Quantification of the physical properties of keloid and hypertrophic scars using the Vesmeter novel sensing device

Abstract

There is still no objective method or reliable device to measure and assess the physical properties of keloid and hypertrophic scars. Using the Vesmeter, we measured the physical properties of keloid and hypertrophic scars, and investigated how their physical properties changed during the process of clinical follow‐up. We followed up 11 patients with keloid (n = 6) and hypertrophic (n = 5) scars for 4 months, and measured their physical properties three times over a 2‐month period using the Vesmeter. Measurements included hardness, elasticity, penetration depth, relaxation time, viscosity and viscoelastic ratio. All physical properties were measured simultaneously while an indenter was pressed onto the lesion and digitalise the measured data by analysing the wave forms of the lesion's surface behaviour. Data collection was repeated three times for each measurement point, and the average of these three values was used. Overall hardness and viscosity decreased in nine patients, whereas penetration depth increased in nine. Relaxation time decreased in nine patients and elasticity increased in six. Vesmeter was considered to be an objective, convenient and comparatively reliable measuring device for the quantification of the physical properties of keloid and hypertrophic scars.

INTRODUCTION

Keloid and hypertrophic scars are proliferative disorders of the skin following trauma burns and surgical procedures (1). Treatment of these disorders can be some of the most challenging and time‐consuming clinical procedures plastic surgeons and burn specialists can encounter.

An objective and reliable method to measure the degree of skin involvement is essential for the evaluation of a novel therapy for keloid and hypertrophic scars. Severity and the extent of skin involvement in keloid and hypertrophic scars are generally assessed subjectively using the Vancouver burn scar scale (1).

Most patients with keloid and hypertrophic scars experience varying degrees of discomfort, such as pruritus, pain and sometimes aesthetic deformities related to abnormal skin conditions, like changes in skin colour or hardness. Abnormal skin conditions such as hardness, pruritus and pain are treated as primary symptoms of keloid and hypertrophic scars using steroids, laser waves and surgical excision. Using these techniques, pain and pruritus can be relieved in a short time and the results can be easily observed by patients or physicians. However, favourable changes in skin hardness and colour are slow, and assessment is generally subjective. Because the assessment of keloid and hypertrophic scars is observer dependent, treatment results and reliability can also be difficult to assess. An objective and reliable measuring instrument for the quantification of the physical properties of keloid and hypertrophic scars is therefore needed.

PATIENTS AND METHODS

The Vesmeter (Wave Cyber Co. Ltd., Saitama, Japan) is a portable sensing device which consists of two parts: personal digital assistant (PDA; Figure 1) and non invasive portable sensing probe (Figure 2) (2).

Figure 1.

The Vesmeter used in this study. The right panel shows the personal digital assistant. The left panel shows the portable probe with battery switch on the top and sensor head in the tip. The sensor head diameter is 3 mm.

Figure 2.

Photograph (A) and configuration (B) of the probe. The results of the measurements are displayed on the personal digital assistant. The numbers in (B) indicate the following components: (1) recognition mark; (2) position sensor; (3) indenter; (4) measurement head; (5) electromagnetic coil; (6) permanent magnet; and (7) power switch.

Simultaneous automatic assessment of six physical properties (i.e. skin elasticity, viscosity, viscoelastic ratio, penetration depth, relaxation time and hardness) of keloid and hypertrophic scars can be performed while the sensor is in contact with the lesion, and measurement data are transmitted to the PDA via bluetooth electromagnetic waves. These procedures can be completed in a few seconds without any pain or discomfort to the patient.

The Vesmeter was originally developed to test the hardness of plastic materials used in industry; recently, it has also been used to assess skin involvement in systemic sclerosis, and its reliability and reproducibility of measurements have been confirmed in a previous study (2).

In this study, we followed up 11 patients (4 of whom joined the study from their second hospital visit) composed of 8 men and 3 women, with an average age of 40 years, who regularly visited our outpatient clinic over a period of 4 months. All patients treated with local injection of triamcinolone (TAC) (Kenacort‐A) 0·1 ml once in a month. Among these 11 patients, 5 had hypertrophic scars (1 on the chest, 2 on the shoulder and 2 on the abdomen) and 6 had keloid scars (4 on the chest and 2 on the abdomen). The average age of the patients with hypertrophic scars was 39·6 years, and that of the patients with keloid scars was 40·3 years. Scar duration ranged from 2 to 16 years for hypertrophic scars and from 2 to 20 years for keloid scars. All scar parameters were measured with the Vesmeter at three sites on each scar (i.e. the central part, a section outside the border of the scar, and a section between these two points) three times over a 2‐month period. These measurements were repeated three times in each position, each time and an average of the three values was used as the final value.

As skin involvement in different body sites was different, we therefore tried to measured the same three points in each patient on their first, second and third visits. Collected data were then compared based on their measured times and locations. The Voigt model was used to calculate skin elasticity (N/m²), viscosity (Ns/m²), viscoelastic ratio (%), penetration depth (mm) and relaxation time (m/s) by analysing the wave forms of the skin's surface behaviour. Hardness (Hs) was calculated by measuring the depth of an indenter pressed onto the skin. These parameters were measured while the Vesmeter was in contact with the lesion, simultaneously analysing the wave forms of the compressed skin when it returned to its original position. Relaxation time was the time taken by the deformed material to return to its original position. Viscosity is related to delayed recovery from deformation. Elasticity is related to rebounding and quick recovery from deformation. Written informed consent was obtained from all patients.

RESULTS

One patient with keloid scars and two with hypertrophic scars were lost to follow‐up after the second visit. Marked changes were observed after the 4‐month clinical follow‐up by analysing the obtained data on hardness, elasticity, penetration depth, viscosity and relaxation time, but there were only slight changes in the viscoelastic ratio in all the patients.

As shown in Figure 3, hardness decreased in nine patients and increased in two patients both of whom had hypertrophic burn scars of 2 years duration. Elasticity increased in five patients and decreased in five patients, without any changes observed in one patient with a keloid scar of 6 years duration (Figure 4). Viscosity decreased in nine patients, and slightly increased in two patients, in one whom keloid scar had been present for 20 years and the other had a hypertrophic scar for 2 years of duration (Figure 5). Relaxation time decreased in eight patients, and only slight changes were noted in two patients both of whom had keloid scars: 1 of 6 years duration and 1 of 5 years duration. A slight delay in relaxation time was observed in one hypertrophic scar of 5 years duration (Figure 6). There were no apparent changes observed in the viscoelastic ratio in any patients (Figure 7). Penetration depth increased in nine patients and decreased in two patients; both patients had hypertrophic scars for 2 years (Figure 8).

Figure 3.

Relationship between skin hardness and study period. Numbers 1–3 indicate measurement points. There was a 2‐month period between points 1 and 2 and points 2 and 3. Each coloured bar represents one patient.

Figure 4.

Relationship between skin elasticity and study period. Numbers 1–3 indicate measurement points. There was a 2‐month period between points 1 and 2 and points 2 and 3. Each coloured bar represents one patient.

Figure 5.

Relationship between skin viscosity and study period. Numbers 1–3 indicate measurement points. There was a 2‐month period between points 1 and 2 and points 2 and 3. Each coloured bar represents one patient.

Figure 6.

Relations between relaxation time (speed) and study period. Numbers 1–3 indicate measurement points. There was a 2‐month period between points 1 and 2 and points 2 and 3. Each coloured bar represents one patient.

Figure 7.

Relationships between viscoelastic ratio and study period. Numbers 1–3 indicate measurement points. There was a 2‐month period between points 1 and 2 and points 2 and 3. Each coloured bar represents one patient.

Figure 8.

Relationship between penetration depth and study period. Numbers 1–3 indicate measurement points. There was a 2‐month period between points 1 and 2 and points 2 and 3. Each coloured bar represents one patient.

In this study, 7 of the 11 patients report that itching and, or burning feelings released in some degree during the follow‐up. In terms of the physical properties of the scars of these seven patients, skin hardness and viscosity decreased, penetration depth and elasticity increased and relaxation time decreased.

Changes in symptoms during follow‐up were not immediately obvious, but changes in the physical properties of the scars were gave us useful information to know the present conditions of the scar, and help full digitalised data to support the given treatment.

There were no clinical changes observed in two of the nine patients in whom skin hardness and viscosity had decreased and penetrating depth had increased. In these two patients, one had keloid scars of 9 years duration and another had hypertrophicscars of 2 years duration, both on the chest.

DISCUSSION

In this study, we tried to objectively measure the physical properties of keloid and hypertrophic scars with Vesmeter, and investigated how their physical properties changed during clinical follow‐up.

Hardness, penetration depth, viscosity and relaxation time showed good correlation, and the results showed that decreases in hardness and relaxation time, and increases in viscosity and penetration depth were signs of improvement in the clinical conditions of keloid and hypertrophic scars.

A decrease in hardness showed that the skin parameters were changing towards the normal range, and indicated that the treatment was effective. In two patients in whom skin hardness increased, shows the scars were recent and, or keloid scar so that the hardness may continue to increase.

With regard to penetration depth, bluetooth electromagnetic waves penetrated the scar layer. Penetration depth increased in nine patients and decreased in two. This indicated that the skin surface of the nine patients had become easier to penetrate. However, in the other two patients, the skin surface became more resistant to electromagnetic wave penetration. In general, the easier the electromagnetic waves penetrate the skin, the closer the skin is to being normal.

Relaxation time decreased in eight patients, with only slight changes observed in two patients with keloid scars (one man, 6 years scar duration and one woman, 5 years scar duration), and a slight delay was observed in one patient with a hypertrophic scar of 5 years duration.

The viscoelastic ratio did not markedly change, and therefore we considered the follow‐up period to be too short for changes in the viscoelastic ratio to be easily observed. Hardness, penetration depth and viscosity showed positive correlation with the physical properties of keloid and hypertrophic scars in nine patients. These three parameters are considered to be a reliable standard in assessing short‐term treatment efficacy for keloid and hypertrophic scars. The usefulness of the viscoelastic ratio and relaxation time as parameters will require further study over a longer follow‐up period.

The efficacy of corticosteroid injections in the treatment of keloids and hypertrophic scars has been well established (3), and one of the regular treating methods in our department. Suppressive mechanisms of corticosteroids on wound healing include (1) interruption of the inflammatory process by inhibition of inflammatory cell migration and phagocytosis, (2) a vasoconstriction effect resulting in disruption of the oxygen and nutrient supply to the wound, and (3) antimitotic activity on fibroblasts and keratinocytes, which may be the most important mechanism (3). The most commonly used corticosteroid is the TAC. It is possible to compare steroid injected cases with not injected cases in another study protocol using Vesmeter, and it would provide quantitative efficacy of steroid injection to keloids and hypertrophic scars.

Of 11 patients, 7 report that itching and/or burning feelings released in some degree during the follow‐up. Regarding the clinically evaluated physical properties of the scars of these seven patients (three of them were hypertrophic scar), skin hardness and viscosity decreased, penetration depth increased and relaxation time decreased. These symptoms reported by patients correlated with the values measured with the Vesmeter.

Possible sex or age differences in skin parameters, and comparing the results of TAC injected cases versus not injected cases were not investigated in this study owing to the relatively small number of study participants and restricted number of not injected cases. Additional investigations are needed to clarify any changes in skin properties that vary according to age or sex, or might be affected by obesity.

Til date, various reliable and easy‐to‐use instruments such as the a tristimulus colorimeter (4), durometer 5, 6 and cutometer 7, 8 have been used to measure individual scar parameters such as pliability, firmness, pigmentation, perfusion, height, indurations and thickness. In addition, ultrasound scanners (9) laser Doppler imaging (10) and three‐dimensional analysis modalities are also used but these involve more complex equipment (11), are expensive and require technical expertise. Moreover, scar measuring devices should be non invasive, accurate, with good reproducibility and be easy‐to‐use for objective data collection. They must also have clinical utility (1). In general, the above devices and modalities have limitations, such as special training required to obtain measurements, cost and difficulty of use.

On the other hand, the Vesmeter has several advantages compared with other devices as follows: (1) not only scar hardness, but also scar elasticity, viscosity, viscoelastic ratio, penetration depth and relaxation time can be measured simultaneously; (2) all measurements can be completed in a few seconds; (3) no particular training or large‐scale equipment is needed; (4) measurements are very simple, and no discomfort or pain is felt; and (5) the Vesmeter is portable.

In particular, the most important advantages of the Vesmeter are its ability to measure the physical properties of keloid and hypertrophic scars at any point during the clinical course and digitalise the data, by this we can assess the given treatment as right or wrong more early stages instead of simply waiting for months or years time to observe some clinical changes as improvement or deterioration.

Furthermore, the Vesmeter is sensitive and can detect very slight changes in skin hardness and elasticity, so that it can be used for the assessment of skin conditions in various skin diseases such as systemic sclerosis (2), keratoderma, atopic dermatitis, dermatomyositis, diffuse psoriasis 3, 5 and ichthyosis.

Despite its numerous advantages, the Vesmeter has some limitations: measurements can be easily affected by subcutaneous tissue. Relocation is difficult. The extent of skin involvement and the measurements thus obtained can differ on different sides of the body, even when measuring the same patient, because of subcutaneous tissue such as bones, body fat, tendons and muscles. In addition, measurement requires the same body position to reproduce accurate data for a certain body side. For example, when measuring different sides of the body like the surface of tendons, the tendon should be flexed, muscles relaxed and extremities extended.

CONCLUSIONS

We used a novel device, the Vesmeter, in the quantification of the physical properties of keloid and hypertrophic scars. The Vesmeter was useful in the measurement of the physical properties of postoperative scars and small size burn scars. However, the Vesmeter is considered less reliable for large burn scars and can lead to confusing results. Relocation is difficult. However, additional long‐term studies with a larger number of patients are needed to further confirm the efficacy of the Vesmeter in keloid and hypertrophic scar evaluation.

ACKNOWLEDGEMENTS

We are indebted to Mr Roderick J. Turner, Assistant Prof. Edward F. Barroga and Prof. J. Patrick Barron, Chairman of the Department of International Medical Communications at Tokyo Medical University, for their review of the English article.