Supplementary Material for: The Recurrence of Onychocryptosis when Treated with Phenolization: Does Phenol Application Time Play a Role? A Follow-Up Study on 622 Procedures

Introduction: Chemical matricectomy using phenol (CMP) is a recognized treatment option for onychocryptosis. However, the appropriate phenol application time to achieve nail matrix destruction is still unknown. Optimal ablation leads to low recurrence rates. The aim of this research was to assess the recurrence rate of onychocryptosis in a cohort of 622 consecutive patients treated with a 4-min CMP. Methods: We recruited all patients undergoing a 4-min CMP for onychocryptosis at the Istituto Podologico Italiano, Rome, Italy, in 2008–2017. Postoperative follow-up visits were set at 24 h, 7, 14, 21, and 28 days, 6 months, and 1 year after surgery. We used adjusted logistic regression to evaluate the potential risk factors for the disease recurrence including age, gender, toe shape, comorbidities, and disease localization. Results: The risk of recurrence in all patients treated with a 4-min CMP was 1.1% (n = 622, 95% CI = 0.5%–2.3%). In the subgroup of patients with cardiovascular disease (n = 39) the recurrence risk was 5.1% (95% CI = 0.61–7.3). Young age was also associated with increased odds of recurrence (p = 0.036). Conclusion: In this observational study, 4 min with no interruptions seems to be the appropriate application time of phenol when using CMP for the treatment of onychocryptosis. A randomized controlled trial should be carried out to confirm our results.