title: Shape of the joint gap for 90 degrees and 120 degrees knee flexion after total knee arthroplasty.
abstract: BACKGROUND
  The joint gap is set rectangular at 90 degrees flexion during total knee arthroplasty (TKA). However, the condition of the joint gap in deep knee flexion is obscure.
  
  
  METHODS
  The method for obtaining a posteroanterior view radiograph of the knee at 90 degrees flexion (the epicondylar view) was modified, and a method to obtain an anteroposterior view radiograph at 120 degrees flexion (deep flexion view) was established. With this method, subjects lie on the radiography table with their thighs placed on a device so their lower legs hang down in neutral rotation with a 1.5-kg weight attached to the ankle. The joint gap angle and medial and lateral joint space widths were measured on epicondylar view and deep flexion view radiographs in 20 normal male subjects, 20 normal female subjects, and 20 subjects after TKA.
  
  
  RESULTS
  The joint gap was almost rectangular at two flexion angles in normal subjects. In the implanted knees, the gap angle was 1.4 degrees varus +/- 3.3 degrees (mean +/- standard deviation), and no significant difference was found between medial and lateral joint space widths at 90 degrees flexion. In contrast, the gap angle was 2.5 degrees varus +/- 2.5 degrees and the lateral joint space width was significantly wider than the medial joint space width at 120 degrees flexion (P < 0.001). The gap angle was more varus with a significant difference in the implanted knees than that in the normal subjects at 120 degrees flexion (P < 0.001).
  
  
  CONCLUSIONS
  The joint gap was trapezoidal with a wider lateral side at 120 degrees flexion even though it was almost rectangular at 90 degrees flexion after TKA.
authors.affiliation: Department of Orthopaedic Surgery, Yoshizuka Hayashi Hospital, 7-6-29 Yoshizuka, Hakata-ku, Fukuoka, 812-0041, Japan.
authors.forename: Ryuji
authors.initials: R
authors.lastname: Nagamine
authors.forename: Keiichi
authors.initials: K
authors.lastname: Kondo
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nomura
authors.forename: Koichi
authors.initials: K
authors.lastname: Kanekasu
authors.forename: Motoki
authors.initials: M
authors.lastname: Sonohata
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Sugioka
mesh_terms: D000328:Adult; D053587:Arthrometry, Articular; D019645:Arthroplasty, Replacement, Knee; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000601:surgery*; D008297:Male; D011859:Radiography; D016059:Range of Motion, Articular; D055815:Young Adult