Background and Objectives: In the field of orthopedic surgery, novel techniques of three-dimensional shape modeling using two-dimensional tomographic images are used for bone-shape measurements, preoperative planning in joint-replacement surgery, and postoperative evaluation. ZedView® (three-dimensional measurement instrument and preoperative-planning software) had previously been developed. Our group is also using ZedView® for preoperative planning and postoperative evaluation for more accurate implant placement and osteotomy. This study aimed to evaluate the measurement error in this software in comparison to a three-dimensional measuring instrument (3DMI) using human bones. Materials and Methods: The study was conducted using three bones from cadavers: the pelvic bone, femur, and tibia. Three markers were attached to each bone. Study 1: The bones with markers were fixed on the 3DMI. For each bone, the coordinates of the center point of the markers were measured, and the distances and angles between these three points were calculated and defined as “true values.” Study 2: The posterior surface of the femur was placed face down on the 3DMI, and the distances from the table to the center of each marker were measured and defined as “true values.” In each study, the same bone was imaged using computed tomography, measured with this software, and the measurement error from the corresponding “true values” was calculated. Results: Study 1: The mean diameter of the same marker using the 3DMI was 23.951 ± 0.055 mm. Comparisons between measurements using the 3DMI and this software revealed that the mean error in length was <0.3 mm, and the error in angle was <0.25°. Study 2: In the bones adjusted to the retrocondylar plane with the 3DMI and this software, the average error in the distance from the planes to each marker was 0.43 (0.32–0.58) mm. Conclusion: This surgical planning software could measure the distance and angle between the centers of the markers with high accuracy; therefore, this is very useful for pre- and postoperative evaluation.
Osteoarthritis (OA) is a disease in which articular cartilage wears down due to degeneration associated with aging, which makes adjacent bones contact each other and causes pain. Considering that OA changes the mechanical properties of cartilage when it degenerates, it is important to investigate its mechanical properties under impact load. Therefore, in this study, dynamic and quasi-static tests using the split-Hopkinson pressure bar (SHPB) were carried out on healthy cartilage and cartilage with collagen fibers degenerated by enzyme treatment. The differences in elastic moduli over a wide range of strain rates were examined. To obtain the mechanical properties of soft tissue, polymethyl methacrylate was used for the input and output bars of the SHPB because of its low mechanical impedance, which is suitable for highly compliant materials. Healthy and degenerated cartilage specimens were prepared to clarify the difference in mechanical properties, and quasi-static compression and SHPB tests were performed. The results showed that the elastic modulus increased with increasing strain rate, revealing that the strain rate dependency affects both healthy and degenerated articular cartilage. However, in the high-strain-rate region, a significant positive correlation was observed in healthy cartilage, but no correlation was observed in degenerated cartilage. This suggests that, in degenerated cartilage, resistance to static and dynamic loads, as well as viscosity, decreased at a high strain rate. According to the biphasic theory, the higher the strain rate is, the more it tends to limit interstitial water flow, which explains the increase in elastic modulus in the high-strain-rate region. Therefore, these results suggest that degeneration of collagen fibers in the cartilage reduces the resistance to internal water flow and to static and dynamic loads.
This paper proposes the concept and fabrication process of titanium alloy rods for spinal fixation. A part of rod for fixing the lower side of the lumbar vertebra is strengthened, while the other part for fixing the upper side has low stiffness. The results obtained by finite element analysis reveal that a rod with partially lowered Young's modulus has higher flexibility and fixity compared with a rod possessing high Young's modulus throughout. Using Ti29Nb13Ta4.6Zr alloys with oxygen contents of 0.2 and 0.4% as the model alloys, rods with partially different Young's moduli were fabricated by aging treatment at 723 K, followed by partial heating up to above the ¢-transus temperature and quenching by highfrequency induction heating (IH-treatment). A single ¢-phase, which has low Young's modulus, is obtained by IH-treatment and has lower strength. With regard to the as-aged parts, the precipitated condition of the ¡-phase can be changed by varying the aging time. The obtained Young's modulus and strength reflect this change. Near the boundary between the as-aged and IH-treated parts, the hardness is gradually changed, and it is possible to gradually soften the material from the as-aged part to the IH-treated part.
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