PubMed · 5556107
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W V James. 1971. The ring total hip replacement.. https://pubmed.ncbi.nlm.nih.gov/5556107/
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Differential scanning calorimetry (DSC) was used to examine thermal and thermooxidative properties of ultrahigh molecular weight polyethylene (UHMW-PE) of five acetabular components of failed orthopedic implants retrieved at revision of total hip arthoplasty. The results were compared with controls (unimplanted acetabular cups, a 20-year-old slab of UHMW-PE, and raw material). Profiles of exothermic peaks indicated increased levels of oxidation in all retrieved cups. In three retrieved cups, DSC revealed an additional peak of endotherm that was not seen in control samples. The additional endotherm peaks were not artifacts due to oxidation during scanning, heat buildup during cutting of the samples, or the sterilization method after retrieval. The additional peak was associated with the bulk of the polymer that was extracted with hexane. It varied in relative area, depending on its original location of the sample in a cup, implicating local variability in the extent of changes in material property. The distribution of the changes suggests that, during implantation, tissue exposure and friction affected the level of oxidation and degree of crystallinity in the UHMW-PE to a greater degree than did loading alone. Overall results showed that DSC may be a useful tool in evaluating changes in the properties of UHMW-PE orthopedic components in vivo.
To evaluate possible relationships between body size and articular architecture, femoral head radius and subchondral plate thickness were assessed in skeletal hip joints from normal primates. The relative "contact pressure" on bearing surfaces was estimated from the measured radius and the normal body mass in species ranging from Cebuella pygmaea (0.1 kg) to Gorilla gorilla (170 kg). Subchondral plate thickness was evaluated by computed tomography in species ranging from Cercopithecus neglectus (4.0 kg) to Gorilla gorilla. Neither the "contact pressure" nor the thickness of the femoral subchondral plate varied substantially among species. In contrast, the acetabular subchondral plate thickened significantly (p = 0.01) as body size increased. This finding is interpreted as an osseous response to tensile acetabular stress, which can be expected to increase directly with the radius of curvature.