The Effect Of Botulinum Toxin Type A Injection Dose On Surgical Scar

Background and ObjectiveScar formation is the final result of surgical incision healing.In patients who undergo invasive surgical procedures,the cosmetic scars that appear after wound healing can cause distress.Preventing and improving postoperative scars has always been one of the research focuses of plastic surgery.The formation of scars is closely related to the local tension on both sides of the wound edge during wound healing;during wound healing,the surrounding muscle contraction and stretching machinery induces a continuous inflammatory response,which leads to excessive deposition of extracellular collagen and mucopolysaccharides,thereby causing hypertrophy and hyperpigmentation of scars.In this regard,early intervention after surgery can make the scar have a better appearance.Currently,scar treatment includes compression therapy,radiation therapy,silica gel therapy and laser therapy,but all have their limitations.Botulinum toxin type A injection is a commonly used treatment in plastic and cosmetic surgery.It induces chemical denervation by acting on presynaptic neurons to prevent the release of acetylcholine,which leads to striated muscle functional denervation.In recent years,studies showed that botulinum toxin type A injection has some positive effects on the prevention and treatment of scars,and can reduce the tension on both sides of the wound due to local muscle contraction.And it can inhibit the proliferation of fibroblasts and change the process of collagen deposition and remodeling.Moreover,many randomized controlled studies have proved that the application of botulinum toxin type A after plastic surgery is beneficial to prevent the surgical scar appearance,in which it could avoid the phenomenon of scar widening and local skin hypertrophy.There are literatures that when botulinum toxin type A is used to treat crow’s feet,hand-foot hyperhidrosis,etc.,different doses of botulinum toxin type A inj ection have different efficacy.Besides,studies have shown that a higher dose of botulinum toxin type A injection is associated with a longer maintenance time and leads to better clinical results.However,the effects of different doses of botulinum toxin type A for scar management has not investigated yet.Therefore,this prospective,split-scar,randomized controlled trial was performed to investigate the effect of different doses of paralesional botulinum toxin type A administration on scar cosmesis after surgical excision and determine the appropriate dose of botulinum toxin type A for surgical scar prevention.MethodsAfter passing ethics and completing clinical trial registration,our team recruited 22 patients from September 2019 to October 2020.The length of the incision of the patient was evaluated before the operation and the total amount of botulinum toxin required was estimated.The two halves of the incision of the patient were randomly divided into the high-dose group and the low-dose group.After excising the original lesion and applying cosmetic sutures,the wound was marked at the midline point.Te postoperative wound was treated,with each side randomized to receive either a low dose of botulinum toxin type A(4 U at every point,with an interval of 1 cm)or a high dose of botulinum toxin type A(8 U at every point,with an interval of 1 cm)injected intradermally from a site 5 mm away from the incision line by both two sides.Disinfect and replace excipients every 2-3 days according to the surgical site and wound healing.The time of suture removal depends on the site of operation.No additional anti-scar therapy,such as stress therapy or silicone application,was given after surgery.Te occurrence of complications or other discomfort was also recorded during the follow-up.Patients,injector and scar evaluators were blinded to the dose received.The scars were then evaluated at postoperative 6 months using the modified Stony Brook Scar Evaluation Scale(mSBSES),and patient satisfaction was evaluated using the Visual Analogue Scale(VAS).Subgroup analysis was conducted by the factors of gender,age and incision length based on the difference between the two groups of scar scale score.The occurrence of complications or adverse events was also recorded.ResultsWhen the scars were evaluated using the modified SBSES after 6 months by plastic surgeons,the mean score was found to be 5.90±1.59 for the high-dose injection side and 4.15±1.31 for the low-dose injection side.The high-dose group score was significantly higher than the low-dose group score(p<0.01).The subcategories of the modified Stony Brook Scar Assessment Scale(mSBSES)include scar width,height,color(redness),and incision visibility line,the details were as following:2.Scar width:compared to the low-dose side,the high-dose side had significantly greater values for width(1.65±0.49 versus 1.05±0.69,p<0.01).3.Scar height:compared to the low-dose side,the high-dose side had no significantly greater values for height(1.65±0.59 versus 1.35±0.59,p=0.11).4.Scar color(redness):compared to the low-dose side,the high-dose side had no significantly greater values for color(redness)(1.55±0.60 versus 1.25±0.64,p=0.13)5.Scar incision visibility line:compared to the low-dose side,the high-dose side had significantly greater values for incision visibility line(1.05±0.51 versus 0.50±0.61,p<0.01).Subgroup analysis was conducted on the difference of scar scale score between the two groups based on factors such as age,gender and incision length.The results of subgroup analysis are as follows.6.Gender subgroup:the difference of scar scale score between two group in male patients and female patients were 1.27±1.62(n=11),and 2.33±1.58(n=9),with no statistical significance(p=0.158).7.Age subgroup:the difference of scar scale score between two groups was 2.10±1.45(n=10)for patients older than average age,and 1.40±1.84(n=10)for patients younger than average age,with no statistical significance(p=0.357).8.Incision length subgroup:The difference of scar scale score between the two groups was 1.30±1.64(n=10)inpatients with higher than average incision length,and 2.2±1.62(n=10)in patients with lower than average incision length,the difference was not statistically significant(p=0.232).9.Patients’ satisfaction about the surgical scar appearance was evaluated using VAS,the mean VAS score for the high-dose side was 7.85±1.27 and the low-dose side was 5.20±1.40,with a statistically significant difference between the two sides(p<0.01).10.No serious adverse reactions or post-injection complications have been observed(such as hematoma,infection,botulism or allergies).ConclusionEarly postoperative high-dose botulinum toxin type A injections can provide better cosmetic effects than low-dose injections.