title: The superficial medial collateral ligament is the primary medial restraint to knee laxity after cruciate-retaining or posterior-stabilised total knee arthroplasty: effects of implant type and partial release.
abstract: OBJECTIVE
  The aim of this study was to quantify the contributions of medial soft tissues to stability following cruciate-retaining (CR) or posterior-stabilised (PS) total knee arthroplasty (TKA).
  
  
  METHODS
  Using a robotic system, eight cadaveric knees were subjected to ±90-N anterior-posterior force, ±5-Nm internal-external and ±8-Nm varus-valgus torques at various flexion angles. The knees were tested intact and then with CR and PS implants, and successive cuts of the deep and superficial medial collateral ligaments (dMCL, sMCL) and posteromedial capsule (PMC) quantified the percentage contributions of each structure to restraining the applied loads.
  
  
  RESULTS
  In implanted knees, the sMCL restrained valgus rotation (62 % across flexion angles), anterior-posterior drawer (24 and 10 %, respectively) and internal-external rotation (22 and 37 %). Changing from CR TKA to PS TKA increased the load on the sMCL when resisting valgus loads. The dMCL restrained 11 % of external and 13 % of valgus rotations, and the PMC was significant at low flexion angles.
  
  
  CONCLUSIONS
  This work has shown that medial release in the varus knee should be minimised, as it may inadvertently result in a combined laxity pattern. There is increasing interest in preserving constitutional varus in TKA, and this work argues for preservation of the sMCL to afford the surgeon consistent restraint and maintain a balanced knee for the patient.
authors.affiliation: Department of Mechanical Engineering, Imperial College London, Exhibition Road, London, SW7 2AZ, UK.
authors.forename: Kiron K
authors.initials: KK
authors.lastname: Athwal
authors.affiliation: Department of Mechanical Engineering, Imperial College London, Exhibition Road, London, SW7 2AZ, UK.
authors.forename: Hadi El
authors.initials: HE
authors.lastname: Daou
authors.affiliation: Department of Mechanical Engineering, Imperial College London, Exhibition Road, London, SW7 2AZ, UK.
authors.forename: Christoph
authors.initials: C
authors.lastname: Kittl
authors.affiliation: Guy's Hospital, Great Maze Pond, London, SE1 9RT, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Davies
authors.affiliation: Department of Orthopaedic Surgery, Newcastle Freeman University Hospital, Newcastle upon Tyne, UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Deehan
authors.affiliation: Department of Mechanical Engineering, Imperial College London, Exhibition Road, London, SW7 2AZ, UK. a.amis@imperial.ac.uk.|Musculoskeletal Surgery Group, Department of Surgery and Cancer, Imperial College London School of Medicine, Charing Cross Hospital, London, W6 8RF, UK. a.amis@imperial.ac.uk.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Amis
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects* / Q000295:instrumentation; D002102:Cadaver; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D007719:Knee Joint / Q000503:physiopathology* / Q000601:surgery*; D007720:Knee Prosthesis; D008297:Male; D017888:Medial Collateral Ligament, Knee / Q000503:physiopathology* / Q000601:surgery*; D008875:Middle Aged; D011183:Postoperative Complications / Q000503:physiopathology; D016059:Range of Motion, Articular; D012399:Rotation; D019415:Torque
keywords: Biomechanics; Ligament release; Medial collateral ligament; Restraint; Stability; Total knee arthroplasty