Expanded butterfly plots: A new method to analyze simultaneous pressure and shear on the plantar skin surface during gait.

The current method of visualizing pressure and shear data under a subject's foot during gait is the Pedotti, or "butterfly" diagram. This method of force platform data visualization was introduced in the 1970s to display the projection of the ground reaction force vector in the sagittal plane. The purpose of the current study was to examine individual sub-components of the vectors displayed in Pedotti diagrams, in order to better understand the relationship between one foot region and another. For this, new instrumentation was used that allows multiple Pedotti diagrams to be constructed at any instant during the gait cycle. The custom built shear-and-pressure-evaluating camera system (SPECS) allows for simultaneous recordings of pressure and both components of the horizontal force vector (medio-lateral and antero-posterior) at distinctive regions under one's foot during gait. Data analysis of such recordings affirms three conclusions: (i) pressure and shear values on individual sites on the plantar surface of the foot are not associated in a linear manner, (ii) force vectors in the heel and forefoot regions exhibit horizontal force components that oppose one another, and similarly, (iii) force vectors in the frontal plane transecting the forefoot region also exhibit medial-lateral shear components that counteract one another. This approach sheds light on individual vectors that collectively sum to each vector displayed in a Pedotti diagram. The results indicate that shearing between the foot and the ground is not simply a passive event. The structures of the arches and/or muscular activities are major contributors to the observed interfacial stresses.

Spatial relationships between shearing stresses and pressure on the plantar skin surface during gait.

Based on the hypothesis that diabetic foot lesions have a mechanical etiology, extensive efforts have sought to establish a relationship between ulcer occurrence and plantar pressure distribution. However, these factors are still not fully understood. The purpose of this study was to simultaneously record shear and pressure distributions in the heel and forefoot and to answer whether: (i) peak pressure and peak shear for anterior-posterior (AP) and medio-lateral (ML) occur at different locations, and if (ii) peak pressure is always centrally located between sites of maximum AP and ML shear stresses. A custom built system was used to collect shear and pressure data simultaneously on 11 subjects using the 2-step method. The peak pressure was found to be 362 kPa ± 106 in the heel and 527 kPa ± 123 in the forefoot. In addition, the average peak shear values were higher in the forefoot than in the heel. The greatest shear on the plantar surface of the forefoot occurred in the anterior direction (mean and std. dev.: 37.7 ± 7.6 kPa), whereas for the heel, peak shear the foot was in the posterior direction (21.2 ± 5 kPa). The results of this study suggest that the interactions of the shear forces caused greater "spreading" in the forefoot and greater tissue "dragging" in the heel. The results also showed that peak shear stresses do not occur at the same site or time as peak pressure. This may be an important factor in locating where skin breakdown occurs in patients at high-risk for ulceration.

Development of a protocol for improving the clinical utility of posturography as a fall-risk screening tool.

BACKGROUND: The usefulness of posturography in the clinical screening of older adults for fall risk has been limited by a lack of standardization in testing methodology and data reporting. This study determines which testing condition and postural sway measures best differentiate recurrent fallers and nonrecurrent fallers. METHODS: One hundred and fifty older adults were categorized based on their fall status in the past year. Participants performed four quiet-standing tasks, eyes open and eyes closed in both comfortable and narrow stance, for 60 seconds while standing on a force-measuring platform. Traditional and fractal measures were calculated from the center of pressure data. Logistic regression was performed to determine the model for each condition that best discriminated between recurrent fallers and nonrecurrent fallers. RESULTS: The eyes closed comfortable stance condition, with its associated model, best differentiated recurrent fallers and nonrecurrent fallers. Medial-lateral sway velocity, anterior-posterior short-term α-scaling exponent, medial-lateral short-term α-scaling exponent, mean frequency, body mass index, and age were included in this model. Sensitivity of the model was 75%, and specificity was 94%. CONCLUSIONS: This resulting model demonstrates potential to differentiate recurrent fallers and nonrecurrent fallers in an eyes closed comfortable stance condition. The inclusion of traditional sway parameters, fractal measures, and personal characteristics in this model demonstrates the importance of considering multiple descriptions of postural stability together rather than using only a single measure to establish fall risk.

Eye motion parameters correlate with level of experience in video-assisted surgery: objective testing of three tasks.

BACKGROUND: Laparoscopic skills vary with experience and training; however, objective measures to ascertain the level of training have not yet been established. New technology allows noninterfering measurement of eye motion parameters that correlate with attention and distraction during visually oriented tasks. Our objective was to apply this new technology in the setting of video-assisted surgery to evaluate eye motion parameters among surgeons of varying experience. MATERIALS AND METHODS: Subjects with various levels of laparoscopic experience (novice, intermediate, and expert) were fitted with a noninvasive, Food and Drug Administration approved, eye motion monitoring device. The device was used to measure and record parameters of eye motion, including saccadic rate (SR), standardized peak velocity (PV), standardized saccadic amplitude (SA), and the duration of gaze fixation (FD), during the performance of 3 basic laparoscopic tasks on a laparoscopic training station. RESULTS: A total of 24 subjects (3 groups of 8 each) participated in this study. Experience level was found to have a main significant effect on SR (P = 0.047) and PV (P = 0.028). Two-way ANOVA demonstrated that experience level approached significance for SA (P = 0.058) and FD (P = 0.055). CONCLUSION: The advancement of laparoscopic techniques and instrumentation relies, in part, on expanding the current understanding of operator/instrument interactions. This places an increasing demand on objective methods of monitoring such interactions during laparoscopy. Our study demonstrates a significant difference in eye motion parameters in surgeons with differing levels of experience. Further testing is needed in actual clinical settings to determine the importance of eye motion during surgery.