Measurement of wound area for early analysis of the scar predictive factor*

Objective: to evaluate the use of the 2D-FlexRuler as a facilitating tool for the early calculation of the predictive scar factor of chronic wounds. Method: a descriptive study with a quantitative, experimental, longitudinal and prospective approach. The sample consisted of 22 outpatients. 32 chronic wounds were analyzed. The wound edges were identified and drawn on the 2D-FlexRuler. The calculations of the areas of chronic wounds were obtained by manual, traditional methods, by software and Matlab algorithm. These areas were compared with each other to determine the efficiency of the proposed ruler in relation to traditional methods. Results: the calculation of the wound area by the traditional method and Kundin’s coefficient show average errors greater than 40%. The manual estimation of the area with the 2D-FlexRuler is more accurate in relation to traditional measurement methods, which were considered quantitatively disqualified. When compared with the reference method, for example, the Klonk software, the data obtained by 2D-FlexRuler resulted in an error of less than 1.0%. Conclusion: the 2D-FlexRuler is a reliable metric platform for obtaining the anatomical limits of chronic wounds. It facilitated the calculation of the wound area under monitoring and allowed to obtain the scar predictive factor of chronic wounds with precocity in two weeks.


Introduction
Wounds may be classified into acute and chronic (1) .
Acute wounds are those that have a controlled inflammatory response, responding predictably to the recommended treatment. They heal without complications, usually in three weeks from the beginning (2) .
Chronic wounds are defined as those that failed to progress in the ordered and overlapping phases of healing, which are 1) hemostasis and inflammation, 2) proliferation and 3) maturation and remodeling. They remain stationary in the inflammatory phase, despite proper wound management (2)(3)(4) .
In this case, the healing process does not occur in the expected period and in an orderly manner to restore the anatomical and functional integrity of the injured tissues (2)(3)5) . After the initial tissue damage, several factors may contribute to the delay in the healing process, either due to the severity of the injury or to the patient's poor state of health (6) . Among the factors related to scar deficit are those considered systemic, such as aging, malnutrition, diabetes, chronic diseases, peripheral vascular disease, sickle cell anemia, vasculitis, use of medications such as corticosteroids (6) . Local factors include ischemia, edema and wound infection (3) .
There is no pre-established consensus for chronicity, but wounds that do not show a reduction in dimensions after 2 to 4 weeks are likely to become chronic (2) .
The main groups of chronic wounds of non-surgical origin are vascular ulcers of the lower limbs, neuropathic ulcers, such as those found in diabetics and pressure injuries (3,5,7) . Surgical wounds can be considered acute when healing happens by first intention and can become complex and chronic when they present complications such as dehiscence and infection, requiring healing by second intention (4,7) .
The scar deficit of chronic, surgical and non-surgical wounds is related to the maintenance of prolonged inflammatory activity (8)(9) resulting from the abundant infiltration of neutrophils, the presence of high levels of pro-inflammatory cytokines, reactive oxygen species and metalloproteinases (3) . This may happen due to a local infectious process, which has an incidence greater than 53% (10) in chronic wounds, as well as by bacterial biofilm (11) present between 60% to 90% of cases of chronic wounds (8)(9)(11)(12) .
Biofilms are complex consortia (8) of mixed microbiological ecosystems, formed by populations developed from one or more bacterial species mainly, but also by fungi, viruses and protozoa (12) . This microbiota forms an extracellular threedimensional polymeric substance that may cover the surface of wounds, compromising healing (11)(12) and helping to understand the recalcitrant behavior of chronic wounds (9) especially in diabetic, elderly and immobilized patients (12) .
About 234 million surgeries are performed worldwide each year. A retrospective study based on data from the US Wound Registry, indicated that 20.8% of all types of wounds are represented by surgical wounds that did not heal, with an average cost of treatment for wound healing of US$ 3,927 (7) . This is an example of how the cost of treating surgical wounds with scar deficits can increase, due to the complexity and longer time of outpatient follow-up (7) .
Often disguised as a comorbid condition, the chronic wound represents a vicious cycle and a silent epidemic that affects a large fraction of the world population (5) . It imposes a significant and often underestimated burden on the individual, the health system and society as a whole (3,5) due to the significant cost of medical assistance and duration of treatment (1,13) .
Chronic wounds have a significant impact on the health and quality of life of patients (1) and their families. They cause pain, loss of function and mobility, depression, anguish and anxiety, embarrassment and social isolation, financial charges, prolonged hospitalizations, chronic morbidity and death (5) .
The assessment and documentation of wounds need to be reliable so that health professionals can make a better diagnosis (14) , effectively quantify the benefits and results of the therapeutic approaches used (6) , identify with greater precocity those who are at risk of non-healing of wounds, which is important for the patient (14) .
The methods for evaluating acute and chronic wounds, surgical or non-surgical, include measuring the area, volume and perimeter (15) . Each of them has strengths and limitations that lead to their varied use in different clinical contexts.
Estimating the wound area by multiplying the largest linear axis, namely, length C by the largest axis perpendicular edge to edge, that is, the greatest width perpendicular L to the wound area, however, is probably the most popular method among health professionals (15)(16) . But this estimate using the smallest rectangular area contained in a wound can overestimate the real value in 40% (16) . In order to minimize the error of this overestimated calculation, the wound area can be determined using an ellipsoidal geometry (16)(17) . This approach assumes the largest www.eerp.usp.br/rlae However, a more accurate way to assess wound healing can be obtained by monitoring the percentage reduction of the area over a given period (16) .
The importance of continuous wound assessment, particularly in the first 2 to 4 weeks of treatment, has been highlighted by several studies (6,14,16,18) that demonstrate a correlation between the percentage of reduction in the wound surface area and progress of treatment (14)(15)(16) . A percentage reduction in the wound area of 10% to 15% per week of treatment predicts healing (19 ). 25% reduction in the wound area within two weeks of treatment (20) or a reduction in the wound area of 20% to 40% within two to four weeks of treatment has proven to be an adequate predictor of healing and a reflection of treatment effectiveness (16) . It is recommended that clinical procedures be reassessed if the wound does not reduce the surface area more than 40% within four weeks (14) .
The percentage rate of reduction in the area of a wound can be used to distinguish between a wound with potential for healing or not (16) and also as an important tool to distinguish between effective and ineffective treatment regimens (6,14,16,18) .
There are several technologies for measuring wounds, both hardware and software (14,18) . From a clinical point of view, these technologies have high costs, hindering their easy access (15) .
These technologies and approaches must take into account that many wounds have irregular borders, requiring the correct identification of the anatomical limits of the wound, recognizing the tissue flexibility of the cavity or deep wound, as well as the natural curvatures of the human body (16) . However, there is a great variability in the literature on how many weeks the wound areas should be calculated (6,(14)(15)(16)(18)(19)(20) in search of the scar predictive factor. Some authors mention that in two weeks of monitoring the area of chronic wounds it is already possible to obtain a predictive factor for healing ( 16,(19)(20) .
The aim of this study was to evaluate the use of the 2D-FlexRuler as a facilitating tool for the early calculation of the scar predictive factor for chronic wounds.

Method
This is a descriptive study with a quantitative, experimental, longitudinal and prospective approach.
Patients with wounds who sought care at the outpatient for wounds and diabetic foot, spontaneously or by referral, were evaluated. The recruitment phase aimed to achieve a minimum of 30 chronic wounds for the research. Wounds with more than 4 weeks of evolution were considered chronic (2) , regardless of nonsurgical or surgical origin.
According to the demand and assessment of each case, patients with chronic wounds who were selected by the researcher were invited to continue the research protocol. They received guidance, read and In total, 32 chronic wounds were identified in a group of 22 diabetic and non-diabetic patients who were eligible for this research, as they met the inclusion criteria. Therefore, there were patients with more than one chronic wound.
Data collection took place from May 2016 to March 2017 and was performed in a clinic for wounds and diabetic foot in Curitiba-Paraná, Brazil, duly adequate to receive patients with wounds.
Among the criteria that were used to suspend or terminate the research were the patient's non-adaptation to the evaluation routines, the need for amputation of the limb affected by the wound and death. None of these situations occurred.
Of the 32 chronic wounds, eight were followed for three consecutive weeks and 24 were followed for two consecutive weeks.
Patient assessments were scheduled regularly from the beginning to the end of the proposed followup period and performed according to the standard procedure provided in the study protocols.
In the measurements of all wounds, a centimeter, flexible, two-dimensional, transparent ruler was used, In Figure 1A, the 2D-FlexRuler is positioned and in contact with the lesion due to abdominal dehiscence. To determine the wound area, an algorithm was implemented using the following basic sequence shown in Figure 2.

Results
The selected patients were 11 men and 11 women, When there was need for debridement to remove devitalized tissues, these were performed before obtaining metrics and photographs. Then, topical agents and topical therapies that contained active principles to control or eliminate biofilm such as PHMB gel, silver and cadexomer iodine were used. There were no complaints by individuals in the study of disabling pain in chronic wounds during the application of the ruler for decaling anatomical limits in the use of topical agents or recommended topical therapies.
The eight wounds that had their anatomical limits recorded for three consecutive weeks, obtaining four readings, were called subset A. The 24 wounds that were followed for two consecutive weeks, obtaining three readings, were called subset B.
The digitalized images of 2D-FlexRuler were manipulated in all three methods aided by computer seeking the estimation of spatial parameters. When three computational methods were compared, no For the same wound in Figure 2, Table 1 illustrates the difference among manual estimation, computer aided techniques, traditional practices and application of the Kundin ellipsoidal coefficient.
The differences are relative to the Klonk value, here considered the standard.

Figure 3 exemplifies six wound areas in subset
A that were normalized, using computer aided area estimation by the three computational methods (21)(22)(23) .
The curves in Figure 3 show the tendency to reduce wound areas after the second reading (between the first and second weeks of monitoring).  The upper curve was an exception and shows the behavior of a wound that, even recovering the lost tissue volume, presents an increasing area due to deep wound tissue flexibility after debridement (16) . The same process occurred in the second curve, but there was a recovery in the tendency to reduce the area between the second and third weeks.

Discussion
For manual estimation, 2D-FlexRuler is much more relevant than traditional measurement methods.
It is flexible, sterilizable and allows the registration of wounds on curved surfaces. The manual estimate summarized in Table 1, when compared with the reference method, i.e., the Klonk software resulted in an error of less than 1.0%.
Although the traditional ruler method (caliper, scalimeter and Kundin's ellipsoidal coefficient) has predictive power for qualitative evaluation of the healing potential, mean errors greater than 40% are found, as shown in Table 2, which weakens the use of this method in quantitative analyzes. This magnitude of error had already been reported in the literature (16) . When using the larger set of 32 wounds, with patients followed for two weeks and three metric values obtained, the relative mean error of the estimated areas was 2.86% for Matlab analyzes, 96.78% for rigid ruler, 141.8 % for Vernier's caliper and 188.58% for the scalimeter, leading to the conclusion that they are qualitatively useful, but quantitatively disqualified.
The limitations of the study in relation to the use of 2D-FlexRuler were found mainly in obtaining the tracing of highly exudative and circumferential wounds of the lower limbs. Specific precautions such as reducing the amount of exudate in the wounds to avoid slipping between the wound bed and 2D-FlexRuler sheet "B" when obtaining the wound limits were necessary. The use of a caliper and a scalimeter to measure wounds also brought some technical difficulties, as these instruments are rigid, which made it difficult to obtain data on wounds in regions with anatomical curvature.
The need for continuous monitoring of chronic surgical and non-surgical wounds in diabetics and nondiabetics is reiterated. We encourage the use of the percentage rate of reduction of the wound area obtained in the first two consecutive weeks of treatment as a predictive factor for the healing of chronic wounds, in diabetics and non-diabetics, as described in the literature (16,(19)(20) . Thus, adjustments in the therapy of chronic wounds can be performed with greater precocity www.eerp.usp.br/rlae 8 Rev. Latino-Am. Enfermagem 2020;28:e3299.
in order to obtain better results and a lower rate of complications.
The study demonstrated that the 2D-FlexRuler rule contributes with simplicity, safety, low cost and as a reliable and reproducible documentation for manual wound measurement. The unit value was around US$ 1.0 which can be much lower if scale production is considered. It can be used in children and adults, in outpatients, hospitals, home care services and others.
The data obtained with this ruler can be stored directly in the medical records and can be easily digitized.
Statistical tests on the progression of healing may be more reliable with the metric data obtained with the methodology, stimulating the research that requires The estimation of the computer-assisted area was implemented with less complexity when the 2D-FlexRuler was used, since it is already centimetric, already serving as a dimensional template for image softwares.
The use of 2D-FlexRuler in low-level laser therapy is also possible for the indication and delimitation of the quadrants that indicated the points of application of the laser in the treatment of wounds.
The developed Matlab algorithm is simple and can be implemented in portable devices, such as cameras and smartphones, to contribute enormously to an initial and reliable assessment of the wound and patient follow-up.

Conclusion
The 2D-FlexRuler is a reliable metric platform for obtaining the image of the anatomical limits of chronic wounds. It facilitates the calculation of the area of the wound under monitoring, which allowed to obtain the scar predictive factor of chronic wounds with precocity, in two weeks, with more accurate results than those obtained with traditional methods. It can be digitized and used as a new tool in clinical practice and wound research.