Go Yamako

Bio: Go Yamako is an academic researcher from University of Miyazaki. The author has contributed to research in topics: Stress shielding & Medicine. The author has an hindex of 8, co-authored 29 publications receiving 178 citations. Previous affiliations of Go Yamako include Niigata University.

Fabrication of a high-performance hip prosthetic stem using β Ti–33.6Nb–4Sn

Abstract: This study used severe cold rolling followed by cold swaging of β Ti-33.6% Nb-4% Sn rods to form a characteristic fiber structure composed of stress-induced α″ martensite with texture and a β phase with texture, resulting in a material with a low Young's modulus of 40GPa. The material's tensile strength of 1270MPa and fatigue strength of 850MPa were attained by heat treatment at 673K for 5h through fine α precipitation in the fiber structure. A new method of fabricating a high-performance hip prosthetic stem was investigated based on the low Young's modulus and high strength obtained. After fabricating the stem by cold rolling, cold swaging, cold die-forging and machining, its neck region was given higher strength through local heat treatment, while the low Young's modulus remained almost unchanged in a distal portion of the stem. When a stem tip in the distal part was heat treated at 423K, reverse α″→β transformation occurred and the tangent modulus decreased to less than 30GPa, accompanied by stress-induced β→α″. It was concluded that the method presented herein provided a low Young's modulus of approximately 40GPa in the distal part and high fatigue strength of approximately 850MPa in the neck region of a high-performance hip prosthetic stem.

Quantification of the sit-to-stand movement for monitoring age-related motor deterioration using the Nintendo Wii Balance Board

Abstract: Simple methods for quantitative evaluations of individual motor performance are crucial for the early detection of motor deterioration. Sit-to-stand movement from a chair is a mechanically demanding component of activities of daily living. Here, we developed a novel method using the ground reaction force and center of pressure measured from the Nintendo Wii Balance Board to quantify sit-to-stand movement (sit-to-stand score) and investigated the age-related change in the sit-to-stand score as a method to evaluate reduction in motor performance. The study enrolled 503 participants (mean age ± standard deviation, 51.0 ± 19.7 years; range, 20–88 years; male/female ratio, 226/277) without any known musculoskeletal conditions that limit sit-to-stand movement, which were divided into seven 10-year age groups. The participants were instructed to stand up as quickly as possible, and the sit-to-stand score was calculated as the combination of the speed and balance indices, which have a tradeoff relationship. We also performed the timed up and go test, a well-known clinical test used to evaluate an individual’s mobility. There were significant differences in the sit-to-stand score and timed up and go time among age groups. The mean sit-to-stand score for 60s, 70s, and 80s were 77%, 68%, and 53% of that for the 20s, respectively. The timed up and go test confirmed the age-related decrease in mobility of the participants. In addition, the sit-to-stand score measured using the Wii Balance Board was compared with that from a laboratory-graded force plate using the Bland–Altman plot (bias = −3.1 [ms]-1, 95% limit of agreement: −11.0 to 3.9 [ms]-1). The sit-to-stand score has good inter-device reliability (intraclass correlation coefficient = 0.87). Furthermore, the test–retest reliability is substantial (intraclass correlation coefficient = 0.64). Thus, the proposed STS score will be useful to detect the early deterioration of motor performance.

Improved Corrosion Resistance on Selective Laser Melting Produced Ti-5Cu Alloy after Heat Treatment

Abstract: A Ti-5Cu alloy produced by selective laser melting exhibits a nonuniform Ti2Cu phase structure, which contains a small amount of α′ phase in melt pool boundaries thereby resulting in reduced corrosion resistance. The heat-treatment process proposed in this work eliminates the deleterious effect of α′ phase and the Ti2Cu phase is refined using different cooling rates, which improves the corrosion resistance. The electrochemical results indicate that the heat-treated Ti-5Cu samples have similar corrosion behavior to pure CP-Ti. A slower cooling rate produces a larger spacing between the Ti2Cu phases in the microstructure of the sample, resulting in higher corrosion resistance. The corrosion behavior of SLM-produced Ti-5Cu and heat-treated counterparts with different microstructure are detailed discussed.

Analysis of the complications of palmar plating versus external fixation for fractures of the distal radius.

Abstract: Purpose To evaluate whether there was a difference in complication rates in our patients treated with external fixation versus volar plating of distal radius fractures. We also looked for a difference in radiographic results; in the clinical outcomes of flexion, extension, supination, pronation, and grip strength; and in scores on the visual analog scale (VAS) for pain and the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire. Methods We reviewed 115 patients with comminuted intrarticular distal radius fractures. Of those patients, 59 were treated with external fixation and 56 with volar plate fixation. Postoperative radiographs, range of motion, and grip strength were measured; DASH and VAS pain questionnaires were administered; and complications were documented. Results The external fixation group had a significantly higher overall complication rate. In the volar plate group, there were more tendon and median nerve complications, but this difference was not significant. Radiographically, the external fixator group demonstrated radial shortening of 0.7 mm, whereas the volar plate group demonstrated 0.3 mm of radial shortening during the postoperative period. There were no significant differences between the groups in the measurement of scapholunate angle or palmar tilt. The mean DASH score at final follow-up was 32 in the external fixation group and 17 in the volar plate group, which was statistically significant. The final VAS scores were statistically different at 3.1 for the external fixation group and 1.1 for the volar plate group. On physical examination, the volar plate group had significantly better arc of motion in pronation–supination and flexion–extension and better grip strength. Conclusions In the patients we studied, volar plate fixation has an overall decreased incidence of complications and significantly better motion in flexion–extension and supination–pronation compared to external fixation. Volar plate fixation also has less radial shortening than the external fixation group, yet the absolute difference in magnitude of ulnar variance was only 1.4 mm, calling into question the clinical significance of this difference. Patients with volar plating also have better pain and functional outcomes and better grip strength. Type of study/level of evidence Therapeutic III.

Femoral stem incorporating a diamond cubic lattice structure: Design, manufacture and testing.

Abstract: Background The current total hip prostheses with dense femoral stems are considerably stiffer than the host bones, which leads to such long-term complications as aseptic loosening, and eventually, the need for a revision. Consequently, the lifetime of the implantation does not match the lifetime expectation of young patients. Method A femoral stem design featuring a porous structure is proposed to lower its stiffness and allow bone tissue ingrowth. The porous structure is based on a diamond cubic lattice in which the pore size and the strut thickness are selected to meet the biomechanical requirements of the strength and the bone ingrowth. A porous stem and its fully dense counterpart are produced by laser powder-bed fusion using Ti-6Al-4V alloy. To evaluate the stiffness reduction, static testing based on the ISO standard 7206-4 is performed. The experimental results recorded by digital image correlation are analyzed and compared to the numerical model. Results & conclusions The numerical and experimental force-displacement characteristics of the porous stem show a 31% lower stiffness as compared to that of its dense counterpart. Moreover, the correlation analysis of the total displacement and equivalent strain fields allows the preliminary validation of the numerical model of the porous stem. Finally, the analysis of the surface-to-volume and the strength-to-stiffness ratios of diamond lattice structures allow the assessment of their potential as biomimetic constructs for load-bearing orthopaedic implants.