title: Joint gap changes with patellar tendon strain and patellar position during TKA.
abstract: Balancing of the joint gap in extension and flexion is a prerequisite for success of a total knee arthroplasty. The joint gap is influenced by patellar position. We therefore hypothesized the state of the knee extensor mechanism (including the patellar tendon) would influence the joint gap. In 20 knees undergoing posterior-stabilized type total knee arthroplasties, we measured the joint gap and the patellar tendon strain from 0 degrees to 135 degrees flexion with the femoral component in position. When the patella was reduced, the joint gap was decreased at 90 degrees and 135 degrees (by 1.9 mm and 5.5 mm, respectively) compared with the gap with the patella everted. The patellar tendon strain increased with knee flexion. Patellar tendon strain at 90 degrees flexion correlated with the joint gap difference with the patella in everted and reduced positions. This suggests that in addition to the collateral ligaments, the knee extensor mechanism may have an influence on the joint gap. Therefore, accounting for extensor mechanism tightness may be important in achieving the optimal joint gap balance during total knee arthroplasty.
  
  
  METHODS
  Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, University of Toyama, 2630 Sugitani Toyama-city, Toyama, 930-0194, Japan. rgejo@med.u-toyama.ac.jp
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Gejo
authors.forename: Yuji
authors.initials: Y
authors.lastname: Morita
authors.forename: Isao
authors.initials: I
authors.lastname: Matsushita
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Sugimori
authors.forename: Tomoatsu
authors.initials: T
authors.lastname: Kimura
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000503:physiopathology / Q000601:surgery*; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation; D001696:Biomechanical Phenomena; D017885:Collateral Ligaments / Q000503:physiopathology; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology / Q000601:surgery*; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000503:physiopathology / Q000601:surgery*; D010329:Patella / Q000503:physiopathology*; D017847:Patellar Ligament / Q000503:physiopathology*; D016059:Range of Motion, Articular; D016896:Treatment Outcome