Equivalent system based inverse dynamics analysis of transfemoral prosthetic legs: Validation and application.

Inverse dynamics analysis of prosthetic legs with polycentric knees is complex due to increased number of links. The present work proposes a simple and general method called equivalent system (ES) analysis. The ES analysis provides forces and moment at hip joint as well as at the functional knee centre (FKC), the instant centre of the polycentric knee. The input to the ES analysis is the motion data. For validation of the proposed method, synthetic motion data for the swing phase of walking with prosthetic legs having different knees are generated by simulations using ADAMS. The hip kinetics evaluated by the proposed method is compared with that from ADAMS. The root mean square errors of the ES analysis are lower than 17 (10-6) N for hip reaction forces and 2.6 (10-6) Nm for the hip moments, thereby validating the proposed method. In order to demonstrate the application of the proposed methodology, the motion data of two transfemoral amputees using single-axis and four-bar knee prostheses are obtained during gait trials. The hip kinetics as well as kinetics at FKC are computed using ES analysis. Hip power during the swing phase is also evaluated and compared. The results are presented in this paper and discussed. The ES analysis is shown to be a versatile tool to provide insights into the human-mechanism interaction.

Swing phase considerations in prosthetic knee design: Case series to validate simulations.

BACKGROUND: Previously reported simulations comparing a new polycentric knee (called IPK) and a single-axis knee suggested that polycentricity could lead to improved performance during swing phase and negate the need for an extension assist. They also showed that an anteriorly translated socket adapter for enhanced stance stability compromises foot clearance during swing. OBJECTIVES: The objectives of this study are to validate those findings using gait trials to enable further improvement in the IPK design before mass production. METHODS: Three subjects regularly using three different passive knees, single-axis knee without extension assist, single-axis knee with extension assist (SAK-EA), and polycentric knee with extension assist (Mobility India-sourced polycentric knee), participated in this study. Their gait with their regular prosthesis and with IPK (having no extension assist) were analyzed, compared, and broadly correlated with simulation results. RESULTS: Extension assist in single-axis knee with extension assist improved swing performance, affected foot clearance in Mobility India-sourced polycentric knee, and was found to be unnecessary in the IPK. With an anteriorly placed socket adapter in the IPK, compensatory strategies were necessary for foot clearance. The IPK was found to provide better knee extension characteristics with lower hip effort (up to 42% reduction) than other knees. CONCLUSIONS: This case series confirmed previously reported simulation results on the swing phase behavior of passive prosthetic knees. The performance of the IPK during swing obviated the need for an extension assist, thereby simplifying the design. Appropriate design changes in the IPK's socket adapter location are required to achieve both stance stability and reduce gait compensations for foot clearance.

Achieving excellent microformability in aluminum by engineering a unique ultrafine-grained microstructure.

During microforming of conventional materials, specimen and microstructural length-scales are close to each other. This leads to an abnormal deformation behavior of the material and reduces microformability. Engineering ultrafine-grained (UFG) microstructure in the material is a possible solution. However, micro-scale deformation behavior of UFG material is not fully understood. Present work attempts to comprehensively investigate the micro-scale deformation of four distinctly engineered microstructures: UFG with residual dislocations and elongated grains, UFG free of residual dislocation with equiaxed grains, bimodal-grained and coarse-grained. The deformation behavior is captured via micro-scale uniaxial tensile test and micro-deep drawing operation. Micro-cups generated from UFG material with equiaxed grains show excellent surface quality, form-accuracy and minimal process scatter. Postmortem microscopy of the formed micro-cups attributes this improved microformability to the activation of grain boundary-mediated plasticity in the material which results in synergetic grain migration and rotation. Presence of residual dislocations and elongated grains hinders the grain migration and rotation leading to strain localization and thinning. In case of bimodal and coarse-grained material, cross-slip based deformation mode progressively dominates over grain migration and rotation, which results in a reduction in microformability due to the influence of size-effect.

Visual acuity outcomes following surgery for idiopathic epiretinal membrane: an analysis of data from 2001 to 2011.

PURPOSE: Pars plana vitrectomy (PPV) is commonly used to remove the epiretinal membrane (ERM), but the timing of surgical intervention guided by visual acuity (VA) performance at presentation is uncertain. PATIENTS AND METHODS: Prospectively entered clinical data of 237 patients on an electronic patient record from 2001 to 2011 were analysed to determine visual outcomes, in particular in relation to pre-operative VA. RESULTS: The mean age of the patients was 68.8 years and 54.4% were female. Median follow-up was 0.55 years. The median pre-operative logMAR VA was 0.60 (SD 0.48-0.78, Snellen equivalent 6/36) and post-operative VA was 0.30 (SD 0.18-0.60, 6/12, P<0.005). Pre-operative VA correlated with post-operative VA (linear R(2)=0.22, P<0.0001). In all, 69.6% of patients showed an improvement in VA, 15.2% showed no change, and the condition of 15.2% worsened. The number of patients with an improvement in logMAR VA of more than 0.3 was greatest in those who had a pre-operative VA of 1.0 (6/60) or worse, followed by those in the range of 0.6-0.9 and then those with pre-operative VA of 0.5 or better (P<0.001). The proportion of patients with visual improvement of logMAR VA of more than 0.3 increased statistically with progressing years (P=0.019). CONCLUSION: In conclusion, this study shows improvement in VA after PPV and ERM removal. Patients with better initial VA achieve higher levels of visual outcome but those with poorer pre-operative VA show a greater change in VA following ERM surgery. Results of surgery improved over the time period of the study.

Characteristics of rhegmatogenous retinal detachment and their relationship to visual outcome.

AIMS: To examine pre-operative characteristics of rhegmatogenous retinal detachment (RRD) and their relationship to visual acuity (VA) following surgery. METHODS: Review of prospectively completed electronic database. Baseline characteristics, retinal drawings and outcomes were analysed. RESULTS: In all, 847 eyes from 847 patients with a mean age of 62.2 years, 60% males, and 56% right eyes were studied. Mean follow-up was 9.6 months. Preoperative VA correlated with final VA (r(2)=0.21, P<0.0001). Median postoperative VA was 6/9 (Logmar 0.18, quartiles=0.0-0.48) and was significantly related to anatomical success: 70.15% achieved 0.18 or better with fully attached retina and primary success, whereas only 8.33% achieved this when the retina was not fully attached at final follow-up (failure) (P<0.0001). Univariate analysis found multiple variables associated with achieving 0.18 postoperative vision, however, multivariate analysis revealed only primary anatomical success with surgery; absence of proliferative vitreo-retinopathy (PVR), better-presenting VA and fewer quadrants of detachment were associated with a better visual outcome (r(2)=0.26, P<0.0001). Patients with a clinically attached fovea achieved better vision than patients with a clinically detached fovea, independent of the visual loss duration. With foveal detachment however, postoperative VA was better in patients with 1-3 days of visual loss compared with 4-6 days (P=0.013). CONCLUSIONS: Failure of primary surgery, PVR, extensive RRD and poor-presenting VA are risk factors for poorer visual outcome following surgery for RRD. Fovea off RRD at presentation achieved poorer postoperative VA than fovea attached and visual outcome was poorer when there was a longer duration of visual symptoms.

Correlates of paid sex among men who have sex with men in Chennai, India.

OBJECTIVES: To assess correlates of paid sex among men who have sex with men (MSM) in Chennai, India. METHODS: A randomised survey was conducted among 200 MSM recruited from public sex environments using time-space sampling. The association of predictors with paid sex was assessed with chi(2) tests and multiple logistic regression. RESULTS: Participants' mean age was 28.5 years (SD 8.7). Most (71.5%) were kothis; 60% had less than high school education and two-thirds had a monthly income less than 2000 Indian rupees. More than one-third (35.0%) reported daily/weekly harassment; 40.5% reported forced sex in the past year. The prevalence of paid sex was 59.5% (95% CI 52.7% to 66.3%). Univariate analyses indicated that paid sex was associated with kothi identity (chi(2) = 14.46; p<0.01), less than high school education (chi(2) = 4.79; p<0.05), harassment (chi(2) = 11.75; p<0.01) and forced sex (chi(2) = 3.98; p<0.05). Adjusted analyses revealed that paid sex was associated with kothi identity (adjusted odds ratio (AOR) 2.62, 95% CI 1.34 to 5.10) and harassment (AOR 2.34, 95% CI 1.16 to 4.72). MSM who engaged in paid sex (versus no paid sex) had a mean of 31 partners in the past month (versus 4, t = 6.17, p<0.001) and 71.2% used condoms consistently (versus 46.4%, chi(2) = 18.34; p<0.01). Overall, 32.5% were never tested for HIV. CONCLUSIONS: Epidemic rates of harassment and sexual violence against MSM who engage in paid sex, predominantly kothis, suggest that interventions should target structural factors placing these men at increased risk of HIV/sexually transmitted infections and other health-compromising conditions. The effectiveness of individual-level, knowledge-based and condom-focused preventive interventions may be constrained in the context of poverty, low education, harassment and sexual violence.

Determinants of sexual risk behavior among men who have sex with men accessing public sex environments in Chennai, India.

We conducted structured interviews with 200 men who have sex with men (MSM) recruited using time-space sampling from public sex environments (PSEs) in Chennai, India. Predictors of sexual risk behavior were assessed with chi2 tests and multiple logistic regression. One-third reported unprotected receptive anal sex (URAS) last time and 36% inconsistent condom use in the past month. URAS was associated with younger age, less than high school education, low income, and low HIV transmission knowledge (adjusted odds ratio [AOR] = 2.1, 2.5, 3.7 and 2.5, respectively). Inconsistent condom use was associated with less than high school education (AOR = 3.2) and low HIV transmission knowledge (AOR = 3.5). Multilevel HIV prevention strategies tailored for low socioeconomic kothis and other MSM in PSEs in Chennai should include peer interventions to increase knowledge of HIV transmission risks and sexually transmitted infections (STIs), and structural interventions to expand economic and educational opportunities, and accessible STI testing and treatment.