title: Effects of four different surgical approaches on intra-operative joint gap in posterior-stabilized total knee arthroplasty.
abstract: OBJECTIVE
  The effects of surgical approaches and patellar positions on joint gap measurement during total knee arthroplasty (TKA) remain unclear. We hypothesized that joint gap changes with different knee flexion angles would not be consistent within four different approaches and two different patellar positions.
  
  
  METHODS
  This study enrolled 80 knees undergoing posterior-stabilized TKA. For 60 varus knees, parapatellar, midvastus, and subvastus approaches were used in 20 knees each. For 20 valgus knees, a lateral subvastus approach was used. Component gap length and inclination were measured intra-operatively using a specific tensor device under 40 lb with the patella reduced or shifted laterally, at 0°, 45°, 90°, and 135° of knee flexion.
  
  
  RESULTS
  Mean gap lengths at 45° and 90° of knee flexion were significantly larger with the parapatellar approach than with midvastus or lateral subvastus approaches (P < 0.05). Regarding gap inclination, varus angle increased linearly through the entire arc of flexion in all four approaches. When the patella was shifted laterally, gap lengths at 45°, 90°, and 135° were significantly reduced compared with those for the patella reduced in the subvastus approach, whereas gap length was constant in the parapatellar approach, regardless of patellar position.
  
  
  CONCLUSIONS
  Joint gap kinematics was not consistent within four different approaches and two different patellar positions. Relatively large gaps at 45° and 90° were unique features for the parapatellar approach. Surgeons should be aware that the flexion gap is reduced when the patella is shifted laterally in vastus medialis-preserving approaches such as the subvastus approach.
  
  
  METHODS
  II.
authors.affiliation: Department of Orthopaedic Surgery, Keio University, 35 Shinanomachi, Tokyo, 160-8582, Japan. y.niki@lib.bekkoame.ne.jp
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Niki
authors.forename: Yuki
authors.initials: Y
authors.lastname: Takeda
authors.forename: Hiroya
authors.initials: H
authors.lastname: Kanagawa
authors.forename: Wataru
authors.initials: W
authors.lastname: Iwamoto
authors.forename: Hideo
authors.initials: H
authors.lastname: Matsumoto
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Enomoto
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Toyama
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Suda
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D001696:Biomechanical Phenomena; D017760:Bone Malalignment / Q000209:etiology / Q000601:surgery; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000150:complications / Q000503:physiopathology / Q000601:surgery*; D010329:Patella / Q000502:physiology / Q000601:surgery*; D016059:Range of Motion, Articular; D016896:Treatment Outcome