title: Different femorotibial contact points between fixed- and mobile-bearing TKAs do not show clinical impact.
abstract: OBJECTIVE
  In anteroposterior (AP)-gliding mobile-bearing total knee arthroplasty (TKA), the femoral component can theoretically slide forward resulting in a more anterior contact point, causing pain due to impingement. A lower lever arm of the extensor apparatus can also attribute to higher patella pressures and pain. The goal of this study was to determine the contact point in a cohort of mobile- and fixed-bearing TKAs, to determine whether the contact point lies more anteriorly in mobile-bearing TKA and to confirm whether this results in anterior knee pain.
  
  
  METHODS
  We used 38 fixed-bearing TKA and 40 mobile-bearing TKA from a randomized trial with straight lateral knee X-rays and measured the contact point. The functional outcome was measured by Knee Society Score at 12 months postoperatively. Pain scores were analysed using a VAS score (0-100 mm) in all patients at rest and when moving. Difficulty at rising up out of a chair was also assessed using a VAS score.
  
  
  RESULTS
  The contact point in mobile-bearing TKA was situated at 59.5 % of the AP distance of the tibia and in the fixed-bearing TKA group at 66.1 % (P< 0.05). Patients with mobile- and fixed-bearing TKAs had similar knee scores, pain scores and difficulty in chair rise. No significant correlation was found between contact point and knee pain.
  
  
  CONCLUSIONS
  The hypothesis of a more anterior contact point in the mobile-bearing cohort was confirmed but no correlation with functional and pain scores in this cohort could be found. The tibiofemoral contact point could not be correlated with a different clinical outcome and higher incidence of anterior knee pain. This study further adds to the knowledge on possible differences between mobile- and fixed-bearing prostheses. Next to that, bad outcomes could not be explained by CP.
  
  
  METHODS
  Case series, Level IV.
authors.affiliation: Sint Maartenskliniek, Hengstdal 3, Postbus 9011, 6500 GM, Nijmegen, The Netherlands. R.A.vanStralen@gmail.com.
authors.forename: R A
authors.initials: RA
authors.lastname: van Stralen
authors.affiliation: Sint Maartenskliniek, Hengstdal 3, Postbus 9011, 6500 GM, Nijmegen, The Netherlands.
authors.forename: P J C
authors.initials: PJ
authors.lastname: Heesterbeek
authors.affiliation: Sint Maartenskliniek, Hengstdal 3, Postbus 9011, 6500 GM, Nijmegen, The Netherlands.
authors.forename: A B
authors.initials: AB
authors.lastname: Wymenga
mesh_terms: D000368:Aged; D018771:Arthralgia / Q000209:etiology; D019645:Arthroplasty, Replacement, Knee; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000601:surgery*; D007720:Knee Prosthesis; D008297:Male; D011474:Prosthesis Design
keywords: Clinical results; Contact point; Fixed bearing; Mobile bearing; Total knee arthroplasty