title: Rotating-platform has no surface damage advantage over fixed-bearing TKA.
abstract: BACKGROUND
  Rotating-platform TKA, although purported to have superior kinematics, has shown no clinical advantages over those of fixed-bearing TKA. Our design-matched retrieval study aimed to investigate if differences in bearing wear damage exist between fixed- and mobile-bearing TKAs with similar condylar geometry.
  
  
  OBJECTIVE
  We asked whether (1) the rotating platform's more conforming tibiofemoral articulation would be associated with less severe damage; (2) the location of damage and wear would be similar on the tibiofemoral or backside surfaces of two contemporary designs with similar condylar geometry; and (3) the combined damage and deformation measured as thickness would differ between the two designs.
  
  
  METHODS
  We performed damage grading and damage mapping on 25 rotating-platform and 17 fixed-bearing inserts. The patient demographic data from each of these cohorts were comparable. Inserts were also laser-scanned from which we obtained thicknesses, and inferior surface three-dimensional scans, from which we determined dimensional changes.
  
  
  RESULTS
  Rotating-platform and fixed-bearing inserts had similar tibiofemoral damage scores. However, the scores on the inferior surface of rotating platforms were greater, often as a result of third-body debris scratching observed on both damage mapping and three-dimensional scans. The extent of damage as a function of surface area was greater for rotating platforms, consistent with the greater tibiofemoral conformity. Dimensional changes on the inferior surfaces of the fixed bearing followed loading areas of the knee. However, no differences were seen in the thicknesses between fixed- and rotating-platform bearings.
  
  
  CONCLUSIONS
  The increased total damage score on the rotating platform, coupled with increased surface area damaged and the propensity for third-body debris, indicates no damage advantage to this mobile-bearing design.
authors.affiliation: Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021, USA.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Stoner
authors.forename: Seth A
authors.initials: SA
authors.lastname: Jerabek
authors.forename: Stephanie
authors.initials: S
authors.lastname: Tow
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Wright
authors.forename: Douglas E
authors.initials: DE
authors.lastname: Padgett
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation* / Q000379:methods; D001696:Biomechanical Phenomena; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013314:Stress, Mechanical