title: Tibiofemoral forces for the native and post-arthroplasty knee: relationship to maximal laxity through a functional arc of motion.
abstract: OBJECTIVE
  Accurate soft tissue balance must be achieved to improve functional outcome after total knee arthroplasty (TKA). Sensor-integrated tibial trials have been introduced that allow real-time measurement of tibiofemoral kinematics during TKA. This study examined the interplay between tibiofemoral force and laxity, under defined intraoperative conditions, so as to quantify the kinematic behaviour of the CR femoral single-radius knee.
  
  
  METHODS
  TKA was undertaken in eight loaded cadaveric specimens. Computer navigation in combination with sensor data defined laxity and tibiofemoral contact force, respectively, during manual laxity testing. Fixed-effect linear modelling allowed quantification of the effect for flexion angle, direction of movement and TKA implantation upon the knee.
  
  
  RESULTS
  An inverse relationship between laxity and contact force was demonstrated. With flexion, laxity increased as contact force decreased under manual stress. Change in laxity was significant beyond 30° for coronal plane laxity and beyond 60° for rotatory laxity (p < 0.01). Rotational stress in mid-flexion demonstrated the greatest mismatch in inter-compartmental forces. Contact point position over the tibial sensor demonstrated paradoxical roll-forward with knee flexion.
  
  
  CONCLUSIONS
  Traditional balancing techniques may not reliably equate to uniform laxity or contact forces across the tibiofemoral joint through a range of flexion and argue for the role of per-operative sensor use to aid final balancing of the knee.
authors.affiliation: , Newcastle upon Tyne, Tyne and Wear, UK.
authors.forename: William A
authors.initials: WA
authors.lastname: Manning
authors.affiliation: , Newcastle upon Tyne, Tyne and Wear, UK.
authors.forename: Kanishka
authors.initials: K
authors.lastname: Ghosh
authors.affiliation: , Newcastle upon Tyne, Tyne and Wear, UK.
authors.forename: Alasdair
authors.initials: A
authors.lastname: Blain
authors.affiliation: , Newcastle upon Tyne, Tyne and Wear, UK.
authors.forename: Lee
authors.initials: L
authors.lastname: Longstaff
authors.affiliation: , Newcastle upon Tyne, Tyne and Wear, UK. david.deehan@nuth.nhs.uk.
authors.forename: David John
authors.initials: DJ
authors.lastname: Deehan
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000379:methods; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D005269:Femur / Q000601:surgery; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular; D012399:Rotation; D013977:Tibia / Q000601:surgery
keywords: Balance; Knee arthroplasty; Laxity; Tibiofemoral force