Passage of the newborn through the pelvis and its muscles during vaginal delivery exerts exceptional stretch and stress and may produce musculoskeletal (MSK) pelvic injuries in some women. Musculoskeletal magnetic resonance imaging (MRI) is the recommended diagnostic imaging test for pelvic stress injuries. It has the best combined specificity and sensitivity for revealing areas of injury and edema.
The aim of this study was to describe the occurrence, recovery, and clinical consequences of bony and levator ani (LA) muscle injuries in the first 8 months postpartum among primiparous women at higher risk for childbirth-related pelvic floor injury. Data were obtained from a longitudinal cohort study, Evaluating Maternal Recovery From Labor and Delivery, which followed primiparous women with recent history of vaginal birth. A total of 68 women who had birth-related risk factors for LA muscle injury (including prolonged second stage, anal tears, and/or older maternal age) were evaluated by MSK-MRI at both 7 weeks and 8 months postpartum. Magnitude of injury was categorized by extent of bone marrow edema, pubic bone fracture, LA muscle edema, and LA muscle tear. Also assessed were the force of LA muscle contraction, urethral pressure, pelvic organ prolapse assessment, and urinary incontinence symptoms.
Among 59 women with complete imaging data, 39 (66%) had pubic bone marrow edema, 17 (29%) had subcortical fracture, 53 (90%) had LA muscle edema, and 28 (41%) had low-grade or greater LA tear at 7 weeks postpartum. By 8 months postpartum, LA muscle edema and bone injuries showed total or near total resolution (P < 0.05), but LA muscle tear did not (P = 0.86). There was a correlation between the magnitude of unresolved MSK injuries with reduced LA muscle force and degree of posterior vaginal wall descent (P < 0.05) but not with urethral pressure, volume of demonstrable stress incontinence, or the severity of self-reported fecal and urinary incontinence (P > 0.05).
Common injuries observed in primiparous women at higher risk of MSK injury after a vaginal birth include pubic bone edema, subcortical fracture, and LA muscle injury. Bone abnormalities recover, but levator tear does not, and is associated with levator weakness and posterior vaginal wall descent.