NexGen® Rotating Hinge Knee
The NexGen Rotating Hinge Knee is designed to address the key issues that relate to many conventional rotating hinge knee designs. The design of the NexGen Rotating Hinge Knee features a modular hinge mechanism that results in 95% of the load being carried by the tibial condyles*, similar to the loading pattern of a primary implant design. Because the femoral condyles remain centered on the tibia throughout the range of motion and the shape of the patella groove is similar to the NexGen design, patella tracking is similar to a primary knee design. Since the NexGen Rotating Hinge Knee takes advantage of modular design by using NexGen Augments, the basic bone cuts are the same as those made for NexGen primary system components. This helps to minimize bone loss and allows use of instrumentation commonly used in primary implant procedures.
Patellofemoral Tracking Like NexGen Femoral Components
The NexGen Rotating Hinge Knee femoral component has the same patellofemoral design as the other NexGen Femoral Components. The groove allows the patella to track deeply - similar to an anatomic patella. This maximizes the patellofemoral contact area, increases the resistance to lateral subluxation, and provides a smooth transition from flexion to extension. The central location of the hinge axis keeps the femoral condyles in a consistent sagittal plane. This allows for more normal patellar tracking since the patella does not shift posteriorly during flexion.Resistance To Subluxation
To resist subluxation, the NexGen Rotating Hinge Knee locking mechanism design offers a minimum "jump height" of 40mm.
Conformity Throughout Range Of Motion
The ratio of conformity between the femoral condyles and the highly dished tibial articular surface is virtually 1-to-1. By maximizing contact area, the stresses in the polyethylene are distributed across a larger surface area.
Impact Dampening Extension Stop
Contact occurs on the frontal radius of the NexGen Rotating Hinge Knee femoral component with the articulating surface just as the implant moves to hyperextension. This will cause the knee to distract slightly, dampening the extension impact. This interaction was designed to dissipate the hyperextension force.
A More Natural Pivot/Rotation
The central location of the NexGen Rotating Hinge Knee hinge mechanism is placed closer to the axis of the tibial component, resulting in more natural and consistent tibiofemoral kinematics when compared to posterior hinge knee designs. The rotation of the NexGen Rotating Hinge Knee platform is designed to displace torsional loads from the cement interfaces to the soft tissues, since it allows up to 25º of movement in internal and external rotation.
Modularity Of Hinge Pin/Locking Mechanism
The modularity of the hinge post extension pin allows the implantation to proceed without requiring the knee to be excessively distracted or held while the components are assembled. The NexGen Rotating Hinge Knee femoral and tibial components are cemented into position, and with minimal distraction, the tibial articular surface is rotated into position. The hinge post extension is inserted into the tibial baseplate and tightened. It's that simple.
Contact Area/Loading Analysis*
The test evaluated the amount of contact that occurs between the NexGen Rotating Hinge Knee femoral component and articular surface. The large Condylar contact patches confirm that the load stays toward the central portion of the tibial articular surface throughout ROM.
* Data on file at Zimmer. The results of this testing have not been shown to correlate with clinical mechanisms.
