A comparison of centre of pressure behaviour and ground reaction force magnitudes when individuals walk overground and on an instrumented treadmill.

BACKGROUND: Instrumented treadmills facilitate analysis of consecutive strides in ways that typical overground gait data collections cannot. Researchers have quantified differences between joint kinetic measures whilst walking on an instrumented treadmill compared to those walking overground. The reason for such differences has not yet been established. RESEARCH QUESTION: Can we identify the source or sources of these errors by comparing centre of pressure and ground reaction force measurements recorded on a treadmill to those collected overground? METHODS: Kinematic and kinetic data were recorded while nineteen individuals walked continuously at their self-selected walking speed overground and on a treadmill. Comparisons of the centre of pressure and ground reaction forces were made between the two conditions using 2-tailed paired t-tests and Cohen's d effect size. RESULTS: The results indicated that participants had significantly faster backwards, lateral and medial centre of pressure velocities when walking on a treadmill compared to when they were walking overground. Additionally, participants also had significantly reduced peak propulsive ground reaction forces when walking on a treadmill than walking overground. SIGNIFICANCE: These results suggest that shear forces caused by the belts sliding over the treadmill force platforms affect the centre of pressure during early stance, and the minimal acceleration of a participant's centre of mass during treadmill walking results in reduced propulsive force during late stance. Therefore, care should be taken during studies when comparing kinetic gait variables between overground and treadmill walking.

Electromagnetically tracked personalized templates for surgical navigation.

PURPOSE: An electromagnetic (EM) surgical tracking system was developed for orthopedic navigation. The reportedly poor accuracy of point-based EM navigation was improved by using anatomical impressions, which were EM-tracked personalized templates. Lines, rather than points, were consistently used for calibration and error evaluation. METHODS: Technical accuracy was tested using models derived from CT scans of ten cadaver shoulders. Tracked impressions were first designed, calibrated, and tested using lines as fiducial objects. Next, tracked impressions were tested against EM point-based navigation and optical point-based navigation, in environments that were either relatively empty or that included surgical instruments. Finally, a tracked impression was tested on a cadaver forearm in a simulated fracture-repair task. RESULTS: Calibration of anatomical impressions to EM tracking was highly accurate, with mean fiducial localization errors in positions of 0.3 mm and in angles of [Formula: see text]. Technical accuracy on physical shoulder models was also highly accurate; in an EM field with surgical instruments, the mean of target registration errors in positions was 2.2 mm and in angles was [Formula: see text]. Preclinical accuracy in a cadaver forearm in positions was 0.4 mm and in angles was [Formula: see text]. The technical accuracy was significantly better than point-based navigation, whether by EM tracking or by optical tracking. The preclinical accuracy was comparable to that achieved by point-based optical navigation. CONCLUSIONS: EM-tracked impressions-a hybrid of personalized templates and EM navigation-are a promising technology for orthopedic applications. The two technical contributions are the novel hybrid navigation and the consistent use of lines as fiducial objects, replacing traditional point-based computations. The accuracy improvement was attributed to the combination of physical surfaces and line directions in the processes of calibration and registration. The technical studies and preclinical trial suggest that EM-tracked impressions are an accurate, ergonomic innovation in image-guided orthopedic surgery.

Personalized Guides for Registration in Surgical Navigation.

Personalized guides are increasingly used in orthopedic procedures but do not provide for intraoperative re-planning. This work presents a tracked guide that used physical registration to provide an anatomy-to-tracking coordinate frame transformation for surgical navigation. In a study using seven femoral models derived from clinical CT scans used for hip resurfacing, a guide characterization FRE of 0.4°±0.2°, drill-path drill-path angular TRE of 0.9°±0.4° and a positional TRE of 1.2mm±0.4mm were found; these values are comparable to conventional optical tracking accuracy. This novel use of a tracked guide may be particularly applicable to procedures that require a small surgical exposure, or when operating on anatomical regions with small bones that are difficult to track or reliably register.

A Toroidal Probe for Measuring Surgically Exposed Joint Centers.

Maintaining the hip center can improve the success of a total hip arthroplasty. A novel probe design, based on mating a toroid with a sphere, was used for kinematic measurements of the femoral head center and implant center in a pre-clinical study of hip joints. In an electromagnetically tracked implementation tested in a laboratory environment, the device measured a spherical center to within 1.2±0.2 mm in a technical validation. Applied to a plastic model of a cadaveric femur, the center of the femoral head was measured to 1.8±0.4 mm and the implant was measured to within 1.5±0.5 mm. Because leg length changes and offset changes in conventional hip arthroplasty can be as much as 16 mm, this device has relatively high accuracy that may improve implant localization for the hip.

Overall wrist biomechanics are conserved by phenol-based embalming.

Although cadaveric specimens that have been fresh-frozen then thawed are considered the gold standard for biomechanics research, because they most closely represent in vivo tissues, potential problems include a relatively short useful time-span and risk of infection. A recently reported new method of phenol-based "soft" embalming has been found to preserve tissues in a fresh-like state over an extended period of time and simultaneously reduced infection risks. This study presents radio-ulnar deviation end-range data from 4 soft-embalmed and refrigerated human cadaveric forearm specimens over 12 months. All end-range comparisons were found to be statistically equivalent to within a clinically acceptable range of ±5 degrees of radio-ulnar deviation with a 95% con. dence measure of p < 0.01 in every case. These soft-embalmed specimens provide promising results for further use in biomechanical studies.

SimITK: visual programming of the ITK image-processing library within Simulink.

The Insight Segmentation and Registration Toolkit (ITK) is a software library used for image analysis, visualization, and image-guided surgery applications. ITK is a collection of C++ classes that poses the challenge of a steep learning curve should the user not have appropriate C++ programming experience. To remove the programming complexities and facilitate rapid prototyping, an implementation of ITK within a higher-level visual programming environment is presented: SimITK. ITK functionalities are automatically wrapped into "blocks" within Simulink, the visual programming environment of MATLAB, where these blocks can be connected to form workflows: visual schematics that closely represent the structure of a C++ program. The heavily templated C++ nature of ITK does not facilitate direct interaction between Simulink and ITK; an intermediary is required to convert respective data types and allow intercommunication. As such, a SimITK "Virtual Block" has been developed that serves as a wrapper around an ITK class which is capable of resolving the ITK data types to native Simulink data types. Part of the challenge surrounding this implementation involves automatically capturing and storing the pertinent class information that need to be refined from an initial state prior to being reflected within the final block representation. The primary result from the SimITK wrapping procedure is multiple Simulink block libraries. From these libraries, blocks are selected and interconnected to demonstrate two examples: a 3D segmentation workflow and a 3D multimodal registration workflow. Compared to their pure-code equivalents, the workflows highlight ITK usability through an alternative visual interpretation of the code that abstracts away potentially confusing technicalities.

The aspherical human hip: implication for early osteoarthritis.

One marker for early-onset hip arthritis is femoral acetabular impingement. The current standard way of quantifying impingement is manual calculation of anatomical measures on plain radiographs, including the α-angle. Such measurements are user-dependent and prone to error. We provided a robust computational alternative and proposed using numerical fitting of geometrical shapes. We applied least-squares fitting of an ellipse to the femoral head contour and used the difference between the ellipse axes as a quantification method. The results showed a good correlation between the new measure and previous definitions of the α-angle.