Original researchCervical Spine Assessment Using Passive and Active Mobilization Recorded Through an Optical Motion Capture
Introduction
Musculoskeletal disorders of the cervical spine have a high incidence and prevalence and are considered a public health problem, especially in developed countries.1, 2 Although there have been significant contributions in different fields to access cervical spine injury, such as whiplash associated disorder (WAD), several diagnostic tests that assess cervical-area alterations, “whiplash severity grading systems,” diagnostic imaging tools, and scales such as the Quebec Task Force, seem to be insufficient for predicting possible complications of symptomatology.3, 4
The diagnostic difficulty is because traumatic cervical spine injuries and their associated symptoms are diverse. Variables that have been measured to quantify the degree of dysfunction are isometric muscle strength,5 motion velocity, smoothness,6 and cervical range of motion (ROM).7, 8, 9, 10, 11, 12, 13, 14 Because of the relationship between joint dynamics and the dysfunction location,9, 11 the ROM is often used to quantify severity and treatment.7 This index is also used by the American Medical Association4, 15 to assess physical damage; it also is used in specific legislation in countries, such as Spain (Law 35/2015)16 for the assessment of damage caused by traffic accidents.
One method to evaluate cervical ROM uses voluntary patient movements under the instructions of an evaluator, called active mobilization (AM). This type of mobilization does not require physical interaction between the patient and the evaluator17 and provides relevant functional information.18 However, application of AM as an isolated technique is questioned.17, 18, 19 Because of the influence of the patient’s subjectivity motivated by psychosocial factors,2, 20, 21, 22 different types of errors may be observed, and the AM technique has high variability of results and a low capacity to predict chronic symptoms.7, 8, 18 Likewise, it does not provide clinical information to determine structural function.20, 22
Another method is passive mobilization (PM).11, 23 In this case, an external force is induced by the examiner to move specific body parts up to the joint limits while the participant relaxes the joint that is being explored.18, 24 Passive mobilization allows the examiner to assess the “physiological barrier,” the structural information of the joint under assessment, which is useful in clinical decision making for treatments.25, 26, 27 It is assumed that this range is not influenced by psychosocial factors, as in AM, because the captured ROM mainly depends on action and perception of the examiner during the test.22, 28 Therefore, authors have reported a lower variability in the results in applying PM techniques.10, 18
Most PM techniques use subjective analyses based on the examiner’s perception,17 so is not considered the gold standard.7, 17, 18 Consequently, the challenge associated with PM is to provide studies that analyze its properties and characteristics through objective kinematic measurements, enabling its validation as a diagnostic technique.
To validate methodologies based on PM, it is necessary to apply criteria related to accuracy and reliability.29, 30 The criteria involve some standards satisfying reliability, which require that the measurement must be repeatable and invariant to external factors (ie, the subjectivity of the evaluator, technical-system commitment, and others).
In a systematic review7 of 46 reliability studies and 21 validation studies where PM and AM techniques were applied, 8 PM studies were found, which described the passive technique used.31 There is a problem when explaining the characteristics and properties using PM combined with objective measures. In general, PM reliability has not been analyzed in depth,7, 8, 32 and only a few have used objective measurements for the analysis of PM techniques.12, 17
If AM and PM were combined for assessment, they could possibly provide greater sensitivity and specific diagnostic information in the clinical-care setting. In addition, the problem concerning the subjectivity of both, which is derived from the evaluator in the PM and is derived from the psychosocial factors of the participant in the AM, might be mitigated by their combination.
Motion capture (MoCap) systems provide precision; however, they are not exempt from sources of errors, such as those derived from the marker placement on particular anatomic areas that move with respect to the underlying bones and those due to the conditions of application in a specific area or use conditions in a specific field.33 The evaluator’s ability to perform a correct grip on the patient is a critical aspect in the measurement of the ROM movements during PM, where the reflective markers can be hidden or even moved by the evaluator if he or she is not sufficiently trained. Consequently, the variability of the system depends on the design of the set and its degree of integration, that is, the placement of markers, the checks, the understanding of the movements by the participant, the instructions to the patient, or the training of the evaluator in the use of the system. Therefore, the added value provided by MoCap technologies can be diminished in the clinical setting if the possible sources of error are studied in their practical application, which is the general purpose of this study.
Therefore, the objectives of this study were the following: (1) to develop a cervical ROM assessment protocol based on PM; (2) to check the system reliability using the PM and AM, individually and combined; (3) to perform a comparison of both techniques, PM and AM; and (4) to understand the influence and interactions between tests when applied together.
Section snippets
Instrumentation
Cervical mobility was recorded through a MoCap system composed of the following components: (1) set of 8 OptiTrack cameras (Flex 13, 1.3 PM, 56° field of view, and 120 frames per second) and the OptiTrack Motive 1.9 application (NaturalPoint Inc, 2016), and (2) software motion characterization Move-Human Sensors (University of Zaragoza, Aragon, Spain),34 implemented in Vizard VR Toolkit35 (WorldViz, Santa Barbara, California) virtual reality platform and the intellectual property of the
Results
The results are displayed in graphs in Figure 6 (AM) and Figure 7 (PM), which are generated from the MoCap application. Statistical analysis (Table 2) shows the results of the exploratory analysis and the average for the movements studied in each session. All movements in both types of assessments, PM and AM, fulfilled the normality hypotheses.
Regarding the comparison results between sessions (S1, S2, and S3) by ANOVA, there were no statistically significant differences for the movements
Evaluated Asymptomatic Population
This study is focused on the design of the system and the protocols for cervical spine assessment through ROM measurement. A sample of asymptomatic participants was selected. This was motivated by the specific objectives of this work, where there are factors that influence AM and PM, either alone or in combination. These factors are the technological and operational system, the placement or possible movement of the markers during capture, the clinical protocol of tests, the environment where
Conclusions
The authors present a cervical ROM assessment based on combined PM and AM protocols at different sessions. This model demonstrated high reliability, individually and combined, and no differences were detected between PM and AM ROMs. Because the evaluator, instrumentation, and the patient are factors that could influence outcomes, the authors suggest that they be combined in protocols. These protocols could be used to evaluate the functional and structural capacity of patients and inform
Acknowledgments
The authors wish to thank Dr. J. Manuel Arredondo and Dr. Dolores Ramón from Instituto de Medicina Legal de Aragón for their contributions when defining the study protocols, and Dr. Mar Pardos from INERMAP Instituto de Ergonomia for her support.
Funding Sources and Conflicts of Interest
This project was cofunded by the Government of Aragon, the European Regional Development Fund, and the University of Zaragoza. It also received cofunding from INERMAP Instituto de Ergonomia. The I3A, University Institute of Research of Engineering of Aragon, University of Zaragoza, Zaragoza, Spain provided materials in their Biomechanics Laboratory for this study. No conflicts of interest were reported for this study.
Contributorship Information
Concept development (provided idea for the research): A.J.M., G.U., J.J.M.
Design (planned the methods to generate the results): A.J.M., J.J.M.
Supervision (provided oversight, responsible for organization and implementation, writing of the manuscript): G.U., J.M., J.J.M., M.B.S.-V., A.C.R.
Data collection/processing (responsible for experiments, patient management, organization, or reporting data): A.J.M.
Analysis/interpretation (responsible for statistical analysis, evaluation, and presentation
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