Background
Perianal fistula is a benign but recurrent condition that causes significant morbidity. A subgroup of patients experiences repeated recurrence despite multiple surgical interventions, resulting in progressive fibrosis of the perianal tissue and increasing risk of sphincter damage with each reoperation. No sphincter-preserving technique consistently achieves cure after multiple surgical failures.
Fistula-tract laser closure (FiLaC) uses a radially emitting diode laser probe to achieve thermal ablation of the fistula tract epithelium. Its principal demonstrated advantage is an exceptional continence safety profile, with no cases of continence deterioration reported in large published series. However, failure rates exceed 40%, leaving a substantial proportion of patients without a definitive solution.
Platelet-rich growth factor (PRGF-Endoret; BTI Biotechnology Institute, Vitoria, Spain) is a fully autologous biological product obtained from the patient's own peripheral blood by low-speed centrifugation, free of leucocytes and exogenous activators. It releases a sustained supply of tissue repair growth factors that promote neoangiogenesis, fibroblast proliferation, and extracellular matrix remodelling. Prior studies combining platelet-rich plasma with surgical techniques for perianal fistula have reported improved clinical healing rates compared to surgery alone. The specific combination of FiLaC laser ablation with perilesional PRGF injection has not been previously evaluated.
Rationale The biological rationale for the PLASMA procedure is synergistic. Laser ablation removes the fistula tract epithelium and creates a receptive tissue bed. Immediate perilesional PRGF injection provides the growth factors required to accelerate healing and reduce the chronic inflammation that drives recurrence in multi-operated fistulas. Mandatory closure of the internal opening eliminates the high-pressure intestinal entry point that perpetuates the fistula. Selection of patients with a seton in situ for at least 6 months without active sepsis ensures a quiescent tissue microenvironment at the time of treatment.
Procedure All procedures are performed by a single surgeon under spinal anaesthesia as ambulatory day surgery. The PLASMA procedure consists of four sequential steps in a single operative session: (1) seton removal; (2) fistula tract laser ablation using a 1000-µm radially emitting FiLaC probe connected to a Leonardo Dual diode laser (1470 nm, 12 W, continuous mode, 1 mm/s withdrawal speed); (3) mandatory direct primary suture closure of the internal opening (Vicryl 2/0) in all patients; (4) perilesional injection of 7 ml of activated autologous PRGF-Endoret around the fistula tract and closure site using a 23-gauge needle under direct vision.
PRGF-Endoret is prepared on the day of surgery from 36 ml of peripheral venous blood collected in four sodium citrate tubes, centrifuged at 580 rpm for 8 minutes. The leucocyte-free platelet-rich fraction is activated with autologous calcium chloride solution immediately before injection. PRGF-Endoret has been authorised as a Sustancia de Origen Humano (SoHo) for use in this study by the Organizacion Nacional de Trasplantes (ONT) of Spain.
Statistical approach This is a descriptive pilot study. The primary endpoint will be expressed as a proportion with exact 95% confidence interval. Continence and quality of life scores will be compared between baseline and follow-up timepoints using the Wilcoxon signed-rank test for paired samples. Factors associated with clinical cure will be explored by exploratory post hoc univariate analysis. No multivariate analysis is planned. All results are hypothesis-generating and will not be interpreted as confirmatory evidence. Analyses will be performed in Python 3.12
