title: Joint gap measurement in total knee arthroplasty using a tensor device with the same articulating surface as the prosthesis.
abstract: BACKGROUND
  We developed a new tensor to measure the joint gap throughout knee flexion during total knee arthroplasty (TKA). This tensor has the same articular shape as that of the tibial liner, including the post structure and the curvature of femorotibial articular surface, to measure the gap intraoperatively under the same conditions as after TKA. The present study aimed to examine the precision of the new tensor for gap measurement after implantation.
  
  
  METHODS
  We performed TKA using the modified gap technique in four cadaveric knees and measured the gaps using the new tensor. The intra-observer and inter-observer error of the tensor was analyzed using 168 measurements of the gaps as determined at least twice by two surgeons. In addition, the gaps in rotating-platform posterior-stabilized TKA were measured at seven positions with the knee bending from extension to full flexion.
  
  
  RESULTS
  The inter-observer and intra-observer errors were 0.8 and 0.3 mm, respectively, indicating precise and reproducible gap measurement. The gaps before implantation in reduced patellar position were 12.1 mm at extension and 12.5 mm at 90° flexion. The gaps after implantation were 9.1, 12.9, 13.1, 13.5, 13.8, 13.3, and 10.1 mm at 0°, 30°, 45°, 60°, 90°, 120°, and full flexion, respectively.
  
  
  CONCLUSIONS
  The new tensor provides precise and reproducible measurements. Although the joint gap before implantation was parallel and equal at extension and 90° flexion, the joint gap after implantation was variable throughout knee flexion. This feature of the gap should be considered during the operation.
authors: Department of Orthopaedic Surgery, Osaka City General Hospital, 2-13-22, Miyakojima-hondori, Miyakojima-ku, Osaka, 534-0021, Japan, ichi23@js3.so-net.ne.jp.
authors: Yoshio
authors: Y
authors: Matsui
authors: Shigeru
authors: S
authors: Nakagawa
authors: Yukihide
authors: Y
authors: Minoda
authors: Shigekazu
authors: S
authors: Mizokawa
authors: Yoshio
authors: Y
authors: Tokuhara
authors: Yoshinori
authors: Y
authors: Kadoya
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation* / Q000379:methods; D001837:Body Weights and Measures / Q000295:instrumentation; D004867:Equipment Design; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000517:prevention & control; D007719:Knee Joint / Q000601:surgery*; D007720:Knee Prosthesis; D020370:Osteoarthritis, Knee / Q000601:surgery*; D010329:Patella / Q000601:surgery; D011187:Posture; D011474:Prosthesis Design; D016059:Range of Motion, Articular; D013977:Tibia / Q000601:surgery; D016896:Treatment Outcome