Anterior or posterior peroral endoscopic myotomy: anatomy may matter more than orientation

Peroral endoscopic myotomy (POEM) has become an established treatment for achalasia, providing durable symptom relief across manometric subtypes. As the procedure has matured, the debate has shifted from whether POEM works to how it should be performed. Among the technical variables that remain unsettled, myotomy orientation—typically anterior at the 1–2 o’clock position or posterior at the 4–5 o’clock position—has prompted persistent debate. The study by Suwatthanarak et al.1 adds prospective randomized data to this practical question.

In this single-center randomized trial, 34 treatment-naïve patients were allocated to anterior or posterior POEM, and 28 patients were included in the final efficacy analysis. Both approaches achieved excellent and durable symptom control, with sustained reductions in Eckardt scores and similar decreases in integrated relaxation pressure over 12 months of follow-up. Procedural parameters and serious adverse events were also comparable. These findings are consistent with previous randomized trials and a meta-analysis showing no clear difference in overall clinical efficacy between the two orientations.2-5

The findings on esophageal emptying are particularly noteworthy. Timed barium esophagography showed better clearance after anterior POEM at 1 and 2 minutes during later follow-up, even though symptom outcomes were similar.1 This finding merits attention because an earlier theory suggested the opposite. The lower esophageal sphincter is not anatomically uniform: the clasp fibers along the lesser curvature are relatively weak, whereas the oblique sling fibers toward the greater-curvature side are stronger. Based on this anatomy, early POEM experts suggested that a posterolateral myotomy crossing part of the sling-fiber complex might open the sphincter more completely and provide greater relief of dysphagia, although it might also increase reflux.6,7 However, a previous randomized study found similar timed barium emptying after anterior and posterior POEM,2 and the present trial raises the opposite possibility: anterior POEM may lead to better bolus clearance over time. This finding should be interpreted cautiously because the study was small, no between-group difference was observed at five minutes, and symptoms were similar. Nonetheless, it challenges the view that posterior POEM necessarily provides better esophageal emptying.

The reflux findings require equally careful interpretation. Abnormal esophageal acid exposure was numerically more frequent after posterior POEM than after anterior POEM (57.1% vs. 28.6%), although the difference was not statistically significant.1 Importantly, the authors state that sling fibers were routinely preserved and suggest that this preservation may have contributed to the absence of severe erosive esophagitis.1 Thus, the numerical excess of abnormal acid exposure after posterior POEM in this trial cannot simply be attributed to sling-fiber division.

This finding makes it less likely that post-POEM reflux can be explained solely by anterior versus posterior orientation. Preserving the sling fibers during posterior POEM has been linked to less severe erosive esophagitis,8 but reflux is likely influenced by several anatomical and technical factors, including the exact path, length, and depth of the gastric myotomy and the extent to which the clasp-sling fibers and other structures of the esophagogastric junction are preserved. Therefore, the clock-face position alone may not accurately indicate the extent of antireflux barrier disruption.9

Taken together, the study presents an interesting paradox. Posterior POEM was performed with efforts to preserve sling fibers, yet abnormal acid exposure was numerically more frequent, whereas anterior POEM unexpectedly showed somewhat better objective esophageal clearance. Neither observation is definitive, but together they suggest that the efficacy and reflux consequences of POEM cannot be explained solely by tunnel orientation. The actual anatomical configuration of the completed myotomy may therefore matter more.

Interpretation of postoperative reflux testing also requires caution. Esophageal acidification after POEM does not invariably represent true gastroesophageal reflux. Stasis of acidic ingested material or fermentation in a poorly emptying esophagus can produce prolonged low-pH episodes, and automated analysis may consequently overestimate reflux burden.10 An abnormal DeMeester score should therefore be interpreted alongside the pH tracing pattern, impedance data when available, endoscopic findings, symptoms, and objective assessment of esophageal emptying. In this regard, the multimodal follow-up used by Suwatthanarak et al.1—including timed barium esophagography, manometry, pH monitoring, and endoscopy—is a notable strength.

The trial should also be interpreted in light of its statistical limitations. With only 14 patients in each efficacy group, a nonsignificant difference cannot establish equivalence, particularly for reflux outcomes, for which a type II error remains plausible. The study was not designed as a formal equivalence or noninferiority trial, and the authors appropriately regard the findings as hypothesis-generating.1 The practical conclusion is therefore not that orientation is irrelevant but that both approaches are acceptable when performed by experienced operators and that procedural strategy should be individualized according to anatomy, prior interventions, fibrosis, and the ability to preserve the antireflux barrier.

As POEM continues to evolve, the more meaningful question may no longer be “anterior or posterior?” but rather “what anatomical configuration of myotomy provides adequate emptying while preserving the antireflux barrier?” The present study simultaneously challenges two intuitive assumptions: that posterior myotomy should necessarily provide better emptying and that excess reflux after posterior POEM can be explained primarily by sling-fiber division. Future trials should therefore characterize not only tunnel orientation but also gastric myotomy trajectory, depth, length, and sling-fiber preservation. Tunnel orientation is likely only one component of a broader anatomical strategy.