Biomedical subjects

Hironobu Oonishi

Publications and source records attributed to Hironobu Oonishi.

6 recordsLinked to original sources

PubMed2006

Wear of highly cross-linked polyethylene acetabular cup in Japan.

The wear characteristics of ultra-high-molecular-weight polyethylene acetabular cups irradiated with 6.0 to 7.5 Gy of gamma-irradiation were studied in a hip simulator and in vivo in 70 hips for 6 to 39 months. The linear wear was 2.5% to 4.5% of the wear seen in conventional polyethylene cups. A biphasic wear pattern was observed over time with a relatively large wear in the first year and a subsequent leveling of the wear rate curve. The linear wear rate in the second phase (steady state) was 0.006 mm/y. The extent of decrease in clinical wear of 6.0-Mrad polyethylene (Aeonian, Kyocera Corp, Kyoto, Japan) cups is comparable with the decrease of the in vitro wear measured by the hip simulation test.

Acetabulum↗

PubMed2005

Change in UHMWPE properties of retrieved ceramic total knee prosthesis in clinical use for 23 years.

The alumina-ceramic total knee prosthesis developed by Kyocera Corp. was implanted in 1979, and was in clinical use for 23 years until total knee arthroplasty revision surgery in January 2002. It is believed that this is the longest clinical period of a ceramic total knee prosthesis reported to date in the world. In the present study, we gave consideration to the long-term clinical stability of the alumina-ceramic femoral component as well as the mechanism of in vivo degradation of ultrahigh molecular weight polyethylene (UHMWPE) based on the evaluated wear, oxidation, and fracture toughness of the retrieved UHMWPE. We concluded that the degradation of UHMWPE by progressive oxidation is an issue to be solved in the future. To moderate stress concentration, use of a thin UHMWPE insert should be avoided. The low wear rate and the mild wear pattern observed this time suggest the possibility of reduced wear of the UHMWPE against the alumina-ceramic femoral component, and the usefulness of the alumina-ceramic total knee prosthesis component was recognized even after long clinical use.

Ceramics↗

PubMed2004

Alumina hip joints characterized by run-in wear and steady-state wear to 14 million cycles in hip-simulator model.

The biphasic wear performance (run-in; steady-state phase) of 28-mm alumina-alumina hip implants was studied by hip simulator methods using bovine serum as the lubricant. The Biolox implants were run to 5.7 million cycles and Bioceram implants to 14.4 million cycles (Mc). Wear with all-alumina total hip replacements (THR) first showed a high wear rate of the order 1.2 mm3/Mc, lasting approximately 0.17 Mc. Overall to 0.7 Mc, the run-in phase appeared curvilinear but could be described by a linear phase averaging 0.3 mm3/Mc. From 0.7 to 1 Mc duration, the wear trend transitioned into a steady-state phase. Wear rates from 1 to 14 Mc were of the order 0.02 mm3/Mc. Surface contamination from the serum lubricant resulted in cyclic weight fluctuations of the order 0.2 mg. The transition from average run-in to steady-state phase represented a wear reduction of 13-fold. Comparing the steady-state wear value to that in standard 28-mm UHMWPE CUPS approaching 75 mm3/year, there was clearly a three-orders-of-magnitude wear superiority in favor of ceramic cups.

Aluminum Oxide↗

PubMed2004

Assessment of wear in extensively irradiated UHMWPE cups in simulator studies.

Higher levels of UHMWPE crosslinking currently are being advocated for improved wear resistance of acetabular cups. Pioneering Japanese studies, begun in 1971, have achieved good clinical results with UHMWPE irradiated to 1000 kGy for use with a cemented-cup design. The objective of our study was to use contemporary simulator techniques to determine the in vitro wear performance of such high-dose irradiated cups. Extruded UHMWPE cups were processed with 500, 1000, and 1500 kGy of gamma-radiation doses under vacuum, annealed, and machined to shape. The cups were mated with 26-mm alumina heads and run in a multidirectional simulator with bovine serum. Over a 6-million cycle (Mc) study, the weight loss of the nonirradiated control cups averaged 52.8 mg/Mc + 1.4% (wear = 57.2 mm(3)/Mc). In contrast, the irradiated wear cups had a consistent weight gain. Thus cups with irradiation of 500-1500 kGy had no detectable wear in this study. The original machining marks still were partially evident in the wear zones, along with some macrofissures in the 1000- and 1500-kGy cups. Areas adjacent to the fissures showed delaminating plaques of 100-300 microm in size. It also was noted that the wear cups systematically gained more weight than their corresponding soak controls. Each 200-kGy radiation gain increased the fluid sorption ratio by 10%. The increased fluid sorption and evidence of some surface deterioration may indicate that such high-dose irradiated cups are more susceptible to mechanical damage. This indicates that we should take care to ensure that our desire to reduce the wear debris to a zero amount does not result in a modified UHMWPE that lacks the necessary mechanical properties for contemporary metal-backed cup designs.

Absorption↗

PubMed2004

Micro-wear features on unique 100-Mrad cups: two retrieved cups compared to hip simulator wear study.

We studied the micro-wear phenomena of unique, extensively cross-linked polyethylene cups (cross-linked with 1,000 kGy-irradiation) that had been used briefly in Japan. Two retrievals (at 15 years) came from the Japanese "SOM" hip system (implanted 1971-78). These were compared to a set of 0 kGy and 500-1,500 kGy cups run in our hip simulator. The polyethylene cups that had not been cross-linked had the greatest wear. The worn areas had a burnished appearance and were clearly separated from the unworn region by a distinct ridge-line. The worn areas had lost all machine tracks, showed a large amount of UHMWPE 'flow', and long PE fibrils. The associated surface rippling was degraded. These features were considered synonymous with severe polyethylene wear. In contrast, the worn areas in the very cross-linked cups had a visibly matte surface and no ridge-line. Micro-examination showed that the machine tracks were still present. Ripple formations were less obvious than in the cups that were not cross-linked, polyethylene surface fibrils were scarcer and all the fibrils were much smaller than in the cups that were not crosslinked. Our two retrieved cups and the simulator cups confirmed the greater wear-resistance of very cross-linked polyethylene. It should also be noted that the SOM cup design and processing were unique and differed greatly from that of modern polyethylene cups.

Biocompatible Materials↗

PubMed2002

Micro-wear patterns on UHMWPE tibial inserts in total knee joint simulation.

The objective of this study was to examine both simulator and retrieved total knee replacement polyethylene inserts to confirm, using scanning electron microscopy, whether similar micro-wear patterns to those seen on retrieved inserts were reproduced on simulator specimens. The simulator specimens consisted of samples subjected to sliding and rolling movement (Experiment 1) and to sliding movement only (Experiment 2). Samples from Experiment 1 demonstrated longitudinal patterns in the middle of the wear track and transverse patterns in the anterior and posterior ends, whereas in Experiment 2, only transverse patterns were observed. In the retrieved specimens, both longitudinal and transverse patterns were observed. The results showed that the simulator study reproduced similar patterns of micro-damage on polyethylene, and that the longitudinal micro-wear pattern was related to the rolling movement that is distinctive in knee kinematics.

Biomechanical Phenomena↗