Characterization of pain following Obstetric Anal Sphincter Injury (OASI)

Objectives: Studies characterizing pain and pain management following Obstetric Anal Sphincter Injuries (OASI) are limited. Our primary objective was to characterize pain at various time points following OASI by analyzing pain severity, location, triggers, and time to pain resolution. A secondary objective was to describe practice patterns for pain management in OASI patients who were seen at a postpartum care clinic (PPCC).

Methods: This is a prospective cohort study of OASI patients seen in PPCC at a tertiary referral center between 2017-2022. Patients who reported unresolved pain since delivery during their initial PPCC visit were included in this study. We collected information on Visual Analog Scale (VAS), pain scores, pain location (left levator ani muscle (LAM), right LAM, left obturator internus (OI), right OI, bilateral OI), pain triggers, and resolution of pain for up to five follow-up (FU) visits following the initial PPCC visit.

Results: A total of 373 patients reported unresolved pain during their initial PPCC visit. Of these patients, 37% (N = 139) were seen for a subsequent FU visit (FU1); the number of patients who attended FUs 2-5 continued to decrease. Of the initial 373 patients with unresolved pain, 24% reported unresolved pain at FU1, 8% at FU2, 2% at FU3, 1% at FU4, and < 1% at FU5. The mean Visual Analog Scale (VAS) pain score at the initial PPCC visit was 2.73 cm on a 0-10 cm scale. There was a significant decrease in mean VAS between the initial PPCC visit and FU1 (mean diff = 0.88, p = 0.0005) and subsequent decreases in mean VAS scores through FU3. There was a notable but non-significant increase in VAS score between FU3 - FU4. During the initial PPCC visit and FU1, patients primarily reported bilateral LAM and bilateral OI pain. During FU2 -5, there was an increased proportion of patients with pain localized to the right or left LAMs and right or left OIs. During the initial PPCC visit, the most commonly reported pain trigger was sitting, followed by bowel movements, then “other” activities (i.e. walking, urination, standing, general movement, etc.). By FU4, pain was primarily triggered by “other” specified activities, followed by intercourse and bowel movements. Of the patients using medication to manage pain, most were using acetaminophen and/or ibuprofen at each FU.

Conclusions: Most postpartum patients with OASI can expect to have improvement in pain over time. They may also have localization of their pain to one side of their pelvic floor muscles. With this understanding, practitioners can better educate OASI patients about expected pain course and appropriately administer pain management options.