title: Decreased extension gap and valgus alignment after implantation of total knee prosthesis in primary varus knees.
abstract: OBJECTIVE
  It was hypothesised that implantation of a total knee prosthesis may change the size and shape of the joint gap. To test this hypothesis, a tensor device was used which was specifically designed to reproduce the conditions before and after implantation, including attachment of the polyethylene insert trial. This study aimed to compare the joint gaps before and after implantation of a total knee prosthesis using this new tensor device.
  
  
  METHODS
  A total of 259 primary varus knees were included in this study. Knees were exposed using a medial parapatellar approach, and the anterior and posterior cruciate ligaments were resected. After the trial reduction, the intraoperative joint gap kinematics was measured using the tensor device.
  
  
  RESULTS
  Implantation of a total knee prosthesis decreased the size of the extension joint gap and made it valgus, but did not influence the size or shape of the flexion joint gap.
  
  
  CONCLUSIONS
  The present findings suggest that the classical gap technique, which creates equal and rectangular extension and flexion joint gaps in the bone cutting surface, results in an imbalance between the extension and flexion joint gaps after implantation. To achieve equal and rectangular extension and flexion joint gaps after implantation, the prepared extension joint gap should be about 2 mm larger than the flexion joint gap and slightly varus before implantation in primary varus knees.
  
  
  METHODS
  Therapeutic study, Level II.
authors.affiliation: Department of Orthopaedic Surgery, Osaka City University Graduate School of Medicine, 1-4-3 Asahi-machi Abeno-ku, Osaka, 545-8585, Japan. yminoda@msic.med.osaka-cu.ac.jp.
authors.forename: Yukihide
authors.initials: Y
authors.lastname: Minoda
authors.affiliation: Department of Orthopaedic Surgery, Osaka Rosai Hospital, 1179-3 Nagasone-cho Kita-ku Sakai, Osaka, 591-8025, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Nakagawa
authors.affiliation: Department of Orthopaedic Surgery, Osaka General Hospital, 3-1-56 Mandaihigashi Sumiyoshi-ku, Osaka, 558-8558, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Sugama
authors.affiliation: Hanwa Joint Reconstruction Center, 3176 Fukaikitamachi Naka-ku Sakai, Osaka, 599-8271, Japan.
authors.forename: Tessyu
authors.initials: T
authors.lastname: Ikawa
authors.affiliation: Department of Orthopaedic Surgery, Shinbeppu Hospital, 3898 Tsurumi Beppu, Oita, 874-0833, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Noguchi
authors.affiliation: Department of Orthopaedic Surgery, Oita University Faculty of Medicine Graduate School of Medicine, 1-1 Idaigaoka Hazama-cho Yufu, Oita, 879-5593, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Hirakawa
authors.affiliation: Department of Orthopaedic Surgery, Osaka Rosai Hospital, 1179-3 Nagasone-cho Kita-ku Sakai, Osaka, 591-8025, Japan.
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Matsui
authors.affiliation: Department of Orthopaedic Surgery, Osaka City University Graduate School of Medicine, 1-4-3 Asahi-machi Abeno-ku, Osaka, 545-8585, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Nakamura
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D001696:Biomechanical Phenomena; D005260:Female; D056304:Genu Valgum / Q000150:complications / Q000601:surgery*; D006801:Humans; D007719:Knee Joint / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D020370:Osteoarthritis, Knee / Q000150:complications / Q000601:surgery*; D011095:Polyethylenes; D016059:Range of Motion, Articular
chemical_list: D011095:Polyethylenes
keywords: Joint gap after implantation; Joint gap before implantation; Total knee arthroplasty