Total Knee Post-Cam Design Variations and Their Effects on Kinematics and Wear Patterns

Abstract

Post-cam designs for posterior-stabilized total knee arthroplasy (TKA) implants have evolved over the last 2 decades. These designs have evolved from symmetric post and cam to asymmetric designs that include anterior post interactions to affect a kinematic change in full extension. All design changes have consequences on the resulting femorotibial contact kinematics and, depending on the amount of constraint built into the design, these changes may have significant consequences on the wear patterns on the tibial polyethylene insert. The current authors review the kinematic effects of symmetric and asymmetric cam designs and use a retrieval database of TKA implants obtained at the time of necropsy to show how different design variables may affect polyethylene wear patterns after 10 or more years of implantation or from modeled wear in simulators. More modern designs seem to have moved the post posteriorly and sloped the anterior aspect to avoid impingement of the anterior post in terminal flexion on the inferior aspect of the patella button. [Orthopedics. 2016; 39(3):S45-S49.].

Different intraoperative kinematics, stability, and range of motion between cruciate-substituting ultracongruent and posterior-stabilized total knee arthroplasty

“…The PS implant maintains a constant posterior femoral rollback during flexion, which is closer to the kinematics of the native knee [2, 3]; however, differences in kinematics as a consequence of different implant designs have been demonstrated [1]. Disadvantages of the PS implant include additional bone resection, which increases the surgical time, the patellar clunk syndrome has been described in some designs [7], and the post‐cam‐mechanism is a possible source of additional wear [18]. The UC design provides an easy option to substitute the PCL without additional bone resection or the use of a cruciate retaining femoral component.…”

Traumatic fracture of the polyethylene tibial post and cone in a posterior-stabilized total knee arthroplasty: A case report

“…If the cam position was more anterior, the post would interact with the cam at an earlier point in the flexion arc; once engaged, the contact of the cam would be maintained in the midportion of the post. The opposite is true if the cam was moved more posteriorly or at the top of the femoral condyles [9] .…”

“…Mihalko and associates described the mechanics of PS-TKA and the interaction between the components [9] . The cam and post geometry in the transverse plane changes how the femur and tibia interact.…”

The Vega advanced third generation posterior stabilized total knee arthroplasty system enables the restoration of range of motion for high demanding daily activities – A 5-years follow-up study

“…For patients with a weak posterior cruciate ligament, the posterior-stabilized Vega System® PS can support the medial pivoting and rollback of the native knee without enforcing it [ 40 ]. With the TKA system, individual rotational patterns were found to be preserved.…”