Sarah T. Ridge

Automated event detection algorithms in pathological gait

Accurate automated event detection is important in increasing the efficiency and utility of instrumented gait analysis. Published automated event detection algorithms, however, have had limited testing on pathological populations, particularly those where force measurements are not available or reliable. In this study we first postulated robust definitions of gait events that were subsequently used to compare kinematic based event detection algorithms across difficult pathologies. We hypothesized that algorithm accuracy would vary by gait pattern, and that accurate event detection could be accomplished by first visually classifying the gait pattern, and subsequently choosing the most appropriate algorithm. Nine published kinematic event detection algorithms were applied to an existing instrumented pediatric gait database (primarily cerebral palsy pathologies), that were categorized into 4 visually distinct gait patterns. More than 750 total events were manually rated and these events were used as a gold standard for comparison to each algorithm. Results suggested that for foot strike events, algorithm choice was dependent on whether the foots motion in terminal swing was more horizontal or vertical. For horizontal foot motion in swing, algorithms that used horizontal position, resultant sagittal plane velocity, or horizontal acceleration signals were most robust; while for vertical foot motion, resultant sagittal velocity or vertical acceleration excelled. For toe off events, horizontal position or resultant sagittal plane velocity performed the best across all groups. We also tuned the resultant sagittal plane velocity signal to walking speed to create an algorithm that can be used for all groups and in real time.

Ambulation speed and corresponding mechanics are associated with changes in serum cartilage oligomeric matrix protein.

Because serum cartilage oligomeric matrix protein (COMP) has been used to reflect articular cartilage condition, we aimed to identify walking and running mechanics that are associated with changes in serum COMP. Eighteen subjects (9 male, 9 female; age=23 ± 2 yrs.; mass=68.3 ± 9.6 kg; height=1.70 ± 0.08 m) completed 4000 steps on an instrumented treadmill on three separate days. Each day corresponded to a different ambulation speed: slow (preferred walking speed), medium (+50% of slow), and fast (+100% of slow). Synchronized ground reaction force and video data were collected to evaluate walking mechanics. Blood samples were collected pre-, post-, 30-minute post-, and 60-minute post-ambulation to determine serum COMP concentration at these times. Serum COMP increased 29%, 18%, and 5% immediately post ambulation for the fast, medium, and slow sessions (p<0.01). When the speeds were pooled, peak ankle inversion, knee extension, knee abduction, hip flexion, hip extension, and hip abduction moment, and knee flexion angle at impact explained 61.4% of total variance in COMP concentration change (p<0.001). These results indicate that (1) certain joint mechanics are associated with acute change in serum COMP due to ambulation, and (2) increased ambulation speed increases serum COMP concentration.

Kinematic and kinetic analysis of planned and unplanned gait termination in children

Gait termination is a task which requires people to alter momentum and stabilize the body. To date, many of the kinematic and kinetic characteristics of gait termination have not been reported, making it difficult for clinicians to design interventions to improve the ability to terminate gait quickly and efficiently. Therefore, the purpose of this study was to describe the lower body mechanics of healthy children as they performed walking trials, planned stopping trials, and unplanned stopping trials. Kinematic and kinetic data were collected from 15 healthy children between the ages of 11 and 17 years (14.3±2.1 years). The timing and magnitude of peak sagittal plane joint angles and moments were compared across the three conditions for the leg that led the stop step. Most differences were found when comparing unplanned stopping to both walking and planned stopping. During unplanned stopping, most subjects used either a hip/knee extension strategy or hip/knee flexion strategy to stabilize and perform the stopping task. The magnitudes of the peak hip extension moment and peak knee flexion angle were significantly greater, while the peak plantarflexion moment was significantly smaller during unplanned stopping than walking and planned stopping. The peak plantarflexion moment occurred significantly earlier during the stop stance phase of planned and unplanned stopping than during walking. This suggests that the ability to create sufficient joint moments in a short period of time is essential to be able to stop quickly and safely. Therefore, possible treatments/interventions should focus on ensuring that patients have appropriate strength, power, and range of motion.

Real-time feedback as a method of monitoring walking velocity during gait analysis

When quantifying the mechanics of gait, it is important to ensure that subjects maintain a consistent walking velocity during gait analysis trials. Most methods of measuring walking velocity do not produce data until after the subject has completed the trial. This often results in discarding completed trials from analysis because the subjects velocity was not within an acceptable range. Real-time feedback of position data can be used to help subjects adjust their walking velocity during the trial, when necessary. Results from 14 subjects who participated in gait analysis using real-time feedback to monitor their walking velocity show that they were able to stay within an acceptable range of their target walking velocities (each subjects preferred velocity and 150% of their preferred velocity) during 90% and 80% of trials, respectively. This method allows for accurate and efficient data collections without the use of additional equipment.

Lateral Extrinsic Foot Muscle Size Best Predicts Time To Stability In Single Leg Landing: 610 Board #3 May 31 1

A single leg, barefoot landing is a functional movement often executed in athletic events. The inability to quickly stabilize the ankle joint during a landing may contribute to injury risk. PURPOSE: To determine whether the size of specific medial and lateral extrinsic foot muscles can be used to predict shorter time to stability in female athletes performing single leg, barefoot landings. METHODS: Twenty-one female collegiate gymnasts and cheerleaders (age: 21.2 ± 1.4 years; height: 1.6 ± 0.06 m; weight: 58.1 ± 5.7 kg) completed a dominant single leg, barefoot landing onto a force plate from a height of 28 cm. The time to stability was calculated from the recorded medial to lateral force after landing. The size of the tibialis anterior (TA), tibialis posterior (TP), flexor digitorum longus (FDL), fibularis brevis (FB), and fibularis longus (FL) were measured using ultrasound imaging (12L probe, GE Logiq P6). The TA, TP, and FL were assessed at a distance of 30% from the knee joint-line to the tip of the lateral malleolus. FDL was measured at a distance of 50% from the knee joint-line to the medial malleolus while FB was measured at a distance of 50% from the knee joint-line to the lateral malleolus. Muscle sizes (thickness for the TA and TP and cross sectional area for FDL, FB, and FL) were measured from the ultrasound images (p≥0.05). RESULTS: A stepwise regression (including height, weight, and muscle size(s)) indicated that the two best predictors of time to stability were the FB and FL (r 2 =0.45, FB p=0.002, FL p=0.083; cross-sectional areas: FB=3.4 ± 1.2 cm 2 , FL=4.8 ± 1.1 cm 2 ). CONCLUSION: It appears athletes with larger FB and FL had shorter time to stability. These results suggest strengthening of the lateral extrinsic muscles may be a key component in both the prevention and rehabilitation of ankle injuries among gymnasts and other barefoot athletes.

Instrumented figure skating blade for measuring on-ice skating forces

Competitive figure?skaters experience substantial, repeated impact loading during jumps and landings. Although these loads, which are thought to be as high as six times body weight, can lead to overuse injuries, it is not currently possible to measure these forces on-ice. Consequently, efforts to improve safety for skaters are significantly limited. Here we present the development of an instrumented figure?skating blade for measuring forces on-ice. The measurement system consists of strain gauges attached to the blade, Wheatstone bridge circuit boards, and a data acquisition device. The system is capable of measuring forces in the vertical and horizontal directions (inferior?superior and anterior?posterior directions, respectively) in each stanchion with a sampling rate of at least 1000?Hz and a resolution of approximately one-tenth of body weight. The entire system weighs 142?g and fits in the space under the boot. Calibration between applied and measured force showed excellent agreement (R?>?0.99), and a preliminary validation against a force plate showed good predictive ability overall (R???0.81 in vertical direction). The system overestimated the magnitude of the first and second impact peaks but detected their timing with high accuracy compared to the force plate.