary ceramic-on-metal interfaces are in the early stages of clinical use, with little data reported to date. Hard-on-hard bearings for total hip arthroplasty have improved dramatically over the past 50 years. As bearing designs continue to improve with new and modified materials and improved manufacturing techniques, it is likely that the use of hard-on-hard bearings will continue to increase, especially in young and active patients.

Control of cellular activity of fibroblasts on size-tuned fibrous hydroxyapatite nanocrystals

We controlled the performance of L929 mouse fibroblasts using various hydroxyapatite (HA) nanocrystals, such as nanofibers, nanoneedles, and nanosheets, to better understand the effects of size and shape of the HA nanocrystals on the cells. The cellular activity on nanofibers with a diameter of 50-100 nm was significantly enhanced relative to that on a flat HA surface because large amounts of the proteins needed for adhesion and proliferation could be stored in the substrate. On the other hand, initial adhesion and subsequent proliferation were inhibited on surfaces consisting of fine nanoneedles and nanosheets with a diameter/thickness of less than 30 nm due to the limited area available for the formation of focal adhesions. These facts indicate that fibroblast activity is highly sensitive to the surface topography. Therefore, size tuning of the nanoscale units composing the substrate is essential to enhance cellular performance.

Evaluation of phase stability in zirconia femoral heads from different manufacturers after in vitro testing or in vivo retrieval

Yttria-stabilized zirconia femoral heads from 3 different manufacturers were tested in vitro with respect to their phase stability and compared with retrieved zirconia heads. The monoclinic content on the surface of unused heads was analyzed by confocal Raman spectroscopy after exposure for increasing times to moist atmosphere. The increase in monoclinic content was then plotted as a function of geometric location on the head surface of the head and compared with that measured at similar locations after in vivo exposure. Profiles of residual stress associated to polymorphic transformation were also measured from the collected Raman spectra. A striking finding was that, in some samples, polymorphic transformation occurred since the very early stage of the environmental exposure even if those samples belonged to new-generation products.