RESUMEN
The performance of novel ceramic-on-metal bearing couples has been compared with metal-on-metal and ceramic-on-ceramic bearing couples in laboratory and short-term clinical studies. Laboratory studies compared ceramic-on-metal with metal-on-metal and ceramic-on-ceramic bearings with diameters of 28 and 36 mm under standard conditions and under adverse conditions with head loading on the rim of the cup. Clinical studies compared metal ion levels in ceramic-on-metal with metal-on-metal, ceramic-on-ceramic, and ceramic-on-polyethylene bearings in a randomized prospective study. In the laboratory studies, friction, wear, and ion levels were lower in ceramic-on-metal bearings compared with metal-on-metal, with results similar to ceramic-on-ceramic couples. Under adverse conditions and rim loading, all bearings showed increased wear with lower wear and absence of stripe wear in ceramic-on-metal compared with metal-on-metal bearings. Short-term studies in 31 patients at 6 months revealed lower metal ion levels (cobalt and chromium) in those with ceramic-on-metal compared with metal-on-metal bearings.
Asunto(s)
Artroplastia de Reemplazo de Cadera/instrumentación , Distinciones y Premios , Cerámica , Aleaciones de Cromo , Articulación de la Cadera/cirugía , Prótesis de Cadera , Artropatías/cirugía , Adulto , Cromo/sangre , Cobalto/sangre , Femenino , Articulación de la Cadera/fisiopatología , Humanos , Artropatías/sangre , Artropatías/fisiopatología , Masculino , Ensayo de Materiales , Persona de Mediana Edad , Estudios Prospectivos , Diseño de Prótesis , Rango del Movimiento Articular , Estrés Mecánico , Factores de Tiempo , Resultado del TratamientoRESUMEN
BACKGROUND: A dark metallic-appearing smear, resembling a lead pencil mark, may be seen on a ceramic femoral head component at revision total hip arthroplasty. The purpose of this study was to investigate the hypothesis that such a mark on a retrieved ceramic femoral head is associated with increased surface roughness of the head and increased polyethylene liner wear in total hip replacement. METHODS: Fifteen ceramic prosthetic femoral heads retrieved from fifteen patients at revision arthroplasty were examined in this study. Thirteen heads had been in vivo for an average of 10.8 years (range, 7.8 to 14.2 years). The remaining two heads had been in vivo for less than one month. The surface roughness characteristics of the explanted ceramic heads, the linear wear of the polyethylene liner, and the patient activity levels after the primary replacement and before the revision were determined. RESULTS: Four of the thirteen ceramic heads that had been in vivo for >/=7.8 years had severe smears (>6% of the surface area), and the remaining nine heads had slight smears (<6% of the surface area). The two heads that had been in vivo less than one month had severe smears. The mean Ra and Rpm, the values for surface roughness, were 44.95 nm and 571.15 nm, respectively, in the hips with slightly smeared regions and 180.77 nm and 1245.88 nm, respectively, in the hips with severely smeared regions (p = 0.002). The mean linear liner wear rate was 0.10 mm/yr in the hips with slightly smeared heads and 0.19 mm/yr in the hips with severely smeared heads (p = 0.002). The activity score for all patients was 5 or 6 points on a 6-point scale. CONCLUSIONS: The results of this study confirm the hypothesis that a visual dark metallic-appearing smear on a ceramic femoral head correlates with increased surface roughness of the head and increased polyethylene wear. These findings imply that contact of a ceramic femoral head with a metallic material, such as may occur with femoral head reduction or dislocation of a total hip replacement, is best avoided to prevent this metallic smear phenomenon.
Asunto(s)
Artroplastia de Reemplazo de Cadera , Cabeza Femoral , Prótesis de Cadera , Cerámica , Humanos , Microscopía Electrónica de Rastreo , Polietileno , Reoperación , Propiedades de Superficie , Factores de TiempoRESUMEN
The separate and combined roles of head diameter and clearance were studied experimentally in simulator tests and also theoretically. Head diameters ranging from 16-54 mm and various clearances were studied. Effective mixed-film lubrication achieved through careful design and manufacture greatly reduced wear. The running-in wear volumes were very low for larger-diameter heads and smaller clearances; but because the subsequent steady-state wear rate was much smaller than the running-in wear rate, the former contributed significantly to the total volume of wear debris even over very long periods of time. The design study has shown that head diameters should be as large as possible and diametral clearances as low as practicable, to ensure that the joints operate well into the mixed lubrication regime.
Asunto(s)
Prótesis de Cadera , Artroplastia de Reemplazo de Cadera , Lubrificación , Modelos Estructurales , Diseño de Prótesis , Falla de PrótesisRESUMEN
The use of metal-on-metal low-wearing bearings has promoted great interest in the factors determining the volume of wear debris generated in such joints, including the developing surface replacement alternatives. Twenty-six pairs of low- and high-carbon components in wrought or cast form of 36 mm nominal diameter and exhibiting similar clearances were studied over 5 million test cycles in a 10-station hip joint simulator. Low-carbon cast materials exhibited higher wear than high-carbon cast or wrought materials. Little difference was found in the running-in wear volumes generated by high-carbon wrought or cast materials, but the wrought material exhibited a slight advantage at the smallest diametral clearance considered of 105 microm. Volumetric wear appeared to decrease as the diametral clearance decreased.