This enhancement of the NexGen CR Knee safely accommodates flexion up to 1550, while maintaining the kinematic function that allows natural femoral rollback. Specific design features of the CR-Flex Knee help maintain adequate tibiofemoral contact during high flexion and provide greater clearance for the patellar tendon. The option of Minus size femoral components provides an additional means of balancing the flexion and extension gaps, without additional bone loss or soft tissue release.
Accommodating Flexion up to 155 degree with Kinematic Rollback
With traditional TKA designs, the contact area between the posterior femoral condyles and the tibial articular surface decreases as the knee moves into higher flexion angles. Also, high flexion may be somewhat limited by impingement of the quadriceps mechanism on the front of the tibial articular surface.
Specific design features of the CR-Flex Knee help maintain adequate tibiofemoral contact during high flexion and provide greater clearance for the patellar tendon. These features allow the kinematics of the NexGen CR design to continue into deep flexion angles.
Lowered height of the Lateral Condyle decreases the tightness of the lateral retinacular ligament during high flexion.
Wider Intercondylar Opening optimizes internal/external rotation during high flexion and provides more space for the PCL.
Lateral Distal Radius Extended Posteriorly to further aid natural anteroposterior rollback when the PCL is present. Posterior femoral radius is extended further in flexion to provide greater femoral/tibial contact area in high flexion.
Deeper Anterior Cutout minimizes the potential for patella impingement during high flexion.
Narrower M/L Width allows for more flexibility in mediolateral positioning of the component, and helps maintain optimal patella tracking.
Options To Fit Specific Needs Minus sizing options
One common problem faced by CR surgeons is a knee that is tight in flexion, but fine in extension. Using a thinner tibial articular surface may address the flexion problem, but it may result in a knee that is loose in extension. Many surgeons will balance the joint either by performing a ligament release, or by removing more bone from the posterior condyles.
The CR-Flex Knee offers Minus sizing options to provide an additional means of adjusting the flexion gap without affecting the extension gap. The Minus size femoral components, which are 2mm smaller in the A/P dimension only, help balance the gaps without removing bone from the posterior condyles or additional soft tissue release.
Re-Creating Nature By Design
In designing cruciate retaining implants, Zimmer carefully considers saggital curvatures and frontal geometry of the femoral component, as well as the shape of the tibial component articular surface.
NexGen® CR/CRA tibiofemoral kinematics
Asymmetrical femoral condyles work in concert with the PCL to facilitate normal asymmetrical rollback of the femur on the tibia during flexion.
NexGen® CR patellofemoral articulation
A deepened patellar groove increases the contact area, and a thinner anterior flange helps relieve tension on the exterior mechanism.
NexGen® CR tibiofemoral conformity
Contact stresses are distributed over a wide area and slightly dished curvature to avoid unnecessary constraint.