Articular cartilage wear tests

In the wear tests, the polyurethane under the tip of the sphere was subjected to a maximum stress of 2.4 MPa whereas articular cartilage(13) typically is subject to average contact stresses of 2.75 MPa. A typical "average" velocity, if only one surface moves, for human hip and knee(14) is 0.05 m/s. The polyurethane was subject to velocity from zero to 0.126 m/s. 

Conclusions. Results from the biocompatibility studies in rabbit supratellar bursa, measurement of hydrophilic properties, lubrication and wear in-vitro studies, determination of viscoelastic properties, measurement of damping coefficient and impact test, total elbow joint replacement design and in-vivo percutaneous implant experiment, all indicate that this series of polyurethanes is an excellent candidate biomaterial for the prosthetic replacement of articular cartilage, artificial joint prostheses and percutaneous implantable devices. 

It has already been shown and discussed — at least in in vitro tests with articular cartilage — that compounds which reduce friction do not necessarily reduce wear the latter was suggested as being more important [10]. It maybe helpful first of all to emphasize once again that friction and wear are different phenomena. Furthermore, certain constituents of synovial fluid (e.g., Swann s Lubricating Glycoprotein) may act to reduce friction in synovial joints while other constituents (e.g., Swann s protein complex or hyaluronic acid) may act to reduce cartilage wear. 

The general comment made here is that the use of synovial fluids — whether derived from human or animal sources and whether healthy or abnormal — is important in in vitro studies of synovial joint lubrication. The documented behavior of synovial fluid in producing low friction and wear with articular cartilage sets a reference standard and demonstrates that useful information can indeed come from in vitro tests. 

No reliable wear tests have been performed on human articular cartilage bearing surfaces under physiologic conditions. 

---