Abstract
Background
The decision to choose CR (cruciate retaining) insert or CS (condylar stabilized) insert during TKA remains a controversial issue. Triathlon CS type has a condylar stabilized insert with an increased anterior lip that can be used in cases where the PCL is sacrificed but a PS insert is not used. The difference of the knee kinematics remains unclear. This study measured knee kinematics of deep knee flexion under load in two insert designs using 2D/3D registration technique.
Materials and methods
Five fresh-frozen cadaver lower extremity specimens were surgically implanted with Triathlon CR components (Stryker Orthopedics, Mahwah, NJ). CR insert with retaining posterior cruciate ligament were measured firstly, and then CS insert after sacrificing posterior cruciate ligament were measured. Under fluoroscopic surveillance, the knees were mounted in a dynamic quadriceps-driven closed-kinetic chain knee simulator based on the Oxford knee rig design. The data of every 10° knee flexion between 0° and 140° were corrected. Femorotibial motion including tibial polyethylene insert were analyzed using 2D/3D registration technique, which uses computer-assisted design (CAD) models to reproduce the spatial position of the femoral, tibial components from single-view fluoroscopic images. We evaluated the knee flexion angle, femoral axial rotation, and anteroposterior translation of contact points.
Results
The amount of femoral axial rotation from 0° flexion to 140° flexion was 11.0±3.6° in CR insert, and 9.4±4.3° in CS insert, respectively. In CR insert, the medial contact point moved 6.3±3.8 mm anteriorly from 30° to 100° flexion, and then moved 7.6±6.4 mm posteriorly from 100° to maximum flexion. The lateral contact point moved 4.0±4.1 mm anteriorly from 30° to 90° flexion, and then moved 8.2±9.7 mm posteriorly from 90° to maximum flexion. In CS insert, the medial contact point moved 5.2±3.5 mm anteriorly from 30°to 120° flexion, and then moved 3.3±1.1 mm posteriorly from 120° to maximum flexion. The lateral contact point moved 2.7±2.2 mm anteriorly from 30° to 110° flexion, and then moved 6.4±2.0 mm posteriorly from 110° to maximum flexion. No significant differences were observed in the amount of posterior translation between the two insert.
Discussion
Triathlon CR and CS insert had a similar kinematics pattern. However, there are some limitations in this study. The deep knee flexion motion was studied in a quasi-static fashion. Additionally, the component positions and rotations were not known relative to the femoral and tibial bones.
