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Validating a new instrument to improve wound measurement

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Alison Metcalfe, PhD, BSc, RN, is senior research fellow; Carol Dealey, PhD, MA, BSc, RCNT, RGN, is senior research fellow; both at University of Birmingham; Tristan Hallowell, BN, RGN, is staff nurse, Heart of England NHS Foundation Trust; Rebecca Stubbs, RGN, is tissue viability research nurse, University Hospital Birmingham NHS Foundation Trust.


Metcalfe, A. et al (2008) Validating a new instrument to improve wound measurement. This is an extended version of the article published in Nursing Times; 104: 16, 30-31.
BACKGROUND: The objective measurement and assessment of wounds in clinical practice has previously proven to be time-consuming and difficult. We have developed a new device, the Clini-Rule, based on a similar device for perineal trauma assessment in midwifery (the Peri-Rule). This article reports early results from research to validate the Clini-Rule.
AIM: To validate the reliability of measurements and assessments of wounds carried out using the Clini-Rule.
METHOD: Two nurses (raters) used the measuring device to assess the same wound independently. The first nurse also took a sterile wound tracing. The surface area dimensions were measured using a digitising pad.
RESULTS AND DISCUSSION: To date 42 participants have had wounds assessed. A strong level of agreement was found between the Clini-Rule measurements of two raters, and the surface area measurements correlated highly with a digitising pad. Assessment using this device was also less painful for participants than wound tracings.
CONCLUSION: The Clini-Rule may now make wound assessment easier and more practical, improving nurse assessment of wound healing and patient outcomes.


This article describes the development of a new device - the Clini-Rule - to improve measurement and assessment of wounds using a pragmatic approach. We outline the history surrounding the development of the device before explaining the device itself in more detail. In addition, we provide a brief overview of other wound assessment methods and explore why wound measurement is so important, before giving an overview of the validation process and relevant findings.

The Peri-Rule

Metcalfe et al (2002) developed a new tool for the assessment of perineal trauma. Perineal trauma affects up to 65% of women who give birth via vaginal delivery and these tears can vary in size (Albers et al, 1999).

Undertaking research to compare outcomes for different sizes of perineal tear required the development of a simple, pragmatic tool for midwives. This resulted in the development of the Peri-Rule, which consists of a medical-grade plastic measuring device and an assessment pro forma to guide midwives in the measurements to be taken and recorded, to ensure tears are measured in the same way. The measurements produced would be meaningless if they are not comparable. This new device - the Peri-Rule - had to be validated to ensure it could provide consistently reliable measurements when used by different midwives in clinical practice.

To validate the Peri-Rule and ensure statistically that reliable measurements could be taken by midwives, the perineal trauma of 128 women had to be assessed (to achieve sufficient statistical power) using the device, with each tear being measured by two midwives (raters). The second midwife had to be blinded to the results of the first.

Participants were all practising midwives from four maternity units. It is not known how many finally took part as they were reluctant to be recognisable despite assurances of confidentiality. Therefore it was agreed they could complete the data collection sheets anonymously.

Each midwife recorded the measurements and, once all the data from the tears of 130 women were collated, kappa score statistical analyses were carried out to ascertain the reliability of measurements obtained by different pairs of midwives.

The kappa scores for the perineal tear measurements ranged from =0.67 (p<0.05) for depth measurements into the perineal body, =0.71 (p<0.05) for length of tear from fourchette to the apex of the vagina, and =0.75 (p<0.05) for length of tear from fourchette along the perineal skin towards the anus. A kappa score greater than 0.6 is considered a good level of agreement (Altman, 1991). Therefore the analyses showed there was a strong level of agreement between midwives measuring the tears. This meant the Peri-Rule could be used as a reliable tool for the measurement of perineal trauma and consequently for further research (Metcalfe et al, 2002).

Safety of the Peri-Rule
The Peri-Rule was introduced as part of a research project. However, several maternity units were interested in purchasing it for use in routine perineal trauma assessment. It was therefore agreed to develop and market the Peri-Rule.

To prepare the device for sale, it had to undergo safety checks by the UK Medicines and Healthcare products Regulatory Agency (MHRA). The agency assesses the efficacy and safety of new clinical products used in patient assessment or treatment, from both patients’ and clinicians’ perspectives.

Anecdotal and audit evidence has shown that the Peri-Rule does not increase distress for women having their tears assessed with the device.

The biggest safety concern with it was the risk of wound infection. To reduce this risk, the Peri-Rule is sterilised before use and is a single-use device (that is, it is disposed of immediately after use). In addition, the assessment pro forma guides midwives through the measurement procedure in a sequence that minimises the risk of wound contamination.

With all these factors taken into account in designing the device, it has been licensed for sale in the UK and European Union as a Class 2b medical device. This means the device and recommended procedure for sterilisation and assessment is considered sufficiently safe for the device to come into contact with wounds during the assessment and, if necessary, can be inserted into deep or penetrating wounds. For more information on the device, see

Current work
Following the development of the Peri-Rule, we were interested to investigate whether a similar device might be used for the assessment of other types of wounds and trauma, for example pressure ulcers and leg ulcers. Wound assessment has been quite a contentious issue in nursing, and we were interested to find out whether a similar device and the development of a guided assessment pro forma might enable consistent measurement and assessment of wounds in a similar way to the Peri-Rule.

Literature review

Wound assessment and evaluation of progress are important aspects of wound management (Dealey, 2005). This involves the need for objective measurements and the requirement to move away from comments in nursing reports such as ‘wound healing well’ that have no evidence to support them. Wound measurement and assessment in clinical practice has been limited by a lack of simple, pragmatic tools.

Many patients have wounds assessed and dressed in community settings, either in patients’ own homes or GP surgeries, as well as in hospitals. The diversity of locations can make accurate assessment of wound healing very difficult due to time constraints, patients’ positioning and lack of accessibility to affordable and reliable assessment tools.

There is a growing need to improve the assessment of wounds and trauma through objective rather than subjective assessment, to confirm that the many expensive wound care products do actually improve healing. In addition, with increasing risk of litigation, it is becoming essential to provide an accurate assessment of wounds, including pressure ulcers, to demonstrate the care provided and careful patient monitoring.

Previously, it has generally been recognised that there is no method of wound measurement which is accurate, repeatable, inexpensive and practical for everyday clinical use (Salcido, 2000). Many widely used methods have their own drawbacks, and using them in routine clinical practice is difficult or impractical because they require specialist equipment or time.

For many nurses working in community settings and in small GP practices, availability of specialist equipment for measuring wounds and trauma is limited.

Simple and cost-effective methods of wound assessment are required. This would help to examine the clinical effectiveness of wound treatment to improve patient care as well as reduce the risk of litigation.

The most widely used methods for measuring wounds are: linear measurements of length and width; wound tracing; and computer-based or digital planimetry.

Length and width measurement
Linear measurements are taken using a ruler, to measure the greatest length and greatest width of a wound, with the measurements taken perpendicular to each other. Although this is seen as the simplest method of measurement, there is potential for wound contamination from the ruler (Keast et al, 2004).

Kantor and Margolis (1998) compared calculations of wound area developed from linear measurements with those developed from the more sophisticated method of computer-based planimetry (see below), and found a significant correlation between the two. They concluded that linear measurements were suitable for clinical settings.

However, a standard ruler cannot be used directly against the wound due to the risk of contamination or cross-infection. Any item coming into contact with the wound ideally needs to be sterilisable to prevent any infection or contamination, especially with the risks of infection from meticillin-resistant or multiple-resistant Staphylococcus aureus (MRSA) and other pathogens that could reduce wound healing or potentially lead to worse outcomes.

Wound tracing
The wound circumference is determined by tracing the wound outline onto acetate film. Again, this is a simple method, but it can sometimes be difficult to identify the precise edge of the wound. It is also difficult to undertake if the wound is large and over a curved surface. The wound surface area can be calculated by placing the tracing over a grid of square centimetres and counting the number of complete squares. However, Keast et al (2004) suggested that this is time-consuming and has potential for error.

Computer-based or digital planimetry
Planimetry is the precise measurement of a wound taken from a wound tracing using either a computer or a digitising pad. Planimetry provides very accurate measurements and is often considered to be the most accurate and reliable method of measuring wounds. However, it is not widely used in the clinical area because it requires computer equipment. It also takes time to carry out an accurate wound tracing, and this technology is most commonly used within research settings.

Developing the Clini-Rule

As a result of developing and validating the Peri-Rule (Metcalfe et al, 2002), we decided to ascertain whether a similar measuring device could be used in a guided assessment of other wounds, for example, pressure sores or leg ulcers. As a result we developed a new instrument, named the Clini-Rule.

The Clini-Rule is a flexible, medical grade plastic tool (Fig 1) and a specially designed assessment pro forma, which guides the nurse (or rater) with a set of simple instructions on the measurements to be taken and recorded. The instrument also possibly allows the measurement of depth to be recorded if its use is carefully defined by specific instructions. Using a simple algorithm, the wound’s surface area can be calculated by a computer programme, which can be used on hand-held devices. The evidence suggests that, for many wounds and skin trauma, these simple measures are likely to be accurate and reliable and the most suitable for use in daily clinical practice (Keast et al, 2004).


Before the instrument can be used in clinical practice, it needs to be validated to assess the reliability of its measurements when used by different nurses. Our aim was therefore to validate the device between different nurses taking measurements and to compare their assessments against a computer-based one. Here we report the early findings from the study currently in progress.


The study was carried out in outpatient wound care clinics for the assessment and treatment of leg and foot ulcers and among inpatients with pressure sores, minor traumatic wounds and surgical wounds that have not healed. Following ethical approval, patients were given an explanation of the study and an information leaflet and asked to sign a consent form if they agree to participate.

Measuring device
The device used to measure the wound is 105mm long, 10mm wide and 4mm deep and has a mm scale measurement on the anterior surface. Before use, each device was cleaned and autoclaved at 130C for three minutes in line with recommended NHS sterilisation procedures. This meant the device could be used in direct contact with the wound, with minimal risk of wound contamination or infection, provided that the procedure was conducted aseptically. A pro forma was developed which guided nurses on the measurements to be taken and recorded.

Following removal of the dressing, the nurse (rater 1) was asked to use the Clini-Rule aseptically by wearing sterile gloves to make specific measurements using the pro forma to guide how these should be taken and recorded. This nurse was asked to request a second nurse (rater 2) to independently repeat the assessment at the same clinic appointment, blinded to the results of the first. The first nurse also took a sterile wound tracing. The surface area dimensions were measured from the tracing using a digitising pad (Quantify One, produced by Klonk in Denmark).

Assessment pro forma
The pro forma guides the measurements to be taken and requests information on the shape of the wound and whether pain is felt. If the participant complained of pain, they were asked to describe the level experienced using a five-point rating scale providing the following options to describe pain during the assessment (i) very small amount of pain, (ii) small amount of pain, (iii) moderate amount of pain, (iv) quite a lot of pain and (v) severe pain. Pain was assessed first while using the Clini-Rule and second while making the wound tracing. General comments were also invited from patient participants and clinicians. The assessment pro forma cannot be made available at present because it is in the process of being trademarked. However, it is hoped to make it available on the website once this process is completed. For more information on the device, see

Levels of agreement between raters’ measurements and assessments were determined using the kappa statistic. To evaluate differences in experiences of pain, a Mann Whitney U test was performed and correlations were tested using Spearman’s rank correlation coefficient (rho or r).

Results to date

The device has so far been validated with 42 participants. Wound types varied, although mainly pressure ulcers and foot ulcers have been measured in the clinic where the study is taking place. The level of inter-rater reliability observed for all wound measurements gave kappa scores greater than 0.78 (p=0.001).

Based on the shape of the wound reported by rater 1 and the measurements recorded, an algorithm was developed to calculate the surface area of each wound. The surface area derived from the algorithm was compared with the surface area calculated by the digitising pad from wound tracings. These showed almost perfect correlations between the method using the Clini-Rule and assessment pro forma and that using the digitising pad (r 0.98, p<0.01).
Participants were more likely to report pain from the wound tracings than with measurements taken using the Clini-Rule (Mann Whitney U = 2.17, p<0.03).


From the preliminary data gathered, the Clini-Rule and assessment pro forma appear to provide a simple and effective method of assessing and measuring wounds. This measuring device therefore has the potential to enable wound measurement to become a standard routine part of clinical practice, improving objective assessment of wounds and trauma.

The Clini-Rule and its assessment pro forma appeared to give similar readings to the digitising pad, which suggests that they both perform in a similar way. It is therefore likely that the pro forma guiding the measurement of the wounds and the subsequent calculation of the surface area is the essential component, because otherwise the measurements would be more haphazard and less likely to correlate consistently with results from the digitising pad.

However, compared to wound tracings, the Clini-Rule is more pragmatic and economical to use and is less time-consuming for both patients and nurses. It can also be used in any clinical setting. This means that the measuring device provides a viable means of objectively assessing wound healing, which is very important when, increasingly, more expensive products are promoted for the treatment of wounds.

Further benefits include the use of the Clini-Rule to assist nurses in providing authentication of their objective assessment of wounds and trauma, which can be used as evidence in planning care. This also assists with risk management because recorded evidence of regular objective assessment and actions taken will also reduce the likelihood of legal action for clinicians and organisations.

Study limitations
To date only 42 participants have had their wound assessed using the Clini-Rule. To ensure sufficient statistical power is achieved, ideally a total of 128 participants would be required.

However, the device has already been licensed for use in clinical practice. This decision was based on the joint evidence of the data collated so far and the data obtained from the use of the Peri-Rule, on the grounds that perineal trauma require similar measurements to other types of wound. The uniqueness of the Clini-Rule is in how that data is transformed to calculate surface area.

Work to recruit the remaining 86 patients for the validation of the Clini-Rule and further studies are needed to test the device on as many different types of wound as possible. Further work could also look at and ascertain the usefulness of the device in measuring the depth of wounds. There are currently no other devices that measure the depth of wounds against which the Clini-Rule can be compared.


The Clini-Rule can be used in the assessment of different types of wound and, because of its simplicity, it can be used in a variety of locations. It is minimally time-consuming, unlike wound tracings, and seems to cause less discomfort to patients.

Further work is under way to increase the number of participants to ensure the study is sufficiently powered before any final conclusions are reached.

Footnote: The Peri-Rule is now in use in research in many countries across the world including the US, South America, Europe and Asia.

We would like to thank all the nurses and participants who contribute to this study. Their support and assistance is greatly appreciated.

  • Potential competing interest: Alison Metcalfe is a non-remunerated director of BHSD Ltd, which manufactures the Peri-Rule and Clini-Rule.

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