Development of robotic assistive surgery system for anterior cruciate ligament reconstruction

Reconstruction surgery for an Anterior Cruciate Ligament (ACL) is becoming increasingly popular, due to the increase in people engaging in sport. In this surgery, four bone tunnels are drilled in the femur and tibia respectively, following which two substitute ligaments extracted from the other part of body, so called grafts, are inserted and fixed to both bones. However, although this surgery allows the knee function to be restored, its empirical method could lead to inappropriate fixation and result in instability of patient's knee after surgery. Therefore a quantified approach is needed with the aid of engineering techniques. In this paper, Robotic Assistive Surgery System is proposed, and for developing robot (graft tension setting device), experiments were performed to quantify two important parameters in surgery; namely the initial knee flexion angle and graft tension. Firstly, the extent of change in ligament length during flexion was measured through Magnetic Resonance Imaging (MRI) and a 3D positional measuring device, allowing non-invasive measurement of the ligament length. Secondly, a load cell was attached to the ligament of a cadaveric knee and the change in the graft tension during flexion was measured under varying initial conditions. This result demonstrated that the location of bone tunnels also have an influence on the level of graft tension. Finally, the relaxation phenomena of pig's ACL was monitored and it showed a high correlation with the ligament tension setting velocity. Based on all these results, a graft tension setting device was designed and the first prototype of it was presented. The initial evaluation indicates the feasibility of the device.