Abstract
Introduction:
While kinematic abnormalities of contemporary TKA implants have been well established, a solution has not yet been achieved. We hypothesized that contemporary TKA implants are not compatible with normal soft-tissue function and normal knee motion. We propose a novel technique for reverse engineering advanced implant articular surfaces (biomimetic surface), by using accurate 3D kinematics of normal knees. This technique accounts for surgical placement of the implants, and allows design of tibial and femoral articular surfaces in conjunction.
Methods:
Magnetic resonance imaging was used to create 3D knee models of 40 normal subjects (24 male, 16 female, age 29.9 ± 9.7 years), and bi-planar fluoroscopy was used to capture 3D knee motion during a deep knee bend. These data were combined to create a 3D virtual representation of an average normal knee and its motion pathway. A TKA femoral component was mounted on the average knee, and moved through its normal kinematic pathway to carve out an articular surface from a tibial template (Fig. 1 and 2). The geometry of the resulting biomimetic tibia was compared to that of the native tibia, and a contemporary TKA tibial insert that uses the same femoral component.
Results:
The biomimetic tibia had a dished medial plateau and a convex lateral plateau similar to the native tibia, with anterior/posterior lips analogous to the native menisci (Fig. 3). The anterior/posterior lips were carved by the femoral component at its end points in extension and full flexion (Fig. 2). In contrast, while the medial geometry of the contemporary TKA tibia was similar to the biomimetic tibia, the lateral geometry was significantly different (Fig. 3). Anteriorly, the contemporary tibia was excessively proud. The resulting soft-tissue tightening would prevent anterior location of lateral femoral condyle in extension, and block screw home femoral rotation. Posteriorly, again the contemporary tibia was excessively proud. The resulting soft-tissue tightening would prevent posterior rollback of the lateral femoral condyle in flexion.
Conclusion:
The non-anatomic geometry of the contemporary TKA tibia, especially on the lateral side, conflicted with normal knee motion. In contrast, a biomimetic tibia reverse engineered directly from normal knee motion, had an anatomic geometry, with anterior/posterior lips similar to the native menisci. Such a biomimetic surface would allow normal soft tissue function and normal knee motion. The reverse engineering technique described herein enables for the first time, the direct use of in vivo knee kinematics to generate advanced implant articular surfaces.
