title: Intraoperative joint gaps and mediolateral balance affect postoperative knee kinematics in posterior-stabilized total knee arthroplasty.
abstract: BACKGROUND
  Adjusting joint gaps and establishing mediolateral (ML) soft tissue balance are considered essential interventions for better outcomes in total knee arthroplasty (TKA). However, the relationship between intraoperative laxity measurements and weightbearing knee kinematics has not been well explored. This study aimed to quantify the effect of intraoperative joint gaps and ML soft tissue balance on postoperative knee kinematics in posterior-stabilized (PS)-TKA.
  
  
  METHODS
  We investigated 44 knees in 34 patients who underwent primary PS-TKA by a single surgeon. The central joint gaps and ML tilting angles at 0°, 10°, 30°, 60°, 90°, 120° and 135° flexion were measured during surgery. At a minimum of two year follow-up, we analyzed in vivo kinematics of these knees and examined the influence of intraoperative measurements on postoperative kinematics.
  
  
  RESULTS
  Gap difference of knee flexion at 135° minus 0° was correlated with the total posterior translation of lateral femoral condyle (r=0.336, p=0.042) and femoral external rotation (r=0.488, p=0.002) during squatting, anteroposterior position of lateral femoral condyle (r=-0.510, p=0.001) and maximum knee flexion (r=0.355, p=0.031) in kneeling. Similar correlations were observed between deep flexion gap differences with respect to the 90° reference and postoperative knee kinematics. Well-balanced knees showed less anterior translation of medial femoral condyle in mid- to deep flexion, consistent femoral external rotation, and the most neutral valgus/varus rotation compared with unbalanced knees.
  
  
  CONCLUSIONS
  These findings indicate the importance of adequate intraoperative joint gaps in deep flexion and ML soft tissue balance throughout the range of motion.
authors.affiliation: Department of Mechanical & Aerospace Engineering, University of Florida, Gainesville, FL, USA; Department of Orthopaedic Surgery, Tsuchiura Kyodo General Hospital, Tsuchiura, Ibaraki, Japan; Department of Orthopaedic Surgery, Tokyo Medical and Dental University Hospital, Tokyo, Japan. Electronic address: watanabe.orj@tmd.ac.jp.
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Watanabe
authors.affiliation: Department of Orthopaedic Surgery, Tokyo Medical and Dental University Hospital, Tokyo, Japan. Electronic address: muneta.orj@tmd.ac.jp.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Muneta
authors.affiliation: Department of Orthopaedic Surgery, Tokyo Medical and Dental University Hospital, Tokyo, Japan. Electronic address: sekiya.orj@tmd.ac.jp.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Sekiya
authors.affiliation: Department of Mechanical & Aerospace Engineering, University of Florida, Gainesville, FL, USA. Electronic address: banks@ufl.edu.
authors.forename: Scott A
authors.initials: SA
authors.lastname: Banks
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D001696:Biomechanical Phenomena; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007432:Intraoperative Period; D007719:Knee Joint / Q000503:physiopathology / Q000601:surgery*; D007720:Knee Prosthesis; D008297:Male; D020370:Osteoarthritis, Knee / Q000503:physiopathology / Q000601:surgery*; D011184:Postoperative Period; D016059:Range of Motion, Articular / Q000502:physiology*; D012189:Retrospective Studies; D016474:Weight-Bearing
keywords: Intraoperative joint gap; Mediolateral balance; Posterior-stabilized; Postoperative knee kinematics; Total knee arthroplasty