Takatoshi Ide

Arthroscopic surgery of the hip joint

Hip arthroscopic examination of 196 joints was performed in 104 patients treated during the past 4 years. Of these, 11 joints were treated by arthroscopic surgery. We have developed a technique using a two-directional approach that facilitates a global view of joint areas and allows simpler performance of surgical procedures. Removal of loose bodies, joint debridement in osteoarthritis, and synovectomy in rheumatoid arthritis are good indications for arthroscopic surgery of the hip joint. Short-term follow-up was satisfactory, and a reduction of pain was obtained in all patients. Although the joint space of the hip is narrower and the operative technique is more difficult to perform than in the knee, we believe that arthroscopic surgery of the hip is a suitable method in selected cases.

Expectations for medical and healthcare robotics

It is no exaggeration to say that we are up against an inordinate lack of hospital staff, with a shortage of labour in non-medical as well as in specialized medical fields in Japan. For these reasons, the necessity for medical and healthcare robotics is examined in this study in order to qualitatively improve medical treatment. In addition, clinical applications of medical and healthcare robotics are also described.

Biomechanical Studies of the Hip Utilizing Computer Simulation

Estimation of the force distribution on the hip joint articulating surface was studied with stress analysis calculated by computer simulation based on Kawai’s Rigid body spring model (RBSM) using plane radiographs. The result of the two-dimensional RBSM, modified to take into consideration the depth of the joint, showed that the maximum compressive stress on the contact surface was estimated at 0.031 body weight (BW)/mm in the normal hip. The maximum stress and the resultant force were decreased with an increase of the center-edge angle, but the change of the resultant force was not remarkable compared with the maximum stress. It was estimated that the maximum compressive stress was about five times with less than 0° of the center-edge angle compared with 27° in the normal hip. With the stress analysis using RBSM it was possible to estimate the biomechanical behavior of the hip precisely. This system is useful for clarifying osteoarthritis of the hip in biomechanical terms and for the prognosis of coxarthrosis in clinical cases.

Validation Study of the Rigid Body Spring Model Using the Metacarpophalangeal Joint

Estimation of the force distribution on the metacarpophalangeal joint surface was studied by using sixteen cadaveric metacarpophalangeal joints, and the results were compared with the stress analysis calculated by computer simulation using Kawais Rigid Body Spring Model (RBSM). According to the results of analysis based on the two-dimensional RBSM (2D-RBSM) computer simulation, displacement was 6.7 times greater than that of the experiment while the peak pressure was only 0.6 times greater. The results of the two-dimensional RBSM modified to take into consideration the depth of the joint, showed that it was comparable with the experimental studies in terms of peak pressure and displacements. The elastic modulus of the cartilage was estimated to be 25.8 MPa and the spring constant of the cartilage was estimated to be 22.6 N/mm/unit area after displacement matching by the modified two-dimensonal RBSM.

—Overview— Ideal Stem Design for Cementless Total Hip System

To improve cementless stem design to achieve long-term stability, simulations using graphic processing systems or cadaver specimens, and biomechanical analyses, using rigid body spring models (RBSM) or finite element models (FEM) have been used. Simulations using graphic processing systems or cadaver specimens are useful for investigating the shape or size of the stem which provides stem press fit into the medullary canal. These methods, however, have a disadvantage in that, when they are used, it is not possible to comprehensively evaluate biomechanical stability, in terms of evaluating such factors as the resection angle of the femoral neck, the stem length, and the absence or presence of calcar femorale, which greatly influence this stability. Biomechanical analysis of computer simulations using the RBSM, on the other hand, makes it possible to comprehensively evaluate biomechanical stability in terms of these factors. Further, the results obtained for such simulations are so reliable as to be consistent with clinical results. Against this background, we performed computer simulations, using the RBSM, to develop a new cementless stem, the model Y 2, which was used for 48 hips in 48 patients. This model has a 35° resection angle of the femoral neck and a stem length of 178 mm The stem has a smooth surface with several longitudinal grooves. In the 29 hips of 29 patients who were followed-up for more than 2 years there was an excellent postoperative course, only 3 patients (10%) being affected by thigh pain. Roentgenographic findings showed no shifting or sinking of the stem and a clear zone less than 2-mm-wide was observed in only seven cases. Based both on our clinical results in patients who received model Y 2 replacements, and on the advantages gained in terms of comprehensively evaluating biomechanical stability, we believe that biomechanical analysis of computer simulations, using the RBSM, is a very useful method for the evaluation of the ideal design for a cementless stem.

Biomechanical Features of Various Cementless Total Hip Replacement Systems

The selection of an implant and the surgical placement of a prosthetic component in total hip replacement are based on limited radiographic and clinical information. To optimize surgical outcome and anticipate intraoperative problems, computer-aided simulation/analysis software was developed based on the rigid body spring model (RBSM), using plane radiographs (two-dimensional [2-D] analysis) to obtain implant/bone interface stress, ligamentous tension, and relative displacement for bony segments and implants. In the study of our total hip replacement (THR) system which features three spikes on the socket, the main assessment criterion used was an implant fixation index based on implant/bone interface stress and relative displacement of the prosthesis in reference to bone. The computer simulation was consistent with the clinical results for our cementless THR system and it showed that implant design and placement significantly affected prosthesis/bone interface stresses. Therefore, this method can be expected to provide useful information in the preoperative planning of difficult reconstructive cases involving the hip.

Development of Y II Cementless Total Hip System Using a Socket with Three Spikes

The advantage of a surgical procedure using the design of the Y II cementless total hip system using a socket with three spikes (Y II THA), which is applied in our department, is reported. The Y II THA has been developed based on the results of the computer simulation using the rigid body spring model (RBSM), animal experiments, and previous clinical experience. The Y II socket consists of a hemispherical metal socket made of titanium alloy and artificial cartilage made of polyethylene, which is screwed into the metal socket, called a metal back system. The thickness of the artificial cartilage is 9mm. The metal socket has three spikes. One of them has a notched surface and the length is 35 mm. The surface of the remaining two spikes is smooth and 23 mm in length. This socket is inserted at a 35° open angle by using an angle finder without removing the residual cartilage or subchondral bone. The Y II stem is made of titanium alloy and has a collar at the neck. The femoral neck angle is 35° and the length is 178 mm. Several longitudinal grooves are engraved on the smooth surface, called a fluted type. There are three sizes: small, standard, and large. The femoral head, made of cobalt-chromium alloy, is 23 mm in diameter. This is called a modular type. The femoral neck is excised at a 35° angle to the horizontal line with 8 mm of calcar left from the base of the lesser trochanter. Then, the femoral medullary canal is reamed to the minimal necessary extent using a rasp whose size was preoperatively determined by a template. Forty-one joints of 41 patients underwent total hip arthroplasty using the Y II THA and were followed up for more than 3 years. All patients achieved excellent clinical results and stable mechanical durability according to radiographic findings.