title: Knee arthroplasty with a medially conforming ball-and-socket tibiofemoral articulation provides better function.
abstract: BACKGROUND
  A knee design with a ball-and-socket articulation of the medial compartment has a femoral rollback profile similar to the native knee. Compared to a conventional, posterior-stabilized knee design, it provides AP stability throughout the entire ROM. However, it is unclear whether this design difference translates to clinical and functional improvement.
  
  
  OBJECTIVE
  We asked whether the medially conforming ball-and-socket design differences would be associated with (1) improved ROM; and (2) improved American Knee Society, WOMAC, Oxford Knee, SF-36, and Total Knee Function Questionnaire scores compared to a conventional, fixed-bearing posterior-stabilized TKA.
  
  
  METHODS
  We enrolled 82 patients in a single-center, single-blinded, randomized, controlled trial comparing the medially conforming ball-and-socket design knee prosthesis to a posterior-stabilized total knee prosthesis. Our primary end point was ROM. Our secondary end points were American Knee Society, WOMAC, Oxford Knee, SF-36, and Total Knee Function Questionnaire scores. All patients were followed at 1 and 2 years.
  
  
  RESULTS
  The mean ROM was 100.1° and 114.9° in the posterior-stabilized and medially conforming ball-and-socket groups, respectively. The physical component scores of SF-36 and Total Knee Function Questionnaire were better in the medially conforming ball-and-socket group. We found no difference in American Knee Society, WOMAC, and Oxford Knee scores.
  
  
  CONCLUSIONS
  Both implant designs similarly relieved pain and improved function. The medially conforming ball-and-socket articulation provided better high-end function as reflected by the Total Knee Function Questionnaire.
  
  
  METHODS
  Level I, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Trauma & Orthopaedics, University College Hospital, 235 Euston Road, London NW1 2BU, UK. f.hossain@doctors.org.uk
authors.forename: Fahad
authors.initials: F
authors.lastname: Hossain
authors.forename: Shelain
authors.initials: S
authors.lastname: Patel
authors.forename: Shin-Jae
authors.initials: SJ
authors.lastname: Rhee
authors.forename: Fares Sami
authors.initials: FS
authors.lastname: Haddad
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D004739:England; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D010149:Postoperative Pain / Q000209:etiology / Q000517:prevention & control; D011446:Prospective Studies; D011474:Prosthesis Design; D011859:Radiography; D016059:Range of Motion, Articular; D020127:Recovery of Function; D016037:Single-Blind Method; D011795:Surveys and Questionnaires; D013997:Time Factors; D016896:Treatment Outcome