Introduction

Pressure ulcers are a frequent secondary condition for individuals with spinal cord injury (SCI), with a long-term prevalence ranging from 15.2 to 30%.1, 2 If pressure ulcers are present, these are often severe and take a long time to heal. Ulcers heal by wound contracture and replacement of normal tissue layers by granulation tissue, collagen and scar formation.3 To detect healing stagnation or deterioration, the ‘Clinical Practice Guidelines’ (CPG) recommend to evaluate the healing progress at least weekly using quantitative measures.4 Routine clinical assessment should include at least a measurement of length, width and depth, besides anatomical location, stage, exudat/odour, necrosis, undermining, sinus tracts infection, healing and wound margins. It is also recommended to modify the conservative treatment or to plan an operation if the ulcer shows no evidence of healing within 2–4 weeks.4

Up to the present, there is no worldwide consensus about the best instrument to measure pressure ulcer healing in SCI rehabilitation. It is, however, already clear that some instruments are not suitable. Staging or grading scales as the National Pressure Ulcer Advisory Panel staging system, European Pressure Ulcer Advisory Panel scale and Stirling scale are not suitable because these classification systems were designed to rate the severity of a pressure ulcer and not its healing.5, 6 In 1997, it was concluded that no ideal instrument to measure pressure ulcer healing was available.3, 7 These and later reviews, however, described only part of available instruments or described instruments used for other kinds of wounds.3, 7, 8, 9, 10

To guide a choice from the large number of instruments described in the literature, we performed a literature review of pressure ulcer assessment instruments to describe their validity, reliability and responsiveness. We also investigated which instrument will be most feasible with respect to time (preferably <1 min for measurement and registration) and costs for use in routine bedside practice in a medical unit specialized in inpatient and outpatient SCI rehabilitation.

Methods

The primary data source was PubMed. Articles were selected using the MeSH Major Topic ‘pressure ulcer’, covering the following terms: pressure ulcers, bedsore(s), bed sore(s), decubitus ulcer(s) and pressure sore(s). The searches consisted of this MeSH Major Topic and one of the following four other MeSH terms: wound healing, severity of illness index, reproducibility of results, and sensitivity and specificity. Articles were included that were written in English and published up to 31 December 2008. Excluded were review articles, articles on staging or grading scales, articles without description of any clinimetric properties of the used pressure ulcer assessment instrument, articles in which the instrument was evaluated using plaster wound models and articles that described a mixed population, for example, patients with pressure ulcers and patients with leg ulcers.

References of included articles were checked, and additional articles were included if clinimetric properties of pressure ulcer assessment instruments were described. Finally, for each of the included instruments, we performed a Pubmed search for additional articles about that instrument, and these articles were also included in this review if they described clinimetric properties. As these searches revealed many different instruments, we selected only instruments that were evaluated in more than one publication.

To evaluate concurrent or criterion validity, we considered correlation coefficients (Pearson, Spearman) >0.60 as support (+), 0.30–0.60 as partial support (±) and <0.30 as no support (−). For multidimensional scales, evidence for construct validity was present if the multidimensional structure was confirmed by factor or principal component analysis (+). For one-dimensional scales, this criterion was not applicable (na). Inter-rater and intra-rater reliability (Kappa, Pearson, ICC) was good if >0.80 (+), partial if 0.70–0.80 (±) or insufficient if <0.70 (−). Some studies evaluated reliability using the coefficient of variation. There are no norms for interpretation of this statistic available, making it difficult to interpret. In this review, a variation of 6% or less was rewarded with a plus. Evidence for responsiveness was found if statistically significant improvements were reported on follow-up measurements and were related to the time after baseline measurement (number of weeks). Feasibility was described as time needed to rate one ulcer (minutes), the types of ulcers for which the test is applicable (types I–IV), the amount of training needed before application (minutes) and the costs of the test, software or hardware in US dollars (USD).

Results

The combination of ‘pressure ulcer’ with the MeSH term wound healing revealed 858 articles, with the term severity of illness index 289, with the term reproducibility of results 190 and with the term sensitivity and specificity 155 articles. Some articles appeared more than once in the search results because they contained two or more of these MeSH terms.

After we applied the exclusion criteria, 33 articles remained. We included seven additional articles from the literature list of these 33 articles. Two of these seven articles were published in a journal, which is not indexed in PubMed. The five other articles were available in PubMed but did not include the MeSH terms we used. To make sure that we had not missed other relevant articles, we performed a final series of searches using the MESH term ‘pressure ulcer’ in combination with MESH terms from these last articles: pressure ulcer/radiography, pressure ulcer/economics, weights and measures, nursing assessment and monitoring, physiologic. We found no further relevant articles using these terms.

The 40 included articles described 21 instruments (Table 1). Only 11 of these instruments were described in more than one publication. A summary of their clinimetric properties is provided in Table 2 and extensive information on each instrument is provided in Table 3.

Table 1 Overview pressure ulcer assessment instruments
Table 2 Clinimetric aspects of pressure ulcer assessment instruments
Table 3 Detailed description of 11 pressure ulcer assessment instruments: (a) volume; (b) surface; (c) scales

Volume was assessed with saline, alginate or with a ruler measuring length, width and depth. When volume was assessed with saline, a sheet was applied tightly over the wound and filled with physiological saline (NaCl) gel11 or fluid12 through a hole in the centre of the sheet. The volume needed was registered.

When volume was assessed with alginate, the compound was applied in the (rinsed) wound while still fluid. The moulds were extracted and weighted, and volume was computed by dividing weight by density.13, 14 Otherwise moulds were immersed in water and volumetric displacement was measured. This was compared with measurement of the volume of the moulds by nuclear magnetic resonance spectrometer.15

For assessment of the volume by measuring length, width and depth, a horizontal cross-arm ruler with a vertical arm for crater wounds was developed.16 The surface area or volume of the wound was calculated with different formulas.

All three-volume assessment instruments showed concurrent validity (Table 2). Only the ‘filling material saline’ was tested for reliability. The reliability with dental-moulding material was insufficient, especially for wounds with deep sinus tracts or deep undermining or shallow wounds.3 The ‘ruler length, width and depth’ method is the most practical instrument of the three. Responsiveness was evaluated for ‘filling material saline’ and ‘ruler length, width and depth’ and was better for the last one.

Surface was assessed with a gridsheet, planimetry, digital stylus, computer pointed device or ruler.

The gridsheet was used in two different ways. A sterilized transparency film was placed over the wound and the wound's perimeter was traced on a metric graph paper and the number of mm2 within the tracing was counted.17 Otherwise the area of the wound surface was outlined from a photograph on a transparent wound diagram consisting of a mm2-scaled grid. The enclosed area was calculated by observers.18

Planimetry was also used in two different ways. A planimeter was used to determine ulcer surface from wound tracings on a grid sheet 11, 13, 17 or tracing of the ulcer was drawn on the photograph before using the planimeter.

Digital stylus was used on a transparency on which the ulcer margins were traced with an inedible pen or on a photograph of the wound. The tracing was outlined using the stylus of a tablet digitizer interface with a computer. The area was calculated using different software programs.19, 20

Computer pointed device was used after a record of the wound taken by video with reference scales at right angles or a digital camera. From the computer image the surface area is traced with a tracker ball, and the surface area is calculated by the number of pixels21 or a software program.22

Rulers are used in different forms calculating the area with different formulas.3, 13, 20 Measurements were taken according to the CPG.4

From the five surface assessment instruments described in Table 2, only the ‘wound tracings with planimetry’ and the ‘ruler length and width’ showed concurrent validity and were also tested for their inter-rater and intra-rater reliability. Reliability of the ‘wound tracings with planimetry’ was evaluated with the coefficient of variation. The ‘wound tracings with planimetry’ method has practical problems: tracing the wound area is often difficult as the ulcer margins are not always clearly visible. Besides that a planimeter can be prohibitively expensive. The ‘ruler length and width’ method, using Kundin device, is cheap, but it slightly over-estimated the areas obtained by planimetry (mean difference of about 1.5 cm2 in ulcers of 1.2–61.6 cm2).13 The responsiveness to change was evaluated in both instruments. Wound tracings with a planimeter and ruler length and width were both sensitive to measure wound change early in treatment as they revealed significant percentage differences 2 weeks after measuring the baseline size of wounds <10 cm2 and 4 weeks after measuring the baseline size of wounds 10 cm2.13 A very high correlation between these two methods was found (r=0.979, P<0.001).13

The following three scales were included: the ‘Pressure Sore Status Tool (PSST)’, ‘Pressure Ulcer Scale for Healing (PUSH)’ and the ‘Sessing scale’.

The PSST assesses 13 domains in 5 categories each. Size and undermining are measured before categorization, while the other domains are descriptive. Location and shape are added as non-scored items.23 The ‘PSST’ assesses the domains recommended by the CPG except for anatomical location and stage.

The PUSH assesses three domains. It categorizes the surface by multiplying greatest length and width and adds this to categories for exudate amount and tissue type.24 The PUSH assesses only the CPG-domains size, exudates/odour and healing.

The Sessing scale is a description of the wound in seven categories without measurements.25 It assesses the CPG-domains exudates/odour, necrosis, infection, healing and wound margins but gives no measurements.

All three scales showed clinimetric problems. The ‘PSST’ used staging scales to prove its concurrent validity. Further problems were the time needed for testing and lack of data on responsiveness.

The ‘PUSH’ scale has not been evaluated for reliability and is not practical to use in small wounds with depth and large wounds. However, it is the only scale tested for its responsiveness.

The ‘Sessing scale’ has a moderate concurrent validity and was not tested for responsiveness. It is easy to learn and quick to use.

Discussion

At least 21 different pressure ulcer assessment instruments have been published to date. They can be divided into volume instruments, surface instruments and scales (Table 1). Their clinimetric properties, however, are poorly described (Table 2). From the PubMed literature until 2009, we can conclude that no pressure ulcer assessment instrument has been completely tested for validity, reliability and responsiveness. In addition, practicality of most instruments is poorly described.

Among the volume instruments, validity is properly investigated but reliability is not. Only for filling material ‘saline’ reliability was investigated, and intra-rater reliability was good but inter-rater reliability was not good. The four general problems with filling instruments are definition of wound boundaries, wound flexibility due to slight movements of the patient, natural curvatures of the human body and cavity formation due to fibrotic scars of a healed wound.26 Moreover, filling material instruments are only useful for grades III and IV pressure ulcers and not for grades I and II. The time needed to apply filling material instruments is poorly investigated but is probably prohibitive for a bedside test. The ruler instrument is validated, but reliability and practicality are not properly investigated. This instrument is useful for grades I–IV ulcers and the time needed is not investigated but seems reasonable.

The surface instruments have been reasonably well validated. They are, however, only useful for grades I–II and not for grades III–IV ulcers. Wound tracings with a planimeter is highly accurate but requires substantial expertise and equipment.3, 13 The time needed to use these instruments is not investigated but seems reasonable. Tracings are probably more time consuming than ruler length and width.

The scales ‘PSST’, ‘PUSH’ and the ‘Sessing scale’ give a description of the ulcer combined with a length/width/undermining (PSST) and length/width (PUSH) measurement. The test time for ‘PUSH’ and the Sessing scale is relatively short, but the time needed for the calculation of the score is prohibitively long for a bedside instrument. The PSST provides the most complete description of the ulcer according to the CPG recommendations.

Conclusion

Many pressure ulcer measurement instruments are not feasible in routine bedside practice due to the time needed for measurement and registration. For bedside measurement of the healing process in pressure ulcers in SCI patients, we advocate the use of the ruler method. To describe this process, we advocate the Sessing scale. Their clinimetric properties (validity and reliability) are promising, but further evaluation of these instruments is necessary.

Conflict of interest

The authors declare no conflict of interest.