AIM: To evaluate the use of photogrammetry and identify the mathematical procedures applied when evaluating spinal posture.

METHODS: A systematic search using keywords was conducted in the PubMed, EMBASE, Scopus, Science and Medicine^® databases. The following inclusion criteria adopted were: (1) the use of photogrammetry as a method to evaluate spinal posture; (2) evaluations of spinal curvature in the sagittal and/or frontal plane; (3) studies published within the last three decades; and (4) written entirely in English. The exclusion criteria were: (1) studies which objective involved the verification of some aspect of validation of instruments; (2) studies published as abstracts and those published in scientific events; and (3) studies using evaluation of the anteriorization of the head to determine the angular positioning of the cervical spine. The articles in this review were included and evaluated for their methodological quality, based on the Downs and Black scale, by two independent reviewers.

RESULTS: Initially, 1758 articles were found, 76 of which were included upon reading the full texts and 29 were included in accordance with the predetermined criteria. In addition, after analyzing the references in those articles, a further six articles were selected, so that 35 articles were included in this review. This systematic review revealed that the photogrammetry has been using in observational studies. Furthermore, it was also found that, although the data collection methodologies are similar across the studies, in relation to aspects of data analysis, the methodologies are very different, especially regarding the mathematical routines employed to support different postural evaluation software.

CONCLUSION: With photogrammetry, the aim of the assessment, whether it is for clinical, research or collective health purposes, must be considered when choosing which protocol to use to evaluate spinal posture.

Photogrammetry is a widely used non-invasive technique for postural evaluation. It is a viable option for healthcare professionals and researchers in the field of posture[1], possibly because it allows a succinct and accurate quantitative evaluation by recording subtle changes in posture in general[2,3]. From the point of view of spinal evaluation, it is capable of providing information in the frontal and sagittal planes[4,5]. Furthermore, the use of photogrammetry undoubtedly contributes to reducing exposure to radiation and thus enables the monitoring of postural treatment. However, the application of this technique in postural evaluation is directly dependent on both the collection procedures and the mathematical methods used to provide measurements and postural diagnoses, and which should provide all the necessary aspects of validation[6,7].

Specifically regarding the application of photogrammetry in spinal evaluation, many studies have performed procedures to validate the technique[4,6,8-11]. Furthermore, in clinical practice, photogrammetry can be useful for evaluating and monitoring changes in spinal treatments by comparing quantitative data on posture[6,12]. Moreover, in scientific studies, its use may be helpful in both transverse and longitudinal observations and in intervention studies.

Although, according to the literature, the use of photogrammetry in spinal evaluation is widespread, its real applicability may be questioned, as it remains unclear how this technique is being used to monitor postural treatment or to map attitudes among populations in observational studies. Furthermore, many studies that have adopted the use of photogrammetry do not explain the methods used to generate the results obtained, thus constituting veritable “black boxes”, which makes it difficult for users both in clinical practice and in scientific research to apply this evaluation method. Hence, the objective of this systematic review was to evaluate the use of photogrammetry and to identify the mathematical procedures involved when it is applied to assess spinal posture.

This study was a systematic review, in which the eligibility criteria were observational studies and randomized and nonrandomized clinical trials that have used photogrammetry as a tool to evaluate the spine in an attempt to understand its importance in the assessment of posture. The systematic review follows methods recommended by the Cochrane Collaboration[13].

A systematic literature search was performed in the PubMed, Embase, Scopus, Science and MEDICINE^® databases in the months of December 2013 and January 2014. The keywords used were found in the Health Sciences Descriptors (DeCS, Descritores em Ciências da Saúde), Medical Subject Headings or Emtree: (“Photogrammetry” OR “Digital Analysis” OR “Digital Photographs” OR “Digital photography”) AND (“Spinal postural evaluation” OR “Spine” OR “Vertebral Column” OR “Column, Vertebral” OR “Columns, Vertebral” OR “Vertebral Columns” OR “Spinal Column” OR “Column, Spinal” OR “Columns, Spinal” OR “Spinal Columns” OR “Vertebra” OR “Vertebrae” OR “Lordosis” OR “Kyphosis” OR “Kyphoses” OR “Scoliosis” OR “Scolioses” OR “Posture” OR “Postures” OR “Spine Curvatures” OR “lumbar curvatures” OR “thoracic curvatures” OR “thoracic curve” OR “lordosis curve” OR “thoracic kyphosis” OR “lumbar lordosis”). The search was limited to articles written entirely in English, because it is the international language.

To constitute this systematic review, the articles identified by the initial search strategy had to meet the following inclusion criteria: (1) use photogrammetry as a method of postural evaluation; (2) evaluate the curvatures of the spine in the sagittal or frontal plane; (3) been published within the last three decades; and (4) been written entirely in English. The exclusion criteria were: (1) studies in which the objective involved verifying some aspect of instrument validation; (2) studies published as abstracts and published in scientific events; and (3) studies that used the evaluation of anteriorization of the head to determine the angular positioning of the cervical spine. These variables are believed to analyze different aspects of body posture and cannot be analyzed together.

All the search procedures, selection, quality assessment, data extraction and the reading of the articles were performed independently and individually by two reviewers. In case of any difference of opinion between the reviewers, a third reviewer was asked to appraise the article.

Initially, the studies were selected by reading the titles and abstracts, and those considered to have the potential to be included in the search were read and analyzed in full. In those cases where the title and the abstract were inconclusive, the full article was obtained and read in order not to risk of leaving out important studies in this review. Complementing this process, the references of each included article were also checked in order to identify items not found in the electronic search.

The studies that met the inclusion criteria were evaluated for their methodological quality using the Downs and Black scale, which consists of a checklist of 26 criteria that are answered “yes”, “no” or “impossible to determine”[14]. This scale was chosen because it is used to evaluate both observational studies and randomized clinical trials (RCTs), while some criteria are designed to assess RCTs exclusively, which were unnecessary in this systematic review. According to the guidelines for the use of the scale[14], the assessment criteria can be chosen based on the study objective, thus in the present study those criteria referring solely to the assessment of RCTs were excluded, and only 12 criteria from the Downs and Black scale were used when assessing methodological aspects.

The Downs and Black scale does not define a minimum score when determining the quality of studies[14]. Therefore, studies were not excluded based on their quality rating and only the total number of criteria rated as “yes” for each article was used. The higher the score for the criteria of article, the better methodological quality[14].

Initially, 1758 articles were found from the keywords used. Of these, 601 were excluded because they were duplicates and 1081 did not meet the inclusion criteria. Thus, 76 studies were initially included in this systematic review. After reading the articles in full, 29 studies were found to meet all the inclusion criteria. Subsequently, their reference lists were analyzed and, based on this analysis, a further that 6 articles were found to meet the inclusion criteria, thus 35 articles were selected for inclusion in this systematic review (Figure 1).

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Figure 1 Flowchart of article selection.

Table 1 presents the assessment of the methodological quality based on Downs and Black scale of the studies selected for review. All 35 items had checklist scores higher or equal to 6. In addition, 9 studies had scores between 7 and 8; 19 studies had scores between 9 and 10; and 6 studies had scores between 11 and 12 (Table 1).

The 35 studies included in this review that use photogrammetry as a tool to evaluate the spine in the sagittal and frontal planes are presented and described (Table 2). The aspects related to the objective, the type of study, the methodology and the results of the studies are also shown.

Of the studies in which photogrammetry is used as a postural assessment tool, only one involves a randomized clinical trial, while the others are observational studies. Regarding study populations, most studies involved adults, followed by children and adolescents, while a few studies involved populations with specific diseases that may affect some aspect of posture was evaluated (Table 2).

The vast majority of studies included in this systematic review are concerned with evaluating the sagittal curvature of the spine, while scoliosis is evaluated in only eight studies. To achieve their objectives, several mathematical routines are used in the postural evaluation software programs to measure the alterations in the spine. Most, whether for the frontal or sagittal plane, used angular and/or linear values to measure the magnitude of the spinal alterations (Table 2).

This systematic review aimed to verify the applicability of photogrammetry and to identify the mathematical procedures involved in the use of this technique to evaluate the posture of the spine. Among the 35 articles included in this study, there is considerable similarity regarding the applicability of photogrammetry within scientific circles. However, there are important differences in the mathematical procedures used to evaluate the spine. Next, the articles included in this review were analyzed by groups, regarding the methodology used to collect and analyze data with photogrammetry: (1) type of study; (2) evaluated population; (3) region of the spine and type of alteration evaluated; and (4) types of mathematical procedures.

Comparing the studies in which photogrammetry is used as a postural evaluation tool, only one study is a randomized clinical trial[25], all the others being observational studies. The reason for not using this tool in “trial” studies of type “trials” is unclear, since photogrammetry is recognized as a valid and reproducible instrument for monitoring treatment progression, both in clinical practice and research[5,6,25,48]. Among the possible explanations for these findings are the lack of free access software for evaluating the spine and/or recent use of digital photographs and analysis software for the use in large intervention studies[1].

Furthermore, the difficulty involved in treating conditions related to spinal posture may also go some way to explain these results, since this body segment is highly influenced by mechanical, social, political and psychological factors[49].

As nearly all the studies presented in this systematic review were cross-sectional, their objectives varied according to the population assessed, making it possible to evaluate some specific characteristics of spinal posture in the groups involved. Moreover, photogrammetry is particularly useful for that purpose because it is capable of recording subtle transformations and so is able to quantify the morphological variables related to posture[2,3]. Some specific populations were evaluated using photogrammetry, such as adults[12,19,20,42,45,47], children and teenagers[3,29,31,35], pregnant women[46] and athletes[44]. In some studies, where the samples consisted of adults, some utensils (e.g., chairs and high-heeled shoes) are used in order to verify any change in the posture of the spine during their use[18,22,32].

Similarly, some studies include patients with various diseases, where the authors believe they have a relationship with spinal posture. There are articles in which the samples comprise patients with asthma[15,26], tetraplegia[37], cerebral palsy[16,36] temporomandibular joint dysfunction[28,40], osteoporosis and osteopenia[30], low back pain[38,43], slow transit constipation[27] and children with mouth breathing[21,24,33,41].

With regard to the region of the spine evaluated, greater difficulty has been documented in evaluating the sagittal plane compared to the frontal plane. This may be explained by the fact that, in the frontal plane, symmetry between the right and left sides and straightness of the spine can be expected[6,12]. By contrast, in the sagittal plane, the spine presents physiological curvatures and changes characterized by an increase or decrease in the magnitude of the curvatures[50], which hinders visual and subjective evaluation. In an attempt to quantify the magnitude of the curvatures, various mathematical procedures have been proposed for evaluating the sagittal curvature of the spine. Possibly for this reason, about 80% of the studies found in this systematic review attempted to evaluate cervical lordosis, thoracic kyphosis and lumbar lordosis, while only eight articles evaluated the existence of scoliosis[16,17,23,29,36,41,44,47].

Nevertheless, in the literature, there is still a need for postural evaluation software that can be used to do more than quantify joint angles and the distances between the segments, which, in addition can, be used to provide a diagnostic classification of changes in the magnitudes of the spine in individuals. To achieve this, normality values of body segments need to be established in the literature. However, regarding the spine, there is some controversy in relation to the reference values for the angles of curvature in the sagittal plane in the ideal alignment[12].

The data collection protocols in the studies using photogrammetry as an evaluation tool tend to be very similar, differing minimally according to the purpose of each evaluation. All the methods are based on basic procedures such as: (1) preliminary preparation of the collection location with standardized location of the camera and the subject; (2) palpation and marking of anatomical reference points; and (3) photographic records of individuals in certain positions[2,8,9,45].

However, concerning the data analysis procedures, various software and digital routines are used for scanning anatomical landmarks. Similarly, the mathematical procedures adopted in software or digital routines are very different[51]. Nevertheless, in most cases, the studies do not provide information on the mathematical procedures adopted in the software or in digital routines that support the evaluation results. Allied to this, in some cases the software is not freely available, which makes it difficult to reproduce the evaluation method in other studies.

Therefore, we emphasize the wide divergence of software and mathematical procedures found in this review. Among the known and validated software packages used repeatedly in the selected articles are ALCimagem^®-2000[12,25,26,28,32,41], Postural Assessment Software (PAS)[15,19,21,22,33], Peak Motus Motion Analysis System[3,31,35], CorelDraw[29,40], AutoCad[16,30] and Image J Software[8,27].

As regards the various mathematical routines embedded in these systems, angular and linear values have been the most widely used to measure alterations of the spine in the frontal and sagittal planes, i.e., to determine the magnitudes of scoliosis and anteroposterior curvatures, respectively. Figure 2 illustrates some of the techniques used to measure the spinal alterations.

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Figure 2 Examples of the techniques used to measure spinal curvature found in the articles composing the present systematic review. A: Linear values for scoliosis evaluation[23]; B: Angular values for scoliosis evaluation[17]; C: Linear values for thoracic and lumbar curvatures[21]; D: Angular values for thoracic curvature[30]. The images used are illustrations prepared for the present study.

The angular values are often used, since the gold standard of postural assessment uses an angular calculation to measure the degree of scoliosis and the magnitude of the sagittal curvature of the spine. In other words, in the X-ray examination of the spine it is possible to calculate the so-called Cobb angle, which is widely used for diagnosis of spinal posture[52].

Some of the selected studies evaluate the angles of scoliosis using photogrammetry in a similar way to the Cobb angle[17,23]. However, while the Cobb angle uses the vertebral bodies for evaluation, photogrammetry calculates the magnitude of the curve through the spinal processes of the vertebrae of interest. For this evaluation, two lines are drawn joining the spinous processes and the angle between these lines gives the angle of curvature[17,23].

The linear values in the frontal plane are established according to the statement that the spine should be a straight line[6]. Hence, methodologies calculate postural alteration by the degree to which marked points, referring to the spinous processes, deviate from the vertical line[23,29,36,47].

In the sagittal plane, angular values are more often used than linear values for evaluating the anteroposterior curvatures of the spine.

Similar to the Cobb angle, photogrammetry is recommended for use in evaluating the spinal curvature based on the calculation of the angle between two points on the spine[30,43,46]. However, it uses the spinous processes as a reference, while radiography uses the vertebral bodies.

Nevertheless, it should be noted that the spinous processes have an angle of inclination in relation to the vertebral body[53] and that this angle may interfere with obtaining the angle of curvature by photogrammetry. Thus, caution is recommended when using a similar method to the gold standard in the mathematical procedures of postural evaluation software, since palpated anatomical landmark and used with reference is totally different.

When the photogrammetric evaluation software resembles the way of measuring the magnitude of the curves, they diverge in relation to vertebral levels used or anatomical landmarks. When distinct marked points are used, the calculation of curvatures will be modified, making it difficult to compare studies. In the studies included in this systematic review, some vertebral levels reported for thoracic kyphosis were between: C7-T12[43], T1-T4-T8[39], T4-T8-T12[39] and T1-T6-T12[20]. For lumbar lordosis they were between T12-L5[43], T12-Anterior superior iliac spine - femur greater trochanter[3,31,35].

Besides the similarity with the calculation of Cobb angle, some recurring angular values were calculated angles for the three curvatures: (1) cervical lordosis: the union of three lines passing through occipital, C4 and C7 until a later vertical line; (2) thoracic kyphosis: The union of three lines passing through C7, T7 and T12 until a posterior-vertical line; and (3) lumbar lordosis: Union of three lines passing through T12, L3 and L5 posterior to a vertical line[12,22,25,26,28]. Among these possibilities for measuring sagittal curvature, routines based on other types of calculations were also found, such as the curvatures of the contour tangent[38,42,45], torso angle[3,16,31,35], and chest angle[37].

According to the theories that use linear values to evaluate the spine in the sagittal plane, alterations in the curvature can be quantified by measuring the distance from the spinous process to a vertical reference line. In rectified curvatures, the distances decrease, while in increased curvatures the distances increase[6].

Despite the wide range of mathematical procedures that can be used to quantitatively evaluate the spine, inserted in photogrammetry, in clinical practice and research, health professionals and students are often faced with a scarcity of tools that allow them to classify an individual’s posture. In other words, the angular or linear results provided by software often lack clinical significance because they are not equivalent to the gold standard. Thus, the benefits, limitations, target audience, and use characteristics of photogrammetry need to be carefully considered when selecting the software and/or mathematical procedure in order to facilitate the correct choice of evaluation methodology for different situations, both in clinical and in scientific research.

The present systematic review shows that photogrammetry can be widely used in the scientific research environment, because it facilitates the collection and analysis of detailed data, thus permitting assessment not only of the spine but also of other body segments in both the sagittal and frontal planes. On the other hand, in the school environment, data collection should prioritize simplified protocols, thus facilitating the assessment of large populations. Moreover, the software and mathematical procedures for the postural analysis should be easily available, as are PAS and ALCimagem^®-2000. In the clinical environment, the choice of photogrammetric data collection and of the assessment protocol will depend on the purpose of the postural evaluation, as well as the health professional’s investigative focus, so that a simplified or more complete assessment protocol can be used.

A wide range of studies was found to use photogrammetry as a tool for non-invasive evaluation of the spine, both for measurement of anteroposterior and lateral alterations. However, most of the selected articles were observational studies, only one being a randomized clinical trial.

Yet, it was also observed that, although the data collection methodologies used are similar across the studies, they are very different concerning aspects of data analysis, especially with regard to the mathematical routines that support the different software packages for postural evaluation. Finally, even though photogrammetry is a viable, valid and reproducible option for the evaluation of the spine, there is still a lack of studies in the literature showing software whose results provide both the magnitude of the curvatures and the diagnostic classification of the posture of the spine, certified with clinical significance.