Koichi Kuramoto

A study of bone micro-cutting characteristics using a newly developed advanced bone cutting machine tool for total knee arthroplasty

Bone cutting experiments were conducted on a cadaver using a newly developed machine tool. The effectiveness of the system was evaluated by comparing the planned shape for the mating surface between the femur and an artificial joint with the cutting result. It is desirable to know the machining phenomena and characteristics at the microscale because the material and the tissue structure are anisotropic in both cortical and cancellous bones. In the paper, the influence of the material characteristics on machining is discussed for cortical bone. Pig cortical bone was used in the experiment for visualizing 2-dimensional micro-cutting.

Comparative biomechanical analysis of an improved novel pedicle screw with sheath and bone cement.

Study Design A human cadaveric biomechanical study of fixation strength of an improved novel pedicle screw (NPS) with cement and a conventional screw. Objective To clarify whether the NPS has adequate fixation strength without leakage in vertebrae with low bone quality. Summary of Background Data The fixation strength of pedicle screws decreases in frail spines of elderly osteoporotic patients. Augmentation of screw fixation with bone cement must be balanced against increased difficulty of screw removal and risk of cement leakage. We developed the NPS consisting of an internal screw and an outer sheath to mitigate the disadvantages of cement augmentation. Methods The T12 and L1 vertebrae obtained from 18 formalin preserved cadavers (11 males and 7 females; mean age, 82.7 y) were used. The mean bone mineral density was 0.39±0.14 g/cm2. The NPS was inserted into one pedicle of each vertebra and the control screw, a Compact CD2 screw, was inserted into the contralateral pedicle. Both screws were 6 mm in diameter and 40 mm in length. Pull-out tests were performed at a crosshead speed of 10 mm/min. Cyclic loading tests were performed with a maximum 250 N load at 2 Hz until 30,000 cycles. Results Cement leakage did not occur in any of the specimens tested. The mean maximum force at pull-out was 760±344 N for the NPS and 346±172 N for the control screw (P<0.01). Loosening of 50% of the screws was observed after 17,000 cycles of the NPS and after 30 cycles of the control screw. The hazard ratio of loosening was 19.6 (95% confidence interval 19.3-19.9) (P<0.001). Conclusions The NPS showed a significantly higher mechanical strength than the control screw in both pull-out tests and cyclic loading tests. The NPS showed more than adequate strength without cement leakage.

Development of a 9 Axes Machine Tool for Bone Cutting

Abstract The femur and the tibia must be shaped to ensure that they are fit firmly to an artificial joint in total knee joint replacement The normal procedure is to manually cut the bones using a bone saw and mechanical jigs. A 9 axes bone cutting machine tool has been developed by the authors to increase cutting accuracy and reduce the hospital stay required for recuperation. As developed, the cut plane is determined by a 5 degree-of-freedom mechanism and the femur and tibia are cut by moving two translational and one rotational degrees of freedom to avoid the ligament. Preoperative planning system as a CAD/CAM system and overview of the assisting system for total knee arthroplasty are also discussed. Experimental results for bone cutting are presented.

The optimal design of an implant to improve bone quality of implant surroundings based on stress analysis

Research on how implant surface shape contributes to long-term stability after implantation is important in the field of orthopaedics. In particular, technology that controls various bone quality parameters and voluntary bone inducement in implant surroundings should be developed for the next generation of implants and this will improve the patients quality of life (QOL). For this research, we focused on the inducement of the appropriate alignment for biological apatite (BAp) crystallites and related collagen (Col.) fibres as a bone quality parameter. In this study, we predicted that when stress is applied to bone, the BAp/Col. preferential alignment can be formed if osteocytes are in an environment that is aligned with the principle stress vector. We tested this idea by introducing grooves in the principal stress direction on the surface of an implant. This work thus analyzes the effect of stress transmission by a load at the proximal femur on the bone inside and near the grooves by using mechanical simulation in which groove angles can be changed on the implant surface. Coordinate data from the mechanical simulation of the combined bone/implant environment was verified against the coordinate data obtained by CT scans of actual canine bone. Results suggest that the tendency of stress transmission differs depending on the position and angle of the grooves and based on a vector diagram of the maximum and minimum principal stresses. The simulation was able to predict bone dynamics in vivo and enabled a best design of an implant to control the BAp/Col. alignment as an index of bone quality.

Development of a Computer-Integrated Minimally Invasive Surgical System for Knee Arthroplasty

Recently, the number of robot-assisted orthopaedic systems has been increased. As one of the backgrounds, it is considered that the error between the plan and the result of bone cutting is not constant because of the individual surgeons skill. The authors developed a bone cutting robot which has 7 degrees of freedom. A prototype of the total system for minimally invasive knee arthroplasty, including navigation system, was implemented. In this paper, the detail of the minimally invasive knee arthroplasty system is described, the resection experiment for a cadaver was performed successfully

Optimal control of cutting feed rate in the robotic milling for total knee arthroplasty

For the total knee arthroplasty, we developed the robotic system, such as the cutting feed rate is controlled depending on the hardness of the bone tissue predicted on the basis of the medical image. Since the cutting force is reduced by this system, the displacement of the bone is minimized during the bone cutting process. Therefore it makes a possibility to fix the target bone using “safer” and less-invasive fixation technique.

Bone Cutting Robot with Soft Tissue Collision Avoidance Capability by a Redundant Axis for Minimally Invasive Orthopedic Surgery

Many of the robots developed so far, including our multi-axis bone cutting robot, use an end mill as the cutting tool, and some problems should be solved to apply them to the minimally invasive orthopedic surgery. Minimally invasive surgery makes the incisions smaller, reduces pain and trauma to the body, and enables faster recovery. The smaller incision means a small and narrow opening area. This means the robot attitude for the bone resection is restricted, and it can result in the collision of the tool with the surrounding tissue, the existence of an untouched area and the degradation of the joint position accuracy. This paper proposes a robot mechanism and a toolpath generation technique specialized for bone cutting is expected to resolve these issues.

Development of a bone cutting robot for total knee arthroplasty

In total knee joint replacement, the femur and the tibia must be precisely shaped to ensure that they firmly mate with the artificial joint. The normal procedure is to manually cut the bones using a bone saw and mechanical jigs. A 9-axis bone cutting machine tool has been developed by the authors to increase cutting accuracy and reduce the hospital stay required for recuperation. As developed, the cut plane is determined by a 5 degree-of-freedom mechanism and the femur and tibia are cut by moving two translational and one rotational degrees of freedom, a system that provides a cutter path which avoids cutting the ligament. A preoperative planning system based on CAD/CAM principles and an overview of a system for total knee arthroplasty is also discussed. Experimental results showed the effectiveness of the developed robot and the system.