Anal Sphincter Research Articles

Investigation of Expanded Human Adipose-derived Stem Cell Dosage and Timing for Improved Defecation Function.

Although certain treatment options exist for intestinal incontinence, none are curative. Adipose-derived stem cells (ADSCs) have emerged as promising therapeutic agents, but most preclinical studies of their effectiveness for anal function have used autologous or allogeneic ADSCs. In this study, the effectiveness, timing of administration, and required dosage of human ADSCs were investigated for clinical application. A 10-mm balloon catheter was used to induce anal sphincter injury in immunodeficient mice in the following experimental groups (n=4 per group): ADSC (injected ADSCs after injury), PBS (injected phosphate-buffered saline after injury), and control (uninjured). The effects of different timing (immediately after injection and 30 days following injury) and number of human ADSCs administered was compared among groups based on defecation status and pathological evaluation. In terms of defecation status, groups receiving ≥1×104 human ADSCs after injection showed improvement. Pathological images showed that compared to the PBS group, the thinnest part of the sphincter was thicker for animals that received ≥1×104 human ADSCs, and fibrosis of the sphincter was notable in those treated with 1×103 human ADSCs or PBS. Furthermore, defecation status was improved by administration of human ADSCs, not only immediately after injury, but also at 30 days following injury. Human ADSC administration in a mouse model of anal sphincter injury was effective. Injection of ≥1×104 human ADSCs was the amount necessary to improve defecation status, an effect detected in both the acute and chronic phases.

Complex Anterior Supralevator Anal Fistula With Prostatic Abscess Treated With Ksharasutra: A Case Report

Anorectal diseases are a major health threat in the field of health sciences. Fistula‐in‐ano is one of the treatable complex benign lesions of the rectum and anal canal. Complex high anal fistulas can reoccur even after surgical treatment. Establishing a cure for cryptoglandular fistula‐in‐ano is problematic, as a significant percentage of these diseases persist or recur if the internal opening of the anal fistula is left untreated. Here, we report a case of complex left anterolateral supralevator anal fistula with communication to the prostate gland that forms a prostatic abscess, as it is very rare. After following Ksharasutra (Ayurvedic medicated seton) treatment with regular wound care, significant regression in the condition was observed. A follow‐up scan showed no evidence of fistula‐in‐ano. A 50‐year‐old businessman presented with complaints of discomfort deep inside the rectum and perineum associated with pain at the base of the scrotum and pus discharge from the perianal region for 1 year. He was diagnosed to have a complex left anterolateral supralevator anal fistula with communication to the prostate substance after a thorough clinical examination and transrectal ultrasonography. After undergoing Ksharasutra treatment for 4 months, pus discharge completely stopped, and sonofistulogram report showed no evidence of fistula‐in‐ano. Images of the sonofistulogram report were documented before and after the treatment. This article highlights the unique feature of Ksharasutra therapy where the fistula extending to the prostate was treated with no loss of function of the anal sphincter.

Research progress on the application of Chinese herbal medicine in anal fistula surgery.

Anal fistula is a rapidly developing anorectal disease that can lead to anal dysfunction if left untreated. Minimally invasive surgery is an important treatment option for anal fistula, as it can reduce the risk of anal sphincter injury and protect anal function. However, postoperative complications such as infection, pain, bleeding, edema, and fat liquefaction can occur, resulting in slow wound healing thus negatively impacting the patient's quality of life. Recent studies have shown that Chinese herbal therapy has distinct pharmacological effects and is more effective in treating postoperative complications in anal fistula patients compared to conventional drug therapy. It not only promotes wound healing but also reduces the occurrence of complications. Chinese herbs can also modulate relevant signaling pathways such as PI3K/Akt, HIF-1, and TGF-β/Smad to enhance the wound healing process. Various methods of Chinese herbal medicine (CHM) have been used to treat post-anal fistula operation wounds, including traditional Chinese medicine (TCM) sitz baths, external application of TCM, internal administration of TCM, anal absorption, and acupuncture, all of which have shown promising therapeutic effects in clinical practice. This article aims to review the theory and clinical application of CHM in anal fistula surgery in recent years and provide valuable references for its treatment.

Differences in rates of severe perineal trauma between midwife-led and obstetrician-led care in the Netherlands: A nationwide cohort study

ObjectiveTo investigate trends and rates of severe perineal trauma (SPT), also known as obstetric anal sphincter injury (OASI), between midwife-led and obstetrician-led care in the Netherlands, and factors associated with SPT. MethodsThis nationwide cohort study included registry data from 2000 to 2019 (n = 2,169,950) of spontaneous vaginal births of term, live, cephalic, single infants, without a (previous) caesarean section or assisted vaginal birth.First, trends of SPT and episiotomy were shown. Second, differences in SPT rates between midwife- and obstetrician-led care were assessed. Third, associations of care factors with SPT were examined. Multivariable logistic regression analyses were used to determine which factors were important in the associations. All outcomes were stratified for parity. ResultsOver time, the SPT incidence increased mainly in midwife-led care and episiotomy rates decreased. Compared to midwife-led care, SPT rates were lower in obstetrician-led care among primiparous women (aOR 0.78; 99 % CI 0.74–0.81) and comparable among multiparous women (aOR 1.04; 99 % CI 0.99–1.10). Among women without epidural analgesia, these differences were smaller for primiparous women (aOR 0.88; 99 % CI 0.84–0.92), but the SPT rate was higher in obstetrician-led care among multiparous women (aOR 1.09; 99 % CI 1.03–1.15). Among women without shoulder dystocia, induction, augmentation, and pain medication, SPT rates were comparable among primiparous women, but higher among multiparous women in obstetrician-led care. In midwife-led care, SPT occurred more often among hospital versus home births. In obstetrician-led care, lower SPT incidences were found among births with epidural analgesia and for multiparous women with induction or augmentation. ConclusionsAmong spontaneous vaginal births, induction, augmentation, and epidural analgesia in obstetrician-led care may be an explanatory factor for the higher incidence of SPT among primiparous women in midwife-led care. More research is needed to explain differences in SPT rates and to understand how SPT can be prevented, while maintaining a high intact perineum rate.

Modified anal sphincter suspension improves anal function in patients with anal fistula.

To compare conventional thread-ligating therapy with the modified anal sphincter suspension procedure on the restoration of anal function in patients with anal fistula. This retrospective study included 120 consecutive patients with anal fistula treated at The First People's Hospital of Lin'an District, Hangzhou between January 2022 and December 2023. Patients were divided into an experimental group (n=66) who underwent the modified anal sphincter suspension procedure with preservation, and a control group (n=54) who received conventional thread-ligating therapy. Clinical data, including age, gender, duration of illness, BMI, medical history, anal function, pain score, quality of life score, overall efficacy assessment, and postoperative complications, were collected from the hospital's electronic medical records. The cure rate was 90.91% in the experimental group and 92.59% in the control group (P>0.05). Compared to the control group, the experimental group showed significantly higher scores in psychological function (89.65±6.87 vs. 89.35±7.67, P=0.004), material life (85.64±6.87 vs. 68.64±6.58, P=0.002), physical function (80.98±5.98 vs. 70.85±5.68, P=0.003), and social function (86.63±5.97 vs. 74.65±6.38, P=0.009) after surgery. Additionally, the Wexner scores, VAS scores, ARP, and RRP were significantly decreased in the experimental group postoperatively (all P<0.05). The modified anal sphincter suspension procedure with preservation significantly reduces postoperative pain and improves anal function, thereby enhancing the quality of life in patients with anal fistula.

56 Transperineal ultrasound-based algorithm advising women after obstetric anal sphincter injury regarding their subsequent delivery mode

56 Transperineal ultrasound-based algorithm advising women after obstetric anal sphincter injury regarding their subsequent delivery mode

Investigation of The Histopathological and Histometric Changes in Rectum Tissue Biopsies of Hirschsprung and Non-Hirschsprung Disease in Neonate and Infant

Hirschsprung disease is one of the most common and problematic infancy and childhood maladies. The most reliable method for diagnosis is the histopathological analysis of colorectal biopsies and the typical finding of Hirschsprung disease is the absence of ganglion cells. The study involved 36 cases of suspected Hirschsprung disease, in which 27 cases were males and 9 cases were females with an age range between (1 day - 1 year). All patients undergo complete history taking, physical examination, radiological investigations, and rectal biopsy. The tissue specimens were obtained from the rectum of neonate and infant patients, maintained in the fixative solution (formalin 10%) for histopathological analysis, and patients were divided into two groups (Hirschsprung disease and non-Hirschsprung disease group) according to histological findings. Statistical analysis was performed on the tabulated data by chi-square, and the automated computer-adopted image analysis program Image J® was utilized for the histometrical examination of rectum tissue. The Hirschsprung disease is more common in males than females. The delayed passage of meconium is the most common symptom of these diseases. We notice that there is a significant difference between the Hirschsprung disease group and the non-Hirschsprung disease group in clinical signs, empty rectum, tight anal sphincter on per rectal examination. Based on histopathology analysis of the rectal biopsy, out of the 36 cases, 27(75%) cases were diagnosed as Hirschsprung disease, and 9 (25%) cases as negative for Hirschsprung disease. In Histometric study of rectal biopsies tissues showed a significant difference in the mucosa, Submucosa, and muscularis externa between Hirschsprung disease and non-Hirschsprung disease patients.

Predicting Urinary Incontinence among Postpartum Women

Urinary incontinence (UI) is common during a pregnancy-puerperium period, with a prevalence of 18.6-75% during pregnancy and 6-31% during postpartum. This study aims to review several published studies on which risk factors impact the incidence of UI.The search was conducted on Pubmed®, Cochrane Library®, and Ovid®, resulted in 57, 30, and 11 studies, respectively. We included cross-sectional, cohort, or case-control studies related to this aim. The risk of bias within the study was assessed using the Cochrane and Forrest plot was analysed using Review Manager 5.3. On maternal characteristics, age less than 35 years (OR 0.49; 95% CI 0.35-0.67), primiparity (OR 0.29; 95% CI 0.22-0.38), and BMI &lt;25 kg/m2 (OR 0.67; 95% CI 0.55-0.83) were considered as protective factors. A low level of education (OR 2.16; 95% CI 1.69-2.77) increased the risk of UI, Meanwhile, they showed heterogeneity among studies (I2&gt;50%). On delivery methods, the most prone to UI was emergency caesarean section followed by instrumental vaginal deliveries, spontaneous vaginal deliveries, and caesarean section. Episiotomy, epidural analgesia, and obstetric anal sphincter injury (OASIS) were not associated with UI (p&gt;0.05). On neonatal parameters, head circumference &lt;35 cm has a protective effect on UI (OR 0.82; 95% CI 0.73-0.93; I2=0%). Methods of delivery and head circumference will affect postpartum UI according to p-value (p&lt;0.05) and homogeneity among studies (I2&lt;50%).

Three-Dimensional Transperineal Ultrasound Guiding Early Secondary Repair of Obstetric Anal Sphincter Injury in an Incontinent Patient without Suture Dehiscence.

We present the case of a 36-year-old primigravida who gave birth to a 3200 g baby by vacuum-assisted (Kiwi OmniCup™) operative vaginal delivery with mediolateral episiotomy. A "y"-shaped perineal tear with a grade IIIC obstetric anal sphincter injury (OASI) was diagnosed and repaired. Two days after delivery, in the absence of suture dehiscence, she started experiencing complete anal incontinence. A decision was made in association with a proctologic surgeon for an early secondary repair. Before surgery, a Three-dimensional transperineal ultrasound (TPUS) was performed. The exam revealed a major defect of the external anal sphincter at the 11 o'clock position. This allowed for the reopening of only a circumscribed area of the perineal suture and repair of the sphincters using the end-to-end technique. The symptoms regressed completely, and follow-up TPUS demonstrated the gradual wound healing process. Anal incontinence, secondary to obstetric anal sphincter injury (OASI), has a severe negative impact on women's quality of life. TPUS is an effective method to detect sphincter defects and monitor the healing process. This report investigates the feasibility of identifying the sphincter tear in an incontinent puerperal patient without suture dehiscence in order to target early secondary repair while minimizing its extent. TPUS has proven a safe and effective tool to guide early secondary repair of symptomatic OASI complications while minimizing the invasiveness of the procedure. Multidisciplinary management is crucial to ensure the adequate standard of care.

UK survey of colorectal surgeons on the management of acute obstetric anal sphincter injuries.

The role of colorectal surgeons in the management of acute obstetric anal sphincter injury (OASI) is an ongoing debate. Their expertise in operating in the anorectal region lends itself to assisting in OASI repair. The aim of this study was to establish the current involvement and recommended management of acute OASI by colorectal surgeons. An online survey of consultant colorectal surgeons was sent to members of the Pelvic Floor Society to assess current involvement in acute OASI management and repair. Forty completed surveys were collated and analysed. Sixty-five per cent of respondents had seen an acute OASI since being a consultant and 50% stated they were involved in the repair of OASI less than once per year. 37.5% felt that a de-functioning stoma was still necessary sometimes. Many agreed with current guidelines for OASI repair in terms of antibiotics, laxatives and follow-up. Colorectal surgeons have varied opinions on the management of OASI. We suggest that multidisciplinary training of obstetricians and colorectal surgeons could lead to more collaboration regarding the management of women with acute OASI.

Condition of the rectal closure system in ostomy patients

Aim of the study. The main idea of the study is to study changes in the functional activity of the rectum closure system in patients with intestinal stomas.Materials and methods. A single-center retrospective and prospective analysis of the results of changes in the function of the rectum closure system in 83 patients before reconstructive operation was performed. For the period from 2016-2018, 42 (50.6 %) men and 41 (49.4 %) women were examined, the average age in the group was 51.8 ± 12.6 years. A statistical analysis of the influence of various factors on the functional state of the obturator apparatus of the rectum was performed.Results and discussion. In all the examined patients, before the intervention, a decrease was found in the indicators characterizing the functional state of the anal closure system: average (ARP) rest anal pressure and maximum squeezing anal pressure (MSP). A statistically significant direct relationship was found between high degree of tightness between the degree of impaired function of the rectum closure system and the age of the patient (Rxy = 0.76, p = 0.005), and the duration of wearing the stoma (Rxy = 0.82, p = 0,0072). The mathematical model of the dependence of the degree of insufficiency of the anal sphincter on the age of patients and the duration of stoma wearing is characterized by a correlation coefficient Rxy = 0.72, a significance coefficient p &lt;0.001.Conclusions. The results of analysis make it possible to assess the condition of the rectal closure system before reconstructive intervention and identify factors affecting it.

Current status and prospects of non-surgical treatment for fecal incontinence

Fecal incontinence is a refractory disease in colorectal surgery. The main clinical manifestation is that patients cannot control the discharge of gas, solid or liquid feces in the rectum autonomously. It is easy to bring shame to patients and seriously affect their physical and mental health. Reducing the frequency of fecal incontinence, restoring anal sphincter function, and improving patient quality of life are important goals for treating fecal incontinence. With the development of medical technology and the improvement of treatment plans for fecal incontinence, patients with fecal incontinence usually undergo conservative treatment first, and if conservative treatment is ineffective, surgery can be chosen. Non-surgical treatment methods commonly used in clinical practice include biofeedback therapy, magnetic stimulation therapy, pelvic floor muscle training, anal sphincter training, Kegel training, and other rehabilitation treatments. This article discusses the non-surgical treatment methods for fecal incontinence, hoping to provide a choice for clinical treatment of fecal incontinence.

Surgical treatment of fecal incontinence

This article describes the surgical treatment of fecal incontinence. There are many surgical methods for fecal incontinence, and each treatment has its own advantages and disadvantages and indications. The appropriate surgical procedure should be selected according to the patient's history, anatomical structure and severity of incontinence. Injectable bulking agents is suitable for passive fecal incontinence. Sphincteroplasty is suitable for patients with sphincter injury caused by vaginal delivery or surgical trauma. Sacral nerve stimulation and posterior tibial nerve stimulation are relatively conservative methods. Gracilomyoplasty, artificial anal sphincter or magnetic anal sphincter can be used in the treatment of refractory fecal incontinence, but with many complications. Colostomy is the ideal choice for patients who have failed to respond to conservative treatment and cannot undergo these procedures.

Progress in pathophysiology research and update on diagnosis and treatment strategies for fecal incontinence

The traditional barrier theory believes that fecal incontinence is related to an imbalance of the recto-anal barrier and the characteristics of stool. However, in clinical practice this theory proves unable to explain all types of fecal incontinence. In recent years, research on the mechanisms related to fecal incontinence has shifted to a new integrative concept with the rectum and anus as functional units, and the central-peripheral nervous system and internal and external anal sphincters as a control loop. The diagnosis and treatment strategy of fecal incontinence, which is replaced by sacral neuromodulation, is undergoing a quiet change. With the progressively aging population in China, the need to improve the diagnosis and treatment of fecal incontinence has become increasingly urgent. This article explores the trends in diagnosis and treatment and mechanism research from the perspective of recent advances in pathophysiological research and updated diagnosis and treatment methods for fecal incontinence.

On a potential morpho-mechanical link between the gluteus maximus muscle and pelvic floor tissues

Stress urinary incontinence presents a condition not only found in female elderlies, but also in young athletes participating in high-impact sports such as volleyball or trampolining. Repeated jumps appear to be a predisposing factor. Yet the pathophysiology remains incompletely elucidated to date; especially with regard to the influence of the surrounding buttock tissues including gluteus maximus. The present study assessed the morpho-mechanical link between gluteus maximus and the pelvic floor female bodies. 25 pelves obtained from Thiel embalmed females were studied in a supine position. Strands of tissues connecting gluteus maximus with the pelvic floor obtained from 20 sides were assessed mechanically. Plastinates were evaluated to verify the dissection findings. In total, 49 hemipelves were included for data acquisition. The fascia of gluteus maximus yielded connections to the subcutaneous tissues, the fascia of the external anal sphincter and that of obturator internus and to the fascia of the urogenital diaphragm. The connection between gluteus maximus and the urogenital diaphragm withstood an average force of 23.6 ± 17.3 N. Cramér φ analyses demonstrated that the connections of the fasciae connecting gluteus maximus with its surroundings were consistent in the horizontal and sagittal planes, respectively. In conclusion, gluteus maximus is morphologically densely linked to the pelvic floor via strands of connective tissues investing the adjacent muscles. Though gluteus maximus has also been reported to facilitate urinary continence, the here presented morpho-mechanical link suggests that it may also have the potential to contribute to urinary stress incontinence. Future research combining clinical imaging with in-situ testing may help substantiate the potential influence from a clinical perspective.

Subtyping irritable bowel syndrome using cluster analysis: a systematic review

BackgroundIrritable bowel syndrome (IBS) is a common chronic functional gastrointestinal disorder associated with a wide range of clinical symptoms. Some researchers have used cluster analysis (CA), a group of non-supervised learning methods that identifies homogenous clusters within different entities based on their similarity.Objective and methodsThis literature review aims to identify published articles that apply CA to IBS patients. We searched relevant keywords in PubMed, Embase, Web of Science, and Scopus. We reviewed studies in terms of the selected variables, participants’ characteristics, data collection, methodology, number of clusters, clusters’ profiles, and results.ResultsAmong the 14 articles focused on the heterogeneity of IBS, eight of them utilized K-means Cluster Analysis (K-means CA), four employed Hierarchical Cluster Analysis, and only two studies utilized Latent Class Analysis. Seven studies focused on clinical symptoms, while four articles examined anocolorectal functions. Two studies were centered around immunological findings, and only one study explored microbial composition. The number of clusters obtained ranged from two to seven, showing variation across the studies. Males exhibited lower symptom severity and fewer psychological findings. The association between symptom severity and rectal perception suggests that altered rectal perception serves as a biological indicator of IBS. Ultra-slow waves observed in IBS patients are linked to increased activity of the anal sphincter, higher anal pressure, dystonia, and dyschezia.ConclusionIBS has different subgroups based on different factors. Most IBS patients have low clinical severity, good QoL, high rectal sensitivity, delayed left colon transit time, increased systemic cytokines, and changes in microbial composition, including increased Firmicutes-associated taxa and depleted Bacteroidetes-related taxa. However, the number of clusters is inconsistent across studies due to the methodological heterogeneity. CA, a valuable non-supervised learning method, is sensitive to hyperparameters like the number of clusters and random initialization of cluster centers. The random nature of these parameters leads to diverse outcomes even with the same algorithm. This has implications for future research and practical applications, necessitating further studies to improve our understanding of IBS and develop personalized treatments.

Distalization of perianal fistulas after loose silicone seton drainage is a myth

BackgroundIt is often stated that loose seton drainage results in distal migration of a fistula tract in perianal fistula. The aim of the present study was to assess this distalization of trans- and suprasphincteric perianal fistulas after a silicone seton has been inserted.MethodsConsecutive patients who underwent loose seton placement for the management of a transsphincteric or suprasphincteric fistula between January 2016 and December 2021 with a pre- and postoperative magnetic resonance imaging (MRI) were included in the present retrospective study. The height of the external anal sphincter (EAS) and the level of penetration of perianal fistula through the EAS or puborectal muscle (PRM) were determined on MRI. Primary outcome was migration of the fistula tract through the EAS and PRM.ResultsThirty-eight patients with perianal fistulas were included. Median height of the EAS was 28 (IQR 25–34) mm before seton placement and 27 (IQR 24–33) mm afterward. Median level of perforation was 32 (IQR 17–40) mm before seton placement and 28 (IQR 17–40) mm afterward (p = 0.37). One fistula (3%) was downgraded from mid to low transsphincteric and was laid open after 14.9 months of loose seton drainage.ConclusionsNo statistically significant distalization of complex fistula tracts after loose silicone seton drainage was found. Some complex fistulas may downgrade to a less complex fistula after long-term seton drainage. However, loose silicone seton drainage should not be offered to patients as a treatment option to downgrade a complex fistula to a simple one or even have the hope to heal it.

Anal sphincter injury by bullfighting trauma.

Anal sphincter injury by bullfighting trauma.

An acquired recto-perineal fistula as the outcome of sacrococcygeal teratoma treatment

Introduction. An acquired recto-perineal fistula in childhood is a quite rare pathology. One of its main causes is trauma of the perineal part of the rectum and anal canal. That is why, acquired rectoperineal fistulas most often develop after the correction of Hirschsprung’s disease and anorectal malformations.&#x0D; Material and methods. The publication presents a rare case of a newborn child with recurrent course of an acquired rectoperineal fistula which developed after sacrococcygeal teratoma treatment. The teratoma was removed when the child was 3 days old. The surgery was complicated with suture dehiscence in the rectal wall defect. After suturing, a separate sigmostoma was placed. At the age of 6 months, the sigmostoma was closed, but after a few days, fistulas were found in the area of drainage and postoperative scar, which required sigmostoma restoration. After the prescribed therapy, the fistulas were obliterated; the stoma was closed again. In 2 weeks, child’s general condition deteriorated, and newly appeared fistulas were noted. It was decided to perform demucosation of the disconnected rectum above the level of anal sphincter and to make fistula through drainage via the rectum lumen.&#x0D; Conclusion. Acquired recto-perineal fistulas in childhood is a rare recurrent disease. Though postoperative complications were detected in time, authors could not get independent closure of the fistula, despite numerous interventions. In fact, only the rectum extirpation allowed to separate the fistulous tract from the intestinal lumen. This type of intervention is considered a quite rare one; usually, such complication can be eliminated in a less radical way.

Prevention of obstetric anal sphincter injuries with perineal support and lateral episiotomy: A historical cohort study.

There are many risk factors for obstetric anal sphincter injury (OASIS) and the interaction between these risk factors is complex and understudied. The many observational studies that have shown a reduction of OASIS rates after implementation of perineal support have short follow-up time. We aimed to study the effect of integration of active perineal support and lateral episiotomy on OASIS rates over a 15-year period and to study interactions between risk factors known before delivery. We performed a historical cohort study over the periods 1999-2006 and 2007-2021 at Stavanger University Hospital, Norway. The main outcome was OASIS rates. Women without a previous cesarean section and a live singleton fetus in cephalic presentation at term were eligible. The department implemented in 2007 the Finnish concept of active perineal protection, which includes support of perineum, control of fetal expulsion, good communication with the mother and observation of perineal stretching. The practice of mediolateral episiotomy was replaced with lateral episiotomy when indicated. We analyzed the OASIS rates in groups with and without episiotomy stratified for delivery mode, fetal position at delivery and for parity, and adjusted for possible confounders (maternal age, gestational age, oxytocin augmentation and epidural analgesia). We observed a long-lasting reduction in OASIS rates from 4.9% to 1.9% and an increase in episiotomy rates from 14.4% to 21.8%. Lateral episiotomy was associated with lower OASIS rates in nulliparous women with instrumental vaginal deliveries and occiput anterior (OA) position; 3.4% vs 10.1% (OR 0.31; 95% CI: 0.24-0.40) and 6.1 vs 13.9% (OR 0.40; 95% CI: 0.19-0.82) in women with occiput posterior (OP) position. Lateral episiotomy was also associated with lower OASIS rates in nulliparous women with spontaneous deliveries and OA position; 2.1% vs 3.2% (OR 0.62; 95% CI: 0.49-0.80). The possible confounders had little confounding effects on the risk of OASIS in groups with and without episiotomy. We observed a long-lasting reduction in OASIS rates after implementation of preventive procedures. Lateral episiotomy was associated with lower OASIS rates in nulliparous women with an instrumental delivery. Special attention should be paid to deliveries with persistent OP position.