Thinner femoral cortical thickness in patients with destructive rheumatoid arthritis of the knee.

BACKGROUND: The examination of femoral cortical bone thickness in patients with rheumatoid arthritis (RA) has been notably limited in prior research. We aimed to compare femoral cortical thickness in patients with rheumatoid arthritis (RA) and healthy controls and to investigate the association between femoral cortical thickness and clinical parameters within the RA group. METHODS: Forty-four patients (58 limbs) with RA who underwent total knee arthroplasty were enrolled. Preoperative computed tomography images of the lower limbs were analyzed. The femoral cortex was divided into the proximal, central, and distal diaphysis regions and further into the anterior, posterior, medial, and lateral regions. The divisions were measured using Stradwin® software and standardized by femoral length. Femoral cortical thickness was compared between RA and healthy control (n = 25) groups. Correlation analyses between standardized cortical thickness and disease parameters were performed in the RA group. RESULTS: The RA group had significantly lower standardized femoral cortical thickness at the anterior and medial distal diaphysis than healthy controls. Standardized proximal lateral and central lateral in the RA group were significantly larger than those in the healthy control groups. Standardized femoral cortical thickness was significantly correlated with bone mineral density (BMD) in 11 areas, except the posterior central diaphysis, and with body mass index in 8 areas, except the central posterior, distal lateral, distal anterior, and distal medial diaphysis. CONCLUSIONS: Femoral cortical thinning was noted in patients with RA complicated with destructive knee, particularly at the anterior and medial distal diaphysis. Femoral cortical thickness was significantly correlated with BMD and body mass index (BMI); thus, patients with RA and low BMD and BMI should be cared for to prevent fragility fractures.

Development of a video camera-type kayak motion capture system to measure water kayaking.

Background: In kayaking, trunk motion is one of the important factors that prevent injury and improve performance. Kinematic studies in kayaking have been reported in laboratory settings using paddling simulators and ergometers. However, such studies do not reflect kayaking on water, the actual competitive environment. Therefore, we developed a video camera-type kayak motion capture system (KMCS) wherein action cameras were fixed to a kayak to capture images of markers attached to an athlete's body. This study aimed to compare the kinematic data between KMCS and an optical motion capture system (OMCS) in kayaking and to determine the accuracy of the KMCS analysis. Methods: In a competition, five elite junior female kayak athletes performed kayak paddling under the unloaded condition using a kayak. The kayak was secured using a tri-folding bench and a towel, and twenty strokes were recorded during maximal paddling. One stroke was defined as the period from right catch to left catch, and the first six strokes were used to evaluate the accuracy. Trunk angles (tilting, turning, and rotation) were examined with the simultaneous use of KMCS and OMCS, and the differences between these systems were evaluated. To ensure reliability, intraclass correlation coefficient (ICC; a two-way mixed model for absolute agreement) was calculated for each angle. Furthermore, Bland-Altman analysis was performed to understand the agreement between the two systems. Results: Root mean square errors (RMSEs) were 1.42° and 3.94° for turning and rotation, respectively, and mean absolute errors (MAEs) were 1.08° and 3.00° for turning and rotation, respectively. The RMSE and MAE for tilting were 2.43° and 1.76°, respectively, which indicated that the validity was comparable to that of other angles. However, the range of motion in tilting was lower than that in turning and rotation. Bland-Altman analysis showed good agreement in the total range of motion, with mean bias values of -0.84°, -0.07°, and -0.41° for tilting, turning, and rotation, respectively. The ICCs for tilting, turning, and rotation were 0.966, 0.985, and 0.973, respectively, and showed excellent reliability. Conclusions: The newly developed KMCS effectively measured the trunk motion with good accuracy in kayaking. In future studies, we intend to use KMCS to measure kayaking on water and collect data for performance improvement and injury prevention.

Weight-shifting-based robot control system improves the weight-bearing rate and balance ability of the static standing position in hip osteoarthritis patients: a randomized controlled trial focusing on outcomes after total hip arthroplasty.

Background: After a total hip arthroplasty (THA), standing and walking balance are greatly affected in the early stages of recovery, so it is important to increase the weight-bearing amount (WBA) on the operated side. Sometimes, traditional treatments may not be enough to improve WBA and weight-bearing ratio (WBR) on the operated side in a satisfactory way. To solve this problem, we came up with a new weight-shifting-based robot control system called LOCOBOT. This system can control a spherical robot on a floor by changing the center of pressure (COP) on a force-sensing board in rehabilitation after THA. The goal of this study was to find out how rehabilitation with the LOCOBOT affects the WBR and balance in a static standing position in patients with unilateral hip osteoarthritis (OA) who had a primary uncemented THA. Methods: This randomized controlled trial included 20 patients diagnosed with Kellgren-Lawrence (K-L) grade 3 or 4 hip OA on the operative side and K-L grade 0 normal hip on the nonoperative side. We used the minimization method for allocation and randomly assigned patients to either the LOCOBOT group or the control group. As a result, 10 patient seach were randomly assigned to the LOCOBOT and control groups. Both groups received 40 min of rehabilitation treatment. Out of the 40 min, the LOCOBOT group underwent treatment for 10 min with LOCOBOT. The control group performed COP-controlled exercises on a flat floor instead of using LOCOBOT for 10 of the 40 min. All theoutcome measures were performed pre-THA and 11.9 ± 1.6 days after THA (12 days after THA). The primary outcome measure included WBR in the static standing position. Results: After12 days of THA, the LOCOBOT group exhibited significantly higher mean WBR and WBA (operated side) values than the control group. Furthermore, the LOCOBOT group exhibited significantly lower mean WBA (non-operated side) and outer diameter area (ODA) values than the control group. From pre-THA to 12 days after THA, the LOCOBOT group exhibited a significant improvement in mean WBR and WBA (operated side). Moreover, the mean WBA (non-operated side) and ODA significantly decreased. From pre-THA to 12 days after THA, the control group showed a significant increase in total trajectory length and ODA. Conclusions: The most important finding of this study was that patients were able to perform the LOCOBOT exercise as early as the second day after THA, and that WBR and ODA significantly improved by the 12th day after THA. This result demonstrated that the LOCOBOT effectively improves WBR in a short period of time after THA and is a valuable system for enhancing balance ability. This expedites the acquisition of independence in activities of daily living after THA and may contribute to optimizing the effectiveness of medical care.

Evaluation of Sit-to-Stand Movement in Older Adults with Locomotive Syndrome Using the Nintendo Wii Balance Board.

Standing up from a chair is a mechanically demanding daily motion, and its biomechanics represent motor performance. In older adults with locomotive syndrome (LS), sit-to-stand (STS) movement with adequate postural control is essential to prevent falls. This study evaluated the characteristics of dynamic balance during STS movement on older adults with LS. A total of 116 participants aged ≥65 years were divided into Non-LS, LS stage 1, and LS stage 2 groups using the LS risk test. The participants were instructed to stand on the Nintendo Wii Balance Board as quickly as possible, and the STS movement was quantified using the vertical ground reaction force (VGRF) and center of pressure (CoP). The STS score, which represented dynamic balance, was significantly different among the groups (p < 0.001). The rate of VGRF development was significantly lower in the LS stages 1 and 2 than in the Non-LS group (p < 0.001). On the other hand, the total distance of the CoP path did not differ among the groups (p = 0.211). These findings indicated a reduction of postural control in older adults with LS. The STS score emphasized the importance of balance training to prevent falls in older adults with LS.

Leg Muscle Activity and Joint Motion during Balance Exercise Using a Newly Developed Weight-Shifting-Based Robot Control System.

A novel and fun exercise robot (LOCOBOT) was developed to improve balance ability. This system can control a spherical robot on a floor by changing the center of pressure (COP) based on weight-shifting on a board. The present study evaluated leg muscle activity and joint motion during LOCOBOT exercise and compared the muscle activity with walking and sit-to-stand movement. This study included 10 healthy male adults (age: 23.0 ± 0.9 years) and examined basic LOCOBOT exercises (front-back, left-right, 8-turn, and bowling). Electromyography during each exercise recorded 13 right leg muscle activities. Muscle activity was represented as the percentage maximal voluntary isometric contraction (%MVIC). Additionally, the joint motion was simultaneously measured using an optical motion capture system. The mean %MVIC differed among LOCOBOT exercises, especially in ankle joint muscles. The ankle joint was primarily used for robot control. The mean %MVIC of the 8-turn exercise was equivalent to that of walking in the tibialis anterior, and the ankle plantar flexors were significantly higher than those in the sit-to-stand motion. Participants control the robot by ankle strategy. This robot exercise can efficiently train the ankle joint muscles, which would improve ankle joint stability.

Biomechanical effect of metal augment and bone graft on cup stability for acetabular reconstruction of total hip arthroplasty in hip dysplasia: a finite element analysis.

BACKGROUND: Different methods of acetabular reconstruction with total hip arthroplasty (THA) for Crowe II and III of adult developmental dysplasia of the hip (DDH) acetabular bone defect have been implemented clinically. However, the biomechanical effect of different augmented materials for acetabular reconstruction in THA on shell stability has never been discussed. METHODS: In the present study, autologous bone graft (BG)and metal (Ti6Al4V) augment (MA) were simulated with several acetabular bone defect models of DDH in THA. The contact pressure and micromotion between the shell and host bone were measured for evaluating the shell stability using a finite element method. RESULTS: The peak contact stress between shell and host bone was higher in the MA situation (12.45 vs 8.71 MPa). And the load transfer path was different, for BG models, the high local contact stresses were found at the junction of bone graft and host bone while for MA models the concentrated contact stresses were at the surface of MA. The peak relative micromotion between shell and host bone was higher in the MA situation (12.61 vs 11.13 µm). However, the peak micromotion decreased in the contact interface of MA and cup compared to the BG models. CONCLUSIONS: The higher micromotion was found in MA models, however, enough for bone ingrowth, and direct stronger fixation was achieved in the MA-cup interface. Thus, we recommended the MA can be used as an option, even for Crowe III, however, the decision should be made from clinical follow-up results.

Biomechanical effect of intertrochanteric curved varus osteotomy on stress reduction in femoral head osteonecrosis: a finite element analysis.

BACKGROUND: Intertrochanteric curved varus osteotomy (CVO) has been widely used to remove the necrotic bone away from the weight-bearing portion in the treatment of osteonecrosis of the femoral head (ONFH). However, whether all types of necrosis will benefit from CVO, in terms of the stress level, the effect of different center-edge (CE) angles of acetabulum on stress distribution of necrosis after CVO, and the relationship between the intact ratio and the stress of necrosis, has never been addressed. The purpose of the study was to evaluate the influence of CVO on the stress reduction in necrotic bone using a finite element analysis (FEA) with different CE angles. METHODS: CVO finite element models of the hip joint were simulated with a lesion of 60°. The osteotomy angles were divided into four configurations (15°, 20°, 25°, and 30°), and three types (A, B, and C1) of lesions were established based on the Japanese Investigation Committee (JIC) classification. In addition, two CE angles (18° and 33°) of acetabulum were considered. The maximum and mean von Mises stress were analyzed in terms of the necrotic bone by a physiological loading condition. Moreover, the correlation of the intact ratio measured in 3D and the stress distribution after CVO was analyzed. RESULTS: Stress reduction was obtained after CVO. For type B, the CVO angle was 20° (0.61 MPa), and for type C1, the CVO angle was 30° (0.77 MPa), if the mean stress level was close to type A (0.61 MPa), as a standard. The maximum and mean von Mises stress were higher in the CE angle of 18°models, respectively. The intact ratio measured in 3D had a good negative correlation with stress after CVO and had more influence on stress distribution in comparison to other geometric parameters. CONCLUSIONS: For making decisions about the biomechanics of CVO, a CVO angle of > 20° was recommended for type B and > 30° was safe for type C1. The risk of progressive collapse was increased in the insufficient situation of the weight-bearing portion after CVO. The intact ratio could provide information about clinical outcomes and stress distribution after CVO.

A Hand-Worn Inertial Measurement Unit for Detection of Bat-Ball Impact during Baseball Hitting.

Swinging a baseball bat at a pitched ball takes less than half of a second. A hitter uses his lower extremities to generate power, and coordination of the swing motion gradually transfers power through the trunk to the upper extremities during bat-ball impact. The most important instant of the baseball swing is at the bat-ball impact, after which the direction, speed, height, and distance of the hit ball determines whether runs can be scored. Thus, analyzing the biomechanical parameters at the bat-ball impact is useful for evaluating player performance. Different motion-capture systems use different methods to identify bat-ball impact. However, the level of accuracy to detect bat-ball impact is not well documented. The study aim was to examine the required accuracy to detect bat-ball impact timing. The results revealed that ±2 ms accuracy is required to report trunk and hand kinematics, especially for higher-order time-derivatives. Here, we propose a new method using a hand-worn inertial measurement unit to accurately detect bat-ball impact timing. The results of this study will be beneficial for analyzing the kinematics of baseball hitting under real-game conditions.

Shadow pitching deviates ball release position: kinematic analysis in high school baseball pitchers.

BACKGROUND: Although shadow pitching, commonly called "towel drill," is recommended to improve the throwing motion for the rehabilitation of pitching disorders before the initiation of a throwing program aimed at returning to throwing using a ball, the motion differs from that of normal throwing. Learning improper motion during ball release (BR) may increase shoulder joint forces. Abnormal throwing biomechanics leads to injures. However, there has been no study of shadow pitching focusing on the BR position. The purpose of the present study was to evaluate the BR position and kinematic differences between shadow pitching and normal throwing. In addition, the effect of setting a target guide for BR position on throwing motion was examined in shadow pitching. METHODS: The participants included in this study were 20 healthy male students who were overhand right-handed pitchers with no pain induced by a throwing motion. Participants performed normal throwing (task 1), shadow pitching using a hand towel (task 2), and shadow pitching by setting a target of the BR position (task 3). A motion capture system was used to evaluate kinematic differences in throwing motions, respectively. Examination items comprised joint angles and the differences in BR position. RESULTS: BR position of task 2 shifted significantly toward the anterior, leftward, and downward directions compared with task 1. The distance of BR position between tasks 1 and 2 was 24 ± 10%. However, task 3 had decreased BR deviation compared with task 2 (the distance between 3 and 1 was 14 ± 7%). Kinematic differences were observed among groups at BR. For shoulder joint, task 2 showed the highest value in abduction and horizontal adduction among groups. In spine flexion, left rotation and thorax flexion, task 2 was significantly higher than task 1. Task 3 showed small differences compared with task 1. CONCLUSIONS: The BR position of shadow pitching deviated significantly in the anterior, leftward, and downward directions compared with normal throwing. Furthermore, we demonstrated that the setting of BR target reduces this deviation. Thus, the target of BR position should be set accurately during shadow pitching exercises in the process of rehabilitation.

Non-anatomical placement adversely affects the functional performance of the meniscal implant: a finite element study.

Non-anatomical placement may occur during the surgical implantation of the meniscal implant, and its influence on the resulting biomechanics of the knee joint has not been systematically studied. The purpose of this study was to evaluate the biomechanical effects of non-anatomical placement of the meniscal implant on the knee joint during a complete walking cycle. Three-dimensional finite element (FE) analyses of the knee joint were performed, based on the model developed from magnetic resonance images and the loading conditions derived from the gait pattern of a healthy male subject, for the following physiological conditions: (i) knee joint with intact native meniscus, (ii) medial meniscectomized knee joint, (iii) knee joint with anatomically placed meniscal implant, and (iv) knee joint with the meniscal implant placed in four different in vitro determined non-anatomical locations. While the native menisci were modeled using the nonlinear hyperelastic Holzapfel-Gasser-Ogden (HGO) constitutive model, the meniscal implant was modeled using the isotropic hyperelastic neo-Hookean model. Placement of the meniscal implant in the non-anatomical lateral-posterior and lateral-anterior locations significantly increased the peak contact pressure in the medial compartment. Placement of the meniscal implant in non-anatomical locations significantly altered the tibial rotational kinematics and increased the total force acting at the meniscal horns. Results suggest that placement of the meniscal implant in non-anatomical locations may restrain its ability to be chondroprotective and may initiate or accelerate cartilage degeneration. In conclusion, clinicians should endeavor to place the implant as closest as possible to the anatomical location to restore the normal knee biomechanics.

Efficacy of Inertial Measurement Units in the Evaluation of Trunk and Hand Kinematics in Baseball Hitting.

Baseball hitting is a highly dynamic activity, and advanced methods are required to accurately obtain biomechanical data. Inertial measurement units (IMUs) can capture the motion of body segments at high sampling rates both indoor and outdoor. The bat rotates around the longitudinal axis of the body; thus, trunk motion plays a key role in baseball hitting. Segmental coordination is important in transferring power to a moving ball and, therefore, useful in evaluating swing kinematics. The current study aimed to investigate the validity and reliability of IMUs with a sampling rate of 1000 Hz attached on the pelvis, thorax, and hand in assessing trunk and hand motion during baseball hitting. Results obtained using the IMU and optical motion capture system (OMCS) were compared. Angular displacements of the trunk segments and spine joint had a root mean square error of <5°. The mean absolute error of the angular velocities was ≤5%. The intra-class correlation coefficient (>0.950) had excellent reliability for trunk kinematics along the longitudinal-axis. Hand velocities at peak and impact corresponded to the values determined using the OMCS. In conclusion, IMUs with high sampling rates are effective in evaluating trunk and hand movement coordination during hitting motion.

Identification of key events in baseball hitting using inertial measurement units.

Quantification of baseball hitting mechanics under game conditions help players to become successful batters and prevent injuries. Inertial measurement units (IMUs) can measure motion without any spatial restriction and are thus becoming a popular tool to investigate sports biomechanics. Biomechanical analysis of hitting requires the accurate detection of key events including "foot-off" while leaning back (FOff), "foot-on" during forward swing (FOn), and ball impact. Ten male university baseball players hit a ball suspended on a T pole five times in kick-hitting and glide-hitting styles. Three IMUs were attached on mid-pelvis and on each hand to record acceleration and orientation data. The key events identified by the three IMUs were compared with those retrieved by an optical motion capture system with force platforms. The timings of the local peak acceleration of the pelvis in the direction of the pitcher that were recorded by the IMU closely matched those of FOff and FOn events detected by the ground reaction force. Root mean square error (RMSE) between each measurement for the FOff and FOn events were 0.024 and 0.031 s, respectively. The timing of the negative peak of acceleration in the proximal direction of the hands corresponded to the impact time determined by an optical motion capture system. RMSEs for the knob and barrel-side hand were 0.009 and 0.011 s, respectively. Our results demonstrate how IMUs can be useful for analyzing baseball hitting mechanics.

Effects of a valgus unloader brace in the medial meniscectomized knee joint: a biomechanical study.

BACKGROUND: Patients undergoing total or partial arthroscopic meniscectomy for treating traumatic meniscal tears are at greater risk of developing knee osteoarthritis (OA) due to increased mechanical load. The purpose of this study was to evaluate the effects of a valgus unloader brace in the medial meniscectomized knee joint during the gait cycle. METHODS: A three-dimensional finite element model of the knee joint was developed using the substructures segmented from magnetic resonance images. Experimentally measured forces and moments for one complete gait cycle, without brace and with brace at three different alignment angles (0°, 4°, and 8°), were applied to the finite element model, and the changes in the tibiofemoral contact mechanics were estimated. RESULTS: The brace in 0°/4°/8° valgus alignment modes reduced the total contact force in the medial compartment by 16%/46%/82% at opposite toe off and 18%/17%/29% at opposite initial contact events, while it increased the total contact force in the lateral compartment by 31%/81%/110% at opposite toe off and 30%/38%/45% at opposite initial contact events, respectively, when compared to the unbraced meniscectomized knee. CONCLUSIONS: Increasing the valgus alignment from 0° to 4° and 8° resulted in a greater reduction of contact conditions (total contact force, total contact area, peak contact pressure) in the medial compartment and vice versa in the lateral compartment. This decrease in contact conditions in the medial compartment infers enhanced knee joint function due to a valgus unloader brace, which translates to increased knee-related confidence. Results suggest choosing a higher valgus alignment angle could potentially increase the risk for the onset of osteoarthritis in the lateral compartment, and this computational model could be used in validating the effectiveness of braces on joint health.

Acetabular reinforcement ring with additional hook improves stability in three-dimensional finite element analyses of dysplastic hip arthroplasty.

BACKGROUND: The stability of acetabulum reconstructions using reinforcement rings and hooks is important for successful replacement surgery. The objective of this study was to biomechanically determine the effects of the hook on stress and the related micromotions of the acetabular reinforcement ring during the immediate postoperative period. METHODS: Acetabular reinforcement ring models were developed using a nonlinear, three-dimensional, finite element method. Using a pre-prepared template, we constructed without-hook and bone graft models of varying volumes and material properties. RESULTS: The stress on the inferior margin of the acetabulum was higher in the with-hook model than in the without-hook model, especially with increased bone graft volumes, and the stiffness of the bone graft material was decreased. Relative micromotions in the without-hook model were higher than in the with-hook models. The highest relative micromotion was observed in the model with increased bone graft volume and lower stiffness of bone graft material. CONCLUSIONS: In biomechanical analyses, the hook effectively dispersed stress and improved the initial fixation strength of the acetabular reinforcement ring.

Biomechanical analysis of supra-acetabular insufficiency fracture using finite element analysis.

BACKGROUND: Supra-acetabular insufficiency fractures (SAIFs) occur in the upper acetabulum and are rare compared with insufficiency sacral, femoral head, or ischial fractures. However, SAIFs are known to occur in low grade trauma, and the underlying mechanism is still remained unclear. METHODS: We performed biomechanical analysis using finite element analysis to clarify the mechanisms underlying the development of SAIFs. Patient-specific models and bone mineral density (BMD) were derived from pelvic computed tomography data from two patients with SAIF (unaffected side) and two healthy young adults. The bone was assumed to be an isotropic, linearly elastic body. We assigned Young's modulus of each element to the pelvis based on the BMD, and reported the relationships for BMD-modulus. Clinically relevant loading conditions-walking and climbing stairs-were applied to the models. We compared the region of failure risk in each acetabulum using a maximum principal strain criterion. RESULTS: The average supra-acetabular BMD was less than that of the hemi-pelvis and femoral head, but was higher than that of the femoral neck and greater trochanter. Greater minimum principal strain was concentrated in the supra-acetabular portion in both the SAIF and healthy models. In the SAIF models, the higher region of the failure risk matched the fracture site on the acetabulum. CONCLUSIONS: Relative fragility causes compressive strain to concentrate in the upper acetabulum when walking and climbing stairs. When presented with a patient complaining of hip pain without apparent trauma or abnormal X-ray findings, physicians should consider the possibility of SAIF and perform magnetic resonance imaging for the diagnosis of SAIF.

Finite element analysis of the tibial bone graft in cementless total knee arthroplasty.

BACKGROUND: Achieving stability of the tibial implant is essential following cementless total knee arthroplasty with bone grafting. We investigated the effects of bone grafting on the relative micromotion of the tibial implant and stress between the tibial implant and adjacent bone in the immediate postoperative period. METHODS: Tibial implant models were developed using a nonlinear, three-dimensional, finite element method. On the basis of a preprepared template, several bone graft models of varying sizes and material properties were prepared. RESULTS: Micromotion was larger in the bone graft models than in the intact model. Maximum micromotion and excessive stress in the area adjacent to the bone graft were observed for the soft and large graft models. With hard bone grafting, increased load transfer and decreased micromotion were observed. CONCLUSIONS: Avoidance of large soft bone grafts and use of hard bone grafting effectively reduced micromotion and undue stress in the adjacent area.

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

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.

Improving stress shielding following total hip arthroplasty by using a femoral stem made of ß type Ti-33.6Nb-4Sn with a Young's modulus gradation.

Stress shielding-related bone loss occurs after total hip arthroplasty because the stiffness of metallic implants differs from that of the host femur. Although reducing stem stiffness can ameliorate the bone resorption, it increases stress at the bone-implant interface and can inhibit fixation. To overcome this complication, a novel cementless stem with a gradient in Young's modulus was developed using Ti-33.6Nb-4Sn (TNS) alloy. Local heat treatment applied at the neck region for increasing its strength resulted in a gradual decrease in Young's modulus from the proximal to the distal end, from 82.1 to 51.0GPa as calculated by a heat transfer simulation. The Young's modulus gradient did not induce the excessive interface stress which may cause the surface debonding. The main purpose of this study was to evaluate bone remodeling with the TNS stem using a strain-adaptive bone remodeling simulation based on finite element analysis. Our predictions showed that, for the TNS stem, bone reduction in the calcar region (Gruen zone 7) would be 13.6% at 2years, 29.0% at 5years, and 45.8% at 10years postoperatively. At 10 years, the bone mineral density for the TNS stem would be 42.6% higher than that for the similar Ti-6Al-4V alloy stem. The stress-strength ratio would be lower for the TNS stem than for the Ti-6Al-4V stem. These results suggest that although proximal bone loss cannot be eliminated completely, the TNS stem with a Young's modulus gradient may have bone-preserving effects and sufficient stem strength, without the excessive interface stress.

Influence of Gender Differences on Range of Motion and Joint Angles During Eating in Young, Healthy Japanese Adults.

OBJECTIVE: Eating is important in rehabilitation and is evaluated using joint angles that serve as kinematic information. Joint angles of the upper extremities during eating have been reported for men and for women; however, no study has investigated these joint angles in terms of gender differences. At present, no information is available on gender differences as individual factors of upper extremity joint angles during eating. Therefore, the present study investigated gender differences in upper limb joint angles during eating tasks involving a spoon or chopsticks. METHODS: We examined eating motions in 12 healthy Japanese men and 13 healthy Japanese women (aged 20-39 years) and compared the two groups. Motions were assessed using inertial sensors and three-dimensional motion analysis. RESULTS: We established, separately for men and women, the maximum angle and the range of motion (RoM) for each upper limb joint. Women generally had greater RoMs for all upper limb joints than men did. When subjects used a spoon, statistically significant differences and large effect sizes were observed for the maximum elbow joint flexion angle and the RoMs of the shoulder joint in abduction, flexion, and internal rotation. When subjects used chopsticks, statistically significant differences and large effect sizes were observed for maximum angles of shoulder joint internal rotation, elbow joint flexion, and wrist joint radial flexion and for the RoM of shoulder joint abduction. CONCLUSIONS: We concluded that there are significant gender differences in upper limb joint angles during eating, and that these differences are influenced by numerous factors.

A novel protocol to test age-related decreases in sit-to-stand movement abilities in healthy subjects.

BACKGROUND: The development of simple approaches to quantitatively estimate functional motor performance in a wide range of ages is crucial for early detection of locomotive syndrome (LS). Sit-to-stand (STS) movements from a chair are important in activities of daily living (ADL), although such tasks are the most mechanically demanding among all ADL. Here, we propose a novel test to score STS abilities to estimate individual functional motor status and investigated age-related changes in STS scores as a method to evaluate reduction in performance. METHODS: A total of 606 healthy subjects (average age, 48.4 years; age range, 20-87 years) without neuromusculoskeletal disorders participated in the study. We designed a test to score STS abilities, based on STS determinant variables, including seat height, foot positioning, and both-leg- or one-leg-standing tasks. STS scores ranged from 0 to 14 points, depending on the difficulty or mechanical demands of the STS task. We evaluated the STS score of the subjects divided into seven 10-year age groups. RESULTS: A significant and negative correlation was observed between STS scores and subject age (men: r = -0.65, P < 0.001; women: r = -0.62, P < 0.001). The proportion of subjects able to stand on one leg from a chair seat height of 100% of knee height decreased with age from 100% for both men and women aged 20-29 years to 0.0% and 7.1% for men and women aged 80-87 years, respectively. A large variation in STS scores was observed for subjects aged >60 years. There was a negative linear correlation between mean STS score per age group and mean age (men: R(2) = 0.93, slope = -0.10, intercept = 16.63 points; women: R(2) = 0.92, slope = -0.08, intercept = 14.76 points). CONCLUSIONS: The ability to perform STS was negatively correlated with age among healthy subjects aged 20-87 years. For subjects aged >60 years, STS abilities decreased, but within-group variability increased. This test was useful to identify the deterioration of functional motor performance and prevent early LS.