Non-invasive postural assessment of the spine in the sagittal plane: a systematic review

Juliana Adami Sedrez^1,*; Cláudia Tarragô Candotti¹; Tássia Silveira Furlanetto¹; Jefferson Fagundes Loss¹

¹ Federal University of Rio Grande do Sul, Porto Alegre, Brasil.

ABSTRACT

Keywords: evaluation; posture; methods; reproducibility of results; validity of tests

INTRODUCTION

The sagittal plain of the spine, in physiological conditions, is composed of a succession of opposed harmonious curves: lumbar lordosis, thoracic kyphosis, cervical lordosis. In several studies, the increase in thoracic curvature has been associated with back pain (Ensrud, Black, Harris, Ettinger, & Cummings, 1997), increased risk of fracture (Huang, Barrett-Connor, Greendale, & Kado, 2006) and falls (Kado, Huang, Nguyen, Barrett-Connor, & Greendale, 2007), as well as provoking reduction in quality of life (Imagama et al., 2011) and increased mortality (Kado et al., 2009). The reduction of lumbar lordosis also has been associated with the presence of back pain (Chaléat-Valayer et al., 2011), an increased risk of falls (Ishikawa, Miyakoshi, Kasukawa, Hongo, & Shimada, 2013), and reduced quality of life (Imagama et al., 2011).

Therefore, assessment of spinal curvature is an important factor in both the clinical and research environments. Clinically such an assessment can be used to select the appropriate treatment, since therapies are prescribed based on the degree of curvature and/or its progression. In the research environment, assessing spinal curvatures is essential to ensure that the results of treatments in intervention studies can be adequately reported.

Hence, there has been a growing interest in non-invasive quantitative methods of evaluating the spine in the sagittal plane, since anatomical and biomechanical assessment of the vertebral column frequently requires quantitative data. Such non-invasive methods provide several advantages such as low cost, reduced technical complexity and absence of side effects. Moreover, the ideal instrument must be effective, precise, small in size, easy to use and affordable (D’Osualdo, Schierano, & Iannis, 1997). Recently, a systematic review of instruments for the evaluation thoracic kyphosis was published (Barrett, McCreesh, & Lewis, 2014), however, that study did not include all the instruments capable of evaluating thoracic curvature nor those for the evaluation of lumbar lordosis.

Therefore, the aim of this systematic review was to verify the scientific evidence regarding the validation of different non-invasive methods of evaluating the spine in the sagittal plane. This will help health professionals when choosing the most suitable instrument for use in different clinical situations or scientific research.

In April 2013, a systematic search was conducted for scientific articles in the following databases: Scopus, Science Direct, Pubmed and Medline. The search terms used  were: “Noninvasive instrument” OR “Non-invasive Monitoring” OR “Measurement” OR “Measurements” OR “Postural Assessment” OR “Postural Evaluation Methods” OR “Non-radiological Measures” AND “Spine Curvatures” OR “Lumbar Curvatures” OR “Thoracic Curvatures” OR “Thoracic Curve” OR “Lordosis Curve” OR “Thoracic Kyphosis” OR “Lumbar Lordosis” OR “Kyphosis” OR “Lordosis” OR “Postural Assessment” AND “Validation” OR “Validity” OR “Repeatability” OR “Reproducibility” OR “Reliability” OR “Accurate” OR “Accuracy”.  To be included in this systematic revision the articles found were required to meet the following inclusion criteria: (a) perform a non-invasive evaluation of the spinal curvatures; (b) perform an evaluation in the sagittal plane of thoracic kyphosis or lumbar lordosis; (c) evaluate some validation aspect; (d) to be written in English and (e) to have been published in the last three decades. All the search, selection, quality evaluation, reading and data extraction procedures were carried out by two independent evaluators. In the case of any divergence of opinion between the evaluators, a third evaluator was invited to analyze the article.

Firstly, the articles were selected based on the titles and abstracts. Those articles considered for inclusion in the review were read in full.  After, only those articles that met all the above-mentioned inclusion criteria were included in this systematic review. Furthermore, the bibliography of each included article was checked with the aim of find any articles not found in the electronic search.

The QUADAS (Quality Assessment of Diagnostic Accuracy Studies) scale was used to evaluate the quality of the articles. This consists of a questionnaire with 14 items which were responded as “yes”, “no” or “unclear”. In the present study, 11 items were applicable to postural evaluation instruments (Whiting et al., 2004). A minimum of three points in the QUADAS scale was used as an exclusion criterion in this systematic review.

Moreover, with the aim of classifying the scientific evidence contained in the articles, the following rule was used based on QUADAS scale: (a) articles with three to five points were classified as presenting “poor evidence”; (b) articles with six to eight points were classified as presenting “moderate evidence”; and (c) articles with nine to eleven points were classified as presenting “strong evidence”.

Given the variation in the terminology used in the studies, to facilitate comparison of their results, in this systematic review the terminology was standardized as follows: repeatability refers to the degree of agreement obtained between successive evaluations conducted by the same evaluator (short period of time); intra-evaluator reproducibility refers to the degree of agreement obtained between evaluations conducted by the same evaluator at different times (minimum interval - one day); inter-evaluator reproducibility refers to the degree of agreement obtained between evaluations conducted by different evaluators; and validity refers to the agreement between the measurements obtained using the instrument being tested and those obtained using the gold standard instrument (Joint Committee for Guides in Metrology, 2012).

RESULTS

Initially, 597 articles were found in a database search, of which 57 were included. When analyzing the bibliographical references in the selected articles, a further 19 articles were obtained, given a total of 76 articles that met the inclusion criteria of this systematic review (Figure 1).

The pre-selected articles were evaluated regarding their methodological quality using the QUADAS scale (Table 1). Of the 76 evaluated articles, 18 were excluded because they did not obtain the stipulated minimum of three points on the scale, thus 58 articles were finally included in this systematic review. Regarding the quality of the scientific evidence in the articles, 29 presented poor scientific evidence, 17 moderate evidence and 12 strong evidence.

DISCUSSION

The aim of this systematic review was to examine the scientific evidence related to the validation of alternative methods of non-invasive evaluation of the spine in the sagittal plane. Of the 58 articles included, only 12 were found to present strong scientific evidence according to the QUADAS scale, indicating the poor quality of the methodology applied in the reviewed validation articles. Given this situation, when conducting validation studies, it is necessary to pay attention to the criteria that determine their quality. Therefore it is important to evaluate both, the reproducibility and concurrent validity, thus avoiding any restriction to the applicability of the instrument for diagnostic use. This systematic review identified 22 different evaluation systems, which were categorized and analyzed below: (1) flexible ruler, (2) photogrammetry, (3) inclinometer, (4) spinal mouse, (5) goniometer and eletrogoniometer, (6) Debrunner’s Kyphometer, (7) surface topography, (8) archometer and (9) other instruments with only one validation study each.

The flexible ruler was the most frequently described instrument, having been tested in 16 studies, four of which evaluated the thoracic region, eight the lumbar region and four both regions. Based on the results (Table 2), the flexible ruler can be seen to be more reproducible and repeatable when used to evaluate the thoracic region by means of the angle (Greendale, Nili, Huang, Seeger, & Karlamangla, 2011; Lundon, Li, & Bibershtein, 1998; Oliveira et al., 2012; Teixeira & Carvalho, 2007) or the kyphosis index (Arnold, Beatty, Harrison, & Olszynski, 2000; Greendale et al., 2011; Macintyre, Bennett, Bonnyman, & Stratford, 2011; Perry, Smith, Straker, Coleman, & O'sullivan, 2008). On the other hand, the same instrument presented lower levels of reproducibility and repeatability for the variables thoracic ‘length’ and ‘width’  (Saad, Colombo, Ribeiro, & João, 2012). Regarding validity, the studies present moderate correlation with the radiological exams for the variable ‘angle’ (Greendale et al., 2011; Oliveira et al., 2012; Teixeira & Carvalho, 2007) and kyphosis index (Greendale et al., 2011). There are no results referring to the concurrent validity for the variables thoracic ‘length’ and ‘width’.

The flexible ruler presented greater variability when used to evaluate the lumbar region, displaying excellent intra-evaluator reproducibility and repeatability in the evaluation of the angle of this region in most of the studies (Hart & Rose, 1986; Lovell, Rothstein, & Personius, 1989; Oliveira et al., 2012; Seidi, Rajabi, Ebrahimi, & Moussavi, 2009; Walker, Rothstein, Finucane, & Lamb, 1987), while there is disagreement in the literature regarding its inter-evaluator reproducibility (Letafatkar, Amirsasan, Abdolvahabi, & Hadadnezhad, 2011; Lovell et al., 1989; Oliveira et al., 2012; Seidi et al., 2009). In relation to the lordosis index, studies were only found to examine the inter-evaluator reproducibility, the results of which were moderate (Hinman, 2004; Macintyre et al., 2011). The validity of the flexible ruler presented a correlation varying from moderate to excellent (Letafatkar et al., 2011; Oliveira et al., 2012; Souza et al., 2009). Therefore, it is suggested that when using the flexible ruler to evaluate both thoracic kyphosis and lumbar lordosis, the angle calculation or index methodology should be used.

Another technique widely used in studies is photogrammetry, which was tested in eight studies, two in the thoracic region, one in the lumbar region and five in both regions. Regarding photogrammetry, it should be pointed out that data collection protocols used in studies tend to be very similar. However, regarding data analysis procedures, each of the methods found used a specific software or digital algorithm. Therefore, each proposed method should be submitted to validation procedures, which explains the large number of articles that validate photogrammetry found in this systematic review. Given this, the health care professional that decides to use any of these software or digital algorithms should ensure that all the steps in the validation procedure have been completed.

The inclinometer was tested in eight studies, one in the thoracic region, three in the lumbar region and four in both regions. When used to evaluate thoracic kyphosis, the studies demonstrated excellent levels of repeatability (Lewis & Valentine, 2010), intra (Czaprowski, Pawlowska, Gebicka, Sitarski, & Kotwicki, 2012; Mellin, 1986) and inter-evaluator reproducibility (Mellin, 1986). However, the concurrent validity of this instrument cannot be affirmed, which limits its use as a diagnostic tool. When used to evaluate lumbar lordosis, the studies demonstrated excellent levels of intra (Czaprowski et al., 2012; Mellin, 1986; Ng, Kippers, Richardson, & Parnianpour, 2001) and inter-evaluator reproducibility (Williams, Haq, & Lee, 2012; Mellin, 1986). Nevertheless, the concurrent validity of this instrument for the evaluation in the lumbar region has only been tested in the flexed position (Adams, Dolan, Marx, & Hutton, 1986) thus further investigations in other positions are necessary to permit its use in clinical practice.

Another instrument, which uses a similar mechanism to the inclinometer, is the Spinal mouse. It has been described in two studies that evaluated both the thoracic and lumbar regions. The Spinal mouse was shown to have excellent levels of intra and inter-evaluator reproducibility, with results referring to evaluations carried out in both adults (Mannion et al., 2004) and children (Kellis, Adamou, Tzilios, & Emmanouilidou, 2008). However, no study was found to demonstrate the concurrent validity of the method and only one study was found for each population, which limits the generalization of the data obtained.

The goniometer was evaluated in two articles, one study evaluated the lumbar region and the other both regions. For the thoracic kyphosis only the concurrent validity, which was found to be excellent, was presented (Gravina, Ferraro, Frizziero, Ferraro, & Masiero, 2012). For the lumbar lordosis excellent inter-evaluator reproducibility was obtained (Burdett, Brown, & Fall, 1986) without presenting adequate validity (Burdett et al., 1986; Gravina et al., 2012). The flexible electrogoniometer was evaluated in four studies, three evaluated the lumbar and one the thoracic region. Among the studies, the validity for the lumbar region presented divergent results (Campbell-Kyureghyan, Jorgensen, Burr, & Marras, 2005; Walsh & Breen, 1995), while the intra-evaluator reproducibility presented excellent levels (Norton, Hensler, & Zou, 2002; Walsh & Breen, 1995). For the thoracic region excellent reproducibility and validity were obtained (Perriman et al., 2010). Notably no studies were found that evaluated all validation aspects of either the goniometer or the electrogoniometer. Thus, their use in clinical situations and scientific research is limited as new studies that evaluate the remaining aspects of validity and in different populations are required.

Four studies were found that assessed surface topography, with excellent concurrent validity reported in the evaluation of kyphosis and lordosis (Fortin, Feldman, Cheriet, & Labelle, 2010; Kovac & Pecina, 1999), as well as excellent reproducibility for both curvatures (Melvin et al., 2010; Schülein, Mendoza, Malzkorn, Harms, & Skwara, 2013). However, these studies cannot be directly compared because they refer to different systems (InSpeck 3D Digitalizer System, Moiré Topography and Jenoptik Formetric). The presented results are not sufficient to test the validity of the system since each one only presents some validations aspects.

The archometer has been described in two studies, one evaluated only the thoracic region and the other both regions. Based on these studies the archometer was found to provide valid and reproducible measurements (Chaise et al., 2011; D’Osualdo et al., 1997). However, the model from Chaise et al. (2011) has the advantage that it can be used to evaluate the lumbar and thoracic region, although all the indices obtained in the evaluation of the lumbar region were lower than those for the thoracic region. Nevertheless, further studies are necessary to evaluate the use of the archometer in the lumbar region in different populations in order to allow its wide scale use.

Each of the other instruments identified in this systematic review (Spinal Wheel, ultra-sound, fastrack video system, VICON, optoelectronic system, BodyGuard Monitor, Spine Epions System, SpineScan, photograph-based visual evaluation, lordosimeter, fiber optics system, kypholordometer and the CODA system) only found to be evaluated in one study.

This systematic review shows that most of the instruments have been submitted to validity tests in only a few or in many cases only one study. In such cases, the validity of the instruments is dependent on the quality of the methodology applied in the study. Moreover, in some studies only the internal validity of the instrument was verified, hence the validity is limited to a specific population with well controlled characteristics. When the same instrument has been evaluated by different studies the external validity is increased, hence, there is greater possibility of using the instrument in various populations.

Furthermore, the important methodological differences found between the studies hamper any attempt to compare the data obtained, as, for example: different gold standards used, different statistical analysis techniques employed and the lack of standardization of terminology, among others. Another important aspect was the methodological quality of the validation studies, as there is a lack of studies in the literature with strong scientific evidence with regard to the validation of non-invasive instruments for evaluating the spine in the sagittal plane.

CONCLUSION

In the literature there is a wide range of non-invasive instruments for evaluating the spine in the sagittal plane, however, of the 58 studies included in this review only 12 presented strong scientific evidence. Moreover, only four instruments were evaluated with regard all the aspects of validity for thoracic kyphosis, namely photogrametry, the flexicurve, the archometer and DeBrunner’s kyphometer. Similarly, for the evaluation of lumbar lordosis, five instruments were evaluated with regard all the aspects of validity, namely photogrametry, the inclinometer, the flexicurve, the archometer and the kypholordometer. Therefore, it is suggested that this instruments are adopted as first choice for conducting evaluation of the spine in the sagittal plane, since they present adequate reproducibility and concurrent validity. While the instruments that present satisfactory results in relation to the aspects of reproducibility can be used in clinical follow-up, it is necessary to note the region the instrument is capable of evaluating and whether it can be used by the same or distinct evaluators. It is particularly important to pay attention to the population for which the instrument was validated, since its use in populations with distinct characteristics may lead to inconsistent results, thus it is suggested that instruments be used only for those populations for which the aspects of validity have been evaluated.

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Manuscript received at January 26^th 2015; Accepted at January 5^th 2016

* Corresponding Author: Escola Superior de Educação Física, Universidade Federal do Rio Grande do Sul, Rua Felizardo, 750, Jardim Botânico, CEP: 90690-200 - Porto Alegre, RS, Brasil. E-mail: julianasedrez@gmail.com