panel met to decide whether to impose new standards, taking into account findings of the study in The Lancet. No new standards, such as routine checking of blood levels of metal ions, were set, but guidance was updated. The U.S. FDA does not require hip implants to be tested in clinical trials before they can be sold in the U.S. Instead, companies making new hip implants only need to prove that they are "substantially equivalent" to other hip implants already on the market. The exception is metal-on-metal implants, which were not tested in clinical trials, but, due to the high revision rate of metal-on-metal hips, the FDA has stated that, in the future, clinical trials will be required for approval, and that post-market studies will be required to keep metal-on-metal hip implants on the market. Modern process The modern artificial joint owes much to the 1962 work of Sir John Charnley at Wrightington Hospital. His work in the field of tribology resulted in a design that almost completely replaced the other designs by the 1970s. Charnley's design consisted of three parts: stainless steel one-piece femoral stem and head polyethylene (originally Teflon), acetabular component, both of which were fixed to the bone using PMMA (acrylic) bone cement The replacement joint, which was known as the Low Friction Arthroplasty, was lubricated with synovial fluid. The small femoral head () was chosen for Charnley's belief that it would have lower friction against the acetabular component and thus wear out the acetabulum more slowly. Unfortunately, the smaller head dislocated more easily. Alternative designs with larger heads such as the Mueller prosthesis were proposed. Stability was improved, but acetabular wear and subsequent failure rates were increased with these designs. The Teflon acetabular components of Charnley's early designs failed within a year or two of implantation. This prompted a search for a more suitable material. A German salesman showed a polyethylene gear sample to Charnley's machinist, sparking the idea to use this material for the acetabular component. The UHMWPE acetabular component was introduced in 1962. Charnley's other major contribution was to use polymethylmethacrylate (PMMA) bone cement to attach the two components to the bone. For over two decades, the Charnley Low Friction Arthroplasty, and derivative designs were the most used systems in the world. It formed the basis for all modern hip implants. An example can be seen at the Science Museum, London. The Exeter hip