Introduction

Pathological scarring, especially hypertrophic scars, poses a substantial challenge after cutaneous surgery. OnabotulinumtoxinA (BTA) shows promise as a prophylactic agent by reducing tension and modulating early wound inflammation. However, its molecular mechanisms in humans remain poorly understood.

Aim

To evaluate the efficacy of a single intraoperative intradermal injection of BTA in improving surgical scar outcomes on the trunk and extremities and to identify novel protein biomarkers associated with treatment response.

Material and methods

A prospective, randomised, double-blind, split-scar trial was conducted at a single tertiary care centre. Forty-five patients scheduled for linear surgical excision on the trunk or extremities were enrolled. Immediately following excision, one wound edge was randomly assigned to receive intradermal injections of BTA (2.5 U/cm), while the contralateral edge received saline. The primary outcome was the difference in total Patient and Observer Scar Assessment Scale (POSAS) scores at 6 months. Secondary outcomes included scar width, Vancouver Scar Scale (VSS), and elasticity measured by cutometry. Additionally, wound fluid was collected from both sides at 24 and 72 h post-surgery via microdialysis. A panel of 10 novel biomarkers, including TGF-b1, CTGF, IL-10, MMP-1, TIMP-1, substance P, periostin, osteopontin, microRNA-29a, and microRNA-21, was quantified using multiplex ELISA and qRT-PCR.

Results

At 6 months, BTA-treated sides demonstrated significantly superior total POSAS scores (mean difference –8.1, 95% CI: –10.3 to –5.9; p < 0.001), narrower scars (1.8 mm vs. 2.7 mm, p = 0.002), and greater elasticity (p = 0.01). Biomarker analysis revealed that BTA-treated wounds had significantly lower levels of pro-fibrotic TGF-b1 (–42%, p = 0.004), CTGF (–38%, p = 0.006), and periostin (–31%, p = 0.01) at 72 h. Conversely, anti-fibrotic microRNA-29a was upregulated (+58%, p = 0.003), and pro-inflammatory substance P was reduced (–45%, p = 0.002) in BTA-treated wounds. MMP-1/TIMP-1 ratios were significantly higher in the BTA group, suggesting enhanced collagen remodelling (p = 0.008).

Conclusions

Intraoperative BTA significantly improves cosmetic and physical scar outcomes. Its efficacy is associated with a distinct molecular signature characterized by downregulation of pro-fibrotic proteins, upregulation of anti-fibrotic microRNAs, and a shift toward a more favourable remodelling environment. These findings identify novel therapeutic targets and biomarkers for scar prevention.