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The in vitro mechanical properties of 14 wrist extensor tendons salvaged at surgery from patients with inflammatory (rheumatoid) arthritis and noninflammatory arthrosis were measured in uniaxial tension and compared. The rheumatoid tendons had higher extensibility at low stresses, lower stiffness in the linear portion of the stress-strain curve, greater rates of stress relaxation, and lower ultimate strengths than did the nonrheumatoid tendons. Differences in tangent modulus, stress remaining at 100 seconds, and ultimate tensile strength were significant at the 95% confidence level. In vivo, mechanically impaired tendons may play an important role in destabilization of the wrist in patients with rheumatoid arthritis.

Surface degradation of UHMWPe is recognized as a leading clinical concern, limiting the long-term performance in total knee replacements. Eight retrieved tibial plateaux and six wear screening test samples were evaluated for surface degradation features and microstructural features. The surface degradation features were assessed using stereomicroscopy and scanning electron microscopy. Microstructural features were evaluated using optical microscopy of thin cross-sections and a permanganate etching technique. The pitting mechanism of wear was observed on all eight retrieved TKR and covered an average of 12.6% of the surface area. The size of the pits were similar to the size of grains observed in the microstructural evaluation - approximately 100 to 200 microm. The presented observations of pitting in retrieved knee implants have shown that the post-processing microstructure may influence this mechanism of surface degradation and hence the wear products.

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