A systematic review and meta-analysis of randomised controlled trials on surgical treatments for ingrown toenails part I: recurrence and relief of symptoms

An ingrown toenail, or onychocryptosis, is a common problem that occurs when the nail plate punctures the periungual skin causing substantial pain, inflammation, discomfort and increased risk of infection if left untreated [1]. Most cases occur in the hallux and typically present in teenagers and young adults, although may present at any age [2, 3]. Several factors have been proposed as contributory to the occurrence or worsening of ingrown toenails with varying degrees of evidence. These include poor nail cutting technique, hyperhidrosis, ill-fitting footwear, nail deformity, trauma, obesity, and peripheral oedema [4, 5].

Multiple semi-quantitative classification systems have been developed to classify ingrown toenails. Most focus on the severity of ingrown toenails, and generally have three stages: mild (stage I), moderate (stage II) and severe (stage III) [6‐8]. Although, more recently an alternative approach has been suggested that focusses on the shape of the nail plate and aetiology of the pathology [8]. The performance of these classification systems has not been evaluated but have been proposed as a basis upon which to base treatment decisions.

Conservative approaches in the form of appropriate nail cutting and spicule removal, soaking in warm water, guttering, and orthonyxia (nail bracing) have all been advocated in the literature for use in mild to moderate stages (stage I and II) with varying success rates and quality of evidence [5, 8]. However, when conservative treatment fails, where there is nail deformity, or in more severe cases (stage II and III), a surgical approach is often recommended aiming to remove the problem part of the nail and destroy the underlying matrix to avoid recurrence [8‐10].

Multiple surgical interventions have previously been described with most including either partial or total avulsion of the nail plate, that is often combined with ablation of the nail matrix to stop regrowth. Nail surgery is performed by a range of health professionals including GPs (general practitioners), orthopaedic surgeons, dermatologists, and podiatrists. Indeed nail surgery forms a substantial part of the workload of podiatrists, having been identified as the tenth most commonly performed procedure performed by the profession [11]. Whilst there is little published data to describe how this common nail pathology is treated in practice, it is clear that a large number of small studies have been published on the topic. Systematically searching for and reviewing these studies, pooling estimates of effectiveness, and providing recommendations for practice and future research is essential to enable evidence-based practice.

A Cochrane review published 10 years ago suggested that use of phenol reduced the likelihood of recurrence but did not differentiate between regrowth of the nail plate (which may be asymptomatic) with recurrence of symptoms [4]. The authors also found that there was insufficient evidence to make recommendations on whether more radical surgery was more effective in cases of more severe disease, or how key patient reported outcomes such as relief of symptoms, patient satisfaction, and post-operative pain were affected by nail surgery. More recent narrative reviews have been written [8, 12], and a systematic review specific to the use of phenol used a very limited search strategy, and did not adhere to key methodological principles such as prospective registration of their review [13]. Accordingly, there is a need for an up-to-date and rigorous systematic review of surgical methods for treating ingrown toenails. The aim of this study, therefore, was to systematically search and synthesise the literature relating to the effectiveness/efficacy of surgical methods for treating ingrown toenails.

The Cochrane Handbook for Systematic Reviews of Interventions [14] was used to guide the conduct of this review. The review was reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [15], This review was prospectively registered at https://​www.​crd.​york.​ac.​uk/​prospero/​ [CRD42021251938].

Ingrown toenails, or onychocryptosis is a common nail pathology. Surgical resolution is often sought when conservative measures fail, or even as a first line intervention in more severe cases. As such, nail surgery is one of the most commonly performed procedures by podiatrists in the UK [11]. Despite the high number of publications on the topic, there has been a lack of robust systematic reviews covering the spectrum of surgical options in the decade since the last Cochrane review [4].

This review followed Cochrane methodology and conducted a prospectively registered systematic review with meta-analysis of surgical treatments for ingrown toenails. This paper includes a detailed description of our methodology and presents findings from our predefined primary outcomes: recurrence and relief of symptoms. Analysis of secondary outcomes will follow in a subsequent publication.

The systematic, search identified 1,641 potential publications which, after screening, enabled 36 studies with 3,756 participants covering a range of techniques that were included in the review. This is a substantial increase on the 24 and 18 studies in the previous Cochrane review [4], and the review by Vinay and colleagues [13], respectively. Recurrence was reported in all but one study, although there were variations in how this was defined and captured. Meta-analysis did not demonstrate a difference in risk of regrowth for most comparisons. Perhaps unsurprisingly, phenolisation was a notable exception to this pattern and when compared to nail avulsion alone, there was a very low certainty of evidence that use of phenol significantly reduced the risk of recurrence [39, 43]. However, use of phenol combined with surgical excision offered no benefit over phenolisation alone [31, 41]. In terms of how long to apply the phenol for, there was a moderate certainty of evidence that application of 1 min had lower risk of regrowth compared to 30 s [51], but there was no additional benefit when it was applied for 2 or 3 min [20]. Studies of peri-operative factors beyond the actual procedure such as use of different local anaesthetic with / without adrenaline [30, 37] and topical antibiotics [35] did not affect rates of regrowth even with such an atypical application technique.

Surprisingly, symptom relief was only reported in five [22, 23, 38, 40, 46] of the 36 studies and in three of those, it was not clear whether this was patient reported, or determined by the clinicians [22, 23, 40]. Even in these studies, exactly what ‘symptoms’ refers to is often unclear. Ingrown toenails are intensely painful though, and that this is rarely captured is a poor reflection on the quality of research in the field: it is no longer acceptable for studies to fail to capture key outcomes that matter to patients, and instead only focus on clinician reported outcomes. The importance of PROMs is well recognised by major national health policy and regulatory authorities [56, 57]. The authors question whether it is acceptable for future trials in ingrown toenails to continue to omit patient reported outcomes. It is important that future clinical trials differentiate between regrowth, which may be asymptomatic, and regrowth which causes pain and infection.

Clinical conclusions from this paper should be interpreted in line with our second paper that considers the secondary outcomes from our review: healing time, postoperative complications, pain of operation, postoperative pain (duration and intensity), and participant satisfaction. Only with these can a broader, more holistic, assessment of outcome be fully appreciated so these are essential for guiding practice.

All 36 studies included in the review were assessed as being either high risk or having some concerns about bias when assessed with the Cochrane RoB 2.0 tool. Similarly, out of the 15 comparisons made here, most were considered to have either very low, or low certainty of evidence when assessed with the GRADE system. Only three reached moderate, and none were considered to have high certainty. The main reasons for downgrading the evidence were risk of bias, indirectness of evidence, and imprecision. In addition, surgical technique was often poorly described, and there was large variation in the use of terms such as recurrence. It is also important that future clinical trials differentiate between regrowth that may be asymptomatic and regrowth that causes pain and infection. To put this another way, 3,756 people have taken part in research studies that do little to guide clinical practice. Some of this may be due to poor reporting, but poor design also plays a major role. Regardless, both of these reasons can, and should be avoided and this topic has been widely discussed in the literature with recommendations made to improve research across healthcare [58‐60]. Findings from this review differ from those of previous reviews. In part, this may be explained by the publication of new research in the decade since the Cochrane review [4] and a broader focus than the review by Vinay and colleagues specific to phenol [13]. However, the risk of bias assessment was also different as was the grading of strength of recommendations that could be made. Whilst there would inevitably be some variation in these relatively subjective assessment systems the authors stand by this assessment and have discussed some of the methodological limitations in the existing evidence base that have led us to this conclusion. More, high quality clinical trials to inform clinical decision making are urgently needed in nail surgery.

This review and meta-analysis both have strengths and limitations. The authors consider the robust methodology of the search, screening, extracted data, synthesis, meta-analysis, and use of tools such as RoB 2.0 and GRADE as methodological strengths. Deliberate attempts have been made to ensure that comparisons within the meta-analysis are clinically meaningful. Whilst some readers may disagree with how these studies have been compared, or want additional comparisons, they have been made in an open and transparent way. As a further note, this process was made more difficult due to the poor procedure descriptions, with many describing more than one procedure i.e., stated as nail edge excision but partial avulsion was described. Well established reporting guidelines such as the SUPER and IDEAL frameworks should be followed in the future [61, 62].

This paper presents the co-primary outcomes from a systematic review with meta-analysis that should be interpreted in conjunction with its second paper. Despite the high number of publications on this topic, the quality of research was poor and the conclusions that can be inferred from existing trials is limited. Phenolisation of the nail matrix reduces the risk of recurrence following nail ablation, and 1 min appears to be the optimum time for application but there is less certainty around this recommendation. Further research is needed to explore the effectiveness of other commonly used ablative agents such as sodium hydroxide and to systematically explore the optimisation of post-operative care.