title: The effect of polyethylene creep on tibial insert locking screw loosening and back-out in prosthetic knee joints.
abstract: A prosthetic knee joint typically comprises a cobalt-chromium femoral component that articulates with a polyethylene tibial insert. A locking screw may be used to prevent micromotion and dislodgement of the tibial insert from the tibial tray. Screw loosening and back-out have been reported, but the mechanism that causes screw loosening is currently not well understood. In this paper, we experimentally evaluate the effect of polyethylene creep on the preload of the locking screw. We find that the preload decreases significantly as a result of polyethylene creep, which reduces the torque required to loosen the locking screw. The torque applied to the tibial insert due to internal/external rotation within the knee joint during gait could thus drive locking screw loosening and back-out. The results are very similar for different types of polyethylene.
authors.affiliation: Department of Mechanical Engineering, University of Utah, Salt Lake City, UT 84112, USA; Ortho Development Corporation, Draper, UT 84020, USA.
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Sanders
authors.affiliation: Department of Mechanical Engineering, University of Utah, Salt Lake City, UT 84112, USA. Electronic address: bart.raeymaekers@utah.edu.
authors.forename: Bart
authors.initials: B
authors.lastname: Raeymaekers
mesh_terms: D001863:Bone Screws; D019544:Equipment Failure Analysis; D007720:Knee Prosthesis; D055595:Mechanical Phenomena; D020959:Polyethylene; D013977:Tibia; D013997:Time Factors
chemical_list: D020959:Polyethylene
keywords: Locking screw; Polyethylene creep; Prosthetic knee; Tibial insert