Descriptions of the meaning of symbols used to BS EN ISO 15223-1:2016 - Medical devices - Symbols to be used with medical device labels, labelling labeling and information to be supplied - Part 1: General requirements is at Annex A.
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What is involved in a clinical gait analysis test? That is, how is it performed?
Since 1984, clinical gait analysis using Vicon Motion System products has involved the measurement of the patient's gait pattern with specialized technology. In the interim, technological improvements have enhanced the ease of use, reliability, sensitivity and specificity of the analysis, but the method has remained unchanged. The medical practitioners and health professionals at each clinic document the pertinent medical history and physical presentation, and this collection of manual and captured information provides the basis upon which treatment decisions are made.
How are gait data interpreted?
Depending on the laboratory capabilities, the process of gait data collection, as described above, yields the following:
These parameters are then evaluated to identify abnormalities, using a database of normal, typically developed subjects and knowledge of normal gait biomechanics as baseline. Deviations from normal are always interpreted in the context of their relative impact on gait function. These multiple sources of data provide useful redundancy, allowing corroborating information to be identified and conflicting observations to be understood.
The role of the interdisciplinary team
At major clinical laboratories, gait data are interpreted by a team that consists of the orthopedic surgeon to whom the patient was referred and the clinical scientist, physiotherapist and/or kinesiologist who collected data. At times, the engineer or technician, who assisted in the data collection, or the biomechanical engineer who developed the mathematical models used to process data, is involved, if questions of data quality arise or if some previously unseen walking mechanism is encountered. Most laboratories will use multi-centrecenter, internationally validated conventional gait models for routine clinical analyses . In general, it is important that the team has at least a rudimentary understanding of the gait model used to produce the results, in addition to a well-developed understanding of normal gait. This knowledge base, underpinned by experience gained from the examination of many pre- and post-treatment cases, is essential to produce a proper interpretation and treatment decision. The use of validated models facilitates the exchange of experience through multi-centre center collaborations and exchange using a common methodology at academic conferences.
What additional information is provided through gait analysis that augments observational analysis?
For gait analysis to be a useful tool in clinical decision-making, it must provide information that is not available through more traditional methods of evaluation. Use of clinical gait analysis systems augments visual observations by using:
With this additional information, the clinician can be more confident about identifying gait deviations, determining their potential causes, and appreciating the treatment outcome. This entire process will ultimately lead to new treatment approaches and a reduction in the use of less effective interventions. The following examples are intended to illustrate how gait analysis can benefit the clinician in treatment decision-making.
Which patients can benefit from a clinical gait analysis?
Quantitative clinical gait analysis techniques are appropriate for any adult or child who has a gait problem that requires treatment. Because of the complexity of gait abnormalities in neuromuscular disorders, gait analysis is most commonly performed in this patient population. Gait analysis is appropriate for guiding decision-making on management in such disorders as cerebral palsy, stroke, traumatic brain injury and myelomeningocele, among others. Because of the complexity and expense of the test, gait analysis is primarily used as part of the surgical decision-making process when all conservative treatments have been exhausted and surgical intervention is being considered. However, gait analysis is not limited to this application only. Questions concerning bracing issues and medication efficacy can be addressed using gait analysis techniques. For example, is the brace performance or drug intervention (ie, Botulinum toxin, baclofen) consistent with the prescriptive objectives? Evaluation of the rate of deterioration in progressive disorders that affect gait can also aid in understanding a patient's abilities and directing countermeasures. As described above, another valuable function of gait analysis is assessing the efficacy of surgical intervention. Routine analyses of postoperative functional status provides the clinician with more objective information to evaluate the effects of treatment as well as a basis for determining the next steps in the treatment plan.
A number of factors must be considered when referring a patient for gait analysis. At many centrescenters, the patient must be ambulatory, with or without assistive devices, for at least 10 consecutive steps. The patient must be able to follow simple directions and to behaviourally tolerate the placement of reflective markers and EMG electrodes on the skin. The level of patient cooperation influences testability, given the time required for a typical gait analysis, particularly in cases of severe cognitive impairment. If a patient has orthoses, testing with and without the devices may be required to address clinical questions concerning brace wear. Usually, testing is conducted with the patient using any necessary walking aids. A full gait analysis that includes all the above parameters takes approximately one to two hours.
Perhaps the most important consideration in using clinical gait analysis is the proper formulation of the specific questions to be addressed by the analysis. For example, what is the cause of the tripping/falling and what is the etiology of idiopathic joint pain? Such questions need to be asked to properly direct the application of the technology and the associated interpretation process. Certainly there is a temptation to believe that the technology, specifically, the computer, not only aids in the analysis, but can also direct the analysis. As illustrated throughout this article, the experience and knowledge of the professionals who collect and interpret gait data are essential to clinical gait analysis.
As previously mentioned, a referral for gait analysis is usually made when all methods of conservative treatment have been tried and surgical options are being considered. This typically occurs after the patient has reached an ambulatory plateau and/or when orthopedic concerns necessitate treatment (ie, hip subluxation or severe joint contractures). In patients with cerebral palsy, multi-level surgeries are now performed to address all dysfunction during one surgical intervention. This not only reduces a patient's exposure to anesthesia, but it also reduces the need for frequent hospitalizations and periods of rehabilitation. Gait analysis is invaluable in identifying the multiple areas of impairment that are difficult to understand by observation and clinical assessment alone. For example, when used as a preoperative tool, the child with cerebral palsy may often need only one surgical package of treatment during the growing years.
- Repeatability: The variation observed when the same system measures the same location or parameter repeatedly.
- Reproducibility: The variation observed when different systems measure the same location or parameter repeatedly.
The engineering and physics problem of capturing and tracking 3D points in space has been solved and well understood within Vicon motion capture systems. However, clinical concerns remain over the loose association between the measurements of points on the skin surface and the underlying bone, commonly described as the soft tissue artefact . Challenges also remain in reliably capturing bony landmark axial rotation, in particular, of the thigh .
Due to inaccuracies related to working with biological systems , there are limitations in the way 3D motion data are acquired. Markers attached to the skin move with respect to the underlying bones that they are intended to represent. Soft tissue artefact artifact (STA) arises from movement or deformation of the subcutaneous tissues associated with muscular contractions, skin movement and inertial effects. The extent of STA for any movement depends upon the physical characteristics of individuals, marker locations and the nature of the movement task performed.
Many researchers and gait laboratories have proposed techniques to move away from existing predictive approaches by instead discovering joint centres centers and axes functionally, and fitting the data to an idealized joint model that also incorporates some form of soft tissue artefact artifact compensation. This work continues and, like the earlier innovations, will gain wide acceptance only after it has been validated through close collaborative efforts between clinicians, scientists and engineers in laboratories, academia and industry.
To ensure where possible that spatio-temporal marker measurement artefact artifact is not introduced into the wider problem, Vicon motion capture systems are designed to achieve performance in all variants to always be below the anticipated soft tissue artefactartifact. The performance upper limit is defined within the published Declaration of Conformity and is common for all published CLASS Im product offerings.
Peters et al  undertook a systematic review to critically evaluate the quantification of STA in lower limb human motion analysis. It has a specific focus on assessing the quality of previous studies and comparing quantitative results. A specific search strategy identified 20 published articles or abstracts that fulfilled the selection criteria. The quality of the articles was evaluated using a customized critical appraisal tool. Data extraction tools were used to identify key aspects reported in the articles. Most studies had small sample sizes of mostly young, slim participants. Eleven of the reviewed articles used physically invasive techniques to assess STA. STA was found to reach magnitudes of greater than 30 mm on the thigh segment, and up to 15 mm on the tibia. The range of soft tissue artefact artifact reached greater than 25 mm in some cases when comparing the results of reviewed studies.
Using a minumum of four optical motion cameras, resolution of the distance between the centres centers of two static 14 mm spherical markers located within a volume not less than 4 m x 4 m x 1.5 m to within 1 mm mean; 1 mm Standard Deviation; sample size no less than 1,000.
This equates to one order of magnitude (1 mm3) better than reported skin movement artefact artifact 10 mm3 .
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Outputs from 3rd Party Kinectic and Electromyographic devices is ± 5 V to ± 10 V. Measurement artefact artifact is assessed at 0.2–0.1% error.