In these days, external fixation is widely used for femoral fractures because of less-invasiveness of surgical exposure. It requires surgical staff their X-ray exposure by fluoroscopy for aligning bone fragments and fixing the bones by a multi-joint external fixator. A surgical navigation system is often employed to reduce the amount of X-ray exposure by indicating intuitive information for surgical tool guidance. Additionally, it can lead high accuracy and time saving for surgeries. Nakajima et a1.⁴⁾ have been proposed a laser navigation method for guiding surgical tool position and orientation. Two laser-beam planes are directly emitted into the surgical field, and the entry point is appeared as the cross-sectional point of two laser-beam lines on the patient's skin and the orientation is shown as two parallel laser-beam lines on the side face of the surgical tool. The accuracy was 1 mm for translation and 1 degree for rotation. The feasibility to apply it to percutaneous surgeries has been predicted in his paper, however it have not been evaluated. Therefore, we evaluate the accuracy of the laser guidance method for percutaneous surgeries in our preliminary experiments and validate the feasibility to apply it to the percutaneous insertion of a surgical pin which uses for external fixation of fractured bones in our phantom tests. We also validate the feasibility of the template surgeries by using a joint-less external fixator for bones. The results show the tool guiding accuracy of 1.39 mm and 1.03 degrees in the condition of percutaneous surgeries and the accuracy of 2.74 mm and 3.28 degrees for bone alignment in the template fracture reduction surgeries.

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This paper describes the development of a new insertion device that uses hydraulic pressure to position the needle of the device. This device simplifies insertion operations into cavities such as insertion for lumber epidural anesthesia; damage that can be caused to the tissue behind the cavities by overrun insertion is also avoided. When a anesthesiologist pushes the plunger, the needle moves forward to insert and then stops automatically when its tip reaches into the cavity; the automatic stopping is caused by the opening of a pressure chamber at the tip of the needle that limits the hydro pressure to the pressure outside the tip of the needle. Insertion experiments to simulators and porcine tissue were performed to verify the function of the proposed device, that is, needle movement and automatic stopping at cavities. These experiments were found to validate the basic formulae of the cross-sectional areas of the cylinders to control the insertion force and plunger force.

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The purpose of this study was development of the 4D gait analysis system with the locus of center of pressure on sole of foot and to compare between pre and post-operative high tibial osteotomy. The subject of this study was a patient with medial compartment osteoarthritis of the varus knee. The data of pre and post-operative walking were acquired using a 4-dimensional motion analysis system combined CT images, motion capture data, and force plate data. The center of pressure on sole of foot was acquired from the force plate data according to reaction-oriented coordinate system. The locus of center of pressure on sole of foot was showed on the photograph as mirror image of the foot by matching the spherical skin marker around the foot of the Vicon coordinate system and the spherical skin marker on the photograph of sole of foot. The coordinate system on sole of foot was defined on the photograph based on the center of the 2^nd metatarsal head and the center of the heel. The pre-operative locus of center of pressure on sole of foot passed through slightly lateral side on sole of foot. The post-operative locus of center of pressure on sole of foot passed through slightly medial side on sole of foot.

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This study aims at presenting the biomechanical brain tissue deformation simulation for development of the virtual reality surgical training system using haptic device. In the training system, it is necessary to generate not only visual view of the surgical scene similar to the surgical field but also tactile sensation due to intraoperative interaction between the brain tissue and the surgical instruments (brain spatula, suction, forceps, scissors, etc.). In this paper, the simulation capability for the intraoperative cerebellum tissue deformation due to retraction with brain spatula for the operation on the posterior fossa surgery by using authors'developed three-dimensional finite element model is demonstrated. The illustrative results successfully demonstrate the interaction between the cerebellum tissue and brain spatula. After retracting the tissue, significant surface deformation was obtained toward the retraction direction and deep structures such as root exit zone of the cranial nerves around pons were exposed in the surgical field. In addition, the results that the spatula retraction speed affected the deformation field show the capability of the evaluation of surgical skill level. Furthermore, the cerebellum model consists of the cerebellum, pons, and medulla oblongata was proposed for achieving drastic computation time reduction of the cerebellum tissue retraction simulation. The retraction simulation using the proposed model successfully achieved up to 83% reduction of computation time compared with that using the whole brain model. All results show that the feasibility of the neurosurgical training system based on the biomechanical brain tissue deformation computation. Authors are now working on developing the new three-dimensional brain deformation model for rendering the deformed tissue surface which can be built into the haptic device.

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