title: Does joint line elevation after revision knee arthroplasty affect tibio-femoral kinematics, contact pressure or collateral ligament lengths? An in vitro analysis.
abstract: BACKGROUND
  Correct restoration of the joint line is generally considered as crucial when performing total knee arthroplasty (TKA). During revision knee arthroplasty however, elevation of the joint line occurs frequently. The general belief is that this negatively affects the clinical outcome, but the reasons are still not well understood.
  
  
  METHODS
  In this cadaveric in vitro study the biomechanical consequences of joint line elevation were investigated using a previously validated cadaver model simulating active deep knee squats and passive flexion-extension cycles. Knee specimens were sequentially tested after total knee arthroplasty with joint line restoration and after 4 mm joint line elevation.
  
  
  RESULTS
  The tibia rotated internally with increasing knee flexion during both passive and squatting motion (range: 17° and 7° respectively). Joint line elevation of 4 mm did not make a statistically significant difference. During passive motion, the tibia tended to become slightly more adducted with increasing knee flexion (range: 2°), while it went into slighlty less adduction during squatting (range: -2°). Neither of both trends was influenced by joint line elevation. Also anteroposterior translation of the femoral condyle centres was not affected by joint line elevation, although there was a tendency for a small posterior shift (of about 3 mm) during squatting after joint line elevation. In terms of kinetics, ligaments lengths and length changes, tibiofemoral contact pressures and quadriceps forces all showed the same patterns before and joint line elevation. No statistically significant changes could be detected.
  
  
  CONCLUSIONS
  Our study suggests that joint line elevation by 4 mm in revision total knee arthroplasty does not cause significant kinematic and kinetic differences during passive flexion/extension movement and squatting in the tibio-femoral joint, nor does it affect the elongation patterns of collateral ligaments. Therefore, clinical problems after joint line elevation are probably situated in the patello-femoral joint or caused by joint line elevation of more than 4 mm.
authors.affiliation: Department of Orthopaedics and Inflammatory Disorders of Locomotor System, The Medical Centre of Postgraduate Education, Otwock, Poland.
authors.forename: Jacek B
authors.initials: JB
authors.lastname: Kowalczewski
authors.affiliation: KU Leuven, Mechanical Engineering Technology TC Geel, Geel, Belgium.
authors.forename: Luc
authors.initials: L
authors.lastname: Labey
authors.affiliation: Labor für Biomechanik und Experimentelle Orthopädie, Orthopädische Klinik und Poliklinik, Klinikum Großhadern, München, Germany.
authors.forename: Yan
authors.initials: Y
authors.lastname: Chevalier
authors.affiliation: Department of Orthopaedics and Inflammatory Disorders of Locomotor System, The Medical Centre of Postgraduate Education, Otwock, Poland.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Okon
authors.affiliation: Bio Electro and Mechanical Systems Department, Université Libre de Bruxelles, Brussel, Belgium.
authors.forename: Bernardo
authors.initials: B
authors.lastname: Innocenti
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Ziekenhuis Oost Limburg, Genk, Belgium.
authors.forename: Johan
authors.initials: J
authors.lastname: Bellemans
keywords: collateral ligaments; contact pressure; kinematics; revision