Individuals with knee osteoarthritis show few limitations in balance recovery responses after moderate gait perturbations.

BACKGROUND: Knee osteoarthritis causes structural joint damage. The resultant symptoms can impair the ability to recover from unexpected gait perturbations. This study compared balance recovery responses to moderate gait perturbations between individuals with knee osteoarthritis and healthy individuals. METHODS: Kinematic data of 35 individuals with end-stage knee osteoarthritis, and 32 healthy individuals in the same age range were obtained during perturbed walking on a treadmill at 1.0 m/s. Participants received anteroposterior (acceleration or deceleration) or mediolateral perturbations during the stance phase. Changes from baseline in margin of stability, step length, step time, and step width during the first two steps after perturbation were compared between groups using a linear regression model. Extrapolated center of mass excursion was descriptively analyzed. FINDINGS: After all perturbation modes, extrapolated center of mass trajectories overlapped between individuals with knee osteoarthritis and healthy individuals. Participants predominantly responded to mediolateral perturbations by adjusting their step width, and to anteroposterior perturbations by adjusting step length and step time. None of the perturbation modes yielded between-group differences in changes in margin of stability and step width during the first two steps after perturbation. Small between-group differences were observed for step length (i.e. 2 cm) of the second step after mediolateral and anteroposterior perturbations, and for step time (i.e. 0.01-0.02 s) of first step after mediolateral perturbations and the second step after outward and belt acceleration perturbations. INTERPRETATION: Despite considerable pain and damage to the knee joint, individuals with knee osteoarthritis showed comparable balance recovery responses after moderate gait perturbations to healthy participants.

The effect of limited sensory information on exoskeleton performance in people with complete spinal cord injury.

Despite the absence of somatosensory information from the lower extremities, people with complete spinal cord injury (SCI) can maintain postural stability in an exoskeleton. This is partly because humans are able to reweigh the relative dependence on each of the senses. However, when the sensory environment is changed, people with complete SCI are limited in their ability to reweigh their sensory organization towards more dependence on somatosensory information. The aim of this study was to investigate the effect of limited visual and/or auditory information on exoskeleton performance in people with complete SCI. Three experienced exoskeleton users performed twelve walking trials in the ReWalk exoskeleton. In each trial, the presence or absence of visual and/or auditory information was varied. Exoskeleton performance was operationalized as the walking distance covered and the amount of crutch loading. In one participant, the distance covered decreased when visual information was limited. The other two participants did not show substantial differences in distance covered between sensory conditions. Two participants decreased crutch loading when visual information was restricted, and one participant decreased crutch loading when auditory information was limited. The current study suggests a limited influence of the presence or absence of visual and auditory information on the distance covered in people with complete SCI walking in an exoskeleton. Interestingly, crutch loading seemed to decrease rather than increase when visual or auditory information was limited.

A single Inertial Measurement Unit on the shank to assess the Shank-to-Vertical Angle.

The Shank-to-Vertical Angle (SVA) is a commonly used parameter to describe orthotic alignment. 3D gait analysis (3DGA) or 2D video analysis are usually used to assess the SVA, but are not always feasible in clinical practice. As an alternative, an Inertial Measurement Unit (IMU) attached and aligned to the shank might be used. This study aimed to investigate the validity, inter-rater reliability and optimal location of a single IMU on the shank to assess the SVA. Thirteen healthy participants (7 m/6f, mean age: 45 ± 18 years) were recorded during quiet standing and barefoot walking using a 3D motion capture system and, simultaneously, with IMUs on the shank. The IMUs were anatomically placed and aligned at two different locations, i.e. anterior, in line with the tibial tuberosity and midline of the ankle (anterior IMU), and lateral, in line with the lateral epicondyle and lateral malleolus (lateral IMU). For each participant, the IMUs were placed by two different researchers. A paired t-test, Bland Altmann analysis (mean difference, repeatability coefficient) and intraclass correlation coefficient (ICC) between the 3DGA and both IMUs, and between raters, was performed. Although validity and reliability of the lateral IMU was low, good validity and inter-rater reliability was found for the anterior IMU (Rater1: mean difference: -0.7 ± 2.1, p = 0.27; ICC = 0.83 and Rater2: mean difference: -0.4 ± 1.9, p = 0.46; ICC = 0.86). Hence, a single IMU placed at the anterior side of the shank is a valid and reliable method to assess the SVA during standing and walking in healthy adults.

Test-retest reliability of stability outcome measures during treadmill walking in patients with balance problems and healthy controls.

BACKGROUND: Improvement of balance control is an important rehabilitation goal for patients with motor and sensory impairments. To quantify balance control during walking, various stability outcome measures have described differences between healthy controls and patient groups with balance problems. To be useful for the evaluation of interventions or monitoring of individual patients, stability outcome measures need to be reliable. RESEARCH QUESTION: What is the test-retest reliability of six stability outcome measures during gait? METHODS: Patients with balance problems (n = 45) and healthy controls (n = 20) performed two times a two-minute walk test (2MWT). The intraclass correlation coefficient (ICC) and Bland-Altman analysis (coefficient of repeatability; CR) were used to evaluate the test-retest reliability of six stability outcome measures: dynamic stability margin (DSM), margin of stability (MoS), distance between the extrapolated centre of mass (XCoM) and centre of pressure (CoP) in anterior-posterior (XCoM-CoPAP) and medial-lateral (XCoM-CoPML) direction, and inclination angle between centre of mass (CoM) and CoP in anterior-posterior (CoM-CoPAP-angle) and medial-lateral (CoM-CoPML-angle) direction. A two way mixed ANOVA was performed to reveal measurement- and group-effects. RESULTS: The ICCs of all stability outcome measures ranged between 0.51 and 0.97. Significant differences between the measurements were found for the DSM (p = 0.017), XCoM-CoPAP (p = 0.008) and CoM-CoPAP-angle (p = 0.001). Significant differences between controls and patients were found for all stability outcome measures (p < 0.01) except for the MoS (p = 0.32). For the XCoM-CoP distances and CoM-CoP angles, the CRs were smaller than the difference between patients and controls. SIGNIFICANCE: Based on the ICCs, the reliability of all stability outcome measures was moderate to excellent. Since the XCoM-CoPML and CoM-CoPML-angle showed no differences between the measurements and smaller CRs than the differences between patients and controls, the XCoM-CoPML and CoM-CoPML-angle seem the most promising stability outcome measures to evaluate interventions and monitor individual patients.

Case Report: Description of two fractures during the use of a powered exoskeleton.

Introduction: Powered robotic exoskeletons are a promising solution to enable standing and walking in patients with spinal cord injury (SCI). Although training and walking with an exoskeleton in motor complete SCI patients is considered safe, the risks of unexpected (technical) adverse events and the risk of fractures are not fully understood. This article reports the occurrence of two different cases of bone fracture during exoskeleton usage. Furthermore, advice is given for extra safety training and instructions. Case presentation: The first case concerns a 47-year-old woman with T12 AIS A SCI. Her exoskeleton shut down unexpectedly probably causing a misalignment of the joints of her lower extremities relative to the joints of the exoskeleton, which resulted in a fracture of her left tibia. The second case involves a 39-year-old man with L1 AIS B SCI. An unexpected fracture of the right distal tibia occurred without a specific prior (traumatic) incident. Discussion: Exoskeleton training instructors, SCI patients and their buddies should be instructed how to handle emergency situations. Furthermore, they should be aware of the risk of stress fractures of the lower extremities. Proper alignment of the exoskeleton relative to the body is of utmost importance to reduce fracture risk. In the case of swelling and discoloring of the skin, radiographic examination should be performed in order to exclude any fracture.

A prospective analysis of motion and deformity at the shoulder level in surgically treated adolescent idiopathic scoliosis.

BACKGROUND: Although posterior spinal correction and fusion surgery (PSF) of adolescent idiopathic scoliosis (AIS) limits counter rotation between thorax and pelvis, the physical function, and more specifically gait of these patients is only slightly affected after PSF. Possibly, shoulders-thorax counter-rotation increases to compensate for the loss in thorax-pelvis motion. This would subsequently result in a higher phase-difference and range of motion (ROM) between the shoulders and thorax. RESEARCH QUESTIONS: What is the effect of PSF on the phase difference and ROM between the shoulders and thorax? What is the effect of PSF on upper body deformity? METHODS: 18 AIS patients underwent gait analysis at increasing walking speeds (0.45 to 2.22 m/s) before, and 3 and 12 months after PSF. The phase difference, ROM, and deformity between the shoulders, thorax, and pelvis were calculated. RESULTS: The shoulders- thorax phase difference was unaffected by surgery. At 3 months postoperatively the shoulders-thorax ROM was decreased (3.5° ± 0.2° versus 2.7° ± 0.2°, p=0.001). This recovered to preoperative values 12 months postoperatively (3.2° ± 0.2°, p=0.213). The shoulder-pelvis phase difference was decreased 3 months postoperatively (-98.9° ± 6.8° vs. -77.2° ± 7.2°, p=0.010), and recovered to pre-op values at the 12 months postoperative measurement (-89.6° ± 6.9°, p=0.290). Walking speed did not influence the effect of surgery on phase difference or ROM. The pre-operative shoulders-thorax asymmetry decreased from 3.4° ± 2.4° to 0.6° ± 3.1° (p<0.001). Shoulders-pelvis and thorax-pelvis asymmetry decreased from 10.0° ± 3.7° to 2.8° ± 4.3° (p<0.001) and from 6.5° ± 3.4° to 1.8° ± 3.2° (p=0.006) respectively. SIGNIFICANCE: No compensatory mechanisms could be identified in the relative motion between the shoulders and the thorax. Possibly, compensatory mechanisms are not required for normal gait after surgery. The asymmetry of the shoulders in the transversal plane improved without specific surgical strategies.

Classifying trunk strength impairment according to the activity limitation caused in wheelchair rugby performance.

International Federations in Paralympic sports should develop evidence-based classification, based on the relative strength of association between impairment and activities that determine sport-specific performance. The purpose of the current study was to assess the relationship between trunk strength impairment and three activities that determine performance in wheelchair rugby, and to determine whether this relationship supports the concept of "natural classes." Trunk muscle strength and three determinants of performance were assessed in 27 athletes. The correlations between lateral trunk muscle strength and the determinant tilting the chair, and between forward trunk muscle strength and the determinants 1 m acceleration and sprint momentum were calculated. To group athletes based on impairment, K-means cluster analysis was used to group athletes according to how much trunk muscle strength affected the activities. There were significant, moderate to strong correlations between left-right strength and chair tilting (r=.50), between forward strength and 1 m acceleration (r=.59), and between forward strength and sprint momentum (r=.79). Cluster analysis indicated at least one cut-point in performance with a decrease in impairment in all three wheelchair activities, supporting the concept of "natural classes."

Spinal fusion limits upper body range of motion during gait without inducing compensatory mechanisms in adolescent idiopathic scoliosis patients.

INTRODUCTION: Previous studies show a limited alteration of gait at normal walking speed after spinal fusion surgery for adolescent idiopathic scoliosis (AIS), despite the presumed essential role of spinal mobility during gait. This study analyses how spinal fusion affects gait at more challenging walking speeds. More specifically, we investigated whether thoracic-pelvic rotations are reduced to a larger extent at higher gait speeds and whether compensatory mechanisms above and below the stiffened spine are present. METHODS: 18 AIS patients underwent gait analysis at increasing walking speeds (0.45 to 2.22m/s) before and after spinal fusion. The range of motion (ROM) of the upper (thorax, thoracic-pelvic and pelvis) and lower body (hip, knee and ankle) was determined in all three planes. Spatiotemporal parameters of interest were stride length and cadence. RESULTS: Spinal fusion diminished transverse plane thoracic-pelvic ROM and this difference was more explicit at higher walking speeds. Transversal pelvis ROM was also decreased but this effect was not affected by speed. Lower body ROM, step length and cadence remained unaffected. DISCUSSION: Despite the reduction of upper body ROM after spine surgery during high speed gait, no altered spatiotemporal parameters or increased compensatory ROM above or below the fusion (i.e. in the shoulder girdle or lower extremities) was identified. Thus, it remains unclear how patients can cope so well with such major surgery. Future studies should focus on analyzing the kinematics of individual spinal levels above and below the fusion during gait to investigate possible compensatory mechanisms within the spine.

Gait analysis before and after corrective osteotomy in patients with knee osteoarthritis and a valgus deformity.

PURPOSE: In this prospective study, the changes in kinetics and kinematics of gait and clinical outcomes after a varus osteotomy (tibial, femoral or double osteotomy) in patients with osteoarthritis (OA) of the knee and a valgus leg alignment were analysed and compared to healthy subjects. METHODS: Twelve patients and ten healthy controls were included. Both kinetics and kinematics of gait and clinical and radiographic outcomes were evaluated. RESULTS: The knee adduction moment increased significantly postoperatively (p < 0.05) and almost similar to the control group. Patients showed less knee and hip flexion/extension motion and moment during gait pre- and postoperatively compared to the controls. A significant improvement was found in WOMAC [80.8 (SD 16.1), p = 0.000], KOS [74.9 (SD 14.7), p = 0.018], OKS [21.2 (SD 7.5), p = 0.000] and VAS-pain [32.9 (SD 20.9), p = 0.003] in all patients irrespective of the osteotomy technique used. The radiographic measurements showed a mean hip knee ankle (HKA) angle correction of 10.4° (95 % CI 6.4°-14.4°). CONCLUSION: In patients with knee OA combined with a valgus leg alignment, the varus-producing osteotomy is a successful treatment. Postoperatively, the patients showed kinetics and kinematics of gait similar as that of a healthy control group. A significant increase in the knee adduction moment during stance phase was found, which was related to the degree of correction. The HKA angle towards zero degrees caused a medial shift in the dynamic knee loading. The medial shift will optimally restore cartilage loading forces and knee ligament balance and reduces progression of OA or the risk of OA. A significant improvement in all clinical outcomes was also found. LEVEL OF EVIDENCE: III.

The impact of trunk impairment on performance-determining activities in wheelchair rugby.

In Paralympic sport, classification of impairment is needed to prevent a one-sided and predictable outcome of competition, in which the least impaired athlete has the best chance to win. To develop evidence-based classification in wheelchair rugby, the impact of trunk impairment, measured by the Trunk Impairment Classification (TIC), on performance-determining activities was assessed. Arm impairment was analyzed as a covariant. Fifty-five athletes, 21 with TIC score 0, 13 with TIC score 0.5, 11 with TIC score 1.0, and 10 with TIC score 1.5 performed standardized sport-specific activities. A multiple step forward regression analysis was performed for all activities to assess the relative impact of trunk and arm impairment on performance. Trunk impairment was the most important factor for tilting the chair and acceleration in the first 2 m. The explained variance of the performance by trunk and arm impairment ranged from 23% for acceleration in the first meter, to 37% for sprint momentum, the tilt test left, and the time to cover 3 and 4 m. This study shows that athletes with limited trunk impairment are more proficient in wheelchair rugby than athletes with severe trunk impairment.

Prediction of walking speed using single stance force or pressure measurements in healthy subjects.

Walking speed is one of the best measures of overall walking capacity. In plantar pressure measurements, walking speed can be assessed using contact time, but it is only moderately correlated with walking speed. The center of pressure might be of more value to indicate walking speed since walking speed alters foot loading. Therefore, the purpose of this study is to assess walking speed using the velocity of the center of pressure (VCOP). Thirty-three subjects walked over a Footscan pressure plate at three speed conditions; slow, preferred, and fast. Walking speed was measured by a motion analysis system. (Multiple) linear regression analysis was used to indicate the relation between walking speed and independent variables derived from the pressure plate such as mean VCOP and stance time for all walking conditions separately and together. The mean VCOP had the highest correlation coefficient value with walking speed for all walking conditions combined (0.94) and for the preferred walking condition (0.80). The multiple regression analysis, based on a number of additional parameters, revealed a small to modest increase in the performance of predicting walking speed (r=0.98 for combined and r=0.93 for preferred). The mean VCOP was the best predictor for walking speed when using a plantar pressure plate. The mean VCOP predicts the walking speed with a 95% accuracy of 0.20m/s when healthy subjects walk at their preferred walking speed.

Foot lengthening and shortening during gait: a parameter to investigate foot function?

INTRODUCTION: Based on the windlass mechanism theory of Hicks, the medial longitudinal arch (MLA) flattens during weight bearing. Simultaneously, foot lengthening is expected. However, changes in foot length during gait and the influence of walking speed has not been investigated yet. METHODS: The foot length and MLA angle of 34 healthy subjects (18 males, 16 females) at 3 velocities (preferred, low (preferred -0.4 m/s) and fast (preferred +0.4 m/s) speed were investigated with a 3D motion analysis system (VICON(®)). The MLA angle was calculated as the angle between the second metatarsal head, the navicular tuberculum and the heel in the local sagittal plane. Foot length was calculated as the distance between the marker at the heel and the 2nd metatarsal head. A General Linear Model for repeated measures was used to indicate significant differences in MLA angle and foot length between different walking speeds. RESULTS: The foot lengthened during the weight acceptance phase of gait and shortened during propulsion. With increased walking speed, the foot elongated less after heel strike and shortened more during push off. The MLA angle and foot length curve were similar, except between 50% and 80% of the stance phase in which the MLA increases whereas the foot length showed a slight decrease. CONCLUSION: Foot length seems to represent the Hicks mechanism in the foot and the ability of the foot to bear weight. At higher speeds, the foot becomes relatively stiffer, presumably to act as a lever arm to provide extra propulsion.

Reliability of the revised wheelchair rugby trunk impairment classification system.

STUDY DESIGN: Observational, cross-sectional. OBJECTIVES: A new classification system for trunk impairment in wheelchair rugby was introduced in 2010. It consists of 10 tests, arranged in an algorithm, to assign four different trunk scores (0, 0.5, 1.0 or 1.5) to athletes. The purpose of this study was to assess the inter-rater reliability of this classification system. SETTING: National competition for wheelchair rugby and wheelchair basketball in the Netherlands and Belgium. METHODS: Three experienced wheelchair rugby classifiers independently assigned trunk scores to wheelchair rugby and wheelchair basketball athletes in two sessions. After each session, test descriptions were adjusted. The inter-rater reliability was evaluated by determining the agreement and Fleiss Kappa. RESULTS: In the first session, all classifiers agreed on the trunk score in 13 out of 16 athletes; the overall Kappa was 0.76 (P<0.001). The Kappa per trunk score ranged from 0.29 to 1. Four test descriptions were adjusted after the first session. In the second session, there was an agreement in trunk score between the classifiers in 15 out of 21 athletes. The overall Kappa was 0.75 (P<0.0001), and the Kappa per trunk scores ranged from 0.58 to 0.92. After the second session, two test descriptions were improved. CONCLUSION: The revised classification system for trunk impairment in wheelchair rugby showed a adequate inter-rater reliability for the allocation of trunk scores.

Classification of forefoot pain based on plantar pressure measurements.

BACKGROUND: Plantar pressure is widely used to evaluate foot complaints. However, most plantar pressure studies focus on the symptomatic foot with foot deformities. The purposes of this study were to investigate subjects without clear foot deformities and to identify differences in plantar pressure pattern between subjects with and without forefoot pain. The second aim was to discriminate between subjects with and without forefoot pain based on plantar pressure measurements using neural networks. METHODS: In total, 297 subjects without foot deformities of whom almost 50% had forefoot pain walked barefoot over a pressure plate. Foot complaints and subject characteristics were assessed with a questionnaire and a clinical evaluation. Plantar pressure was analyzed using a recently developed method, which produced pressure images of the time integral, peak pressure, mean pressure, time of activation and deactivation, and total contact time per pixel. After pre-processing the pressure images with principal component analysis, a forward selection procedure with neural networks was used to classify forefoot pain. FINDINGS: The pressure-time integral and mean pressure were significantly larger under the metatarsals II and III for subjects with forefoot pain. A neural network with 14 input parameters correctly classified forefoot pain in 70.4% of the test feet. INTERPRETATION: The differences in plantar pressure parameters between subjects with and without forefoot pain were small. The reasonable performance of forefoot pain classification by neural networks suggests that forefoot pain is related more to the distribution of the pressure under the foot than to the absolute values of the pressure at fixed locations.

Multi-channel NIRS of the primary motor cortex to discriminate hand from foot activity.

The poor spatial resolution of near-infrared spectroscopy (NIRS) makes it difficult to distinguish two closely located cortical areas from each other. Here, a combination of multi-channel NIRS and a centre of gravity (CoG) approach (widely accepted in the field of transcranial magnetic stimulation; TMS) was used to discriminate between closely located cortical areas activated during hand and foot movements. Similarly, the possibility of separating the more anteriorly represented discrete movements from rhythmic movements was studied. Thirteen healthy right-handed subjects performed rhythmic or discrete ('task') hand or foot ('extremity') tapping. Hemodynamic responses were measured using an 8-channel NIRS setup. For oxyhemoglobin (OHb) and deoxyhemoglobin (HHb), a CoG was determined for each condition using the mean hemodynamic responses and the coordinates of the channels. Significant hemodynamic responses were found for hand and foot movements. Based on the HHb responses, the NIRS-CoG of hand movements was located 0.6 cm more laterally compared to the NIRS-CoG of foot movements. For OHb responses no difference in NIRS-CoG was found for 'extremity' nor for 'task'. This is the first NIRS study showing hemodynamic responses for isolated foot movements. Furthermore, HHb responses have the potential to be used in multi-channel NIRS experiments requiring differential activation of motor cortex areas linked to either hand or foot movements.

TMS: a navigator for NIRS of the primary motor cortex?

Near-infrared spectroscopy (NIRS) is a non-invasive optical imaging technique, which is increasingly used to measure hemodynamic responses in the motor cortex. The location at which the NIRS optodes are placed on the skull is a major factor in measuring the hemodynamic responses optimally. In this study, the validity of using transcranial magnetic stimulation (TMS) in combination with a 3D motion analysis system to relocate the TMS derived position was tested. In addition, the main goal was to quantify the advantage of using TMS to locate the optimal position in relation to the most commonly used EEG C3 position. Markers were placed on the TMS coil and on the head of the subject. In eleven subjects, a TMS measurement was performed to determine the individual motor-evoked potential center-of-gravity (MEP-CoG). This procedure was repeated in nine subjects to test the validity. Subsequently, hemodynamic responses were measured at the MEP-CoG position and at the C3 position during a thumb abduction and adduction task. On average, the MEP-CoG location was located 19.2mm away from the C3 position. The reproducibility study on the MEP-CoG relocation procedure revealed no systematic relocations. No differences in early and delayed hemodynamic responses were found between the C3 and MEP-CoG position. These results indicate that using TMS for NIRS optodes positioning on the motor cortex does not result in higher hemodynamic response amplitudes. This could be explained if NIRS and TMS assess slightly different functions.

Linear dependence of peak, mean, and pressure-time integral values in plantar pressure images.

Dynamic plantar pressure images are routinely used in clinical gait assessment, and peak pressure, mean pressure, and pressure-time integral are the most frequently used parameters to summarize these images. Many studies report only one parameter, but other studies report all three. The interdependency of these variables has not been explicitly studied previously. The purpose of this study was to describe the linear relation between these three pressure parameters. 327 subjects walked normally over a pressure plate. Peak pressure, mean pressure and pressure-time integral were calculated for 10 different anatomical areas and, after applying a previously described spatial normalization procedure, these variables were also calculated for each pixel. Mean pressure was highly correlated with peak pressure (r=0.90+/-0.09) and pressure-time integral (r=0.81+/-0.13) for pixels. Peak pressure and pressure-time integral showed a linear correlation coefficient of r=0.78+/-0.21. The pressure parameters of the forefoot pixels were more highly correlated than the heel pixels. The current results have two major implications: (1) plantar pressure parameters (peak, mean, and impulse) can be reasonably compared across studies, even across parameters, and (2) the variables most commonly used to characterize plantar pressures are highly inter-correlated, implying that a smaller set of parameters may more efficiently capture the biomechanical behavior of interest.

Ligament releases do not lead to increased postoperative varus-valgus laxity in flexion and extension: a prospective clinical study in 49 TKR patients.

This prospective study investigated whether ligament releases necessary during total knee replacement (TKR) led to a higher varus-valgus laxity during intraoperative examination after implantation of the prosthesis and after 6 months. The laxity values of TKR patients were also compared to healthy controls. Varus-valgus laxity was assessed intra- and postoperatively in extension and 70 degrees flexion in 49 patients undergoing TKR, implanted using a balanced gap technique. Knees were catalogued according to ligament releases performed during surgery. Postoperative varus-valgus laxity and laxity after 6 months had not increased following release of the posteromedial capsule, iliotibial tract, and the superficial medial collateral ligament. The obtained postoperative laxity compares well with a healthy equally aged control group. It can be concluded that the balanced gap technique results in stable knees and that releases can safely be performed to achieve neutral leg alignment without causing postoperative laxity.

A new method to normalize plantar pressure measurements for foot size and foot progression angle.

Plantar pressure measurement provides important information about the structure and function of the foot and is a helpful tool to evaluate patients with foot complaints. In general, average and maximum plantar pressure of 6-11 areas under the foot are used to compare groups of subjects. However, masking the foot means a loss of important information about the plantar pressure distribution pattern. Therefore, the purpose of this study was to develop and test a simple method that normalizes the plantar pressure pattern for foot size, foot progression angle, and total plantar pressure. Moreover, scaling the plantar pressure to a standard foot opens the door for more sophisticated analysis techniques such as pattern recognition and machine learning. Twelve subjects walked at preferred and half of the preferred walking speed over a pressure plate. To test the method, subjects walked in a straight line and in an approaching angle of approximately 40 degrees . To calculate the normalized foot, the plantar pressure pattern was rotated over the foot progression angle and normalized for foot size. After normalization, the mean shortest distance between the contour lines of straight walking and walking at an angle had a mean of 0.22 cm (SD: 0.06 cm) for the forefoot and 0.14 cm (SD: 0.06 cm) for the heel. In addition, the contour lines of normalized feet for the various subjects were almost identical. The proposed method appeared to be successful in aligning plantar pressure of various feet without losing information.