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While strain gauges are commonly used in a force sensor, we used multiple digital Hall-Effect magnetic sensors for developing a three-dimensional force sensor. We are aiming to develop a round shape three-dimensional force sensor. In order to get three-dimensional unknown force components, three independent outputs from the sensor are at least necessary. Four or more outputs however, would not be useless but redundant data sets, which could be useful to improve sensor accuracy. We calculated the unknown three-dimensional force values using nine outputs or less and estimated how many redundant outputs we should use to get good accuracy. As a result, when three outputs were used, the sensor accuracy was ranging from 8.2 to 15.7% depending on which outputs were used. When six outputs were used, the sensor accuracy was ranging from 5.5% to 5.6%. When nine outputs were used, the sensor accuracy was 4.1%. Although the best accuracy was acquired when we used all nine outputs, improvements were minimal when we used six or more outputs.

Purpose Instability and fractures may result from tensioning errors during reverse total shoulder arthroplasty (RTSA). To help understand tension, we measured intraoperative glenohumeral contact forces (GHCF) during RTSA. Methods Twenty-six patients underwent RTSA, and a strain gauge was attached to a baseplate, along with a trial glenosphere. GHCF were measured in passive neutral, flexion, abduction, scaption, and external rotation (ER). Five patients were excluded due to wire issues. The average age was 70 (range, 54–84), the average height was 169.5 cm (range, 154.9–182.9), and the average weight was 82.7 kg (range, 45.4–129.3). There were 11 females and 10 males, and thirteen 42 mm and 8 38 mm glenospheres. Results The mean GHCF values were 135 N at neutral, 123 N at ER, 165 N in flexion, 110 N in scaption, and 205 N in abduction. The mean force at terminal abduction is significantly greater than at terminal ER and scaption (p Conclusions These findings could help reduce inappropriate tensioning.

Background Correction of coronal plane deformity by osteotomies around the knee is theoretically three-dimensional (3D) and can be associated with changes in other planes. It has been shown that 3D rotational changes are induced by biplanar high tibial osteotomy; however, relevant information in biplanar lateral closed-wedge distal femoral osteotomy (LCW-DFO) has not been reported in literatures. This study aimed to investigate rotational changes in axial and sagittal planes in LCW-DFO using computer-aided design (CAD) simulations. Methods LCW-DFO is composed of three cuts: one ascending cut and two transverse cuts. In the simulations, the following geometrical parameters were adopted as factors potentially influencing 3D changes occurring in the osteotomy. The ascending cut angle measured as the angle between the edge of the ascending cut and the edge of the transverse cut in the lateral view, and the ascending cut obliquity measured as the angle corresponding to anterior/posterior inclination of the ascending cut with reference to the posterior condylar tangent line in the axial view. In the analysis, the effects of these bony cut angles on associated rotational changes in the axial and sagittal planes (internal/external rotation and flexion/extension) were calculated. Variation of wedge size ranged from 2 to 8 mm. Results The degree of the ascending cut obliquity substantially correlated with associated change in the sagittal plane (extension/flexion) while inducing only minimal change in rotation in the axial plane (internal/external rotation). When the osteotomy was made without ascending cut obliquity, the change in knee extension/flexion was minimal for the conditions analyzed while coupled internal rotation of the distal bony segment was induced. Conclusions In biplanar LCW-DFO, the ascending cut angle substantially influenced the amount of internal rotation of the distal bony segment with little effect on flexion/extension angles. By contrast, ascending cut obliquity in the axial plane yields an effect on flexion/extension angles and little effect on internal rotation of the distal bony segment.

The purpose of this study was to analyse the resultant stress induced by joint-line obliquity after HTO for varus knee deformity using a three-dimensional (3D) finite element model analysis. The geometrical bone data used in this study were derived from commercially available human bone digital anatomy media. The 3D knee models were developed using 3D computer-aided design software. The articular surface was overlaid with a 2-mm-thick cartilage layer for both femoral and tibial condyles. Ligament structures were simulated based on properties reported in previous anatomical studies. Regarding the loading condition, isolated axial loads of 1200 N with lateral joint-line inclinations of 2.5°, 5°, 7.5°, and 10° in reference to the horizontal axis were applied to the femur to simulate the mechanical environment in a knee with joint-line obliquity. A steep rise of shear stress in the medial compartment was noted in the model with obliquity of 5° or more. This laterally directed shear stress exhibited an incremental increase in accordance with the obliquity angle. The maximum shear stress value in the medial cartilage increased from 1.6 MPa for the normal knee to 3.3, 5.2, and 7.2 MPa in the joint-line obliquity models with 5°, 7.5°, and 10° of obliquity, respectively. The effects of HTO for varus knee deformity on the amount/distribution of stresses in the articular cartilage were analysed using a 3D finite element model. It was shown that joint-line obliquity of more than 5° induced excessive shear stress in the tibial articular cartilage. A large amount of correction in OWHTO with a resultant joint-line obliquity of 5° or more may induce detrimental stress to the articular cartilage. Double-level osteotomy should be considered as a surgical option in this situation.

Background During total hip arthroplasty (THA), the accurate placement of the femoral components is an important determinant of the success of the procedure. This study assessed the accuracy of cemented stem placement using a new angle-measuring instrument. The primary objective was to investigate the accuracy of the intraoperative measurements of cemented stem anteversion obtained using the angle-measuring instrument. Our secondary objective was to evaluate the accuracy of stem positioning performed using the angle-measuring instrument. Methods We compared the intraoperative stem anteversion measurements obtained using the angle-measuring instrument with postoperative stem anteversion measurements obtained using computed tomography in 149 hips (measurement accuracy). We also compared the target angle and postoperative stem anteversion in 105 hips (implantation accuracy). Results The mean amount of intraoperative stem anteversion was 37.9° ± 10.1°, and the mean amount of postoperative stem anteversion was 37.0° ± 10.4°. The mean measurement accuracy was 0.9° ± 6.1°, and the absolute measurement accuracy was 4.9° ± 3.7°. The correlation coefficient for the relationship between the intraoperative and postoperative stem anteversion measurements was 0.824 (p = 0.000). The mean amount of target angle was 37.4° ± 7.6°, and the mean amount of postoperative stem anteversion was 35.9° ± 9.1°. The mean implantation accuracy was 1.4° ± 5.6°, and the mean absolute implantation accuracy was 4.3° ± 3.6°. The correlation coefficient for the relationship between the target angle and postoperative stem anteversion was 0.795 (p = 0.000). Conclusions The angle-measuring instrument measured intraoperative stem anteversion accurately, and cemented stem was implanted accurately during THA with the angle-measuring instrument.

Soft tissue tension is thought to have a great effect on the clinical performance of total joint replacement; such as shoulder, hip, knee, or ankle. However, there have been no reports quantifying these soft tissue tensions intraoperatively. For the shoulder, reverse total shoulder arthroplasty has been used in Japan since 2014. So the purpose of this study is to develop an instrument which tells us soft tissue tension intraoperatively. Surgeons would be able to utilize the measured values when assessing stability of the joint intraoperatively. We are developing the instrument using capacitive one-dimensional force sensors to measure the soft tissue tension for reverse shoulder arthroplasty. A capacitive one-dimensional force sensor can be made less than 1mm in thickness. And an electric circuit which measures its amount of capacitances also could be made pretty small. That's because we use capacitive force sensors for measuring the soft tissue tension. The whole instruments have to be sufficiently small enough such that its outer geometry could be same to an existing prosthesis. While a capacitive force sensor is good in its dimensions, however, it is very sensitive to noise. We try to improve signal noise ratio having whole dimensions small enough. Now, we have designed a 5mm diameter capacitive one-dimensional force sensor to operate in the 0–150N force range. This direction hopefully would be one of the promising ways for good clinical outcomes of joint replacement.

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited., Background: It has been reported that the function of the labrum is to ensure that an increased surface area encountered the femoral head and spares the cartilage from excessive strain. The purpose of this study was to determine whether early deformation of the hip articular cartilage occurs under high-load conditions in the presence/absence of the labrum. Methods: The hip joints of 4 beagle dogs were retrieved. A continuous static load of 80 Kg was applied for 2.5 hours. Magnetic resonance imaging (MRI) was performed immediately after the loading and at 30, 60, 90, 120, and 150 minutes after the loading. The load was then removed, and the specimens were stored for 14 h to allow the cartilage to recover. The labrum was then carefully removed, and the experiment was performed again. Results: The maximum percentage change in cartilage thickness was 35.3 ± 17.4% when the labrum was intact and 55.7± 7.5% after the labrum had been excised (p=0.060). Labral excision resulted in a reduction in cartilage thickness. Cartilage thickness was significantly decreased in the normal and labral excision models immediately after loading (p=0.003 and p=0.022, respectively). Conclusion: The labrum plays a role in dispersing loads equally across the joint cartilage and reduces the load placed on the maximum weight-bearing region of cartilage. Early articular cartilage deformation occurred under high-load conditions both before and after the excision of the labrum.

The success of total hip arthroplasty (THA) in improving joint function and reducing pain is regarded as one of the great achievements of modern medicine. Today, most femoral stems with cementless fixation are made of either cobalt-chrome-molybdenum (CoCrMb) or titanium-aluminum-vanadium (TiAlV) alloys. In order to obtain adequate initial stability of the cementless femoral stem, the implant must be placed in contact with bone of sufficient strength to support the prosthesis rigidly. This study introduces a unique approach in this research category, making use of shape memory alloys (SMA) for cementless stems to obtain adequate initial stability. Using SMA that exhibits a shape memory effect, better proximal fit and fill with smooth insertion will be accomplished. In this study, numerical evaluation is intended with initial stability of a cementless stem for which SMA is utilized. A result of the numerical analysis reveals that use of SMA is found to be effective enough to obtain rigid initial stability.

Severe anal incontinence is a socially incapacitating disorder and a major unresolved clinical problem that has a considerable negative impact on quality of life. In this study, we developed a new artificial anal sphincter using shape memory alloys (SMAs) in order to improve the quality of life of such patients and evaluated the influence of this sphincter on blood serum chemistry in animal experiments. The artificial anal sphincter was driven by two Ti-Ni SMA actuators sandwiching the intestine and was implanted in three female goats. Blood was collected from the jugular vein on days 1 and 4; at weeks 1 and 2; and at months 1, 2, and 3, postoperatively. Biochemical parameters including total protein, albumin, total bilirubin, aspartate amino-transferase, blood urea nitrogen, creatinine, and C-reactive protein were examined. The time courses of total bilirubin and aspartate amino transferase of the three goats were within the baseline levels after 1 week of implantation and remained normal, demonstrating no liver function complications. The blood urea nitrogen and creatinine levels remained within the normal range, indicating no renal function complications. The total protein and albumin fluctuated within the normal range throughout the duration of this study. In these goats, it was also found that the level of C-reactive protein did not increase and that there was no stricture of the intestine where the artificial sphincter was attached. Our findings indicate that the artificial sphincter SMA demonstrated no adverse influence on blood serum chemistry and exhibited an effective system performance.

The authors propose a novel concept for less invasive hemostatic forceps. The proposed hemostatic forceps employ superelastic shape memory alloys that enable one to maintain the clamping pressure within a safe range. In this paper, the basic design of these hemostatic forceps is described. The validity of the concept is demonstrated by experimental results using a prototype.

This study is aimed to show if hip joint loads during walking could be reduced by a slight gait modification. Six healthy adult subjects (mean (SD) age 22 (0.0) years, mean (SD) height 1.68 (0.04) m, mean (SD) weight 60.2 (7.9) kg) took part in this study. A series of normal walking trials at a selfselected speed (step length and cadence) and stride width were performed. After subjects had gait retraining during in which they were asked to alter their stride width by increasing abduction angles without changing any other kinematics. Subjects walked 10 trials for each gait pattern. A total of 20 trials were performed. Experimental gait data (joint angles and ground reaction forces) and musculoskeletal computer models were used to quantify individual hip joint moments. We used adduction moments as an indicator of internal hip joint loads. An inverse dynamics approach was also used to calculate the hip moments during a stance phase.

The number of stem designs for total hip arthroplasty is increasing, and occasionally design changes have yielded unexpected clinical results. At present, we are not able to clearly identify which parameter of the stem is most important, and the optimum value of many parameters. The goals of this study were to identify which parameter is most important, to understand the effect of design change, and to find the optimum stem shape. For this purpose, we used adaptive p-method together with three-dimensional computer-aided design software program for the design sensitivity analysis (DSA) and shape optimization of the stem. The results suggested that increasing the lateral and medial width of the distal cross-section together with decreasing the medial-lateral width and the medial radius of the distal cross-section from the default value would lead to a decrease in the largest maximum principal stress of the distal cement. The medial width of middle cross-section, however, was not so simple. The result of DSA suggested that decreasing this parameter from the default value decreased the stress in the distal cement, but the optimum shape was obtained by increasing this parameter. The method used in this study will assist our engineers and surgeons in the process of modifying and optimizing the stem design.

This article presents some progress in the development for preclinical trials of an artificial anal sphincter using shape memory alloys. The novel device has been proposed and developed by the author's group at Tohoku University. It has two dominant features different from other systems, which are either clinically available or still under development. One is that a solid driving element, a combination of shape memory alloy (SMA) ribbons and silicone elastomer sheets with a layered structure, is adopted for the opening and closing functions of the artificial sphincter. The other is a sandwich mechanism for the closing of bowel to reduce the risk of buckling induced ischemia which has been reported in hydraulically driven artificial sphincters with a radial squeezing mechanism. The device has fewer parts inside the body and therefore be implanted more easily. A new design eliminating the risk of heat burns enables long-term implantation and brings the device closer to practical use. Functionality and safety of the device have been proved in three-month animal experiments.

Severe dysfunction of muscle tissues can be treated by transplantation but the success rate is still not high enough. One possibility instead is to replace the dysfunctional muscle with artificial muscles. This article introduces a unique approach using shape memory alloys (SMAs) to replace the anal sphincter muscle for solving the problem of fecal incontinence. The use of SMAs that exhibit a two-way shape memory effect allows the device to function like a sphincter muscle and facilitates simple design. In this article, we will give a brief introduction to the functional material - SMA - together with its medical applications, and will follow this with a description of the recent progress in research and development of an SMA-based artificial sphincter. The possibility of its commercialization will also be discussed.

Where is a place to be assisted for the patients with congestive heart failure? It is contraction of myocardium. We do not need to exchange the whole hearts. We started the ARTIFICIAL MYOCARDIUM development project. In the first step, pneumatic drive type artificial myocardium was developed. Next, development of an implantable type device was started. The animal experiment which studies the direct ventricle supporting effect by this motor was conducted. Although cardiac assistance of the right ventricle was enough as a result of repeating an animal experiment, the left ventricle supporting effect was inadequate. By such reason, we planned the development of an electrohydraulic driving system with grass fiber belt for fixation. The drive system with which it equipped between ribs controls silicon oil in our plan. Energy is supplied by transcutaneous energy transmission system from the outside of the body. As the results, this device is easily attached to the ventricle and the left ventricle and the right ventricle were able to be assisted as a result of the animal experiment. The cardiac output increased and blood pressure rose in the time series data during artificial myocardium support. Since this device is not a pump, it does not have a valve and does not have the risk of a thrombus, either. Therefore, it is also possible to implant in prevention to a slight heart failure patient. It is expected that it becomes an important artificial organ with a big market.

The present paper introduces an optimum design of the hip prosthesis and a method for shape optimization which minimizes the stress concentration within the cement mantle. A gradient projection method of numerical optimization and a p-version three-dimensional FEM of stress analysis were employed. A generic three-dimensional FEM model of the proximal femur containing a cemented fomoral stem of a total hip arthroplasty was developed. The three types of analysis was then performed in this study. First, stastic stress analysis measuring the stress in the bone cement was performed. The generic model was then valified parametrically by changing the each parameters individually that compose the stem geometry measureing the stress occuring within the cement mantle concurrently. As it is called design sensitivity analysis was performed. Finally, optimal stem shape was desigend using shape optimization. The design objective was to minimize the largest maximum principal stress in the cement. The results of shape optimization showed considerable reduction in stress concentration within the cement mantle compared to the starting design that were used. Moreover, the optimal stem shape obtained in this study showed unique geometry differ from the standard trend that has been believed to be better. The results of this study has shown to be attractive for evaluating stem design and develop the optimal new stem shape.

This study proposes novel optimized stem geometry with low stress values in the cement using a finite element (FE) analysis combined with an optimization procedure and experimental measurements of cement stress in vitro. We first optimized an existing stem geometry using a three-dimensional FE analysis combined with a shape optimization technique. One of the most important factors in the cemented stem design is to reduce stress in the cement. Hence, in the optimization study, we minimized the largest tensile principal stress in the cement mantle under a physiological loading condition by changing the stem geometry. As the next step, the optimized stem and the existing stem were manufactured to validate the usefulness of the numerical models and the results of the optimization in vitro. In the experimental study, strain gauges were embedded in the cement mantle to measure the strain in the cement mantle adjacent to the stems. The overall trend of the experimental study was in good agreement with the results of the numerical study, and we were able to reduce the largest stress by more than 50% in both shape optimization and strain gauge measurements. Thus, we could validate the usefulness of the numerical models and the results of the optimization using the experimental models. The optimization employed in this study is a useful approach for developing new stem designs.

Passive muscle tension around the hip joint following total hip arthroplasty (THA) plays an important role in post-surgery dislocation mechanisms, especially posterior dislocation. To analyze dislocation objectively and to clarify the distinction between implant-to-implant impingement and dislocation, three-dimensional finite element (FE) models of hybrid THA components were generated. An acetabular component was implanted into the acetabulum in 20 degrees of anteversion and 45 degrees of inclination. The bearing surface had 26 mm hemispherical plus 1 mm flat depth and a chamfered edge. In this study, posterior dislocation-prone movements such as flexion, adduction, internal rotation, and their combinations were analyzed, starting with the femoral component oriented in a manner corresponding to the hip being flexed to impingement with 0°, 10°, 20°, and 30° of internal rotation and 0°, 10°, 20°, and 30° of adduction. The nonlinear explicit FE simulations were driven by inputting a series of incremental flexion moments and hip joint forces concurrently. The angles of internal rotation and adduction affected both impingement and dislocation angles of flexion. The flexion angles both at impingement and dislocation decreased by increasing the internal rotation angles. Although the peak flexion moment to make the hip joint dislocate increased by increasing the internal rotation angle, it didn’t always increase with an increase in the adduction angle. The highest value of the peak flexion moment to dislocation was observed at 30° of internal rotation. Conversely, the lowest value of the peak flexion moment was observed at 10° of adduction. This lowest value means that the hip joint is easy to dislocate at this adduction angle.

New surface structure with regular patterning for the frictional surfaces of the artificial joints was designed to improve the wear problems. The lubrication properties for the cup ( ultrahigh molecular weight polyethylene, UHMWPE) vs. ball ( Co-Cr alloy) were studied to evaluate the wear and surface roughness. The surface structure is the dents pattern which has diameter of 0.5mm, pitch of 1.2mm. In this study, such surface patterns were applied to artificial hip joints, and the effects of regular patterning on the frictional surface were investigated by using a joint simulator. The amount of wear of the cup that was in contact with the patterned head was only half that of the cup that was in contact with the non-patterned head, and the surface roughness of the cup with a non-patterned head was three-times greater than that of the cup with a patterned head. These results demonstrates that the lubrication properties can be improved by patterning of the frictional surface of the artificial joint. Consequently, the life of the artificial joint can be extended by the patterning on the frictional surfaces.

There are many designs of the femoral stem of a cemented total hip arthroplasty, and mechanical failure of the stem is caused by several factors related to the cement, such as failure of the cement. Optimization of the shape of the stem, especially multiobjective optimization, is required to solve these design problems because a cement fracture is caused by multiple factors. The objective of this study was to determine a stem geometry considering multiple factors at the same time. A three-dimensional finite element model of the proximal femur was developed from a composite femur. A total of four objective functions--two objective functions, the largest maximum principal stress of proximal and distal sections in the cement mantle, for each of the two boundary conditions, walking and stair climbing--were used. The neighborhood cultivation genetic algorithm was introduced to minimize these objective functions. The results showed that the geometry that leads to a decrease in the proximal cement stress and the geometry that leads to a decrease in the distal cement stress were not the same. However, the results of the walking and the stair climbing conditions matched. Five dominant stem designs were considered to be the Pareto solution, and one design was identified as the "better design" for all objective functions. It was shown that multiobjective optimization using a genetic algorithm may be used for optimizing the shape of the femoral stem in order to avoid cement fracture.

Quantifying soft-tissue tension around the hip joint during total hip arthroplasty remains difficult. In this study, a three-dimensional computer-aided design model was developed to clarify how component position in total hip arthroplasty contributes to the primary cause of posterior dislocation in cases of flexion, adduction and internal rotation. To better understand the influences of anteversion angle of the acetabular component, its effects on the primary causes of dislocations and the range of motion were investigated. Three different primary dislocation mechanisms were noted: impingement of the prosthetic femoral neck on the cup liner; impingement of the osseous femur on the osseous pelvis; and spontaneous dislocation caused by soft-tissue traction without impingement. Spontaneous dislocation could be detected by calculating hip forces at any thigh position using the computer-aided design model developed. In computer analysis, a transition from prosthetic impingement rate to osseous impingement rate occurred with increasing anteversion angle of the acetabular component. Spontaneous dislocation was detected at angles > 10° of anteversion of the acetabular component when flexion occurred with extreme adduction and internal rotation. This study demonstrated the possibility of spontaneous dislocation that results not from prosthetic or bony impingement but from muscle traction with increased range of motion.

As the heart failure is caused by the decrease in the myocardial contraction, the direct mechanical myocardial assistance in response to physiological demand, that is, the synchronous support of the contractile function from outside of the heart, might be effective. The purpose of this study was to develop an artificial myocardium which was capable of supporting the cardiac contraction directly by using the shape memory alloy fibres based on nanotechnology. Some methodologies using novel devices other than the artificial hearts are proposed so far with severe heart disease. However, it was also anticipated that the decrease in cardiac functions owing to the diastolic disability might be caused by using those ‘static’ devices. Then, this study was focused on an artificial myocardium using shape memory alloy fibres with a diameter of 100 – 150 um, and the authors examined its mechanism in a mock circulatory system as well as in animal experiments using goats. Basic characteristics of the material were evaluated prior to the hydrodynamic or hemodynamic examination using a mock ventricular model. The results were as follows: a) The length of the structure was able to be adjusted so that the system could wrap the whole heart effectively. b) In the hydrodynamic study using the mock circulatory system, the myocardial system was able to pump a flow against the afterload of arterial pressure level. c) In the animal experiments, aortic pressure and flow rate were elevated by 7 and 15% respectively by the mechanical assistance of the artificial myocardium, which was driven synchronising with the electrocardiogram, and also, d) The anatomically-identical shape of the artificial myocardium might be more effective for the assistance. In conclusion, it was indicated that this controllable artificial myocardial support system was effective for the mechanical cardiac support for the chronic heart failure.