THE OTTO AUFRANC AWARD Highly Cross-linked Polyethylene in Total Hip Arthroplasty Randomized Evaluation of Penetration Rate in Cemented and Uncemented Sockets Using Radiostereometric Analysis Georgios Digas, MD, PhD; Johan Kärrholm, MD, PhD; Jonas Thanner, MD, PhD; Henrik Malchau, MD, PhD; and Peter Herberts, MD, PhD The annual wear rate in polyethylene articulations should be 0.1 mm or less to avoid future osteolysis. Highly cross-linked polyethylene shows an 80 to 90% wear reduction in hip simu- lator testing, but the clinical documentation of this new poly- ethylene is still inadequate. We evaluated the highly cross- linked polyethylene in two prospective randomized clinical studies. Thirty-two patients (12 men, 20 women; 64 hips) with a median age of 48 years (range, 29–70 years) with bilateral primary or secondary arthrosis of the hip had hy- brid total hip arthroplasty with liners made of highly cross- linked polyethylene on one side and conventional polyethyl- ene on the other. Twenty-seven patients in this study have passed 2 years followup. A further group, comprised of 60 patients (61 hips) with a median age of 55 years (range, 35–70 years), was randomized to receive either highly cross-linked polyethylene or conventional cemented all-polyethylene of the same design. Forty-nine of these 60 patients have been observed for 3 years. In both studies all patients received Spectron stems with 28-mm Co-Cr heads. Radiostereometric examinations with the patient supine or standing were done at regular intervals. Wear was measured in the supine posi- tion from the first postoperative week, whereas standing ex- aminations were initiated 3 months after the operation. The penetration rate almost was identical in the study and con- trol groups at 6 months after the operation. Thereafter, the penetration rate leveled out in the two groups with highly cross-linked polyethylene. At 2 years the highly cross-linked polyethylene liner showed 62% lower proximal penetration and 31% lower total (three-dimensional) penetration when the patients were examined in supine position. The highly crosslinked all-polyethylene cemented cups showed lower proximal penetration in both positions. The better wear per- formance of highly cross-linked polyethylene could increase the implant longevity. Longer followup is needed to evaluate if this new material is associated with less occurrence of osteolysis. Osteolysis thought to originate from polyethylene (PE) wear debris has become one of the most notable factors affecting long-term survivorship of the total hip replace- ment (THR). 1,7,9,14 Alternative bearing surfaces have been suggested to reduce this problem but have some other disadvantages. 4,6,11 The long history and popularity of ul- tra-high molecular weight polyethylene (UHMWPE) as a bearing surface has stimulated the development of more wear-resistant PE materials. In the 1970s, Oonishi et al 30 found increased wear resistance of high-dose gamma- irradiated PE (1000 kGy) using a cylinder-on-flat wear test machine. Between 1971 and 1978, 62 patients had THRs using this material in the socket with excellent results. 29 Recently, several methods, such as radiation, peroxide, or silane treatments, have been used to increase cross-linking of the PE. 17 Each of these methods has been reported by their respective proponents to improve the wear character- istics relative to noncross-linked or nominally cross-linked PE. 18,19,22,35 From the Department of Orthopaedics, Institute of Surgical Science, Sahl- grenska University Hospital, Göteborg University, Göteborg, Sweden. Each author certifies that his institution has approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research, and that informed consent was obtained. The institution of the authors has received funding from the Swedish Re- search Council (Project nr.K2002-73X-0741-16D); the Göteborg Medical Society; Centerpulse, Switzerland; and Zimmer, USA. Correspondence to: Georgios Digas, MD, PhD, Department of Orthopaedics, Institute of Surgical Science, Sahlgrenska University Hospital, Göteborg University, S-41345 Goteborg Sweden. Phone: 46 31 3424441; Fax: 46 31 8255991; E-mail: georgios.digas@vgregion.se. DOI: 10.1097/01.blo.0000150314.70919.e3 CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Number 429, pp. 6–16 © 2004 Lippincott Williams & Wilkins 6