Shape of Cemented Cups and Shape & Surface Roughness of Cemented Stems

The history of successful cemented total hip arthroplasty (THA) began with the pioneering development of the low-friction arthroplasty in England by Sir Dr. Charnley (1911–1982), who combined an ultrahigh molecular weight polyethylene (UHMWPE) cup with a 22.2 mm nonmodular metal head. This UHMWPE cup is the prototype of the present cemented cups. Charnley, born in 1911, moved to Wrightington Hospital, West Lancashire, in 1958, to set up a hip surgery center where he conducted extensive research on hip biomechanics. He continued performing basic research on THA in a hospital laboratory. To mimic the very low coefficient of friction (0.001) of the cartilage-to-cartilage sliding surfaces of biological joints, he thought that a material with a smooth surface (low coefficient of friction) that did not rely on joint fluid lubrication would be most suitable to construct the sliding surface of the joint prosthesis; he thus introduced polytetrafluoroethylene (PTFE) cups. However, PTFE wear debris was so large and plentiful, and the tissue reaction was so strong that most cases required early revision surgery. This led Charnley to recognize the importance of wear debris, and he discontinued the use of PTFE in 1961. While searching for other materials, he discovered UHMWPE, which, despite having a coefficient of friction more than five times higher than that of PTFE, had 500–1000 times higher wear resistance. In addition, boundary lubrication by the joint fluid promoted reduced friction for UHMWPE. In 1962, Charnley began to perform cemented THA with UHMWPE cups and 22.2 mm stainless steel heads. He termed THA with this combination as a low-friction arthroplasty, and excellent clinical results were reported in sequence in the 1970s [2–4]. Subsequently, low-friction arthroplasty was adopted worldwide. The 22.2-mm-inner diameter cup was the most commonly used cup for cemented THA until 1998, when highly crosslinked polyethylene (HXLPE) began to be applied clinically, and its excellent abrasion resistance was confirmed in the 2000s.