Comparison study of temperature and deformation changes in the femoral component of a novel ceramic-on-ceramic hip resurfacing bearing to a metal standard, using a cadaveric model.

Hip resurfacing is an attractive alternative to total hip replacement preserving bone and reducing dislocation risk. Recent metal-on-metal designs have caused failure due to metal wear debris. Ceramic implants may mitigate this risk. Temperature increase in periprosthetic bone during cementation can lead to osteonecrosis, while deformation of the component can affect joint lubrication and may increase wear through clamping. Both processes may lead to implant loosening. This study quantifies the temperature and deformation change in a novel ceramic hip resurfacing femoral component compared to a metal standard during cemented implantation in a fresh frozen cadaveric model. Study design and methods Eight femora were prepared from four fresh frozen cadavers. One surgeon experienced in hip resurfacing surgery (J.H.) prepared the femora by reaming. Four ceramic and four metal implants of equal and varying size were cemented in place. Bone and surface temperatures were taken using a probe in the periprosthetic bone and an infrared laser thermometer, respectively. Deformation was measured using a micrometre. Measurements were taken before implantation and every 5-min intervals up to 30 min. The average bone-temperature increment was lower for ceramic heads than for metal heads. Although this difference was not statistically significant, the average bone temperature incremental change in small sizes (42 and 46 mm) was higher than in the large sizes (48 and 50 mm). Most metal heads sustained bearing diameter change that was still near its peak value 30 min after implantation, whereas the ceramic heads suffered a lower diameter change and most of the samples recovered their original diameter 30 min after implantation. Both implants behave similarly, however, a lower temperature rise in bone was observed with ceramic heads. This may lower the risk for thermal damage on periprosthetic bone. The ceramic heads deformed less during surgical implantation. This was not significant.

Comparing the cup deformation following implantation of a novel ceramic-on-ceramic hip resurfacing bearing to a metal standard in a cadaveric model.

Hip resurfacing is an attractive alternative to total hip replacement preserving bone and reducing dislocation risk. Recent metal-on-metal designs have caused failure due to metal wear debris. Ceramic implants may mitigate this risk. Deformation of the acetabular cup can affect the lubrication, producing high friction torques between the femoral head and the cup that would increase wear and/or lead to cup loosening due to femoral head clamping. Our objective was to quantify the deformation of a novel monobloc ceramic hip resurfacing cup component compared to a metal standard, in a fresh frozen cadaveric model using a press-fit technique representative of standard surgical conditions. For this study eight acetabula were prepared from four fresh frozen cadavers. One surgeon with extensive experience in hip resurfacing surgery (J.H.) prepared the acetabulum by sequential reaming. The implants were then impacted into the acetabulum. Four ceramic and four metal implants were used of equal and varying size. Deformation was measured peri-implantation, and at 30 min, using an optical high-precision deformation sensor (GOM GmbH, Braunschweig, Germany). The maximum inscribed circle and the measurement of radial segment techniques were used. Deformation was greater in the metal implants (mean: 34-22mm) immediately after implantation. At 30 min after implantation, the deformation increased to 36mm in the metal and 26mm in the ceramic cup. Greater diameter changes were observed in larger cups. Metal and ceramic implants did not return to the initial diameter. We conclude the ceramic resurfacing acetabular implants undergo similar deformation to existing metal-on-metal implants. The deformation observed was significantly less in the ceramic component at 30 min on one measure. Less deformation may result in better surface conditions and wear characteristics. Deformation change did not resolve after 30 min for both implants.

Transitions in insurance coverage from before pregnancy through delivery in nine states, 1996-1999.

Efforts to extend coverage to pregnant women, along with an expanding economy, did not prevent increases in the uninsured in the latter 1990s. Welfare reform may have led to declining Medicaid enrollments and caseloads. Data representative of live births in nine states show that in some states more than one-third of all pregnant women and almost two-thirds of low-income pregnant women lacked insurance before their pregnancy in 1996 and 1999. More than one-third of all pregnant women made some change in coverage by the time they delivered their baby. Among low-income women, the largest change was from uninsured status before pregnancy to Medicaid at delivery.