Abstract
Introduction
Achieving high flexion after total knee arthroplasty is very important for patients in Asian countries where deep flexion activities are an important part of daily life. The Bi-Surface Total Knee System (Japan Medical Material, Kyoto, Japan), which has a unique ball-and-socket mechanism in the mid-posterior portion of the femoral and tibial components, was designed to improve deep knee flexion and long-term durability after total knee arthroplasty (Figure 1). The purpose of this study was to determine the in vivo three dimensional kinematics of Bi-Surface Total Knee System in order to evaluate and analyze the performance of this system with other conventional TKA designs currently available in the market today.
Materials and Methods
Three dimensional kinematics were evaluated during a weight-bearing deep knee bend activity using fluoroscopy and a 2D-to-3D registration technique for 66 TKA. Each knee was analyzed to determine femorotibial kinematics, including weight-bearing range of motion, anterior/posterior contact position, and tibio-femoral rotation.
Results
The average weight-bearing range of motion for the entire group was 125.5∗∗∗∗∗. Forty three of sixty six knees had greater range of motion than 120∗∗∗∗∗. At full extension, the average contact positions were −0.5mm (range, from −12.2mm to 6.8mm; standard deviation 3.5mm), and −3.8mm (range, from −14.1mm to 6.0mm; standard deviation 4.9mm) for the medial compartment and the lateral compartment, respectively. At maximum flexion, the average contact position was −9.2mm (range, from −17.8mm to 2.4mm; standard deviation 3.7mm), and −14.8mm (range, from −20.1mm to 5.7mm; standard deviation 2.7mm) for the medial compartment and the lateral compartment, respectively (Figure 2). From full extension to maximum flexion, the average posterior femoral rollback observed was −8.7mm (range, from −22.1mm to 1.0mm; standard deviation 4.3mm) for the medial compartment, and −11.0mm (range, from −21.9mm to 6.6mm; standard deviation 5.4mm) for the lateral compartment. At full extension, the average axial orientation was 3.8∗∗∗∗∗ (range, from −5.3∗∗∗∗∗ to 26.4∗∗∗∗∗; standard deviation 5.2∗∗∗∗∗) of external femoral rotation. At maximum flexion, the average axial orientation was 9.5∗∗∗∗∗ (range, from −5.9∗∗∗∗∗ to 27.7∗∗∗∗∗; standard deviation 6.7∗∗∗∗∗). Therefore, from full extension to maximum flexion, the average amount of axial rotation was 5.7∗∗∗∗∗ (range, from −15.1∗∗∗∗∗ to 22.2∗∗∗∗∗; standard deviation 6.4∗∗∗∗∗).
Discussion
The Bi-Surface Knee System was designed to accommodate the life style led by Asian populations, by aiming to improve both, knee flexion and long-term durability. Though durability of the device is beyond the scope of this study, subjects in this study did achieve high weight-bearing flexion, excellent posterior femoral rollback of both condyles and a normal axial rotation patterns, albeit, less than the normal knee. Also, this is the first in vivo study conducted to understand the kinematic patterns generated for subject implanted with this device. The amount of posterior rollback and axial rotation were found to be similar in nature to the normal knee as well as other established TKA devices available for implantation today, but again less than the normal knee.
