title: In vitro kinematics of fixed versus mobile bearing in unicondylar knee arthroplasty.
abstract: OBJECTIVE
  When performing unicondylar knee arthroplasty (UKA), the surgeon can choose between two fundamentally different designs: a mobile-bearing (MB) inlay with high conformity, or a low-conformity, fixed bearing (FB) inlay. There is an ongoing debate in the orthopaedic community about which design is superior. To date, there have been no comparative biomechanical studies regarding each system's effects on the quadriceps force and the medial contact pressure. The purpose of this study was to investigate these alterations in vitro before and after UKA with two prosthesis systems, representing the MB and FB designs.
  
  
  METHODS
  FB and MB unicondylar knee prosthesis designs were tested in sequence under isokinetic extension in an in vitro simulator. In each case, the required quadriceps extension force was determined before and after implantation of a medial UKA. Furthermore, the tibiofemoral contact pressures were evaluated for both prosthesis designs.
  
  
  RESULTS
  The quadriceps force maximum was achieved at 106° and 104° of flexion with the FB and MB designs, respectively. Implantation of the FB UKA resulted in a significant increase in the necessary maximum quadriceps force (p = 0.006). In addition, implantation of the MB UKA resulted in a significantly higher extension force (p = 0.03). The difference between the two groups was statistically significant in deep flexion (p = 0.03), with higher forces in MB UKA.
  
  
  CONCLUSIONS
  The MB design showed significantly increased quadriceps extension force compared with the FB inlay in deep flexion. Although the FB design showed higher maximum peak pressures concentrated on a smaller area, the pressure introduction in deep flexion was lower, compared to MB inserts.
authors: Department for Orthopaedic Surgery, Hannover Medical School, Anna-von_Borries-Str. 1-7, 30625, Hannover, Germany, max.ettinger@ddh-gruppe.de.
authors: Max
authors: M
authors: Ettinger
authors: Johanna Marie
authors: JM
authors: Zoch
authors: Christoph
authors: C
authors: Becher
authors: Christof
authors: C
authors: Hurschler
authors: Christina
authors: C
authors: Stukenborg-Colsman
authors: Leif
authors: L
authors: Claassen
authors: Sven
authors: S
authors: Ostermeier
authors: Tilman
authors: T
authors: Calliess
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D001696:Biomechanical Phenomena; D002102:Cadaver; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology* / Q000601:surgery; D007720:Knee Prosthesis; D008875:Middle Aged; D011474:Prosthesis Design; D016059:Range of Motion, Articular / Q000502:physiology*