title: Clinical biomechanics of instability related to total knee arthroplasty.
abstract: BACKGROUND
  Tibiofemoral instability is a common reason for total knee arthroplasty failure, and may be attributed to soft tissue deficiency and incorrect ligament balancing. There are many different designs of implant with varying levels of constraint to overcome this instability; however there is little advice for surgeons to assess which is suitable for a specific patient, and soft tissue balance testing during arthroplasty is very subjective.
  
  
  METHODS
  The current theories on primary and secondary soft tissue restraints to anterior/posterior, varus/valgus, and internal/external rotational motion of the knee are discussed. The paper reviews biomechanics literature to evaluate instability in the intact and implanted knee.
  
  
  RESULTS
  The paper highlights important intra- and extra-capsular structures in the knee and describes the techniques used by clinicians to assess instability perioperatively. In vitro cadaveric studies were found to be a very useful tool in comparing different implants and contributions of different soft tissues.
  
  
  CONCLUSIONS
  In vitro cadaveric studies can be utilised in helping less experienced surgeons with soft tissue releases and determining the correct implant. For this to happen, more biomechanical studies must be done to show the impact of release sequences on implanted cadavers, as well as determining if increasingly constrained implants restore the stability of the knee to pre-deficient conditions.
authors: Department of Mechanical Engineering, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
authors: Kiron K
authors: KK
authors: Athwal
authors: Department of Orthopaedic Surgery, Newcastle Freeman University Hospital, Newcastle upon Tyne, UK; Institute of Cellular Medicine, Medical School, Framlington Place Newcastle University, Newcastle upon Tyne NE2 4HH, UK.
authors: Nicola C
authors: NC
authors: Hunt
authors: Guy's Hospital, Great Maze Pond, London SE1 9RT, UK.
authors: Andrew J
authors: AJ
authors: Davies
authors: Department of Orthopaedic Surgery, Newcastle Freeman University Hospital, Newcastle upon Tyne, UK; Institute of Cellular Medicine, Medical School, Framlington Place Newcastle University, Newcastle upon Tyne NE2 4HH, UK.
authors: David J
authors: DJ
authors: Deehan
authors: Department of Mechanical Engineering, Imperial College London, Exhibition Road, London SW7 2AZ, UK; Orthopaedic Surgery Group, Imperial College London School of Medicine, Charing Cross Hospital, London W6 8RF, UK. Electronic address: a.amis@imperial.ac.uk.
authors: Andrew A
authors: AA
authors: Amis
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000379:methods; D001696:Biomechanical Phenomena / Q000502:physiology; D002102:Cadaver; D006801:Humans; D007593:Joint Instability / Q000175:diagnosis / Q000209:etiology / Q000517:prevention & control; D007719:Knee Joint / Q000601:surgery*; D007720:Knee Prosthesis; D008023:Ligaments, Articular / Q000502:physiology; D011474:Prosthesis Design; D012086:Reoperation; D017211:Treatment Failure
keywords: Instability; Knee biomechanics; Primary and secondary restraints; Soft tissue; Total knee arthroplasty (TKA)