Michael Carroll

Kneeling is safe for patients implanted with medial-pivot total knee arthroplasty designs.

Nine ADVANCE (Wright Medical Technology, Arlington, TN)) Medial-Pivot (MP) and 9 ADVANCE Double-High total knee arthroplasties were analyzed under radiographic surveillance at standing, mid kneeling, and full kneeling. In vivo tibiofemoral contact positions were obtained using the 3- to 2-dimensional image registration technique. The contact in Double-High knee was always more posterior than that in the MP knee presumably because of the presence of the posterior cruciate ligament. The contact positions in both the designs moved anterior from standing to mid kneeling, moved posterior from mid kneeling to full kneeling, and remained within the intended articulation range of the implants. This study indicates that kneeling is safe in MP total knee arthroplasty even in the absence of a cam-post or posterior cruciate ligament.

Assessment of a Medial Pivot Total Knee Arthroplasty Design in a Cadaveric Knee Extension Test Model

A total knee has been designed to mimic less-compliant medial and more-compliant lateral behavior. In vivo testing compared open-kinematic chain behaviors of cadaver knees in their normal state and after implantation of the knee prosthesis. Specimens limbs were computed tomography scanned, and infrared arrays on tibia and femur were registered to bone markers. Motion of the joint and quadriceps force were reported from 90° flexion to full extension. Less medial and more lateral anterior-posterior motion was seen in both the intact and the implanted knees. Tibiofemoral rotation and translation were similar in direction but were reduced in magnitude for the prosthetic knees. Quadriceps force, defined as that applied force required to extend the knee, required after implantation was variable between specimens but not statistically different from the intact condition. The prosthesis tested exhibits kinematic behavior similar to that in their normal state, with no difference in quadriceps force required for extension.