Summary of main results

Currently, the evidence for our review objectives consists of a small single center pilot randomized controlled trial (RCT) and ten retrospective controlled cohort studies (NRS). Due to the lack of further RCT evidence, we still included NRS in this updated version of our Cochrane Review. All included NRS reported the primary outcome (parastomal hernia), and one study (145 participants), also reported one of the secondary outcomes (stomal prolapse (Leong 1994)). Eight of the ten included cohort studies (594 participants), did not find a statistically significant difference in parastomal herniation rates after lateral pararectal compared to transrectal stoma formation. In contrast, the remaining two studies found a significant reduction of parastomal herniation if the stoma was pulled out through the belly of the rectus abdominis muscle (Eldrup 1982; Sjodahl 1988).

Pooling the data of all included NRS did not provide conclusive results. Reasons for the widely differing estimates of the intervention effect (heterogeneity) across studies could be due to the lack of standardization of the surgical procedure, as well as the absence of a uniform definition and detection method for parastomal hernia. An I² value of 64% indicated substantial statistical heterogeneity in the meta‐analysis (Analysis 1.2). The I² statistic describes the percentage of total variation across studies that is caused by heterogeneity rather than by chance (Deeks 2011). In Analysis 1.2, the calculated P value was interpreted as a finding of uncertainty. The wide confidence interval could be the result of the small number of studies combined in the meta‐analysis, as well as the substantial heterogeneity.

The wide confidence intervals in the other analyses were likely caused by the small sample size of the only included RCT, the PATRASTOM trial, which found inconclusive results between lateral pararectal and transrectal stoma placement for the incidence of parastomal herniation, other stoma‐related complications, and quality of life (Hardt 2016). However, due to the limited sample size and the wide confidence intervals, a small and even a moderately sized difference in favor of one of the two stoma placement techniques cannot be entirely ruled out.

In conclusion, there is no evidence supporting the surgical dogma that the transrectal route of stoma formation should be preferred in order to prevent parastomal herniation.

Overall completeness and applicability of evidence

The present review aimed to compare lateral pararectal to transrectal stoma placement for prevention of parastomal herniation and other patient‐relevant stoma‐related complications. This was only partly accomplished. All included studies reported parastomal herniation, the primary outcome, but only one of the NRS and the RCT presented data on stomal prolapse. Only the RCT, but none of the NRS, reported any other secondary outcomes. Furthermore, we could only conduct one of the planned subgroup analyses and none of the sensitivity analyses because the required data were not reported in the included studies. Thus, the evidence with regard to the review objective is very limited, and the identified studies could not address all of the objectives of the review. The NRS identified are all retrospective cohort studies and at high risk of bias, especially with regard to selection bias and incomplete outcome data (attrition bias). Since the participants were not randomly assigned to the two intervention groups, the risk of selection bias is high. Moreover, it mostly remained unclear whether the individual participants were representative of the population. Hence, external validity and generalizability of the results from the meta‐analysis of NRS remain unclear. Although overall risk of bias is considered moderate to low in the included RCT, there are some obvious limitations (small sample size, short follow‐up, non‐blinding of the surgeons assessing the primary endpoint), which restrict the applicability of the study results.

Quality of the evidence

We included one RCT and ten retrospective cohort studies in this systematic review. For key methodological features and limitations of the studies, please see Characteristics of included studies. Confidence in the estimates of the treatment effect is limited because of risk of bias, publication bias, imprecision, inconsistency, and indirectness. All these issues are included in the GRADE system and are summarized in the summary of findings Table for the main comparison. Overall risk of bias in the included observational studies is high, especially due to possible selection bias (no randomization, unclear representativeness and comparability of the two cohorts), and high risk of attrition bias. It remains unclear whether publication bias affected the estimates of treatment effect, but it cannot be excluded, because observational studies reporting higher rates of parastomal herniation and other stoma‐related complications might be less likely to be published than studies presenting lower complication rates. This may be a particular concern in surgery. Since the 95% confidence interval around the estimate of effect includes both no effect and appreciable benefit or appreciable harm, and because the total number of events is less than 300, we assume that there is considerable imprecision. Moreover, the quality of evidence is diminished due to inconsistency, because of the widely differing estimates of the intervention effect (heterogeneity) across studies, for which we failed to identify a plausible explanation. However, we did not find any evidence of indirectness with respect to the target population, intervention, or outcome of interest.

Hence, we downgraded the quality of the evidence from NRS for the primary endpoint (parastomal herniation) by one level, from low to very low, due to high risk of bias, imprecision, and inconsistency.

In summary, the body of evidence identified does not allow a robust conclusion regarding the objectives of the review.

Potential biases in the review process

Although we followed a strict protocol consistent with the new version of the MECIR, published in 2016 (Higgins 2016), and the Meta‐analysis of Observational Studies in Epidemiology (MOOSE) statements (Stroup 2000), and applied a comprehensive search strategy, this review is still prone to bias. For example, publication bias cannot be excluded in our review because NRS are not consistently indexed in trials registers (Reeves 2011). Consequently, it must be taken into consideration that we may have missed completed or ongoing NRS. Moreover, we did not screen conference proceedings, which could potentially lead to further publication bias.

As also stated in the "Declarations of interest" paragraph, four of the review authors (JH, FH, PK, SP) conducted one of the included studies, the PATRASTOM trial. In order to prevent confounding and to guarantee transparency and objectivity, an external clinician not involved in the trial checked data extraction, risk of bias assessment and interpretation of the PATRASTOM trial.

Agreements and disagreements with other studies or reviews

To our knowledge, this is the only systematic review addressing this particular review question. However, several narrative reviews have discussed the objective of our review (Carne 2003; Hotouras 2013; Israelsson 2008; Martin 1996; Pearl 1989).

Regardless of the fact that until recently, when the results of the PATRASTOM trial were published, there was no evidence from randomized trials, surgical dogma has emerged that a stoma should be placed through the rectus abdominis rather than lateral to the muscle, in order to prevent parastomal herniation. This credo has been persistently repeated in the surgical literature, usually without any scientific evidence (Park 1999; Pearl 1985). But how could this surgical dictum arise? And why does it still persist, despite the lack of evidence? In the mid 1930s, Gabriel and Lloyd‐Davies recommended transrectal colostomy formation to prevent parastomal herniation, which was approved by Turnbull 20 years later (Gabriel 1935; Turnbull 1958). In the mid‐1970s, a study from St. Mark's Hospital in London, UK, was published, reporting data on 227 people undergoing surgery for rectal adenocarcinoma. In 35 of the included participants, the colostomy was created transrectally, and after a follow‐up of one to six years, six of the 35 participants were diagnosed with a parastomal hernia (Marks 1975). Thus, on the basis of their data, the authors concluded that the transrectal route could not generally be recommended. One explanation of why surgeons continued to adhere to the thesis that the stomata should be placed transrectally could be the assumption that pulling the stoma through the rectus abdominis muscle provided a more snug fit, since the muscle contracted around the stomal aperture. On the other hand, the same thinking could lead to the concern that there was a higher risk of stoma‐related stenosis and ileus, due to tight muscle contractions around the enterostomy.

In 2010, Stephenson described a novel approach to stoma formation, the lateral rectus abdominis positioned stoma (LRAPS), being convinced that preservation of the rectus abdominis muscle and its sheath could prevent parastomal herniation (Stephenson 2010). The new technique implied that the anterior and posterior rectus sheath were only divided horizontally (not vertically) and that the rectus muscle was not incised, but separated from its sheath, by sharp and blunt dissection and was then retracted medially. After the bowel was delivered, any defect of the medial margins of the incisions in the anterior and posterior sheath was closed with interrupted absorbable sutures. Stephenson presented data from 29 consecutive, unselected people who received a LRAPS. After a mean follow‐up of 13 months (range 7 to 18), no parastomal hernia had been detected. In 2011, Evans published a further follow‐up of the LRAPS; at one year of follow‐up, the authors observed parastomal hernias in 5% of the participants with a LRAPS (3/62), and at two years, the parastomal hernia rate had increased to 10% (4/41 (Evans 2011)). Although the follow‐up duration was still rather short, the reported parastomal herniation rates were lower than what was usually reported in the literature (Israelsson 2008; Robertson 2005).

Another emerging surgical trend is the use of prophylactic mesh for prevention of parastomal herniation. In the last decade, multiple systematic reviews of randomized trials addressed the question of whether prophylactic implantation of prosthetic mesh could reduce the rate of parastomal herniation. The most recently published systematic reviews pooled the data of six to ten RCTs; meta‐analyses showed that mesh reinforcement at the time of stoma formation significantly reduced the incidence of clinically‐ and radiologically‐detected parastomal herniation without increasing stoma‐ or mesh‐related morbidity and other surgical complications (Chapman 2017; Cornille 2017; Cross 2017; López‐Cano 2017; Patel 2017; Pianka 2017; Wang 2016). However, these results should be interpreted with caution, due to the heterogeneity among the included studies, the high risk of bias, and the small sample sizes of the individual studies (the median sample size of the RCTs included in the systematic review by Chapman was 54 (range 34 to 113)). Because of these severe limitations, some of the authors of the most recent systematic reviews call for larger, higher‐quality RCTs, which also assessed different mesh types, locations, and techniques, as well as long‐term cost‐effectiveness (Chapman 2017; Cornille 2017; Patel 2017; Wang 2016). Interestingly, the very recently published high‐quality multicenter double‐blinded RCT from Sweden, STOMAMESH, with a remarkably larger sample size than all previously conducted RCTs (211 analyzed participants), could not confirm the findings of the above‐cited meta‐analyses: Odensten and colleagues described that mesh reinforcement around the stoma did not alter the rate of parastomal herniation at one‐year follow‐up (Odensten 2019). In summary, there is still contradictory evidence for the effect of prophylactic mesh placement at the time of stoma formation, and at least on the basis of the results of the current large RCT, the standard use of prophylactic mesh reinforcement cannot be recommended.