title: Kinematics of the knee after unicompartmental arthroplasty is not the same as normal and is similar to the kinematics of the knee with osteoarthritis.
abstract: OBJECTIVE
  It is common to assert that restoration of normal knee kinematics is essential for the best functional result after knee arthroplasty. Previous studies using the progression of the geometric centre axis have suggested that kinematics after unicompartmental arthroplasty is markedly different from the normal. For this study, the transepicondylar axis was used because this axis is closer to the flexion axis and should be a better reference for motion. The following hypothesis was tested: the transepicondylar axis would again show that the postoperative kinematics does not restore normal motion and is closer to that before replacement.
  
  
  METHODS
  Seventeen osteoarthritic knees were tested before and after unicompartmental arthroplasty using a three-dimensional to two-dimensional registration technique tracking the transepicondylar axis to calculate translation and rotation of this axis. Results were compared for the seventeen knees before and after arthroplasty and were compared to the normal knee as measured in our previous study.
  
  
  RESULTS
  Similar motion patterns in the pre- and postoperative knees were shown but both the pre- and postoperative motion were markedly different from the normal knee.
  
  
  CONCLUSIONS
  This result supported our hypothesis. The clinical relevance is that medial unicompartmental arthroplasty cannot restore the motion of the knee to normal in the living knee. Therefore, it would be expected that the patient for unicompartmental knee might not feel normal. It may not be possible depending on ligaments alone to restore the knee to normal, and the changes in the articular shapes and the surgical procedure may also be necessary.
authors.affiliation: Department of Orthopedic Surgery, Department of Regenerative and Transplant Medicine, Niigata University Graduate School of Medical and Dental Science, 1-757 Asahimachi-dori Chuo-ku, Niigata City, Niigata, 951-8510, Japan, tomo07301977@yahoo.co.jp.
authors.forename: Tomoharu
authors.initials: T
authors.lastname: Mochizuki
authors.forename: Takashi
authors.initials: T
authors.lastname: Sato
authors.forename: John David
authors.initials: JD
authors.lastname: Blaha
authors.forename: Osamu
authors.initials: O
authors.lastname: Tanifuji
authors.forename: Koichi
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamagiwa
authors.forename: Satoshi
authors.initials: S
authors.lastname: Watanabe
authors.forename: Munenori
authors.initials: M
authors.lastname: Matsueda
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Koga
authors.forename: Go
authors.initials: G
authors.lastname: Omori
authors.forename: Naoto
authors.initials: N
authors.lastname: Endo
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000379:methods*; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D011859:Radiography; D016059:Range of Motion, Articular