There are two main designs used for unicompartmental tibial components. The first design, an all plastic component called an inlay, preserves bone on the outer edge of the tibia which is feasible using a robotically-controlled burring tool. Also, the depth of resection is small, preserving the strongest cancellous bone which is near the surface. The second design, called an onlay, resects the entire condyle and includes a metal backed plate which rests on the resected tibia. This component requires more bone removal but metal-backing has previously been shown to distribute the load more uniformly. The purpose of this study was to investigate the hypothesis that while inlay components require less bone removal, the peak stresses and strains at the surface of the bone will be greater when compared to onlay components.

The ability of tibial tray component shapes to appropriately fit boney geometry is an important aspect of implant design in total knee arthroplasty. Overhang of components in the knee has been associated with soft tissue damage and joint pain [1,2]. Good coverage establishes stability through adequate cortical bone support of the tray component, and reduces the likelihood of loosening and subsidence [3–5], and therefore serves as a key factor in component fixation, especially in those that rely on biological growth into porous component backings such as Trabecular Metal ™ Material. More importantly, rotational malalignment of the tibial tray can disrupt the natural kinematics and implant longevity [6]. Previous studies investigated coverage of multiple tibial trays on digitized bone resection contours [1,7]. However the methodology for rotational alignment during implantation was not identified. Although rotational alignment has been investigated in numerous studies, most of the studies were carried out by either investigating the impact of malalignment [6], or assessing different definitions of the tibia rotational axis [8]. No correlation between the size of the rotational alignment window and the amount of coverage has been shown.

The selection of a tracking system for locating patient anatomy and/or surgical tools is of critical importance for many computer aided techniques in minimally invasive surgery. A mechanical tracking system has many advantages in a medical situation since it avoids the occlusion and distortion issues of optical and electromagnetic systems. However, few mechanical tracking systems exist due to the challenges of minimizing error accumulation along a serial linkage. To minimize error, the existing mechanical tracking linkages are large and bulky, making them impractical for a surgical setting.

Through billions of years of evolution, nature has produced remarkably elegant solutions to a whole range of real-world problems. An increasing number of engineers is turning towards nature for design inspiration, as the evolutionary adaptation of organisms is in many ways comparable to the design cycle used in engineering: changes in functionality are tested on their fitness and thereafter either reinforced or rejected.

Osteoarthritis is a progressive and debilitating joint disease that is the leading cause of physical disability in industrial nations around the world [1]. It not only negatively affects the comfort and functional activity of individuals, but as a result also taxes the health care system of these countries.

The ability to predict medial and lateral contact forces accurately in the knee could be useful for research on neuromuscular coordination, the development of treatments for knee osteoarthritis, and the design of knee replacements with improved durability and functionality. To improve their ability to predict medial and lateral contact forces, researchers have recently developed knee implants capable of measuring four [1] or six [2] in vivo loads applied to the tibia. These implants provide data that is useful for validating in vivo knee load predictions from computational models. A difficulty in using these experimental measurements is translating them into clinically significant measurements, i.e. medial and lateral contact force. A simple and quick method for finding these contact forces from the experimental implant data would be ideal.