title: Medial placement of the acetabular component in an alumina-on-alumina total hip arthroplasty: a comparative study with propensity score matching.
abstract: OBJECTIVE
  In an alumina-on-alumina total hip arthroplasty (THA), recommended with a small inclination angle <45°, the acetabular component (cup) may be positioned more medially to be covered almost completely by host bone. The purpose of this study was to identify the correlating factors and to evaluate the outcomes of medial placement of the cup in patients with alumina-on-alumina THAs.
  
  
  METHODS
  Using the propensity score matching with age, gender, body mass index, initial diagnosis, and the length of follow-up as variables, 38 hips with a medialized cup and 38 hips with a non-medialized one were identified from 389 hips in 347 who patients underwent primary alumina-on-alumina THA and followed up for more than 7 years. Clinical and radiological outcomes were compared between the two groups.
  
  
  RESULTS
  Preoperative acetabular medial wall thickness and the cup inclination angle were significantly smaller in the medialization group compared to the non-medialization group. Center edge angle, cup size, and coverage by host bone were not significantly different between the two groups. The hip center of rotation was significantly medialized in the medialization group. The Harris hip scores were not significantly different between the two groups. No component loosening or osteolysis was observed and no revision was required in either groups.
  
  
  CONCLUSIONS
  Thin acetabular medial wall and a small inclination angle of the cup were the correlating factors of medial placement of the cup in patients who underwent an alumina-on-alumina THA. Medial placement did not lead to differences in the clinical or radiological outcomes.
authors.affiliation: Department of Orthopedic Surgery, Seoul National University College of Medicine, 101 Daehak-ro, Jongno-gu, Seoul, South Korea. jjyos@snu.ac.kr
authors.forename: Jeong Joon
authors.initials: JJ
authors.lastname: Yoo
authors.forename: Hyeong Jo
authors.initials: HJ
authors.lastname: Yoon
authors.forename: Pil Whan
authors.initials: PW
authors.lastname: Yoon
authors.forename: Young-Kyun
authors.initials: YK
authors.lastname: Lee
authors.forename: Hee Joong
authors.initials: HJ
authors.lastname: Kim
mesh_terms: D000077:Acetabulum / Q000601:surgery*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000537:Aluminum Oxide; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation / Q000379:methods*; D001672:Biocompatible Materials; D005260:Female; D006621:Hip Joint; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D061825:Metal-on-Metal Joint Prostheses; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000601:surgery*; D057216:Propensity Score; D011474:Prosthesis Design; D055815:Young Adult
chemical_list: D001672:Biocompatible Materials; D000537:Aluminum Oxide