Recurrent Neural Network Methods for Extracting Dynamic Balance Variables during Gait from a Single Inertial Measurement Unit.

Monitoring dynamic balance during gait is critical for fall prevention in the elderly. The current study aimed to develop recurrent neural network models for extracting balance variables from a single inertial measurement unit (IMU) placed on the sacrum during walking. Thirteen healthy young and thirteen healthy older adults wore the IMU during walking and the ground truth of the inclination angles (IA) of the center of pressure to the center of mass vector and their rates of changes (RCIA) were measured simultaneously. The IA, RCIA, and IMU data were used to train four models (uni-LSTM, bi-LSTM, uni-GRU, and bi-GRU), with 10% of the data reserved to evaluate the model errors in terms of the root-mean-squared errors (RMSEs) and percentage relative RMSEs (rRMSEs). Independent t-tests were used for between-group comparisons. The sensitivity, specificity, and Pearson's r for the effect sizes between the model-predicted data and experimental ground truth were also obtained. The bi-GRU with the weighted MSE model was found to have the highest prediction accuracy, computational efficiency, and the best ability in identifying statistical between-group differences when compared with the ground truth, which would be the best choice for the prolonged real-life monitoring of gait balance for fall risk management in the elderly.

Children with Duchenne muscular dystrophy display specific kinematic strategies during obstacle-crossing.

Duchenne muscular dystrophy (DMD) is a genetic disease characterized by progressive muscle weakness with increased neuromechanical challenge and fall risks, especially during obstructed locomotion. This study aimed to identify the kinematic strategies for obstacle-crossing in DMD via synthesizing the changes in the joint kinematics and associated end-point control. Fourteen boys with DMD (age: 9.0 ± 2.5 years) and fourteen typically developed controls (age: 9.0 ± 2.8 years) each crossed obstacles of three different heights (10%, 20% and 30% of leg length) while the angular motions of the trunk-pelvis-leg apparatus and foot-obstacle clearances were measured. Two-way analyses of variance were used to analyze group and obstacle height effects. Compared to the controls, the DMD group crossed obstacles with significantly increased step width, but decreased crossing speed, crossing step length, trailing toe-obstacle clearance and leading heel-obstacle horizontal distance (p < 0.05). When the leading toe was above the obstacle, the patients showed significantly increased pelvic hiking, pelvic and trunk anterior tilt and ankle plantarflexion, but decreased hip flexion in both limbs (p < 0.05). Similar kinematic changes were found during trailing-limb crossing, except for an additional increase in swing-hip abduction and decrease in contralateral trunk side-bending and stance-knee flexion. Patients with DMD crossed obstacles via a specific kinematic strategy with altered end-point control, predisposing them to a greater risk of tripping during trailing-limb crossing. These results suggest that crossing kinematics in DMD should be monitored-especially in the proximal segments of the pelvis-leg apparatus-that may lead to an increased risk of falling.

Integration of statistical shape modeling and alternating interpolation-based model tracking technique for measuring knee kinematics in vivo using clinical interleaved bi-plane fluoroscopy.

Background: A 2D fluoroscopy/3D model-based registration with statistical shape modeling (SSM)-reconstructed subject-specific bone models will help reduce radiation exposure for 3D kinematic measurements of the knee using clinical alternating bi-plane fluoroscopy systems. The current study aimed to develop such an approach and evaluate in vivo its accuracy and identify the effects of the accuracy of SSM models on the kinematic measurements. Methods: An alternating interpolation-based model tracking (AIMT) approach with SSM-reconstructed subject-specific bone models was used for measuring 3D knee kinematics from dynamic alternating bi-plane fluoroscopy images. A two-phase optimization scheme was used to reconstruct subject-specific knee models from a CT-based SSM database of 60 knees using one, two, or three pairs of fluoroscopy images. Using the CT-reconstructed model as a benchmark, the performance of the AIMT with SSM-reconstructed models in measuring bone and joint kinematics during dynamic activity was evaluated in terms of mean target registration errors (mmTRE) for registered bone poses and the mean absolute differences (MAD) for each motion component of the joint poses. Results: The mmTRE of the femur and tibia for one image pair were significantly greater than those for two and three image pairs without significant differences between two and three image pairs. The MAD was 1.16 to 1.22° for rotations and 1.18 to 1.22 mm for translations using one image pair. The corresponding values for two and three image pairs were 0.75 to 0.89° and 0.75 to 0.79 mm; and 0.57 to 0.79° and 0.6 to 0.69 mm, respectively. The MAD values for one image pair were significantly greater than those for two and three image pairs without significant differences between two and three image pairs. Conclusions: An AIMT approach with SSM-reconstructed models was developed, enabling the registration of interleaved fluoroscopy images and SSM-reconstructed models from more than one asynchronous fluoroscopy image pair. This new approach had sub-millimeter and sub-degree measurement accuracy when using more than one image pair, comparable to the accuracy of CT-based methods. This approach will be helpful for future kinematic measurements of the knee with reduced radiation exposure using 3D fluoroscopy with clinically alternating bi-plane fluoroscopy systems.

Mid-vastus total knee arthroplasty for medial osteoarthritis recovers gait balance control better than lateral parapatellar approach three months post-surgery.

Total knee arthroplasty (TKA) approaches affect recovery outcomes, with different levels of residual loss of muscle strength and functional deficits. The current study compared the gait balance control in older individuals 3 months after TKA via the lateral parapatellar approach (LPPA) and mid-vastus approach (MVA) in terms of the inclination angle (IA) of the center of pressure (COP) to the body's center of mass (COM) vector, and the rate of change of IA (RCIA). In a gait laboratory, 12 patients with severe medial knee osteoarthritis who had undergone bilateral TKA via LPPA and 12 via MVA were evaluated and compared against 12 healthy controls for their balance control during gait 3 months after surgery. The participants' kinematic data and ground reaction forces were measured synchronously using an 8-camera motion capture system and three forceplates, respectively, from which the COM, COP, IA and RCIA were calculated using a 13-body-segment model. The LPPA group showed significantly greater sagittal IA during DLS (p < 0.01) but less sagittal and frontal RCIA throughout the gait cycle (p < 0.04) compared to controls. The MVA showed better recovery in the balance control with most IA and RCIA variables similar to those of the healthy controls throughout the gait cycle. The patients with LPPA walked with a compromised balance control throughout the gait cycle while the MVA group showed close-to-normal balance control with a slight decrease in sagittal RCIA during SLS. The current between-approach findings were likely related to the differences in the muscles involved during surgery, suggesting that MVA may be a better choice than LPPA when taking short-term gait balance control into consideration.

Contribution of lower extremity muscles to center of mass acceleration during walking: Effect of body weight.

Overweight or obesity is known to be associated with altered activations of lower extremity muscles. Such changes in muscular function may lead to the development of mobility impairments or joint diseases. However, little is known about how individual lower extremity muscles contribute to the whole-body center of mass (COM) control during walking and the effect of body weight. This study examined the contribution of individual lower extremity muscle force to the COM accelerations during walking in overweight and non-overweight individuals. Musculoskeletal simulations were performed for the stance phase of walking with data collected from 11 overweight and 13 non-overweight adults to estimate lower extremity muscle forces and their contributions to the COM acceleration. Mean time-series data from each parameter were compared between body size groups using Statistical Parametric Mapping. Compared to the non-overweight group, the overweight group revealed a greater gastrocnemius contribution to the mediolateral (p = 0.006) and vertical (p < 0.001) COM accelerations during mid-stance, and had a lower vastus contribution to the anteroposterior COM acceleration (p < 0.001) during pre-swing. Increased contributions from the large posterior calf muscles to the mediolateral COM acceleration may be related to efforts to alleviate COM sway in overweight individuals.

Effects of lateral instability on ankle coupled motions in vivo using 3D fluoroscopy.

Lateral ankle instability (LAI) compromises the normal kinematics of the ankle, affecting activities of daily living. In vitro kinematics of ankles with LAI during single-plane motions are available, but the active control stability of these motions remains unclear. The current study measured the 3D ankle kinematics during unresisted single-plane motion tests using a bi-plane fluoroscope with a CT model-based 2D/3D registration method in 12 patients with LAI and 14 healthy peers. The coupling of the kinematic components at the talocrural and subtalar joints was quantified by the path difference between the forward and return paths of the coupled motion. Significantly increased path differences were found in the subtalar dorsiflexion/plantarflexion and inversion/eversion components during internal/external rotation tests (p < 0.05). During inversion/eversion, significantly reduced tibiocalcaneal ranges of motion and the path differences in the talocrural and subtalar dorsiflexion/plantarflexion components were noted (p < 0.05). The current results suggest that chronic LAI had compromised control stability at the subtalar joint during internal/external rotation tests and a conservative motion control strategy with significantly reduced ranges of motion to maintain good control of out-of-plane motion components in response to direct challenges of the anterior talofibular ligament during inversion/eversion tests. The current results also suggest that, compared to kinematic patterns of individual components, the path difference of the coupled motion may serve as a better measure of the motion control stability of the ankle in differentiating LAI from healthy controls.

Kinematic strategies for obstacle-crossing in older adults with mild cognitive impairment.

Introduction: Mild cognitive impairment (MCI) is considered a transitional stage between soundness of mind and dementia, often involving problems with memory, which may lead to abnormal postural control and altered end-point control when dealing with neuromechanical challenges during obstacle-crossing. The study aimed to identify the end-point control and angular kinematics of the pelvis-leg apparatus while crossing obstacles for both leading and trailing limbs. Methods: 12 patients with MCI (age: 66.7 ± 4.2 y/o; height: 161.3 ± 7.3 cm; mass: 62.0 ± 13.6 kg) and 12 healthy adults (age: 67.7 ± 2.9 y/o; height: 159.3 ± 6.1 cm; mass: 61.2 ± 12.0 kg) each walked and crossed obstacles of three different heights (10, 20, and 30% of leg length). Angular motions of the pelvis and lower limbs and toe-obstacle clearances during leading- and trailing-limb crossings were calculated. Two-way analyses of variance were used to study between-subject (group) and within-subject (obstacle height) effects on the variables. Whenever a height effect was found, a polynomial test was used to determine the trend. A significance level of α = 0.05 was set for all tests. Results: Patients with MCI significantly increased pelvic anterior tilt, hip abduction, and knee adduction in the swing limb during leading-limb crossing when compared to controls (p < 0.05). During trailing-limb crossing, the MCI group showed significantly decreased pelvic posterior tilt, as well as ankle dorsiflexion in the trailing swing limb (p < 0.05). Conclusion: Patients with MCI adopt altered kinematic strategies for successful obstacle-crossing. The patients were able to maintain normal leading and trailing toe-obstacle clearances for all tested obstacle heights with a specific kinematic strategy, namely increased pelvic anterior tilt, swing hip abduction, and knee adduction during leading-limb crossing, and decreased pelvic posterior tilt and swing ankle dorsiflexion during trailing-limb crossing. The current results suggest that regular monitoring of obstacle-crossing kinematics for reduced toe-obstacle clearance or any signs of changes in crossing strategy may be helpful for early detection of compromised obstacle-crossing ability in patients with single-domain amnestic MCI. Further studies using a motor/cognitive dual-task approach on the kinematic strategies adopted by multiple-domain MCI will be needed for a complete picture of the functional adaptations in such a patient group.

Synergistic multi-joint kinematic strategies to reduce tripping risks during obstacle-crossing in older long-term Tai-Chi Chuan practitioners.

Introduction: Losing balance or tripping over obstacles is considered one of the most common causes of falls in the elderly. Tai-Chi Chuan (TCC) has been shown to improve muscle strength, inter-joint coordination and balance control in the elderly. This study aimed to determine whether older long-term TCC practitioners would show multi-joint kinematic strategies that would reduce the risk of tripping during obstacle-crossing compared to peers without TCC experience. Methods: Three-dimensional motions of the pelvis and lower extremities were measured using a motion capture system in fifteen older long-term TCC practitioners (TCC group) and 15 healthy controls without TCC experience during walking and crossing obstacles of three different heights. Crossing angles of the pelvis and lower limbs and toe-obstacle clearances were obtained and analyzed using two-way analyses of variance to study the between-subject (group) and within-subject (height) effects. A multi-link system approach was used to reveal the relationship between joint angular changes and toe-obstacle clearances. Results: Compared to the controls, the TCC group showed increased leading and trailing toe-obstacle clearances (p < 0.05) with increased pelvic hiking and hip flexion but decreased hip adduction on the swing side and decreased knee flexion on the stance side during leading-limb crossing (p < 0.05), and increased pelvic hiking and anterior tilt but decreased hip adduction on the swing side, and decreased knee flexion on the stance side during trailing limb crossing (p < 0.05). All significant joint angular changes contributed to the increases in the toe-obstacle clearances. Conclusion: The current study identified the kinematic changes of the pelvis and the lower limb joints and revealed a specific synergistic multi-joint kinematic strategy to reduce tripping risks during obstacle-crossing in older long-term TCC practitioners as compared to non-TCC controls. The observed multi-joint kinematic strategies and the associated increases in toe-obstacle clearances appeared to be related to the training characteristics of TCC movements. Long-term TCC practice may be helpful for older people in reducing the risk of tripping and the subsequent loss of balance.

A Non-Linear Osteometric Modeling Method for Three-Dimensional Mandibular Morphological Changes During Growth: One-Year Monitoring of Miniature Pigs Using Cone-Beam Computed Tomography.

Knowledge of mandibular growth and development is essential for diagnosis of malformation and early interception. A previous method of quantifying mandibular growth using the distances between selected anatomical landmarks over the growth period does not provide a complete, quantitative description of the continuous growth patterns. The current study aimed to bridge the gap by measuring the 3D continuous growth of the mandible in miniature pigs using cone-beam computerized tomography (CBCT). The mandibles of the pigs were CBCT-scanned monthly over 12 months, and the 3D mandibular models were reconstructed. A new non-linear, time-dependent osteometric modeling approach was developed to register two consecutive mandible models by searching for the corresponding points with the highest likelihood of matching the anatomical and morphological features so that the morphological changes patterns for each month could be described using color maps on the models. The morphological changes of the mandible were found to decrease anteriorly, with the condyle region and the posterior part of the ramus growing faster than the rest of the mandible. The condyle region showed the fastest growth rate and the posterior ramus the second during the growth period, while the middle and anterior corpus regions showed the slowest growth rates. In conclusion, the current results revealed the non-linear patterns and rates of morphological changes in different growth regions and the whole mandible. The new approach may also be useful for future studies on the growth of the mandible in other animals.

Do Serum C-Reactive Protein Trends Predict Treatment Outcome in Patients with Knee Periprosthetic Joint Infection Undergoing Two-Stage Exchange Arthroplasty?

Two-stage exchange arthroplasty is the standard treatment for knee periprosthetic joint infection (PJI). This study aimed to determine whether serial changes in C-reactive protein (CRP) values can predict the prognosis in patients with knee PJI. We retrospectively enrolled 101 patients with knee PJI treated with two-stage exchange arthroplasty at our institution from 2010 to 2016. We excluded patients with spacer complications and confounding factors affecting CRP levels. We tested the association between treatment outcomes and qualitative CRP patterns or quantitative CRP levels. Of the 101 patients, 24 (23.8%) had recurrent PJI and received surgical intervention after two-stage reimplantation. Patients with a fluctuating CRP pattern were more likely to receive antibiotics for a longer period (p < 0.001). There was greater risk of treatment failure if the CRP levels were higher when antibiotics were switched from an intravenous to oral form (p = 0.023). The patients who received antibiotics for longer than six weeks (p = 0.017) were at greater risk of treatment failure after two-stage arthroplasty. Although CRP patterns cannot predict treatment outcomes, CRP fluctuation in the interim period was associated with longer antibiotic duration, which was related to a higher treatment failure rate.

Avascular Necrosis of the Hip Compromises Gait Balance Control in Female Juveniles With Unilateral Developmental Dysplasia Treated in Toddlerhood.

Avascular necrosis of the hip (AVN) is one of the most severe complications of surgical reduction when treating developmental dysplasia of the hip (DDH). The current study identified the differences in the balance control during walking in terms of the inclination angle (IA) of the center of pressure (COP) to the center of mass (COM), and the rate of change of IA (RCIA) between female juveniles with and without secondary AVN at the hip who were treated for unilateral DDH during toddlerhood as compared to their healthy peers. When compared to female healthy controls, the non-AVN group showed bilaterally similar compromised balance control with significantly decreased IA (p < 0.05) but increased RCIA (p < 0.04) in the sagittal plane during single-limb support (SLS) of the unaffected side, and in the frontal plane during terminal double-limb support (DLS) of the affected side. In contrast, the AVN increased between-side differences in the sagittal IA (p = 0.01), and sagittal and frontal RCIA during DLS (p < 0.04), leading to bilaterally asymmetrical balance control. Secondary AVN significantly reduced IA and RCIA in the sagittal plane (p < 0.05), and reduced range of RCIA in the frontal plane during initial DLS (p < 0.05). The trend reversed during terminal DLS, indicating a conservative COM-COP control in the sagittal plane and a compromised control in the frontal plane during body weight acceptance, with a compromised COM-COP control in the frontal plane during weight release. The current results suggest that increased between-side differences in the sagittal IA, and sagittal and frontal RCIA during DLS are a sign of AVN secondary to treated unilateral DDH in female juveniles, and should be monitored regularly for early identification of the disease.

Discriminating features of ground reaction forces in overweight old and young adults during walking using functional principal component analysis.

BACKGROUND: Limited attention has been paid to age- or body size-related changes in the ground reaction forces (GRF) during walking despite their strong associations with lower limb injuries and pathology. RESEARCH QUESTION: Do the features of GRF during walking associate with age or body size? METHODS: Fifty-four participants were subdivided into four groups according to their age and body size: overweight old (n = 12), non-overweight old (n = 13), overweight young (n = 13), and non-overweight young (n = 16). Participants were asked to walk at their self-selected speeds on level ground with force plates embedded in the center of walkway. Functional principal component analysis (FPCA) was performed to extract major modes of variation and functional principal component scores (FPCs) in three-dimensional GRFs. Analysis of variance models were employed to investigate the effect of age, body size, or their interactions on the FPCs of each component of the GRF, with the adjustment to gait speed. RESULTS: Significant age and body size effects were observed in FPC1 across all three-dimensional GRF. Both overweight and older groups showed greater braking force after heel-strike and greater propulsive forces during pre-swing when compared to the non-overweight and younger groups, respectively. The overweight old group displayed greater medial forces during mid-stance and the overweight young group showed prominently larger medial forces during pre-swing, while non-overweight old showed a tendency of flatter medial-lateral GRF waveforms during the entire stance phase. FPC2 revealed that only body size had an effect on three-dimensional GRF with the highest FPC2 scores in the overweight old group. SIGNIFICANCE: Three-dimensional GRF during walking could be altered by the body size and age, which were more pronounced in the overweight and older group. The more dynamic GRF pattern with greater and/or lower peaks could be contributing factors to the increased joint load and injury rates observed in overweight aged individuals.

Effects of long-term Tai-Chi Chuan practice on whole-body balance control during obstacle-crossing in the elderly.

Older people are subject to an increased risk of falling compared to the young, especially during obstacle negotiation. This study aimed to quantify the effects of long-term Tai-Chi Chuan (TCC) practice on the balance control during obstacle-crossing in older people in terms of the inclination angles (IA) of the body's centre of mass (COM) relative to the centre of pressure (COP), and the rate of change of IA (RCIA). Fifteen healthy older adults who had practised TCC for at least 13 years and 15 healthy controls without any experience in TCC performed obstacle-crossing in a gait laboratory. The TCC group showed significantly greater leading and trailing toe-obstacle clearances but smaller trailing stride lengths when compared to controls. In the sagittal plane, the TCC group showed significantly smaller average anterior IA when the COM was anterior to the COP but greater average posterior IA when the COM was posterior to the COP, with significantly smaller average and peak RCIA over the crossing cycle. Long-term TCC practitioners showed an obstacle-crossing technique for less risk of tripping and better balance control, as indicated respectively by significantly increased toe-obstacle clearances and more posterior COM position relative to the COP with smaller anterior IA and RCIA during leading crossing and greater posterior IA and frontal RCIA at trailing-toe crossing. These benefits appeared to be related to the main features of TCC movements that emphasized maintaining balance during single-leg support and keeping the body weight on the trailing limb during the slow weight-shifting of double-limb support.

Recovery of balance control in bilateral medial knee osteoarthritis after total knee arthroplasty during level walking.

Older adults are at higher risk of falling following total knee arthroplasty (TKA). However, it remains unclear how long a full recovery of the balance control during gait post-TKA will take. The current study aimed to bridge this knowledge gap via long-term follow-up gait analyses. Twelve older adults with severe bilateral medial knee osteoarthritis (OA) before, 3 and 12 months after TKA, and twelve healthy controls were evaluated for their balance control during level walking, in terms of the inclination angle (IA) of the center of pressure to center of mass vector, and the rate of change of IA (RCIA). The patients before TKA showed significantly increased sagittal IA but decreased RCIA throughout the gait cycle (p < 0.04) compared to controls, suggesting a compromised balance control. Three months post-TKA, deviations in IA remained, although those in RCIA were improved to normal. One-year post-TKA, no significant differences were found in any of the IA- and RCIA-related variables between patient and Control groups. The results show that TKA surgery was effective in reducing the deviations in the center of mass-center of pressure control in patients with severe bilateral knee OA, and full recovery of balance control can be expected 1 year after surgery.

Bilateral Asymmetry in Balance Control During Gait in Children with Treated Unilateral Developmental Dysplasia of the Hip.

INTRODUCTION: About 1% of the newborn population has developmental dysplasia of the hip (DDH), altering joint biomechanics, gait performance and balance control. Pemberton's osteotomy is used in early treatment but it remains unclear whether it will help the patient regain normal balance control during gait. The current study aimed to identify the changes of the whole-body balance control during level walking in children treated for unilateral DDH during toddlerhood, in terms of inclination angles (IA) of the line joining the body's center of mass (COM) and center of pressure (COP), and the rate of change of IA (RCIA). MATERIALS AND METHODS: Twelve girls (DDH group; age: 7.1 ± 2.1 years) who had been treated with Pemberton's osteotomy for unilateral DDH during toddlerhood and twelve healthy controls (Control group; age: 7.6 ± 2.1 years) walked at their preferred walking speed while IA, RCIA and temporal-spatial parameters were calculated from measured kinematic and forceplate data, and were compared using independent t-tests. RESULTS: Compared to the Control group, the DDH group showed significantly decreased sagittal IA (p = 0.042) but increased range of sagittal RCIA during SLS on the unaffected side (p = 0.006), and increased peak sagittal RCIA during DLS (p < 0.008). In the frontal plane, the altered COM-COP control occurred mainly during stance phase of the affected side, showing a decreased range of RCIA during SLS (p = 0.033) followed by decreased IA (p = 0.045) with an increased peak value of RCIA (p = 0.023) during terminal DLS. CONCLUSIONS: The children with treated unilateral DDH showed compromised, bilaterally different balance control strategies with altered COM-COP control during gait, not only during stance in the frontal plane as expected, but even more so during swing in the sagittal plane. It is thus suggested that routine assessment of the morphological changes and/or altered balance control of both the unaffected and affected hips is equally important for early identification of any signs of insidious hip problems, deteriorating balance control or increased risk of loss of balance.

Best-Compromise Control Strategy Between Mechanical Energy Expenditure and Foot Clearance for Obstacle-Crossing in Older Adults: Effects of Tai-Chi Chuan Practice.

Background: Obstacle-crossing increases the risk of falls in older people. This study aimed to identify the effects of long-term Tai-Chi Chuan (TCC) practice on the control strategies for obstacle-crossing in older people. Methods: A multi-objective optimal control technique with measured gait data was used to identify the control strategies adopted by 15 long-term TCC practitioners and 15 healthy controls when crossing obstacles of different heights, in terms of the best-compromise weighting sets for the conflicting objectives of minimizing energy expenditure and maximizing the toe-obstacle and heel-obstacle clearances. Results and Conclusions: The long-term TCC older practitioners adopted a best-compromise control strategy similar to those adopted by young adults, with greater weightings on the minimization of the mechanical energy expenditure and smaller weightings on foot-clearance as compared to non-TCC controls (TCC: 0.72, 0.14, 0.14; Control: 0.55, 0.225, 0.225). This strategy enabled the long-term TCC older practitioners to cross obstacles with significantly greater leading-toe clearances but with relatively less mechanical energy expenditure. With the current approach, further simulations of obstacle-crossing mechanics with a given weighting set will be useful for answering clinically relevant what-if questions, such as what abilities would be needed if the non-TCC older people were to cross obstacles using the crossing strategy of the TCC people.

Trend of serum C-reactive protein is associated with treatment outcome of hip Periprosthetic joint infection undergoing two-stage exchange arthroplasty: a case control study.

BACKGROUND: Serum C-reactive protein (CRP) trends are critical for monitoring patients' treatment response following a two-stage exchange arthroplasty for periprosthetic joint infection (PJI) of the hip. However, CRP trends are poorly described in the literature. The primary aim of this study was to identify the relationships between PJI treatment outcomes and our proposed CRP trend definitions, parameters, and microbiological data. The secondary aim was to investigate CRP trends after the occurrence of spacer-related complications. METHODS: We conducted a retrospective review of 74 patients treated with a two-stage exchange protocol for PJI in a tertiary referral joint center between 2014 and 2016. Patients with factors that may affect CRP levels (inflammatory arthritis, concomitant infections, liver and kidney diseases, and intensive care admissions) were excluded. CRP trends were categorized into five types and PJI treatment outcome was defined as "success" or "failure" according to the Delphi criteria. RESULTS: Treatment was successful in 67 patients and failed in 7 patients. Multivariate logistic regression analysis showed that type 5 CRP, defined as serum CRP fluctuation without normalization after first stage surgery (odds ratio [OR]: 17.4; 95% confidence interval [CI]: 2.3-129.7; p = 0.005), and methicillin-resistant Staphylococcus aureus (MRSA; OR: 14.5; 95% CI: 1.6-131.7; p = 0.018) were associated with treatment failure. Spacer-related complications occurred in 18 patients. Of these, 12 had elevated CRP levels at later follow-up, while six had no elevation in CRP levels. CONCLUSIONS: We found that MRSA infection and type 5 CRP were associated with PJI treatment failure.

Three-Dimensional Subject-Specific Knee Shape Reconstruction with Asynchronous Fluoroscopy Images Using Statistical Shape Modeling.

Background and objectives: Statistical shape modeling (SSM) based on computerized tomography (CT) datasets has enabled reasonably accurate reconstructions of subject-specific 3D bone morphology from one or two synchronous radiographs for clinical applications. Increasing the number of radiographic images may increase the reconstruction accuracy, but errors related to the temporal and spatial asynchronization of clinical alternating bi-plane fluoroscopy may also increase. The current study aimed to develop a new approach for subject-specific 3D knee shape reconstruction from multiple asynchronous fluoroscopy images from 2, 4, and 6 X-ray detector views using a CT-based SSM model; and to determine the optimum number of planar images for best accuracy via computer simulations and in vivo experiments. Methods: A CT-based SSM model of the knee was established from 60 training models in a healthy young Chinese male population. A new two-phase optimization approach for 3D subject-specific model reconstruction from multiple asynchronous clinical fluoroscopy images using the SSM was developed, and its performance was evaluated via computer simulation and in vivo experiments using one, two and three image pairs from an alternating bi-plane fluoroscope. Results: The computer simulation showed that subject-specific 3D shape reconstruction using three image pairs had the best accuracy with RMSE of 0.52 ± 0.09 and 0.63 ± 0.085 mm for the femur and tibia, respectively. The corresponding values for the in vivo study were 0.64 ± 0.084 and 0.69 ± 0.069 mm, respectively, which was significantly better than those using one image pair (0.81 ± 0.126 and 0.83 ± 0.108 mm). No significant differences existed between using two and three image pairs. Conclusion: A new two-phase optimization approach was developed for SSM-based 3D subject-specific knee model reconstructions using more than one asynchronous fluoroscopy image pair from widely available alternating bi-plane fluoroscopy systems in clinical settings. A CT-based SSM model of the knee was also developed for a healthy young Chinese male population. The new approach was found to have high mode reconstruction accuracy, and those for both two and three image pairs were much better than for a single image pair. Thus, two image pairs may be used when considering computational costs and radiation dosage. The new approach will be useful for generating patient-specific knee models for clinical applications using multiple asynchronous images from alternating bi-plane fluoroscopy widely available in clinical settings. The current SSM model will serve as a basis for further inclusion of training models with a wider range of sizes and morphological features for broader applications.

Balance control and lower limb joint work in children with bilateral genu valgum during level walking.

BACKGROUND: Genu valgum results in lower limb malalignment and altered joint mechanics. The study aimed to identify the effects of genu valgum on balance control and muscular work at the joints during gait in children. RESEARCH QUESTION: Would bilateral genu valgum affect balance control and muscular work at the joints during gait in children? METHODS: Thirteen children with genu valgum and thirteen healthy peers walked at their preferred speed while the body's motions and ground reaction forces were measured to calculate the inclination angles (IA) and the rates of change of IA (RCIA) of the body's center of mass (COM) relative to the center of pressure (COP), as well as the muscular work done at the joints. An independent t-test was used to compare the variables between groups (α = 0.05). RESULTS: Compared to the controls, the patients showed significantly increased step width with altered frontal IA and RCIA variables (p < 0.05), including increased average IA over single-limb support and increased peak RCIA during double-limb support (p < 0.05). The patients significantly increased posterior RCIA at heel-strike but decreased anterior RCIA at toe-off (p < 0.05). The patients showed increased muscular work at both the hip and knee during single-limb support (p < 0.05). SIGNIFICANCE: The children with genu valgum showed a specific balance control strategy during gait. In the frontal plane, greater hip and knee muscular work was needed to maintain balance under an increased IA, likely owing to increased step width associated with the valgus alignment. In the sagittal plane, less smooth and less stable COM-COP control with increased RCIA at the key gait events indicates faster weight transfer between double-limb and single-limb support. It is suggested that patients with genu valgum, especially in more severe cases, should be monitored for signs of decreased ability and/or muscular strength in maintaining balance during gait.