Paolo Caravaggi

New insights into the plantar pressure correlates of walking speed using pedobarographic statistical parametric mapping (pSPM)

This study investigates the relation between walking speed and the distribution of peak plantar pressure and compares a traditional ten-region subsampling (10RS) technique with a new technique: pedobarographic statistical parametric mapping (pSPM). Adapted from cerebral fMRI methodology, pSPM is a digital image processing technique that registers foot pressure images such that homologous structures optimally overlap, thereby enabling statistical tests to be conducted at the pixel level. Following previous experimental protocols, we collected pedobarographic records from 10 subjects walking at three different speeds: slow, normal, and fast. Walking speed was recorded and correlated with the peak pressures extracted from the 10 regions, and subsequently with the peak pixel data extracted after pSPM preprocessing. Both methods revealed significant positive correlation between peak plantar pressure and walking speed over the rearfoot and distal forefoot after Bonferroni correction for multiple comparisons. The 10RS analysis found positive correlation in the midfoot and medial proximal forefoot, but the pixel data exhibited significant negative correlation throughout these regions (p<5x10(-5)). Comparing the statistical maps from the two approaches shows that subsampling may conflate pressure differences evident in pixel-level data, obscuring or even reversing statistical trends. The negative correlation observed in the midfoot implies reduced longitudinal arch collapse with higher walking speeds. We infer that this results from pre- or early-stance phase muscle activity and speculate that preferred walking speed reflects, in part, a balance between the energy required to tighten the longitudinal arch and the apparent propulsive benefits of the stiffened arch.

A dynamic model of the windlass mechanism of the foot: evidence for early stance phase preloading of the plantar aponeurosis

SUMMARY In the present study we have estimated the temporal elongation of the plantar aponeurosis (PA) during normal walking using a subject-specific multi-segment rigid-body model of the foot. As previous studies have suggested that muscular forces at the ankle can pre-load the PA prior to heel-strike, the main purpose of the current study was to test, through modelling, whether there is any tension present in the PA during early stance phase. Reflective markers were attached to bony landmarks to track the kinematics of the calcaneus, metatarsus and toes during barefoot walking. Ultrasonography measurements were performed on three subjects to determine both the location of the origin of the PA on the plantar aspect of the calcaneus, and the radii of the metatarsal heads. Starting with the foot in a neutral, unloaded position, inverse kinematics allowed calculation of the tension in the five slips of the PA during the whole duration of the stance phase. The results show that the PA experienced tension significantly above rest during early stance phase in all subjects (P<0.01), thus providing support for the PA-preloading hypothesis. The amount of preloading and the maximum elongation of the slips of the PA decreased from medial to lateral. The mean maximum tension exerted by the PA was 1.5 BW (body weight) over the three subjects.

Dynamics of longitudinal arch support in relation to walking speed: contribution of the plantar aponeurosis

The plantar aponeurosis (PA), in spanning the whole length of the plantar aspect of the foot, is clearly identified as one of the key structures that is likely to affect compliance and stability of the longitudinal arch. A recent study performed in our laboratory showed that tension/elongation in the PA can be predicted from the kinematics of the segments to which the PA is attached. In the present investigation, stereophotogrammetry and inverse kinematics were employed to shed light on the mechanics of the longitudinal arch and its main passive stabilizer, the PA, in relation to walking speed. When compared with a neutral unloaded position, the medial longitudinal arch underwent greater collapse during the weight‐acceptance phase of stance at higher walking speed (0.1°±1.9° in slow walking; 0.9°±2.6° in fast walking; P = 0.0368). During late stance the arch was higher (3.4°±3.1° in slow walking; 2.8°±2.7° in fast walking; P = 0.0227) and the metatarsophalangeal joints more dorsiflexed (e.g. at the first metatarsophalangeal joint, 52°±5° in slow walking; 64°±4° in fast walking; P < 0.001) during fast walking. Early‐stance tension in the PA increased with speed, whereas maximum tension during late stance did not seem to be significantly affected by walking speed. Although, on the one hand, these results give evidence for the existence of a pre‐heel‐strike, speed‐dependent, arch‐stiffening mechanism, on the other hand they suggest that augmentation of arch height in late stance is enhanced by higher forces exerted by the intrinsic muscles on the plantar aspect of the foot when walking at faster speeds.

Repeatability of a multi-segment foot protocol in adult subjects

Despite the numerous protocols for multi-segment kinematic analysis of the foot, the literature is scarce regarding relevant measures of reliability. The aim of the present work was to assess the inter-trial, inter-session and inter-examiner variability of one of these protocols by an established method. The kinematics of the joints of the foot of two volunteers were analyzed by four examiners with different degrees of experience in three sessions, two-to-four weeks apart. In each session the data of five trials of level walking were collected and the rotations in the three anatomical planes between foot segments were calculated. The mean value over stance phase duration of the standard deviation of these rotations was calculated for groups of trials according to the statistical method as in Schwartz et al. [6]. For each rotation, the inter-examiner variability was larger than the inter-session, and the latter larger than the inter-trial. The inter-session variability was found in the same order of magnitude for standard lower limb protocols for the two expert examiners, but much higher for the inexperienced examiners.

Validation of the angular measurements of a new inertial-measurement-unit based rehabilitation system: comparison with state-of-the-art gait analysis

BackgroundSeveral rehabilitation systems based on inertial measurement units (IMU) are entering the market for the control of exercises and to measure performance progression, particularly for recovery after lower limb orthopaedic treatments. IMU are easy to wear also by the patient alone, but the extent to which IMU’s malpositioning in routine use can affect the accuracy of the measurements is not known. A new such system (Riablo™, CoRehab, Trento, Italy), using audio-visual biofeedback based on videogames, was assessed against state-of-the-art gait analysis as the gold standard.MethodsThe sensitivity of the system to errors in the IMU’s position and orientation was measured in 5 healthy subjects performing two hip joint motion exercises. Root mean square deviation was used to assess differences in the system’s kinematic output between the erroneous and correct IMU position and orientation.In order to estimate the system’s accuracy, thorax and knee joint motion of 17 healthy subjects were tracked during the execution of standard rehabilitation tasks and compared with the corresponding measurements obtained with an established gait protocol using stereophotogrammetry.ResultsA maximum mean error of 3.1 ± 1.8 deg and 1.9 ± 0.8 deg from the angle trajectory with correct IMU position was recorded respectively in the medio-lateral malposition and frontal-plane misalignment tests. Across the standard rehabilitation tasks, the mean distance between the IMU and gait analysis systems was on average smaller than 5°.ConclusionsThese findings showed that the tested IMU based system has the necessary accuracy to be safely utilized in rehabilitation programs after orthopaedic treatments of the lower limb.

Evolutionary Robotic Approaches in Primate Gait Analysis

Understanding how primates move is particularly challenging because many of the experimentation techniques that would normally be available are unsuitable for ethical and conservation reasons. We therefore need to develop techniques that can maximize the data available from minimally intrusive experimentation. One approach for achieving this is to use evolutionary robotic techniques to build a musculoskeletal simulation and generate movement patterns that optimize some global parameter such as economy or performance, or to match existing kinematic data. If the simulation has a sufficiently high biofidelity and can match experimentally measured performance criteria then we can use it to predict aspects of locomotor mechanics that would otherwise be impossible to measure. This approach is particularly valuable when studying fossil primates because it can be based entirely on morphology and can generate movements spontaneously. A major question in human evolution is the origin of bipedal running and the role of elastic energy storage. By using an evolutionary robotics model of humanoid running we can show that elastic storage is required for efficient, high-performance running. Elasticity allows both energy recovery to minimize total energy cost and also power amplification to allow high performance. The most important elastic energy store on the human hind limb is the Achilles tendon: a feature that is at best weakly expressed among the African great apes. By running simulations both with and without this structure we can demonstrate its importance, and we suggest that identification of the presence or otherwise of this tendon—perhaps by calcaneal morphology or Sharpey’s fibers—is essential for identifying when and where in the fossil record human style running originated.

Regional peak plantar pressures are highly sensitive to region boundary definitions

Traditional pedobarographic analyses subsample pressure data over a number of discrete anatomical regions of interest (ROIs). To our knowledge, the sensitivity of these data to ROI boundary definitions has not been previously addressed. Eight subjects each performed 20 trials of self-paced walking; commercial software was used to define 10 ROIs for each of the 160 total peak pressure images, and regional peak pressures (RPPs) were extracted for each image (total: 1600 values). We then asked three specific questions regarding RPP sensitivity to ROI boundary definition: (1) Is the ROI centroid representative of the RPP location? (2) How frequently do RPPs lie on the ROI boundary? and (3) By how much do RPP values change if the ROI boundary is changed by one pixel (resolution: 5.08 x 7.62 mm)? We found that the RPP locations differed from the ROI centroid in 80% of the cases and that the RPPs lay on the ROI boundary with a probability of 65%. We also found that a single-pixel change in the ROI boundary caused a mean RPP change of 10.8%. The most sensitive region was the midfoot for which a single-pixel ROI change yielded a median 29.4% change in RPP. These results indicate that RPP data are biased by regionalization schemes, which delineate pressure fields based on anatomy rather than on the fields geometric properties, and ultimately that regionalization may constitute a poor method of quantifying complex pressure fields. RPP sensitivity should be considered when making statistical inferences regarding foot function.

Correlates between kinematics and baropodometric measurements for an integrated in-vivo assessment of the segmental foot function in gait.

Baropodometry and multi-segmental foot kinematics are frequently employed to obtain insight into the mechanics of the foot-ground interaction in both basic research and clinical settings. However, nothing hitherto has been reported on the full integration of kinematics with baropodometric parameters, and only a few studies have addressed the association between intersegmental kinematics and plantar loading within specific foot regions. The aim of this study was to understanding the relationships between foot joint mobility and plantar loading by focusing on the correlation between these two measures. An integrated pressure-force-kinematics system was used to measure plantar pressure and rotations between foot segments during the stance phase of walking in 10 healthy subjects. An anatomically-based mask was applied to each footprint to obtain six regions according to the position of the markers; hence each kinematic segment was paired with a corresponding area of the plantar surface. Relationships between segmental motion and relevant baropodometric data were explored by means of correlation analysis. Negative, weak-to-moderate correlations (R(2)<0.5) were found between pressure (mean and peak) and inter-segmental range of motion across all foot joints except the Calcaneus-Midfoot. Temporal profiles of sagittal-plane kinematics and baropodometric parameters were well correlated, particularly at the ankle joint. Larger motion in the foot joints during walking was associated with lower plantar pressure in almost all regions. The study helps improve our understanding of the relationship between joint mobility and plantar loading in the healthy foot and represents a critical preliminary analysis before addressing possible clinical applications.

Kinematic correlates of walking cadence in the foot.

Evidence has frequently been reported of modifications in gait patterns within the lower limb related to the cadence of walking. Most reports have concerned relationships between cadence and kinematic and the kinetic changes occurring in the main joints and muscles of the lower limb as a whole. The aim of the present study was to assess whether significant changes are also measurable in kinematics of the foot segments. An existing 15 marker-set protocol allowed a four-segment foot and shank model to be defined for relative rotations between the segments to be calculated. Stereophotogrammetry was employed to record marker position data from ten subjects walking at three cadences. The slow- and normal cadence datasets showed similar profiles of joint rotation in three anatomical planes, but significant differences were found between these and the fast cadence. At all joints, frame-by-frame statistical analysis revealed increased dorsiflexion from heel-strike to midstance (p < 0.05) and increased plantarflexion from midstance to toe-off (p < 0.05) with increasing cadence. From foot-flat to heel-rise, the fast cadence kinematic data showed a decreased range of motion in the sagittal-plane between forefoot and rearfoot (3.2 degrees +/- 1.2 degrees at slow cadence; 2.0 degrees +/- 0.8 degrees at fast cadence; p < 0.05). The cadences imposed and the multisegment protocol revealed significant kinematic changes in the joints of the foot during barefoot walking.

Multi-segment foot mobility in a hinged ankle-foot orthosis: the effect of rotation axis position.

Hinged ankle-foot orthoses are prescribed routinely for the treatment of ankle joint deficits, despite the conflicting outcomes and the little evidence on their functional efficacy. In particular, the axis of rotation of the hinge is positioned disregarding the physiological position and orientation. A multi-segment model was utilized to assess in vivo the effect of different positions for this axis on the kinematics of foot joints. A special custom-made hinged orthosis was manufactured via standard procedures for a young healthy volunteer. Four locations for the mechanical axis were obtained by a number of holes where two nuts and bolts were inserted to form the hinge: a standard position well above the malleoli, at the level of the medial malleolus, at the level of the lateral malleolus, and the physiological between the two malleoli. The shank and foot were instrumented with 15 reflective markers according to a standard protocol, and level walking was collected barefoot and with the orthosis in the four mechanical conditions. The spatio-temporal parameters observed in the physiological axis condition were the closest to normal barefoot walking. As expected, ankle joint rotation was limited to the sagittal plane. When the physiological axis was in place, rotations of the ankle out-of-sagittal planes, and of all other foot joints in the three anatomical planes, were found to be those most similar to the natural barefoot condition. These preliminary measures of intersegmental kinematics in a foot within an ankle-foot orthosis showed that only a physiological location for the ankle mechanical hinge can result in natural motion at the remaining joints and planes.