title: Limited rotation of the mobile-bearing in a rotating platform total knee prosthesis.
abstract: The hypothesis of this study was that the polyethylene bearing in a rotating platform total knee prosthesis shows axial rotation during a step-up motion, thereby facilitating the theoretical advantages of mobile-bearing knee prostheses. We examined 10 patients with rheumatoid arthritis who had a rotating platform total knee arthroplasty (NexGen LPS mobile, Zimmer Inc. Warsaw, USA). Fluoroscopic data was collected during a step-up motion six months postoperatively. A 3D-2D model fitting technique was used to reconstruct the in vivo 3D kinematics. The femoral component showed more axial rotation than the polyethylene mobile-bearing insert compared to the tibia during extension. In eight knees, the femoral component rotated internally with respect to the tibia during extension. In the other two knees the femoral component rotated externally with respect to the tibia. In all 10 patients, the femur showed more axial rotation than the mobile-bearing insert indicating the femoral component was sliding on the polyethylene of the rotating platform during the step-up motion. Possible explanations are a too limited conformity between femoral component and insert, the anterior located pivot location of the investigated rotating platform design, polyethylene on metal impingement and fibrous tissue formation between the mobile-bearing insert and the tibial plateau.
authors: Department of Orthopaedics, Leiden University Medical Center, Leiden, The Netherlands; Department of Radiology, Division of Image Processing, Leiden University Medical Center, Leiden, The Netherlands. E.H.Garling@lumc.nl
authors: E H
authors: EH
authors: Garling
authors: B L
authors: BL
authors: Kaptein
authors: R G H H
authors: RG
authors: Nelissen
authors: E R
authors: ER
authors: Valstar
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000601:surgery; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D005260:Female; D005471:Fluoroscopy; D006801:Humans; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D009043:Motor Activity; D020959:Polyethylene; D011474:Prosthesis Design; D016059:Range of Motion, Articular
chemical_list: D020959:Polyethylene