PREVENTION AND CURATIVE MANAGEMENT OF HYPERTROPHIC SCAR FORMATION

3 PREVENTION AND CURATIVE MANAGEMENT OF HYPERTROPHIC SCAR FORMATION

ABSTRACT Although hypertrophic scarring commonly occurs following burns, many aspects such as incidence of and optimal treatment for scar hypertrophy remain unclear. This review will focus on hypertrophic scar formation after burns in particular, exploring multiple treatment options and describing their properties as well as their effectiveness. To evaluate treatment efficacy and scar development, clinical scar assessment is of eminent importance. Recommendations regarding the classification of hypertrophy in the daily practice and in clinical trials are implemented in this review. Monica C.T. Bloemen 1, Willem M. van der Veer 2, Magda M.W. Ulrich 1, Paul P.M. van Zuijlen 3, Frank B. Niessen 2, Esther Middelkoop 1,2 1 Association of Dutch Burn Centers, Beverwijk, The Netherlands; 2 Department of Plastic and Reconstructive Surgery, VU University Medical Center, Amsterdam, The Netherlands; 3 Department of Plastic and Reconstructive Surgery, Red Cross Hospital, Beverwijk, The Netherlands Burns, 2009;35(4):463-75.

MANAGEMENT OF HYPERTROPHIC SCAR FORMATION 45 1. INTRODUCTION Hypertrophic scarring following surgical procedures, trauma and especially burns is a great concern for patients and a challenging problem for clinicians. Peacock defined hypertrophic scarring as a scar raised above the skin level that stays within the confines of the original lesion 1. Hypertrophic scars may cause significant functional and cosmetic impairment, symptoms of pruritus and pain, which are all responsible for a decrease in quality of life 2-4. Hypertrophic scars result from general failure of normal wound healing processes 5. After burn injury they typically appear on the trunk and extremities. Frequently, hypertrophic scars are misdiagnosed as keloids. Their gross appearance is similar, although keloids proliferate or originate beyond wound margin 1. Furthermore, a hypertrophic scar typically decreases in size over time as opposed to keloid, which may have phases of reactivation and enlargement 6. The occurrence of keloid scars after burns is less common 7,8. This review will therefore focus on hypertrophic scarring. In the developed world four million patients acquire scars as a result of burns each year and the incidence is even greater in the developing world 9,10. Previous studies reported diverging incidences of hypertrophic scarring. Incidence rates vary from 40% to 94% following surgery and from 30% up to 91% following burns 11-17. Explanations for the wide spread in incidence are numerous, but an inadequate scar evaluation seems to be the most likely cause. Hypertrophic scars usually develop within one to three months after injury, in contrast with keloid scars that may appear up to 12 months after injury 6. Many factors such as race, age, genetic factors, hormone levels, atopy and immunologic responses of the individual patient appear to play a role. The type of injury, wound size and depth, anatomic region and mechanical tension on the wound are important as well 18. Also, complicating factors such as bacterial colonization and infection of the wound seem to induce hypertrophic scarring 6,16,18-21. To predict the development of a hypertrophic scar in a burn wound, the time to heal is the most important factor and is closely related to depth and size of the wound 22,23. Unfortunately, in the majority of the published reports these factors are not defined accurately 14,17 and only a few authors have used validated criteria or a classification to define hypertrophic scarring 12,13,22,24. Incidence percentages are shown in Tables 1 and 2, however the limitations discussed above should be taken into consideration. 2. SCAR EVALUATION For the assessment of (hypertrophic) scars various tools are currently available. The Vancouver Scar Scale (VSS) (Figure 1) is a validated subjective scale scored by the provided 25-27. An important disadvantage of the VSS is that not all parameters are equal in weight; e.g. pliability has a 5-number score, whereas the others can value from 0 to 3. This means that the numbers cannot be simply added to calculate a total score. Another subjective and valid scale, the Patient and Observer Assessment

46 CHAPTER 3 Table 1. Hypertrophic scarring rates after burn injury in adults. Study Patients Follow-up Rate Comment Gangemi et al. 108 2008 retrospective Bombaro et al. 17 2003 prospective Bombaro et al. 17 2003 retrospective Lewis et al. 12 1990 prospective? McDonald and Deitch 89 1987 prospective Deitch et al. 22 1983 retrospective 703 Patients Up to 12 years 72% + Treatment and patient characteristics described + Classification for scar is used - Race not documented 30 Patients 1-2 Years 0% - Race, depth and definition of hypertrophic scar not described 73 Adults - 75% In non-white 58 Chinese patients 113 Burn sites in adults 121 Burn sites in 41 adults 63% In white + Race documented - Depth, follow-up period, time of healing and treatment not mentioned 3-9 Months 91,4% + Scale is used for definition of hypertrophy + Only Chinese patients - Depth, age and treatment not mentioned 1 Year 25% In black 7% In white + Only grafted wounds included + Race, age and time of healing are described 9-24 Months 30% In black 16% In white + Only superficial or moderate partial thickness depth burns included, all not grafted + Treatment and time of healing are well described - No exclusion of keloids Scale (POSAS) (Figure 2), consists of a patient and an observer part to evaluate the scar 28,29. Besides the use of an assessment scale to define hypertrophic scarring, we now believe that the area of elevation in a burn scar is also of significance. Particularly in clinical trials, it is of interest to document which percentage of the originally treated wound surface has become hypertrophic. Objective measurements for the analysis of hypertrophy are scarce. Reports have been published on the use of negative impressions of the scar, ultrasound images, laser Doppler flow, color measurements and three-dimensional systems for the analysis of hypertrophy 25,30,31. Although management of hypertrophic scars has advanced in the past years, the lesions remain difficult to prevent and treat. Thereby, hypertrophic scars after burns require a special approach as the scars are often not linear, but widespread 24. Extensive research has lead to an increase of knowledge in the pathophysiologic processes of wound healing and the formation of scars 5, but still there is no consensus regarding the best treatment to reduce or prevent hypertrophic scarring. Recurrences remain common and satisfaction of patients is variable 24. In this review various treatment methods to prevent and treat hypertrophic burn scars, will be reviewed.

MANAGEMENT OF HYPERTROPHIC SCAR FORMATION 47 Table 2. Hypertrophic scarring rates after burn injury in children. Study Patients Follow-up Rate Comment Cubison et al. 23 2006 retrospective Bombaro et al. 17 2003 retrospective Spurr and Shakespeare 14 1990 retrospective McDonald et al. 89 1987 prospective Deitch et al. 22 1983 retrospective 170 Children 4 Months 74% Wounds healed spontaneous 13 Children <15 years of age 152 Children <5 years of age 60 Burn sites in? children <14 years of age 124 Burn sites in 59 children <14 years of age 57% Wounds grafted - 100% In non-white 75% In white + Distinction grafted and spontaneous healed wounds + Time of healing and follow-up period documented - Race and depth not mentioned + Race documented - Depth, follow-up period, time of healing and treatment not mentioned - 51% In 1968 - No distinction spontaneous 63% In 1984 healed and grafted wounds - Follow-up period and race not mentioned 1 Year 57% In black + Only grafted wounds 31% In white included + Race, age and time of healing are described 9-24 Months 31% In black + Only superficial or moderate partial thickness 13% In white depth burns included, all not grafted + Treatment and time of healing are well described - No exclusion of keloids Figure 1. Vancouver Scar Scale 26 modified according to Baryza and Baryza 27.

48 CHAPTER 3 A B Figure 2. Patient and Observer Scar Assessment Scale. A, The Observer scale. B, The Patient scale.

MANAGEMENT OF HYPERTROPHIC SCAR FORMATION 49 3. PREVENTIVE MANAGEMENT Optimal treatment of the burn wound is of eminent importance for wound healing and the prevention of hypertrophic scar formation. Deitch et al. demonstrated that wound closure should be achieved within three weeks to reduce the risk for hypertrophic scar development 22. Timing of grafting is still under debate, both for survival of the patients as well as the quality of the outcome with respect to hypertrophy. Adequate topical wound treatment allows for wound healing with controlled inflammation and should be applied to obtain fast wound closure. The autologous split thickness skin graft is still the mainstay of burn wound surgery. Although autologous split thickness skin graft may result in faster wound closure, it may not prevent hypertrophic scar formation in the operated area. In the long term, mesh grafts frequently can be recognized by the former interstices of the mesh where generally more hypertrophy is observed. The use of sheet grafts or mesh grafts with a small expansion ratio is therefore advocated to obtain superior functional and cosmetic results 32,33. Thickness of the split thickness skin graft is still subject of discussion. Both very thin (0.008 inch) and very thick (0.025 inch) split thickness skin grafts are associated with hypertrophic scarring 34. In the last decades, the survival of the burn patient has increased significantly, necessitating further development of methods for skin resurfacing. This has lead to the development of skin substitutes. Initially, most attention was focused on the epidermal replacement by cultured autologous keratinocytes 35. Later, more and more attention was focused on the role of dermal substitutes in wound resurfacing, specifically with respect to improvement of the quality of the scar and with that scar hypertrophy. Nowadays, dermal substitutes are considered to play a more prominent role in burn surgery and have shown to minimize hypertrophic scarring, contractures and increase scar elasticity in acute burn wounds 36-38. More studies on tissue engineering and skin substitution may result in more evidence and support for long-term clinical effectiveness. Besides methods for wound closure, corticosteroids, silicone and pressure therapy can also play an important role in the prevention of hypertrophic burn scars and will now be described. 3.1 Silicone In 1982 the use of silicone materials in the treatment of hypertrophic burn scars was first described by Perkins et al. 39. Since then, many authors reported silicone as the key in noninvasive scar management, because it improves the appearance and reduces complaints of the scars, it is easy to apply and painless 9,24,40-42. Silicone can be used as rubber, gel or fluid 16. Numerous types of silicone products have been produced, such as silicone gel sheeting or silicone-filled cushions. Currently, product development has been focused on silicone gel, because it is easier to apply, can be used on more areas of the body and gives a higher patient compliance 43. Several studies have shown the efficacy of silicone gel sheeting in the prevention of hypertrophic scars 16,41,44, although the contrary has been described as well 45. It appears that it is important that the application starts from the second week at least until the third month of the

50 CHAPTER 3 postoperative period. The exact mechanism of action of silicone in the prevention and management of hypertrophic scars is unclear, although it is likely to influence the collagen remodeling phase of wound healing. Potential mechanisms are summarized in Table 3. It is recommended to wear silicone sheeting 12 24 hours a day for at least 2 3 months. Daily cleaning of the material and underlying skin is necessary to prevent irritation and heat rash. Other side effects of silicone are skin maceration and itching 9. 3.2 Pressure therapy Mechanical compressive force by pressure garments to treat hypertrophic scars in burn patients was already described in 1860 46. It was only until the 1960s that this treatment became standard in several burn centers to accelerate the remodeling Table 3. Possible mechanisms of action in silicone treatment. Cause Hydration Temperature Polarization Silicone oil Oxygen tension Mast cells Blood flow and pressure effect Hypothesis Hydration can be caused by the occlusion of the underlying skin. It decreases capillary activity and collagen production, through inhibition of the proliferation of fibroblasts 16,19,90. A rise in temperature increases collagenase activity and therefore silicone reduces hypertrophic scars by breaking down collagen 104. The negative charge within silicone causes polarization of the scar tissue, resulting in involution of the scar 91-93. PRO: The presence of silicone has been detected in the stratum corneum of skin exposed to silicone 104. CON: Other researchers suggest the effects are not likely to be due to silicone release, as other occlusive products without silicone have also shown good results 40,94-96. PRO: After silicone treatment the hydrated stratum corneum is more permeable to oxygen and thus oxygen tension in the epidermis and upper dermis rises. Increased oxygen tension will inhibit the hypoxia signal from this tissue. Hypoxia is a stimulus to angiogenesis and tissue growth in wound healing, as a consequence removing the hypoxia stops new tissue growth 19,107. CON: The contrary has also been described 97. PRO: Some reports have suggested that silicone has influence on the number of mast cells in hypertrophic scar tissue. A higher number of mast cells in hypertrophic scars compared to normal scars has been reported in several studies. An increased number of mast cells was found in keloid and hypertrophic scars treated with silicone and it was suggested that silicone results in an increase of mast cells in the cellular matrix of the scar with subsequent accelerated remodeling of the tissue 43,74,106. CON: Some studies have reported no difference of the number of mast cells in hypertrophic scars. compared with normal scars 21,98. Beneficial effects of silicone are not mediated by changes in blood flow or a pressure effect 104,105.

MANAGEMENT OF HYPERTROPHIC SCAR FORMATION 51 phase of wound healing 6,43,46. Prophylactic pressure is recommended in burn patients if spontaneous closure of the wound takes longer than 10 14 days or those requiring grafting 18,22,47,48. Pressure therapy is thought to have an effect on the collagen remodeling phase of wound healing. Several mechanisms of action have been described and are shown in Table 4. As soon as the wounds are fully closed and able to tolerate pressure, patients are fitted with pressure garments. Garments must be worn for at least 23 h a day until the scar is mature 48. The required amount of pressure lies between 24 and 40 mmhg 47-50. A significant difference was reported regarding thickness of burn scars that were preventively treated with garments with a mean value of 15 mmhg pressure compared with a mean pressure of 10 mmhg 50. A shortcoming of pressure garments is the difficulty to use them for scars in anatomical flexures and areas of high movement. Moreover, treatment is expensive as garments are custom-made and must be replaced regularly. Furthermore, they can be uncomfortable to wear and they have a poor appearance, which brings low patient compliance 19,48,51. Table 4. Possible mechanisms of action in pressure therapy. Cause Hydration Blood flow Prostaglandine E2 release Hypothesis PRO: Decreased scar hydration results in mast cell stabilization and a subsequent decrease in neovascularization and extracellular matrix production 6. CON: This hypothesis is in contrast with a mechanism of action of silicon, in which an increase of mast cells causes scar maturation 6,48,51. 1. A decrease in blood flow causes a decrease in 2-macroglobulin and a subsequent increase in collagenase mediated collagen breakdown, normally inhibited by 2-macroglobulin 6. 2. A decrease in blood flow causes excessive hypoxia resulting in fibroblast degeneration and decreased levels of chondroitin-4-sulfate, with a subsequent increase in collagen degradation. Hypoxia would also loosen the collagen fibrils aligned to the skin surface 6. Induction of prostaglandine E2 release, which can block fibroblast proliferation as well as collagen production 99. 3.3 Corticosteroids Intralesional injection of corticosteroids is a second-line prophylaxis for patients with severe burns 24. Prevention of hypertrophic scarring by the use of corticosteroids is not frequently used as there are often large surfaces to deal with and it is not known whether or not the scars will become hypertrophic. Corticosteroids can reduce scar formation by affecting the collagen remodeling and inflammation phase of wound healing. Various explanations are described in Table 5. Steroid injections can be commenced at one month postoperative and can be repeated monthly with reassessments of the scar condition. Disadvantages of this treatment are the burning sensation caused by the injections (in spite of the use of

52 CHAPTER 3 Table 5. Possible mechanisms of action in corticosteroid therapy. Hypothesis 1 Decrease of fibroblast proliferation and therefore collagen synthesis 6,47,57. 2 Vasoconstriction responsible for a reduction of oxygen and nutrient supply to the wound 6,47,57. 3 Activation of endogenous collagenase 91. 4 Suppression of inflammatory mediators such as TGF- and the inhibition of leucocyte and monocyte migration as well as phagocytosis 6,47,57. anesthesia), skin atrophy, depigmentation, telangiectasias and the required long-term follow-up 6,52. 4. CURATIVE MANAGEMENT 4.1 Silicone Silicone can be used to prevent hypertrophic scar formation, but it is also a recognized therapy to treat these scars. Several clinical controlled and randomized studies have proven the effectiveness of silicone gel sheeting in hypertrophic scar management 13,40,42,52. However, not all clinical studies showed good results 53, possibly due to the fact that treatment and control areas were adjacent, the possible overlapping of the silicone sheet or the immaturity of the scars which could have improved with or without treatment. Recently, a comparative study was published in which the efficacy of silicone sheeting, silicone gel and a combination were evaluated and compared with an untreated control area in hypertrophic scars resulting from laser exfoliation 43. Only scars that were still in the erythematous and raised stage of healing, were included. Treated scars showed statistically significant improvement (elevation, erythema, pliability and symptoms of pain, burning and itching) compared with untreated control scars. Scars treated with silicone gel also showed less elevation compared with the scars following treatment with silicone sheeting 43. In a comparative study between the use of silicone gel filled cushions and silicone sheets or gel in the treatment of hypertrophic and keloid scars, improvement was found in both treatments. However, scars treated with silicone cushions obtained a superior and faster response in 100% of the scars 54. It is recommended to apply silicone gel twice daily or to wear silicone gel sheeting 12 24 hours per day for 6 12 months with temporary interruption when adverse effects appear. 4.2 Pressure therapy At present, pressure therapy is a preferred method for conservative management of scars, especially in treating hypertrophic burn scars, to increase thinning and improve pliability of the scars 18,24,47,51. Clinical effectiveness has never been scientifically proven, although previous authors claim to have achieved success rates of 60 85% 55. Treatment is most effective when the scar is still active. Therefore, it loses some efficacy after

MANAGEMENT OF HYPERTROPHIC SCAR FORMATION 53 6 months 51. It is recommended to be worn for 18 24 hours a day with a pressure between 24 and 40 mmhg until the scar matures 24,47-49. Early release of the garments tends to be followed by rebound hypertrophy 18. 4.3 Corticosteroids Intralesional corticosteroid injection is a possible approach to reduce hypertrophic scars. Rates of response vary from 50 100% with a recurrence rate of 9 50% 18,56. Injections may be used alone or in combination with other therapies 57-59. For instance, Mustoe et al. emphasize the combination of silicone gel sheeting and intralesional corticosteroids in the treatment of hypertrophic scars 24. A combination of intralesional corticosteroids with pulsed dye laser treatment (PDL) did not improve the hypertrophic scars 59. Steroids, most commonly triamcinolone acetonide 10 40 mg/ml 18,24,47,49, can be injected intralesionally at 4 6 week intervals 6. The maximum dose is 1 mg (=0.1 ml of 10 mg/ml) per injection with at least 1 cm between injection sites. The maximum amount of injections is not known, although the authors of this review find the total dosage should not exceed 30 40 mg. This means the maximum treatable scar surface is approximately 40 cm 2. Therefore, one should realize that this therapy is not suitable for extensive burn scars. Steroids can also be administered topically, however, due to poor tissue absorption, it is likely to be effective in relatively superficial lesions only 6,47. 4.4 Laser therapy In scar management the use of lasers has become more important. When the first carbondioxide and argon lasers were used in the treatment of hypertrophic scars, recurrence rates of 90% and higher were seen 18,24,60. In combination with corticosteroid injections outcomes improved, although recurrence rates remained 16 74% 18,61. In the past decade, improvement of postsurgical hypertrophic scars in 57 83% of the cases has been described after treatment with flashlamppumped PDL, which targets oxyhemoglobin 57,59,62. Various authors have reported the effectiveness of PDL in the treatment of hypertrophic scarring, both post-surgically as post-burn 63-65, and in combination with intralesional corticosteroids 57,59. Not all results are positive though. Wittenberg et al. reported no difference in outcome of hypertrophic scars treated with the 595-nm PDL and the control sections in a single-blind randomized controlled study 53. In this study, patients received four laser treatments at 8 week intervals. The mechanism by which laser achieves improved clinical outcome is still unclear. It probably influences the collagen remodeling phase and/or the angiogenesis (Table 6). One to six treatment sessions at 4 8-week intervals have been reported as most effective 47,53,57,64. Wavelength (optimally close to the oxyhemoglobin absorption peak 542 nm), fluence (range of 3.5 7.5 J/cm 2 ) and adjunctive therapies (e.g. corticosteroids, 5-fluorouracil) are parameters that affect outcome of this treatment 66,67. Minimal side effects and treatment discomfort have been reported 59,63. Temporary purpura, hypoand hyperpigmentation are the most common adverse effects 64,68.

54 CHAPTER 3 Table 6. Possible mechanisms of action in new developments. Therapy Laser Cryotherapy Interferon Hypothesis Light energy emitted from the majority of the lasers is absorbed by hemoglobin, generating heat and leading to damage of the microvasculature. This results in hypoxia which leads to 1. collagen fiber heating and subsequent alignment, and 2. histamine release which influences fibroblast activity, possibly due to mast cell activation. It was also reported that a 585-nm PD laser can decrease fibroblast proliferation and collagen type III deposition 59,62,64,66,68. The freezing of cryotherapy induces ischemic damage of the microcirculation. As a result the cellular destruction and anoxia promotes shrinkage of the hypertrophic scar tissue. A tendency to normalization of the collagen structure after treatment in hypertrophic burn scars suggests recovery of normal collagen synthesis 70,103. Interferon causes a decrease of the synthesis of collagen type I and III by fibroblasts and an increase of collagenase activity. Biopsies of hypertrophic burn scars treated with systemic interferon-alpha 2b showed a decreased number of fibroblasts compared to biopsies of immature burn scars and normotrophic scars. A reduction in serum transforming growth factor (TGF)- concentration could also play a role in scar reduction. Thereby, it was suggested that improvement of hypertrophic scars after injection is associated with induction of myofibroblast apoptosis. Most recently, it was reported that improvement of hypertrophic burn scars after treatment with interferon-alpha 2b is associated with decreased numbers and activity of fibrocytes 6,11,74,100-102. 5-Fluorouracil It inhibits rapidly proliferating cells, such as fibroblasts, by blocking DNA synthesis and transcription 58. 4.5 Cryotherapy Cryotherapy, freezing scar tissue, is used as a monotreatment for hypertrophic and keloid scars as well as in combination with other treatments, such as intralesional corticosteroids. A good response in 76% of the patients with hypertrophic scars without recurrence during 32 months of follow-up has been shown 69. Additionally, over 50% scar volume reduction was reported after one intralesional treatment in hypertrophic scars and keloids, without recurrence during 18 months of follow-up 70. Cryotherapy is thought to influence the collagen remodeling phase of wound healing, which is further described in Table 6. For good results, up to 20 treatment sessions are needed 70. Cryotherapy may be less desirable to patients than other treatments, because of the resulting pain, skin atrophy and hypopigmentation, especially with the use of surface techniques (e.g. contact and spray probes) 11,19,70 and because of the high frequency of treatment. Intralesional cryotherapy by use of a cryoprobe causes less damage of the epithelium and maximizes cell destruction deep in the lesion 70. 4.6 Radiation Radiation for the treatment of hypertrophic scars has not been described frequently, in contrast to the application in keloids in which especially brachytherapy is successful.

MANAGEMENT OF HYPERTROPHIC SCAR FORMATION 55 Most likely, this is due to lack of efficacy in hypertrophic scars and the serious adverse effects. Therefore, it will not be discussed in this review. 4.7 Surgery Many aspects of surgery for hypertrophic scarring have been debated. The decision to operate on hypertrophic scars is based on many parameters such as age of the scar, location, surface area, cause, irresponsiveness to conservative treatments, opinion and expectations of the patient, as well as opinion and expertise of the surgeon. The scar should be critically evaluated for its appearance, as hypertrophic scars are frequently misdiagnosed as keloids. The recurrence rate of keloid scars that have been excised is high (45 100%) 6,24,71. Gentle handling of the tissue, removal of residual inflammatory tissue, and reorientation of scars within the lines of minimal tension should be considered as surgical dogmas 6,18. Small hypertrophic scars can be excised and the defect should be closed primarily. Both intra- and extralesional excision of the scar has been advocated. In larger surface areas of hypertrophic scarring excision may be considered, but adequate closure of the defect should be provided. Healthy skin that surrounds the hypertrophic scar may be utilized to cover the defect. Surgery by means of tension releasing Z-plasties has proven to be effective in reducing scar hypertrophy, as one of the main effects of Z-plasty is to convert the direction of the scar from vertical to parallel to the lines of minimal tension 56. Tissue expansion and (local pedicled or free) flaps are also commonly applied solutions. The use of dermal substitutes in reconstructive surgery has increased the surgical armentarium and has been shown to improve the outcome of wound healing. Improvement in scar quality (i.e. elasticity and hypertrophy) has been found with the use of dermal substitutes in reconstructive and acute burn wounds 32,38,72,73. The dermal replacement serves as a temporary matrix for the ingrowth of fibroblasts, macrophages, lymphocytes and endothelial cells 38 and is thought to guide the cells to deposit collagen in a more randomized fashion, comparable with normal skin. Additionally, it is hypothesized that the substitute bridges the interstices of the autograft. It replaces the dermis of the graft which is otherwise lacking in the gaps and consequently prevents hypertrophy 32. Due to the high recurrence rate of hypertrophy after surgery, compression therapy, silicone application, intralesional corticosteroids or radiation is recommended following excision 6,18,49. 5. NEW DEVELOPMENTS 5.1 Interferon Interferons are naturally occurring antifibrotic cytokines that are reported to have beneficial therapeutical effect in abnormal scars. Tredget et al. showed a significant improvement of hypertrophic burn scars in 78% of the patients after interferon therapy 74. Explanations for the effects of interferon are shown in Table 6. Adverse effects of interferon therapy include flu-like symptoms and pain on injection 6,11.

56 CHAPTER 3 5.2 5-Fluorouracil 5-Fluorouracil is a pyrimidine analogue with antimetabolite activity 75, which has been used against many malignancies 47. The experience and several case reports of 5-fluorouracil in hypertrophic (burn) scars were described, as well as the therapy in combination with corticosteroid injections and PDL therapy 58. Rarely a hypertrophic scar did not respond favorable and recurrence did not occur. Furthermore, significant clinical improvement (scar height, erythema and pliability) was seen in the monotreatment of hypertrophic scars with 5-fluorouracil 57. 5-Fluorouracil probably affects the collagen remodeling phase (Table 6). Adverse effects of this treatment include pain, hyperpigmentation, wound ulceration, purpura at injection sites and tissue sloughing 11,47,58. An additional remark regarding 5-fluorouracil as well as interferon, is the utility for the treatment of extensive areas of burn scars, as systemic (side) effects may become more important. 5.3 Other therapies Other experimental therapies include intralesional injection of bleomycin, onion extract/heparin gel, enalapril, basic fibroblast growth factor (FGF2) and the blockage of transforming growth factor (TGF)-. Bleomycin is an antineoplastic agent and cytotoxic antibiotic that has been used successfully for many years in the treatment for recalcitrant plantar warts 76. The efficacy of intralesional bleomycin in the treatment of hypertrophic scars has been shown in several small studies; complete flattening of scars in 53.8 73.3% of the patients was achieved, without recurrences 76,77. A possible hypothesis is the inhibition of collagen synthesis as a result of bleomycin 77. Also onion extract/heparin gel has been used in the treatment of hypertrophic scars 78,79. In a comparative study of 107 patients, Ho et al. showed that scar development after surgery was less in onion extract/heparin gel treated scars than in untreated scars 79. The onion extract possesses fibroblast inhibiting properties, reducing fibroproliferative activity and the production of the extracellular matrix 47. Heparin may also play an important role as it interacts with collagen molecules 78. Unfortunately, heparin will also have systemic effects. Iannello et al. described substantial improvement with the use of low-dose enalapril, an angiotensin-converting enzyme (ACE)-inhibitor, in two patients with postsurgical hypertrophic scars and keloids, within 1 6 months 80. It is suggested that the ACE is related to fibrous tissue formation and enalapril would therefore reduce scar mass 80. FGF2 in burn wounds is suggested to be a mediator that is released from injury sites and plays an important role in early wound healing. In a comparative study, 20 patients with burn wounds were either treated with FGF2 solution or treated conservatively. Clinical evaluation of pigmentation, pliability, height and vascularity showed significant improved results in the FGF2 scars. The occurrence of hypertrophic scarring however, was not significantly less in patients receiving FGF2 treatment 81. In other reports, burn wounds treated with FGF2 were significantly less hard than burnwounds not treated with FGF2 and surgical wounds developed significantly less hypertrophy after the administration of FGF2 82,83.

MANAGEMENT OF HYPERTROPHIC SCAR FORMATION 57 During tissue remodeling TGF- is expressed at high levels and significantly influences the formation of connective tissues. Especially TGF-1 and 2, two of the three isotypes of TGF-, have been identified as key players in hypertrophic scar formation 84-86. A new treatment option for hypertrophic scars is the blockade of TGF-1 and 2 by use of anti-tgf-1 and 2 monoclonal antibodies and/or administration of TGF-3, which target the fibroblasts. The effects of the antibodies in rabbit wounds were studied and a reduction in scar hypertrophy was found when antibodies were injected one week after wounding 87. Another option is the inhibition of TGF- receptor II-mediated signaling, which has been reported to reduce hypertrophic scars in a rabbit cutaneous model 88. Treatment options and recommendations are summarized in Figure 3. 6. CONCLUSION Research into the biological nature of the scar has lead to an increased understanding of mechanisms in hypertrophic scar formation, resulting in the development of more specific therapeutic options. Unfortunately, hypertrophic scars remain difficult to treat. In this review, multiple therapies and studies have been discussed. A great deal of the published studies to determine incidence of hypertrophic scarring or to asses the efficacy of a treatment, have shortcomings. Additionally, the differences in study designs makes evaluating and comparing therapies difficult. It is of importance that a consensus concerning the definition of a hypertrophic scar, according to an assessment tool, will be developed and internationally used. Our recommendation regarding hypertrophic scarring in the daily practice is to classify and assess the scar by means of the VSS or POSAS, taking into account that the VSS is a more qualitative scale and the POSAS a more quantitative. Scars with a VSS height score of >1 or a POSAS thickness score of 3, can be defined as hypertrophic. Regarding the assessment of scars in clinical trials, we recommend the use of the POSAS or VSS and additional documentation of the percentage of the original wound surface area that is involved. To determine the incidence of hypertrophic scarring or to assess treatment effectiveness, the following data should be taken into account: skin type, age, wound depth, time of healing, treatment, time of surgery, wound area and hypertrophic scar area (percentage of the original wound area with hypertrophy according to VSS and/ or POSAS). Additional research is required to determine best possible treatment. Since there is no optimum treatment option present-day, patient expectations, adverse effects and costs should be considered in order to determine the best treatment individually.

58 CHAPTER 3 Figure 3. Treatment options and recommendations. VSS, Vancouver Scar Scale; POSAS, Patient and Observer Scar Assessment Scale; TGB-, transforming growth factor-; FGF2, Basic fibroblast growth factor.

MANAGEMENT OF HYPERTROPHIC SCAR FORMATION 59 REFERENCES 1. Peacock, E.E., Jr., Madden, J.W. & Trier, W.C. Biologic basis for the treatment of keloids and hypertrophic scars. South Med J 63, 755-760 (1970). 2. Bock, O., Schmid-Ott, G., Malewski, P. & Mrowietz, U. Quality of life of patients with keloid and hypertrophic scarring. Arch Dermatol Res 297, 433-438 (2006). 3. Atkinson, J.A., McKenna, K.T., Barnett, A.G., McGrath, D.J. & Rudd, M. A randomized, controlled trial to determine the efficacy of paper tape in preventing hypertrophic scar formation in surgical incisions that traverse Langer s skin tension lines. Plast Reconstr Surg 116, 1648-1656 (2005). 4. Van Loey, N.E., Bremer, M., Faber, A.W., Middelkoop, E. & Nieuwenhuis, M.K. Itching following burns: epidemiology and predictors. Br J Dermatol 158, 95-100 (2008). 5. van der Veer, W.M., et al. Potential cellular and molecular causes of hypertrophic scar formation. Burns 35, 15-29 (2009). 6. Brissett, A.E. & Sherris, D.A. Scar contractures, hypertrophic scars, and keloids. Facial Plast Surg 17, 263-272 (2001). 7. Alhady, S.M. & Sivanantharajah, K. Keloids in various races. A review of 175 cases. Plast Reconstr Surg 44, 564-566 (1969). 8. Sharquie, K.E. & Al-Dhalimi, M.A. Keloid in Iraqi patients: a clinicohistopathologic study. Dermatol Surg 29, 847-851 (2003). 9. Fette, A. Influence of silicone on abnormal scarring. Plast Surg Nurs 26, 87-92 (2006). 10. Aarabi, S., Longaker, M.T. & Gurtner, G.C. Hypertrophic scar formation following burns and trauma: new approaches to treatment. PLoS Med 4, e234 (2007). 11. Leventhal, D., Furr, M. & Reiter, D. Treatment of keloids and hypertrophic scars: a meta-analysis and review of the literature. Arch Facial Plast Surg 8, 362-368 (2006). 12. Lewis, W.H. & Sun, K.K. Hypertrophic scar: a genetic hypothesis. Burns 16, 176-178 (1990). 13. Li-Tsang, C.W., Lau, J.C. & Chan, C.C. Prevalence of hypertrophic scar formation and its characteristics among the Chinese population. Burns 31, 610-616 (2005). 14. Spurr, E.D. & Shakespeare, P.G. Incidence of hypertrophic scarring in burn-injured children. Burns 16, 179-181 (1990). 15. Dedovic, Z., Koupilova, I. & Brychta, P. Time trends in incidence of hypertrophic scarring in children treated for burns. Acta Chir Plast 41, 87-90 (1999). 16. Chan, K.Y., Lau, C.L., Adeeb, S.M., Somasundaram, S. & Nasir-Zahari, M. A randomized, placebo-controlled, doubleblind, prospective clinical trial of silicone gel in prevention of hypertrophic scar development in median sternotomy wound. Plast Reconstr Surg 116, 1013-1020 (2005). 17. Bombaro, K.M., et al. What is the prevalence of hypertrophic scarring following burns? Burns 29, 299-302 (2003). 18. Niessen, F.B., Spauwen, P.H., Schalkwijk, J. & Kon, M. On the nature of hypertrophic scars and keloids: a review. Plast Reconstr Surg 104, 1435-1458 (1999). 19. Berman, B., et al. A review of the biologic effects, clinical efficacy, and safety of silicone elastomer sheeting for hypertrophic and keloid scar treatment and management. Dermatol Surg 33, 1291-1302 (2007). 20. Baker, R.H., Townley, W.A., McKeon, S., Linge, C. & Vijh, V. Retrospective study of the association between hypertrophic burn scarring and bacterial colonization. J Burn Care Res 28, 152-156 (2007). 21. Niessen, F.B., Schalkwijk, J., Vos, H. & Timens, W. Hypertrophic scar formation is associated with an increased number of epidermal Langerhans cells. J Pathol 202, 121-129 (2004). 22. Deitch, E.A., Wheelahan, T.M., Rose, M.P., Clothier, J. & Cotter, J. Hypertrophic burn scars: analysis of variables. J Trauma 23, 895-898 (1983). 23. Cubison, T.C., Pape, S.A. & Parkhouse, N. Evidence for the link between healing time and the development of hypertrophic scars (HTS) in paediatric burns due to scald injury. Burns 32, 992-999 (2006). 24. Mustoe, T.A., et al. International clinical recommendations on scar management. Plast Reconstr Surg 110, 560-571 (2002). 25. Roques, C. & Teot, L. A critical analysis of measurements used to assess and manage scars. Int J Low Extrem Wounds 6, 249-253 (2007). 26. Sullivan, T., Smith, J., Kermode, J., McIver, E. & Courtemanche, D.J. Rating the burn scar. J Burn Care Rehabil 11, 256-260 (1990). 27. Baryza, M.J. & Baryza, G.A. The Vancouver Scar Scale: an administration tool and its

60 CHAPTER 3 interrater reliability. J Burn Care Rehabil 16, 535-538 (1995). 28. Draaijers, L.J., et al. The patient and observer scar assessment scale: a reliable and feasible tool for scar evaluation. Plast Reconstr Surg 113, 1960-1965 (2004). 29. van de Kar, A.L., et al. Reliable and feasible evaluation of linear scars by the Patient and Observer Scar Assessment Scale. Plast Reconstr Surg 116, 514-522 (2005). 30. Van den Kerckhove, E., Staes, F., Flour, M., Stappaerts, K. & Boeckx, W. Reproducibility of repeated measurements on post-burn scars with Dermascan C. Skin Res Technol 9, 81-84 (2003). 31. van Zuijlen, P.P., Angeles, A.P., Kreis, R.W., Bos, K.E. & Middelkoop, E. Scar assessment tools: implications for current research. Plast Reconstr Surg 109, 1108-1122 (2002). 32. van Zuijlen, P.P., et al. Dermal substitution in acute burns and reconstructive surgery: a subjective and objective long-term follow-up. Plast Reconstr Surg 108, 1938-1946 (2001). 33. Archer, S.B., Henke, A., Greenhalgh, D.G. & Warden, G.D. The use of sheet autografts to cover extensive burns in patients. J Burn Care Rehabil 19, 33-38 (1998). 34. Mann, R., et al. Prospective trial of thick vs standard split-thickness skin grafts in burns of the hand. J Burn Care Rehabil 22, 390-392 (2001). 35. Rheinwald, J.G. & Green, H. Serial cultivation of strains of human epidermal keratinocytes: the formation of keratinizing colonies from single cells. Cell 6, 331-343 (1975). 36. Haslik, W., et al. First experiences with the collagen-elastin matrix Matriderm as a dermal substitute in severe burn injuries of the hand. Burns 33, 364-368 (2007). 37. Ryssel, H., Gazyakan, E., Germann, G. & Ohlbauer, M. The use of MatriDerm((R)) in early excision and simultaneous autologous skin grafting in burns-a pilot study. Burns (2007). 38. Dantzer, E., Queruel, P., Salinier, L., Palmier, B. & Quinot, J.F. Dermal regeneration template for deep hand burns: clinical utility for both early grafting and reconstructive surgery. Br J Plast Surg 56, 764-774 (2003). 39. Perkins, K., Davey, R.B. & Wallis, K.A. Silicone gel: a new treatment for burn scars and contractures. Burns Incl Therm Inj 9, 201-204 (1983). 40. Ahn, S.T., Monafo, W.W. & Mustoe, T.A. Topical silicone gel: a new treatment for hypertrophic scars. Surgery 106, 781-786 (1989). 41. Gold, M.H. Topical silicone gel sheeting in the treatment of hypertrophic scars and keloids. A dermatologic experience. J Dermatol Surg Oncol 19, 912-916 (1993). 42. Ahn, S.T., Monafo, W.W. & Mustoe, T.A. Topical silicone gel for the prevention and treatment of hypertrophic scar. Arch Surg 126, 499-504 (1991). 43. Chernoff, W.G., Cramer, H. & Su-Huang, S. The efficacy of topical silicone gel elastomers in the treatment of hypertrophic scars, keloid scars, and post-laser exfoliation erythema. Aesthetic Plast Surg 31, 495-500 (2007). 44. Cruz-Korchin, N.I. Effectiveness of silicone sheets in the prevention of hypertrophic breast scars. Ann Plast Surg 37, 345-348 (1996). 45. Niessen, F.B., Spauwen, P.H., Robinson, P.H., Fidler, V. & Kon, M. The use of silicone occlusive sheeting (Sil-K) and silicone occlusive gel (Epiderm) in the prevention of hypertrophic scar formation. Plast Reconstr Surg 102, 1962-1972 (1998). 46. Linares, H.A., Larson, D.L. & Willis- Galstaun, B.A. Historical notes on the use of pressure in the treatment of hypertrophic scars or keloids. Burns 19, 17-21 (1993). 47. Atiyeh, B.S. Nonsurgical management of hypertrophic scars: evidence-based therapies, standard practices, and emerging methods. Aesthetic Plast Surg 31, 468-492 (2007). 48. Macintyre, L. & Baird, M. Pressure garments for use in the treatment of hypertrophic scars--a review of the problems associated with their use. Burns 32, 10-15 (2006). 49. Alster, T.S. & Tanzi, E.L. Hypertrophic scars and keloids: etiology and management. Am J Clin Dermatol 4, 235-243 (2003). 50. Van den Kerckhove, E., et al. The assessment of erythema and thickness on burn related scars during pressure garment therapy as a preventive measure for hypertrophic scarring. Burns 31, 696-702 (2005). 51. Zurada, J.M., Kriegel, D. & Davis, I.C. Topical treatments for hypertrophic scars. J Am Acad Dermatol 55, 1024-1031 (2006).

MANAGEMENT OF HYPERTROPHIC SCAR FORMATION 61 52. Sproat, J.E., Dalcin, A., Weitauer, N. & Roberts, R.S. Hypertrophic sternal scars: silicone gel sheet versus Kenalog injection treatment. Plast Reconstr Surg 90, 988-992 (1992). 53. Wittenberg, G.P., et al. Prospective, single-blind, randomized, controlled study to assess the efficacy of the 585-nm flashlamp-pumped pulsed-dye laser and silicone gel sheeting in hypertrophic scar treatment. Arch Dermatol 135, 1049-1055 (1999). 54. Amicucci, G., Schietroma, M., Rossi, M. & Mazzotta, C. Silicone occlusive sheeting vs silicone cushion for the treatment of hypertrophic and keloid scars. A prospective-randomized study. Ann Ital Chir 76, 79-83 (2005). 55. Reno, F., et al. In vitro mechanical compression induces apoptosis and regulates cytokines release in hypertrophic scars. Wound Repair Regen 11, 331-336 (2003). 56. Sherris, D.A., Larrabee, W.F., Jr. & Murakami, C.S. Management of scar contractures, hypertrophic scars, and keloids. Otolaryngol Clin North Am 28, 1057-1068 (1995). 57. Manuskiatti, W. & Fitzpatrick, R.E. Treatment response of keloidal and hypertrophic sternotomy scars: comparison among intralesional corticosteroid, 5-fluorouracil, and 585-nm flashlamppumped pulsed-dye laser treatments. Arch Dermatol 138, 1149-1155 (2002). 58. Fitzpatrick, R.E. Treatment of inflamed hypertrophic scars using intralesional 5-FU. Dermatol Surg 25, 224-232 (1999). 59. Alster, T.S. Laser scar revision: comparison study of 585-nm pulsed dye laser with and without intralesional corticosteroids. Dermatol Surg 29, 25-29 (2003). 60. Apfelberg, D.B., Maser, M.R., White, D.N. & Lash, H. Failure of carbon dioxide laser excision of keloids. Lasers Surg Med 9, 382-388 (1989). 61. Alster, T.S. Laser treatment of hypertrophic scars, keloids, and striae. Dermatol Clin 15, 419-429 (1997). 62. Alster, T.S. Improvement of erythematous and hypertrophic scars by the 585-nm flashlamp-pumped pulsed dye laser. Ann Plast Surg 32, 186-190 (1994). 63. Manuskiatti, W., Wanitphakdeedecha, R. & Fitzpatrick, R.E. Effect of pulse width of a 595-nm flashlamp-pumped pulsed dye laser on the treatment response of keloidal and hypertrophic sternotomy scars. Dermatol Surg 33, 152-161 (2007). 64. Kono, T., et al. The flashlamp-pumped pulsed dye laser (585 nm) treatment of hypertrophic scars in Asians. Ann Plast Surg 51, 366-371 (2003). 65. Kono, T., Ercocen, A.R., Nakazawa, H. & Nozaki, M. Treatment of hypertrophic scars using a long-pulsed dye laser with cryogen-spray cooling. Ann Plast Surg 54, 487-493 (2005). 66. Kuo, Y.R., et al. Activation of ERK and p38 kinase mediated keloid fibroblast apoptosis after flashlamp pulsed-dye laser treatment. Lasers Surg Med 36, 31-37 (2005). 67. Manuskiatti, W., Fitzpatrick, R.E. & Goldman, M.P. Energy density and numbers of treatment affect response of keloidal and hypertrophic sternotomy scars to the 585-nm flashlamp-pumped pulsed-dye laser. J Am Acad Dermatol 45, 557-565 (2001). 68. Bouzari, N., Davis, S.C. & Nouri, K. Laser treatment of keloids and hypertrophic scars. Int J Dermatol 46, 80-88 (2007). 69. Zouboulis, C.C., Blume, U., Buttner, P. & Orfanos, C.E. Outcomes of cryosurgery in keloids and hypertrophic scars. A prospective consecutive trial of case series. Arch Dermatol 129, 1146-1151 (1993). 70. Har-Shai, Y., Amar, M. & Sabo, E. Intralesional cryotherapy for enhancing the involution of hypertrophic scars and keloids. Plast Reconstr Surg 111, 1841-1852 (2003). 71. Berman, B. & Flores, F. Recurrence rates of excised keloids treated with postoperative triamcinolone acetonide injections or interferon alfa-2b injections. J Am Acad Dermatol 37, 755-757 (1997). 72. van Zuijlen, P.P., et al. Graft survival and effectiveness of dermal substitution in burns and reconstructive surgery in a onestage grafting model. Plast Reconstr Surg 106, 615-623 (2000). 73. Clayman, M.A., Clayman, S.M. & Mozingo, D.W. The use of collagenglycosaminoglycan copolymer (Integra) for the repair of hypertrophic scars and keloids. J Burn Care Res 27, 404-409 (2006). 74. Tredget, E.E., et al. Transforming growth factor-beta in thermally injured patients with hypertrophic scars: effects of interferon alpha-2b. Plast Reconstr Surg 102, 1317-1328 (1998).

62 CHAPTER 3 75. Kontochristopoulos, G., et al. Intralesional 5-fluorouracil in the treatment of keloids: an open clinical and histopathologic study. J Am Acad Dermatol 52, 474-479 (2005). 76. Saray, Y. & Gulec, A.T. Treatment of keloids and hypertrophic scars with dermojet injections of bleomycin: a preliminary study. Int J Dermatol 44, 777-784 (2005). 77. Espana, A., Solano, T. & Quintanilla, E. Bleomycin in the treatment of keloids and hypertrophic scars by multiple needle punctures. Dermatol Surg 27, 23-27 (2001). 78. Hosnuter, M., Payasli, C., Isikdemir, A. & Tekerekoglu, B. The effects of onion extract on hypertrophic and keloid scars. J Wound Care 16, 251-254 (2007). 79. Ho, W.S., Ying, S.Y., Chan, P.C. & Chan, H.H. Use of onion extract, heparin, allantoin gel in prevention of scarring in chinese patients having laser removal of tattoos: a prospective randomized controlled trial. Dermatol Surg 32, 891-896 (2006). 80. Iannello, S., Milazzo, P., Bordonaro, F. & Belfiore, F. Low-dose enalapril in the treatment of surgical cutaneous hypertrophic scar and keloid--two case reports and literature review. MedGenMed 8, 60 (2006). 81. Akita, S., et al. The quality of pediatric burn scars is improved by early administration of basic fibroblast growth factor. J Burn Care Res 27, 333-338 (2006). 82. Akita, S., Akino, K., Imaizumi, T. & Hirano, A. A basic fibroblast growth factor improved the quality of skin grafting in burn patients. Burns 31, 855-858 (2005). 83. Ono, I., et al. Basic fibroblast growth factor reduces scar formation in acute incisional wounds. Wound Repair Regen 15, 617-623 (2007). 84. Shah, M., Foreman, D.M. & Ferguson, M.W. Neutralisation of TGF-beta 1 and TGF-beta 2 or exogenous addition of TGF-beta 3 to cutaneous rat wounds reduces scarring. J Cell Sci 108 ( Pt 3), 985-1002 (1995). 85. Wang, R., et al. Hypertrophic scar tissues and fibroblasts produce more transforming growth factor-beta1 mrna and protein than normal skin and cells. Wound Repair Regen 8, 128-137 (2000). 86. O Kane, S. & Ferguson, M.W. Transforming growth factor beta s and wound healing. Int J Biochem Cell Biol 29, 63-78 (1997). 87. Lu, L., et al. The temporal effects of anti- TGF-beta1, 2, and 3 monoclonal antibody on wound healing and hypertrophic scar formation. J Am Coll Surg 201, 391-397 (2005). 88. Reid, R.R., et al. Reduction of hypertrophic scar via retroviral delivery of a dominant negative TGF-beta receptor II. J Plast Reconstr Aesthet Surg 60, 64-72 (2007). 89. McDonald, W.S. & Deitch, E.A. Hypertrophic skin grafts in burned patients: a prospective analysis of variables. J Trauma 27, 147-150 (1987). 90. Chang, C.C., et al. Hydration, not silicone, modulates the effects of keratinocytes on fibroblasts. J Surg Res 59, 705-711 (1995). 91. Hirshowitz, B., et al. Static-electric field induction by a silicone cushion for the treatment of hypertrophic and keloid scars. Plast Reconstr Surg 101, 1173-1183 (1998). 92. Har-Shai, Y., et al. Negatively charged static electricity stimulation as a possible mechanism for enhancing the involution of hypertrophic and keloid scars. Isr Med Assoc J 1, 203-205 (1999). 93. Mustoe, T.A. Evolution of silicone therapy and mechanism of action in scar management. Aesthetic Plast Surg 32, 82-92 (2008). 94. Fulton, J.E., Jr. Silicone gel sheeting for the prevention and management of evolving hypertrophic and keloid scars. Dermatol Surg 21, 947-951 (1995). 95. de Oliveira, G.V., et al. Silicone versus nonsilicone gel dressings: a controlled trial. Dermatol Surg 27, 721-726 (2001). 96. Sawada, Y. & Sone, K. Hydration and occlusion treatment for hypertrophic scars and keloids. Br J Plast Surg 45, 599-603 (1992). 97. Quinn, K.J., Evans, J.H., Courtney, J.M., Gaylor, J.D. & Reid, W.H. Non-pressure treatment of hypertrophic scars. Burns Incl Therm Inj 12, 102-108 (1985). 98. Beer, T.W., Baldwin, H., West, L., Gallagher, P.J. & Wright, D.H. Mast cells in pathological and surgical scars. Br J Ophthalmol 82, 691-694 (1998). 99. Reno, F., Grazianetti, P. & Cannas, M. Effects of mechanical compression on hypertrophic scars: prostaglandin E2 release. Burns 27, 215-218 (2001). 100. Berman, B. & Flores, F. The treatment of hypertrophic scars and keloids. Eur J Dermatol 8, 591-595 (1998). 101. Nedelec, B., Shankowsky, H., Scott, P.G., Ghahary, A. & Tredget, E.E. Myofibrob-