Using a new, non-invasive method, we measured the patellofemoral force (PFF) in cadaver knees mounted in a rig to simulate weight-bearing. The PFF was measured from 20° to 120° of flexion before and after implanting three designs of knee prosthesis. Medial unicompartmental arthroplasty with a meniscal-bearing prosthesis and with retention of both cruciate ligaments caused no significant change in the PFF. After arthroplasty with a posterior-cruciate-retaining prosthesis and division of the anterior cruciate ligament, the PFF decreased in extension and increased by 20% in flexion. Implantation of a posterior stabilised prosthesis and division of both cruciate ligaments produced a decrease in the PFF in extension but maintained normal load in flexion. There was a direct relationship between the PFF and the angle made with the patellar tendon and the long axis of the tibia. The abnormalities of the patellar tendon angle which resulted from implantation of the two total prostheses explain the observed changes in the PFF and show how the mechanics of the patellofemoral joint depend upon the kinematics of the tibiofemoral articulation

Aims

The intra-articular administration of tranexamic acid (TXA) has been shown to be effective in reducing blood loss in unicompartmental knee arthroplasty and anterior cruciate reconstruction. The effects on human articular cartilage, however, remains unknown. Our aim, in this study, was to investigate any detrimental effect of TXA on chondrocytes, and to establish if there was a safe dose for its use in clinical practice. The hypothesis was that TXA would cause a dose-dependent damage to human articular cartilage.

Previous research has shown an increase in chromosomal aberrations in patients with worn implants. The type of aberration depended on the type of metal alloy in the prosthesis. We have investigated the metal-specific difference in the level of DNA damage (DNA stand breaks and alkali labile sites) induced by culturing human fibroblasts in synovial fluid retrieved at revision arthroplasty.

All six samples from revision cobalt-chromium metal-on-metal and four of six samples from cobalt-chromium metal-on-polyethylene prostheses caused DNA damage. By contrast, none of six samples from revision stainless-steel metal-on-polyethylene prostheses caused significant damage. Samples of cobalt-chromium alloy left to corrode in phosphate-buffered saline also caused DNA damage and this depended on a synergistic effect between the cobalt and chromium ions.

Our results further emphasise that epidemiological studies of orthopaedic implants should take account of the type of metal alloy used.