Machine Learning-Driven Design Optimization of Buckling-Induced Quasi-Zero Stiffness Metastructures for Low-Frequency Vibration Isolation.

Metastructures, artificial arrangements of micro/macrostructures, possess unique properties and are of significant interest in aerospace, stealth technology, and various other applications. Recent studies have focused on quasi-zero stiffness metastructures, providing an outstanding vibration isolation capability. However, existing methods are constrained to low preloads and lack the consideration of structural analysis, despite their intended use in practical structures. This study introduces metastructures with quasi-zero stiffness characteristics under high preloads by inducing local buckling. An optimization framework combining deep reinforcement learning and finite-element analysis is employed to derive an optimal model that considers both structural safety and quasi-zero stiffness characteristics. To validate the optimization results, quasi-zero stiffness metastructures are fabricated via 3D printing, and compression and vibration experiments are conducted. The fabricated metastructures exhibit quasi-zero stiffness characteristics under a high target preload along with outstanding vibration reduction performance, even in the low-frequency range.

Improving the Deformability and Recovery Moment of Shape Memory Polymer Composites for Bending Actuators: Multiple Neutral Axis Skins and Deployable Core.

Shape memory polymer composite (SMPC) actuators have received significant attention for applications in space deployable structures because of their light weight and simple actuating process without any additional components. However, conventional SMPC actuators exhibit limited deformation owing to damages caused by the slight elongation of fibers and microbuckling. In this study, we designed a sandwich-structured SMPC bending actuator to increase deformability and the recovery moment with two novel features: multiple neutral axis (MNA) skins and a deployable core. The MNA skins were fabricated as layered structures of a soft layer (the polydimethylsiloxane/ethoxylated polyethylenimine layer) and hard layers (the SMPC layer) based on the MNA effect derived from the large modulus difference between the soft and hard layers. Under the bending deformation, the large shear strain in the soft layer significantly decreases the axial strain in SMPC layers and increases deformability. Applying the deployable core on the sandwich-structured SMPC bending actuator increases the recovery moment owing to the deploying force of the core. To the best of our knowledge, the sandwich-structured SMPC bending actuator composed of two MNA skins and a deployable core yielded the world's largest width-normalized recovery moment of 51.2 N·m/m with the smallest bending radius of 15 mm.

New Skeletal Muscle Mass Index in Diagnosis of Sarcopenia

BACKGROUND: We sought to develop a novel index based on the skeletal muscle mass that reflects the change of quality of life (QOL), and is the most appropriate index for the body composition of the elderly in Korea. Whether lower extremity skeletal muscle mass index (LESMI) is an appropriate novel new index to diagnose patients with sarcopenia was also evaluated. A cut-off value for each index was reported to facilitate the diagnosis of patients with sarcopenia in a Korean population. METHODS: We used the 5th Korean National Health and Nutrition Examination Survey data from 2010. We analyzed 409 elderly patients, including 231 men and 178 women, aged ≥65 years. Patients were diagnosed by calculating their skeletal muscle index based on the skeletal muscle mass measured using dual energy X-ray absorptiometry. Obesity and osteoporosis were used to screen data and EuroQOL-5 dimension as a health questionnaire. RESULTS: The prevalence of sarcopenia in each index was obtained based on its cut-off value for diagnosing sarcopenia. There was a significant difference between the obesity rate of elderly patients diagnosed with sarcopenia and those who were not based on each index. There was no significant difference in the prevalence of osteoporosis between the groups. Sarcopenia diagnosis based on the LESMI was significantly correlated with QOL. CONCLUSIONS: LESMI, a novel index based on skeletal muscle mass, reflects changes in QOL and is appropriate for the body composition of elderly people in Korea.

The Mid-Term Result after Osteosynthesis of Intra-Articular Fractures of Distal Femur

PURPOSE: This study was to evaluate the radiological and clinical mid-term results and the presence of post-traumatic osteoarthritis after osteosynthesis in patients under the age of 50 years undergoing osteosynthesis for distal femur intra-articular fractures (AO/OTA 33-B & C) from high-energy trauma. MATERIALS AND METHODS: Between January 2008 and January 2013, a total of twenty-one patients with more than three years of follow-up were enrolled. Recovery of the alignment of the lower extremity, union period, and the presence of post-traumatic osteoarthritis were confirmed by follow-up radiographs. Clinically, the range of motion, pain on fracture lesion, and Knee Society score (KSS) were evaluated. RESULTS: The average duration of union was 18.2 weeks (10-28 weeks), and the alignment of the lower extremity was within normal range in all patients. Seven patients showed post-traumatic osteoarthritis at the final follow-up after more than three years. The presence of post-traumatic osteoarthritis was associated with the classification of fractures, coronal plane fracture, and age. The average range of motion, knee score among KSS, and function score at the last follow-up were 128.7°, 86.1, and 85.1, all showing a greater improvement when compared with the one-year follow-up scores. CONCLUSION: The mid-term result was radiologically and clinically satisfactory. Furthermore, only 33.3% of patients showed a slight progress of post-traumatic osteoarthritis, which critically effects the prognosis.

Effects of Teriparatide Administration on Fracture Healing after Intramedullary Nailing in Atypical Femoral Fractures / 대한정형외과학회잡지

PURPOSE: The purpose of this study is to evaluate the effects of teriparatide administration on fracture healing after intramedullary nailing in atypical femoral fractures. MATERIALS AND METHODS: We retrospectively reviewed 26 patients (26 cases) with atypical femoral fracture who were treated using intramedullary nailing between January 2009 and December 2013. Teriparatide was not administered to 15 patients (non-injection group) and was administered to 11 patients after surgery (injection group). Clinical results were assessed using the Nakajima score and the visual analogue scale (VAS). Radiographic results were compared for the time of callus formation, callus bridge formation, and bone union between the groups. RESULTS: Time to recover walking ability and to decrease pain in the surgery region (VAS≤2) were significantly shorter in the injection group than in the non-injection group. The time of callus formation, callus bridge formation, and bone union was significantly shorter in the injection group than in the non-injection group. There were 5 cases of delayed bone union (33.3%) and 1 case of none union (6.7%) in the non-injection group and all cases obtained bone union in injection group. CONCLUSION: The injection group showed better clinical and radiographic results than the non-injection group after intramedullary nailing in atypical femoral fracture. Therefore, we think that teriparatide administration after intramedullary nailing could be a useful treatment option to promote bone union.

Usefulness of K-Point Injection for the Nonspecific Neck Pain in So-Called K-Point Syndrome

BACKGROUND: Shoichi Kokubun introduced his successful experience with local anesthetic injection at the occipital insertion of the sternocleidomastoid muscle in K-point syndrome. The purpose of this study was to evaluate the short-term and long-term effectiveness of K-point injection and investigate factors affecting treatment results. METHODS: K-point injection was performed in 58 patients with K-point syndrome at Yeungnam University Medical Center. The syndrome was associated with cervical whiplash injury in 10 patients and was of nonspecific origin in the rest. One milliliter of 2% lidocaine mixed with 1 milliliter of dexamethasone was injected in 50 patients and 2 milliliters of 1% lidocaine alone in the rest. Initially, the severity of local tenderness at the K-point and other tender points was examined and the degree of immediate pain relief effect was assessed within 1 hour after injection. Early effect within 1 month after the injection and current effect were evaluated in 27 patients using a modified Kim's questionnaire with regard to the duration of improvement, degree of improvement in pain and daily living activities, and satisfaction. RESULTS: Of the total 58 patients, 44 (75.8%) apparently had immediate pain relief after K-point injection. The only factor associated with successful immediate pain relief was the whiplash injury associated with traffic accident (TA). The early pain control effect was associated with the immediate effect. The current effect was associated with the early effect alone. Satisfaction with the K-point injection was related to early successful pain relief. CONCLUSIONS: K-point injection would be useful for early pain relief in nonspecific neck pain syndrome so called K-point syndrome, but not for current pain relief. Especially, it was very effective for early pain control in the whiplash injury associated with TA.

When Do Clinical and Radiographic Results Stabilize after Proximal Chevron Osteotomy in Hallux Valgus? / 대한족부족관절학회지

PURPOSE: The purpose of this study is to evaluate the sequential changes of clinical and radiographic results after proximal chevron osteotomy in patients with moderate to severe hallux valgus. MATERIALS AND METHODS: Between January 2008 and December 2009, 93 patients (117 feet) were treated with proximal chevron osteotomy and distal soft tissue procedure for symptomatic moderate to severe hallux valgus deformity. The mean age of patients was 51 years (range, 19 to 71) and the mean duration of follow-up was 27.5 months (range, 24 to 35). Clinical results were evaluated using visual analogue scale (VAS) and American Orthopaedic Foot and Ankle Society (AOFAS) score preoperatively, at 3, 6, and 12 months after surgery, and at the last follow-up. Radiographic parameters including hallux valgus angle, intermetatarsal angle, and sesamoid position were evaluated preoperatively, immediately postoperatively, at 6 weeks, at 3, 6, and 12 months after surgery, and at the last follow-up. RESULTS: VAS and AOFAS score showed significant improvement until 12 months after surgery. Hallux valgus angle and sesamoid position stabilized at 12 months after surgery and intermetatarsal angle stabilized at 6 months after surgery. CONCLUSION: Clinical and radiographic results were stabilized beyond 12 months after proximal chevron osteotomy in patients with moderate to severe hallux valgus.

A Two-Stage Approach to Primary Total Knee Arthroplasty in Recurrent Septic Arthritis / 대한정형외과학회잡지

PURPOSE: The purpose of this study is to evaluate the usefulness of a two-stage approach to primary knee arthroplasty with recurrent septic arthritis. MATERIALS AND METHODS: We studied 22 patients with recurrent septic arthritis, and we observed them for more than one year of follow-up survey from January 2005 to April 2012 at Yeungnam University Medical Center. The clinical assessment was performed following Knee Society knee score, Knee Society function score, and International Knee Documentation Committee Score (IKDC) subjective assessment. In addition, we analyzed the causative organisms, significant medical comorbidities (diabetes mellitus), period up to primary knee arthroplasty, and radiologic assessment with reference to disease prognosis. RESULTS: The average range of postoperative knee motion showed a good result, with an average of 115degrees. Knee Society knee score improved from 23.5 to 81.0, and Knee Society function score also increased from 22.5 to 73.2. Subjective assessment by IKDC was divided into 15 normal patients and 7 nearly normal patients. No significant difference was observed between patients with causative organisms and those with diabetes mellitus. In the final follow-up survey, recurrence of infection was not reported. CONCLUSION: A two-stage approach to primary knee arthroplasty with recurrent septic arthritis is a useful method, because it showed good clinical and radiologic results and favorable subjective assessment.