PubMed · 13503245
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W E TUCKER. 1958-01-18. The difficult knee.. https://doi.org/10.1016/s0140-6736(58)90654-8
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New porous polyurethane urea and polyurethane amide scaffolds for meniscal reconstruction have been developed in a solvent-free process. As soft segments, copolymers of 50/50 L-lactide/epsilon-caprolactone have been used. After terminating the soft segment with diisocyanates, chain extension was performed with adipic acid and water. Reaction between the isocyanate groups and adipic acid or water provides carbon dioxide and results in a porous polymer. Extra hydroxyl-terminated prepolymer was added in order to regulate the amount of carbon dioxide formed in the foaming reaction. Furthermore, salt crystals ranging in size from 150 to 355 microm were added in order to induce macroporosity. The pore size was regulated by addition of surfactant and by the use of ultrasonic waves. The resulting porous polymer scaffolds exhibit good mechanical properties like a high-compression modulus of 150 kPa. Chain extension with adipic acid results in better mechanical properties due to better defined hard segments. This results from the lower nucleophilicity of carboxylic acids compared to water and alcohols. By adjusting the reaction conditions, materials in which macropores are interconnected by micropores can be obtained. On degradation only non-toxic products will be released; importantly, the materials were obtained by a simple, reproducible and solvent-free procedure.
Lateral instability of the knee is less frequent but more disabling than medial instability of a comparable amount. At the same time the diagnostic tests for lateral instability are more subtle and more frequently misinterpreted. Posterolateral rotatory subluxation is demonstrated by an apparently positive posterior drawer test with the tibia in neutral rotation or by the external rotation-recurvatum test with the knee in extension. Anterolateral rotatory subluxation is present when the anterior drawer test with the tibia in neutral rotation demonstrates that the lateral tibial condyle appears to become more prominent or that both condyles appear to become equally prominent.
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