Excessive food intake and obesity was induced in one member of parabiotic pairs by electrical stimulation (three 30-min sessions/day for 2 wk) of the lateral hypothalamus (LH). The nonstimulated partners reduced spontaneous food intake the fatter the stimulated animals became. This reduced food intake resulted in a decreased body weight, fat content, and fat-free solid body mass. The decrease of food intake was not due to changed social behavior of the obese partner. It must be attributed to transmission of a humoral satiety factor. The very first stimulation of the LH in the stimulated partners resulted in a large increase in blood glucose and glucagon level without much change in the insulin level. These changes in blood parameters were probably due to strong sympathetic arousal. In the nonstimulated animals there were practically no changes in these parameters. One week of fattening resulted in increased basal glucose and insulin levels in the stimulated animals and decreased glucose levels in the nonstimulated partners, in which the basal insulin levels remained nearly normal. Basal glucagon levels were the same in both partners and did not differ from the prefattening situation. At that time during stimulation the obese animals showed a large increase in glucose and glucagon levels and a decrease in insulin level. On the other hand the nonstimulated animals showed a slow gradual increase in glucose and insulin level due to transmission from their fat partners because of the large gradient in these substances between the animals. These phenomena were still more pronounced after 2 wk of fattening. It is tentatively concluded that the humoral satiety factor is neither circulating insulin nor glucagon nor one of the major circulating nutrients.

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BackgroundConventional total knee replacement designs show high success rates but in the long term, the stiff metal components may affect bone quality of the distal femur. In this study we introduce an all-polymer total knee replacement device containing a PEEK femoral component on an UHMWPE tibial implant and study its mechanical integrity, fixation, and stress shielding of the periprosthetic femur.MethodsThe implant was analysed in finite element simulations of level gait, adopted from the ISO 14243-1 standard. Mechanical integrity of the implant and underlying cement mantle were tested, and the fixation strength of the cement-implant interface was studied. Stress shielding was assessed based on strain energy density distributions in the distal femur. We compared PEEK and CoCr implants for mechanical performance and fixation, and compared both versions against an intact case to determine the change in bone strain energy density.ResultsThe mechanical integrity of the PEEK and CoCr components was similar in magnitude, but differences in stress patterns were found. Moreover, the cement mantle was loaded more heavily in the CoCr configuration. Under similar interface properties, the CoCr-cement interface was more at risk of failure than the PEEK-cement interface. The bone strain energy density distribution of the PEEK implant was similar to the intact case, while the CoCr implant showed signs of stress shielding, and a different distribution than the intact and PEEK models.ConclusionsDuring gait, the PEEK femoral component performed similarly to CoCr, with no added risk for the cement mantle. The reduction in stress shielding for PEEK was evident and confirms the potential reduction in long-term loss of bone stock for this all-polymer knee implant.

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The current study was designed to investigate the mechanical response of a polyetheretherketone-on-polyethylene total knee replacement device during a deep squat. Application of this high-demand loading condition can identify weaknesses of the polyetheretherketone relative to cobalt-chromium. This study investigated whether the implant is strong enough for this type of loading, whether cement stresses are considerably changed and whether a polyetheretherketone femoral component is likely to lead to reduced periprosthetic bone loss as compared to a cobalt-chromium component. A finite element model of a total knee arthroplasty subjected to a deep squat loading condition, which was previously published, was adapted with an alternative total knee arthroplasty design made of either polyetheretherketone or cobalt-chromium. The maximum tensile and compressive stresses within the implant and cement mantle were analysed against their yield and fatigue stress levels. The amount of stress shielding within the bone was compared between the polyetheretherketone and cobalt-chromium cases. Relative to its material strength, tensile peak stresses were higher in the cobalt-chromium implant; compressive peak stresses were higher in the polyetheretherketone implant. The stress patterns differed substantially between polyetheretherketone and cobalt-chromium. The tensile stresses in the cement mantle supporting the polyetheretherketone implant were up to 33% lower than with the cobalt-chromium component, but twice as high for compression. Stress shielding was reduced to a median of 1% for the polyetheretherketone implant versus 56% for the cobalt-chromium implant. Both the polyetheretherketone implant and the underlying cement mantle should be able to cope with the stress levels present during a deep squat. Relative to the cobalt-chromium component, stress shielding of the periprosthetic femur was substantially less with a polyetheretherketone femoral component.