title: Improved design decreases wear in total knee arthroplasty with varus malalignment.
abstract: OBJECTIVE
  Controversy still exists whether coronal malalignment would influence the long-term survival of total knee arthroplasty (TKA). The hypothesis was that an improved design of the articular surface of modern TKA would prevent the increase in contact stresses and thus decrease the wear even when the implant was placed in a varus position. Two different designs of TKA were compared biomechanically and clinically.
  
  
  METHODS
  The patients whose prosthesis was initially placed in a varus alignment by the postoperative long-leg radiographs were selected. Seventeen knees using the NexGen LPS and 16 knees using the MG I were examined. Changes in postoperative alignment and the thickness of the polyethylene insert in a follow-up period of approximately 7 years were evaluated. Additionally, an in vitro biomechanical testing was conducted to measure the contact stresses and the contact area at the tibiofemoral joint of the NexGen LPS and the MG I components mounted on a servohydraulic testing device.
  
  
  RESULTS
  Although the long-leg alignment did not change in NexGen LPS, the varus alignment significantly progressed in MG I. The thickness of polyethylene insert in MG I decreased a significantly greater amount compared with that in NexGen LPS. Biomechanical test showed that the NexGen LPS had a larger contact area and lower mean and peak contact stresses than the MG I significantly.
  
  
  CONCLUSIONS
  These results suggest that comprehensive factors of modern prosthesis including improved implant designs could improve the durability of polyethylene insert and decrease implant failures due to component malalignment.
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan.
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Nishikawa
authors.forename: Ken
authors.initials: K
authors.lastname: Okazaki
authors.forename: Shuichi
authors.initials: S
authors.lastname: Matsuda
authors.forename: Yasutaka
authors.initials: Y
authors.lastname: Tashiro
authors.forename: Shinya
authors.initials: S
authors.lastname: Kawahara
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nakahara
authors.forename: Shigetoshi
authors.initials: S
authors.lastname: Okamoto
authors.forename: Takeshi
authors.initials: T
authors.lastname: Shimoto
authors.forename: Hidehiko
authors.initials: H
authors.lastname: Higaki
authors.forename: Yukihide
authors.initials: Y
authors.lastname: Iwamoto
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D011474:Prosthesis Design; D011859:Radiography; D012189:Retrospective Studies