John Charnley’s Assistant: Harry Craven and the Charnley Hip

The years 1958 to 1966 represent a period in which the modern hip replacement operation was developed by John Charnley at the Wrightington Hospital, based on Charnley’s concept of Low Frictional Torque Arthroplasty (LFA) in which a stainless steel femoral prosthesis with a head of only 7/8″ (22.225 mm) acts against a plastic acetabulum. The original PTFE socket material, however, was found after a couple of years to wear rapidly, with the wear debris causing an adverse tissue reaction requiring surgical revision. It was at this time that Charnley was considering discontinuing work on the hip operation, when a new plastic RH1000 (UHMWPE) was tested, against Charnley’s instructions, by his assistant Harry Craven. This material proved the turning point, and the Charnley Total Hip Arthroplasty has come to be described as the operation of the century. With little funding for materials, most of the test equipment was constructed by Craven, after scavenging from a local scrap yard. Despite the important part played by Craven, he remains largely unknown to a wider engineering audience and when mentioned is often not named, being only referred to as Charnley’s assistant.