Stones that do not require EPLBD can be successfully extracted by EST in resource‐limited settings. Conversely, those who require EPLBD indicate that the CBD stone in question is difficult to remove, ⁶ requiring further procedures, equipment, or an experienced endoscopist. Our data and subsequent multivariable analysis suggest that stones larger than distal CBD exceeding 2 mm and square or round‐shaped stones are good predictors of difficult CBD stones. Hence, endoscopic stone removal becomes more difficult with increasing stone size and a narrow distal CBD diameter. However, larger stones alone may not predict difficult removal; larger stones lodged within a wide distal CBD may not be difficult to remove and may not require a further procedure. In contrast, small stones lodged in a narrow distal CBD may require an additional removal procedure.

Endoscopic clearance of the CBD is difficult because of a number of stone‐related variables, bile duct anatomy, and stone–bile duct relationships. However, little information is available on the relationship between stone and distal CBD diameter, which affects endoscopic CBD stone extraction in these individuals. Stone size and distal bile duct diameter are significant in predicting the technical outcomes of endoscopic CBD stone extraction. The stone size to bile duct diameter ratio of >1.0 was found to be a significant predictor of mechanical lithotripsy failure in a retrospective investigation. ¹⁷ Sharma and Jain ¹⁴ compared small stone diameters (median diameter of 8 mm [range 7–9 mm]) and narrow distal CBDs (median diameter of 3 mm [range 3–4 mm]) with large stones (median diameter 15.5 mm [range 15–20 mm]) and wide distal CBDs (median diameter of 16 mm [range 13–24 mm]) and found that the removal of small stones with narrow distal CBDs was more likely to succeed with mechanical lithotripsy, whereas the removal of large stones in wide distal CBDs was more likely to succeed with EST and basket extraction. Thus, the study concluded that any stone larger than 2 mm in diameter than the lower CBD diameter should be considered a large stone, regardless of the size. Based on this research ¹⁴ and our findings, the difference in CBD stone and distal diameter was classified into two categories, suggesting potential predictive value for difficult CBD stones requiring EPLBD. Any stone wider than a lower limit of CBD diameter exceeding 2 mm requires endoscopic techniques other than EST. Endoscopists have difficulty extracting CBD stones when the ampullary orifice or the distal CBD narrows; this may be due to insufficient relaxation of the sphincter muscles surrounding the ampulla or to a large stone compared to distal CBD.

No publication to date has examined the influence of CBD stone shape on endoscopic removal. In this study, the stone's shape (square or round) could predict the requirement for ELPBD. The univariable study for round and square‐shaped stones was mainly insignificant, while the multivariable analysis was significant. These results may be explained by the fact that shape may be a variable influencing the requirement for ELPBD, but the confounding factor overshadowed its influence. However, in a multivariable analysis adjusted for confounding variables, the effect of shape was detected. Square‐shaped stones may contribute to technical difficulty because their angles and equal transverse and longitudinal diameters make them difficult to pass, necessitating a large orifice. Likewise, round‐shaped stones have equal transverse and longitudinal diameters, contributing to their greater difficulty passing than oval‐shaped stones with smaller transverse diameters.

In this study, large stone size did not significantly predict the requirement for ELPBD. However, numerous studies have shown that stone size strongly indicates the difficulty of managing CBD stones using endoscopy. The explanations for these results are based on a relatively limited sample size. Therefore, there was no significant relationship between stone size and the necessity for ELPBD in multivariable analysis. Although many factors affect the overall success of stone extraction, these variables were adjusted as confounders in this study. In multivariable analysis, confounders were adjusted using a confounder summary score that included non‐stone factors such as age, gender, underlying disease, acute cholangitis, previous cholecystectomy, BMI, and mechanical lithotripsy. Impact stones were infrequent in this study and are not a factor that requires exploration. However, the notion that the number of balloon extraction attempts during the procedure and the affected on stone consistency, whether it was rigid or fragile, may benefit from future investigations.

This study is the first to explain how the disparity between the diameters of the stone and distal CBD affects endoscopic stone removal. Additionally, this is the first study to determine that the shape of CBD stones influences the technical difficulty of endoscopic extraction. Despite our study's observational and retrospective nature, we attempted to adjust the confounding factors but were unable to accomplish this for several factors. In future, randomized controlled trials and large sample sizes should be employed. In addition, in this study stone and CBD diameter measurements during ERCP were taken in just two dimensions; this may have resulted in an underestimation of the stone's size, shape, and CBD diameter, which would have been more accurate if measured in three dimensions. Future research could correct this to improve stone and bile duct assessments.