ReGo gait analyses for functional assessment of lower limbs braces and prostheses in orthopedic aids retail

Addressing the industry’s challenges with reimbursement

Just a teasing title or is there real benefit for the orthopedic aids sector? As a matter of fact, the requirements for documenting supply services are constantly increasing. In order to reduce internal costs and strengthen the position vis-à-vis cost reimbursement, innovative methods are required that can be used as time-savingly as possible while providing valid results.

This article addresses the application of automated gait analyses using sensor insoles for the assessment of the biomechanical function of braces and prostheses at the lower limbs. The main value proposition for the industry is that it enables objective, quantifiable assessments of movement sequences, thus facilitating comparative analyses of different aids or changes over time.

What constitutes normal gait? Perspectives on assessing gait quality

When establishing the objective of achieving a physiologically sound gait cycle for the provision of braces or prostheses to a patient, the question arises: What constitutes a normal gait? Human gait patterns exhibit significant variability, and not every deviation from the norm, as observed in an average healthy individual, necessarily results in discomfort, damage, or is indicative of pathology. The diversity of biomechanical characteristics within a gait pattern is influenced by factors including anatomy, history of injuries, gender, and age.

Furthermore, in the assessment of ‘gait’ within the context of provisioning orthopedic aids, three distinct sources have a stake (Tab-1), which do not necessarily correspond well with each other.

Stakeholder	Assessment
Patient	A patient will subjectively assess the functionality of a brace or prosthesis, and therefore evaluate the ergonomic feel of the aid.
Expert	Assessment by experts usually involves visual analysis and interpretation, often supplemented by video recordings. The assessment is intended to be objective, but is in fact susceptible to the so-called experimenter effect (results vary between observers).
Measurement Technology	Objectivized assessments by measurement technology entail the capturing and evaluation of biomechanical gait parameters using force, plantar pressure, angle and timing sensing solution.

As of the current date (April 2024), the process of documentation by providers of medical aids, including medical supply stores and orthopedic technology specialists, for the reimbursement of orthoses and prostheses by health insurance companies in Germany is not standardized. Consequently, there are no reliable criteria from the three areas of the patient’s perception, expert assessment, and objective gait analysis using measurement technology that urge reimbursement. Often, either an assessment by the specialist alone is used, or a combination of expert expertise and qualitative video recording is employed, both of which result in written documentation. The time expenditures, and thus the costs, for these measures are significant.

ReGo provides the orthopedic retail sector with automated evaluations for standardized gait tests, which can lead to significant cost savings. Staff obtains quantitative results on the function of a brace or prosthesis with minimal time expenditure. This objective database facilitates the creation of documentation and the reasoning for reimbursement with health insurance companies.

Furthermore, the standardization of testing helps achieve patient- and product-wide comparability and consistency in data management, which benefits quality management requirements. Finally, an objective gait report as a communication tool for additional services also contributes to improving individual customer retention. To date, however, ReGo is not capable of generating a reliable single number rating with respect to the function of an orthopedic aid which would allow ad-hoc comparison of different aid types.

Workflow of the gait analysis

ReGo gait analyses are conducted in the framework of gait tests using wireless sensor insoles. The sensors measure plantar pressure distribution, vertical ground reaction forces, and foot movement to determine cycle times, angular positions, stride lengths, and walking speeds. Various different gait tests are available for specific use cases, such as straight walking parcours or treadmills.

To conduct a ReGo gait test, the user needs a pair of sensor insoles and a smartphone or tablet with the ReGo app. The basic steps in conducting gait tests, including evaluation, are shown in Tab-2.

Step	Task
1. Sensor insoles	Insert sensor insoles into the shoes, allow them to warm up and perform a few steps to zero.
2. Test type & settings	Select gait test, make settings for audio instructions and self-reported outcomes.
3. Test execution	Perform gait test either on normal ground or on treadmill, following the visual or screen instructions. Biofeedback functions are available.
4. Report generation	Create individual reports using flexible presets, export and share in PDF format.

If a new customer is to be tested for the first time, a customer profile must be created and a one-time individual calibration carried out (step 1). The actual test procedure (step 3) in the app is designed with clear user guidance so that the gait analysis can be conducted in as short a time as possible. All gait parameters are available as test results immediately after the test is completed. The creation of dedicated gait reports, for example to pass them on to the customer in PDF format or to use as proof for the health insurance company, takes place in a separate step (step 4). Report presets can be saved, allowing the selection of gait parameters to be made only once and applied for all gait test results in the same way.

In preparation for the gait analysis, no additional efforts are required, as the ReGo sensor insoles are completely wireless, eliminating the need for attaching cables, tabs, and a data logger. Since each sensor insole incorporates independent measuring electronics, multiple tests can be conducted simultaneously, provided there are several mobile devices available to carry out the tests. All technical settings, such as the recording rate of the sensor data (also called sample rate) or the requirements for determining the zero value of the sensors, are automatically set depending on the type of test.

Results of the functional gait analysis

The results of a gait analysis are to serve as a basis for assessing knee or ankle braces’ and prostheses’ functional effectiveness. Therefore, the orthopedic aids retail staff shall possess or develop skills to interpret the individual gait parameters. The responsibility for making a diagnosis based on each patient or customer’s context rests with the expert at the orthopedic aids retail shop.

Out of the total 70 gait parameters available in ReGo gait tests, here we present a selection of particularly relevant gait parameters. The examples are based on real patient data gathered by Germany’s top 5 orthopedic aids retail company Stolle GmbH & Co. KG (Hamburg, Germany). The patient had a severe bicycle accident, suffering from multi fractures on the lower limbs. Five months post-op, new ankle braces had to be fitted on both legs as shown in Vid-2.

Gait Line

The gait line is a fundamental outcome of a gait analysis and describes the way a foot rolls over the ground. It is defined by the center of pressure trajectory during the stance phases of a trial. Its relevance originates in the fact that it describes if a foot’s movement is incomplete, or if it shows limitations or compensation patterns.

As shown in Fig-1 and described in Tab-1, there are a number of additional outcome parameters available, which describe the form and extent of a gait line in a numerical way such that progress can be displayed over time. The left-to-right difference is indicated for each parameter as well.

Gait Parameters

Biomechanical Interpretation

Gait Line Length Gait Line Width Forefoot Hindfoot Dominance Medial Lateral Dominance

With both ankle braces, the patient’s gait lines are shortened and develop in the forefoot only. This indicates that the patient primarily walks on the forefoot, lacking the ability to carry out dorsal flexion in the ankle joint. The left foot/leg is more limited than the right foot. When comparing the patient’s gait line to the normal’s gait line (Trial 3), it becomes clear that a physiological foot roll-over-the-ground should start with the heel and end with the forefoot, with little left to right difference.

Initial and Final Contact Points, Gait Line Progression

The ground reaction force curve (vGRF) contains rich information on the dynamics of the walking and is related to the timeline on which certain events, such as force peaks, occur.

Gait Parameter

Biomechanical Interpretation

Initial / Final Ground Contact Points Gait Line Progression

A normal gait shows little variability with regards to the initial and final ground contact points (Trial 3). The gait line progression is evenly distributed with smaller left-to-right differences until the foot reaches the lift-off zone (forefoot/toes), on which it rests longer for pushing off the floor (indicated by little point-to-point distances).The patient’s point distribution shows greater variability. The left leg is more consistent in Trial 1, while in Trial 2 the right leg shows better results. This may indicate that the toe-off brace works better for the left leg and the spirale brace works better for the right leg. Both gait line progressions reveal that the foot rests on the metatarsals quite long before slightly moving forward for push-off.

Ground Reaction Force, Plantar Pressure Distribution, Load Distribution

The vertical ground reaction force (vGRF) here presents a kinetic outcome which describes the fierceness of a foot hitting the ground, the dynamics involved and how it develops throughout the stance phases. The plantar pressure distribution (PD), on the other hand, indicates the locations of high or low pressure across the entire plane of the foot. In order to make pressure distribution quantifiable, the load distribution was introduced. It divides the foot area into six zones such that medial-lateral forefoot, midfoot and hindfoot load can be displayed as percentage of the overall load.

Gait Parameter	Biomechanical Interpretation
Ground Reaction Force Mean Pressure Distribution Load Distribution	A normal’s gait vGRF curve shows 2 force peaks, with the 2nd equal or higher than the first (see Trial 3). The patient’s Trial 1 and Trial 2 show a much higher first peak, which indicates that the forefoot (as shown in the PD) hits the ground really hard. The left to right comparison shows an opposite force development in Trial 1 and Trial 2.

As shown in Fig-3 and Tab-5, a patient’s force development and load distribution may vary largely from a normal person’s gait pattern in case of functional limitations or compensation patterns. This refers both to left to right differences and to the shape and distribution of force curves and loads, respectively.

Strike Angle, Lift-Off Angle

The strike and lift-off angles indicate the orientation of the foot against the ground plane when hitting the ground and when taking off from the ground.

Gait Parameter

Biomechanical Interpretation

Strike / Lift-Off Angle

The patient’s strike and lift-off angles in Trial 1 and Trial 2 are consistently larger for the right leg compared to the left leg, which indicates uneven range of motion which cannot be compensated by the ankle braces. Generally, braces used in Trial 2 seem to work better as strike angle can be improved by 95.2% while lift-off angle decreased by only 7.9%.At large, the patient’s strike and lift-off angles are way smaller compared to the normal’s outcomes, indicating a severe limitation in the range of motion.

As shown in Fig-4 and Tab-6, spatio-temporal gait parameters are important outcomes for evaluating the foot’s movement and orientation in space. They complement the force and pressure based parameters (kinetics). We suggest that the combination of both outcome entities offers a more complete understanding of gait biomechanics, thus potentially revealing functional insights which may not be detected if only spatio-temporal (inertial sensor or video based) or kinetic (in-shoe pressure sensors or force plates).

The complete parameter lists for the respective tests can be requested on the ReGo website.

Data quality aspects

The standards for data quality in movement and load analyses for use in orthopedic technology is high, as these analyses underpin decisions made by professionals in providing patients with assistive devices. Consequently, a high standard of data quality is required with respect to the measurement method used: The accuracy of measurements (validity) and the comparability of results in repeat measurements (retest reliability) must meet these demands.

Measurement systems with outstanding levels of data quality, however, such as the complex expert systems used in scientific laboratories, are impractical in a retail store setup due to the limited time budget per patient. Often, just setting up these systems requires 15-20 minutes.

In contrast, the ReGo measurement system for commercial gait analysis presented here can be used almost anywhere in a very time-efficient manner and at the same time offers a number of advantages in terms of ensuring high data quality.

Quality Feature	User Benefit
200 Hz sampling rate	High measurement frequency for all tests ensures sufficient number of data points in each gait phase, avoiding bias by cut-off.
Automatic zero-point tracking	The continuous zeroing of the pressure sensors during gait analysis allows compensation of effects caused by temperature fluctuations and wearout.
Multi-point calibration	Individual multi-point calibration takes anatomical influences and specific motion patterns into account and allows highest force accuracy (<5% error compared to force plate).
Self-check sensor function	Continuous self-checks of the sensors for proper function and prevention of tests if errors occur.

In independent scientific studies conducted by Rush Medical College (Chicago, USA), important gait metrics of the Moticon ReGo system were validated with excellent outcomes (1, 2).

For practical application in orthopedic technology, it is furthermore crucial that repeated gait analyses are performed under identical conditions to foster comparability of results. ReGo ensures this by embedding the data collection into standardized gait tests with a fixed execution procedure. Algorithms for automatic movement detection are used to identify steps and eliminate outliers, such as too few steps within a test or curved paths instead of straight walking distances. This standardization helps maintain high data quality and reliability as for each type of movement and execution variant, a separate ReGo test is available.

Product features for seamless operation in a retail store

For seamless operation in orthopedic technology stores, the preparation and setup of the measurement system, the data collection process, the data post-processing, and data maintenance play a crucial role. ReGo offers the product features for cost-effective deployment of gait analyses as shown in Tab-8.

Productivity Feature	User Benefit
Automated test results	Computation of test results is completely automated and results are available within seconds.
Presets for gait report	Standardized gait reports can be created with just a few clicks using presets.
Wireless sensor insoles	The sensor insoles are completely wireless, fit into almost any shoe, and are ready to use without setup efforts.
Intuitive in-app guidance	The gait test is supported by visual user guidance and audio prompts, making the process intuitive for both the operator and the customer.
Test wise data acquisition settings	Technical settings for gait analyses are automatically adjusted, thus preventing wrong settings by mistake.
Fast user setup	New customer profiles can be created using only a name or patient ID and do not require full scope registration (Unverified Client).
Data labeling	Labels for marking test results, such as for types of prostheses or the purpose of the gait analysis, can be used to tag data for filtering and reports.

Literature

1. Leora A. Cramer, et al. Validity and Reliability of the Insole3 Instrumented Shoe Insole for Ground Reaction Force Measurement during Walking and Running. Sensors 2022.

2. Abhiroop Ganguly, et al. Accuracy of the fully integrated Insole3’s estimates of spatiotemporal parameters during walking. Medical Engineering & Physics 2023.