PSI design and its unique features. (a) PSI design of the tibia. (b) PSI design of the femur. The green wires simulate the K-wires and show where and how the PSI will be pinned onto the bone surface. Pin tract design is mostly perpendicular to the bone to avoid shear forces during placement. (c) Each PSI was designed to fit onto a unique position on the bone surface. When the cartilaginous surface was in the cutting trajectory, the PSI was bridging over it, with a minimum of 2 mm, to avoid any contact yielding to a potential malpositioning (cartilage is not visible in a CT acquisition). (d) The width of the cutting platform was around 10 mm, to get a sufficient support for the saw blade. Spherical holes that fit the pointer tool from the CAS system were used to check the position of the guide.