title: Mechanics of post-cam engagement during simulated dynamic activity.
abstract: Posterior-stabilized (PS) total knee arthroplasty (TKA) components employ a tibial post and femoral cam mechanism to guide anteroposterior knee motion in lieu of the posterior cruciate ligament. Some PS TKA patients report a clicking sensation when the post and cam engage, while severe wear and fracture of the post; we hypothesize that these complications are associated with excessive impact velocity at engagement. We evaluated the effect of implant design on engagement dynamics of the post-cam mechanism and resulting polyethylene stresses during dynamic activity. In vitro simulation of a knee bend activity was performed for four cadaveric specimens implanted with PS TKA components. Post-cam engagement velocity and flexion angle at initial contact were determined. The experimental data were used to validate computational predictions of PS mechanics using the same loading conditions. A lower limb model was subsequently utilized to compare engagement mechanics of eight TKA designs, relating differences between implants to geometric design features. Flexion angle and post-cam velocity at engagement demonstrated considerable ranges among designs (23°-89°, and 0.05-0.22 mm/°, respectively). Post-cam velocity was correlated (r = 0.89) with tibiofemoral condylar design features. Condylar geometry, in addition to post-cam geometry, played a significant role in minimizing engagement velocity and forces and stresses in the post. This analysis guides selection and design of PS implants that facilitate smooth post-cam engagement and reduce edge loading of the post.
authors.affiliation: Center for Orthopaedic Biomechanics, University of Denver, 2390 S. York St., Denver, Colorado 80208, USA.
authors.forename: Clare K
authors.initials: CK
authors.lastname: Fitzpatrick
authors.forename: Chadd W
authors.initials: CW
authors.lastname: Clary
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Cyr
authors.forename: Lorin P
authors.initials: LP
authors.lastname: Maletsky
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Rullkoetter
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects*; D001696:Biomechanical Phenomena; D002102:Cadaver; D005269:Femur / Q000601:surgery; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology* / Q000601:surgery; D007720:Knee Prosthesis; D020959:Polyethylene; D011474:Prosthesis Design; D011475:Prosthesis Failure; D016059:Range of Motion, Articular / Q000502:physiology*; D020127:Recovery of Function / Q000502:physiology; D013314:Stress, Mechanical; D013977:Tibia / Q000601:surgery; D016474:Weight-Bearing / Q000502:physiology
chemical_list: D020959:Polyethylene
keywords: finite element analysis; joint mechanics; knee arthroplasty; posterior-stabilized; total knee replacement