Objective
We sought to describe occurrence, recovery, and consequences of musculoskeletal (MSK) injuries in women at risk for childbirth-related pelvic floor injury at first vaginal birth.
Study Design
Evaluating Maternal Recovery from Labor and Delivery is a longitudinal cohort design study of women recruited early postbirth and followed over time. We report here on 68 women who had birth-related risk factors for levator ani (LA) muscle injury, including long second stage, anal tears, and/or older maternal age, and who were evaluated by MSK magnetic resonance imaging at both 7 weeks and 8 months’ postpartum. We categorized magnitude of injury by extent of bone marrow edema, pubic bone fracture, LA muscle edema, and LA muscle tear. We also measured the force of LA muscle contraction, urethral pressure, pelvic organ prolapse, and incontinence.
Results
In this higher-risk sample, 66% (39/59) had pubic bone marrow edema, 29% (17/59) had subcortical fracture, 90% (53/59) had LA muscle edema, and 41% (28/68) had low-grade or greater LA tear 7 weeks’ postpartum. The magnitude of LA muscle tear did not substantially change by 8 months’ postpartum ( P = .86), but LA muscle edema and bone injuries showed total or near total resolution ( P < .05). The magnitude of unresolved MSK injuries correlated with magnitude of reduced LA muscle force and posterior vaginal wall descent ( P < .05) but not with urethral pressure, volume of demonstrable stress incontinence, or self-report of incontinence severity ( P > .05).
Conclusion
Pubic bone edema and subcortical fracture and LA muscle injury are common when studied in women with certain risk factors. The bony abnormalities resolve, but levator tear does not, and is associated with levator weakness and posterior-vaginal wall descent.
See related editorial, page 121
Childbirth is arguably one of the most dramatic musculoskeletal (MSK) events the human body undergoes. Passage of the newborn through the pelvis and its muscles requires an exceptional degree of soft-tissue stretch. Childbirth exerts remarkable stresses on maternal pelvic bones from the pressures of the fetal head and the forces of abdominal muscles used during maternal pushing that originate from the pelvic bones. Such stretch and stress may produce injury in some women.
In the last decade, new imaging techniques have brought important new insights into understanding the mechanisms of soft-tissue and bony injury. Special sequences in MSK magnetic resonance imaging (MRI) offer advantages over other imaging techniques for studying deep bony and soft-tissue changes. Fluid-sensitive sequences have the best combined specificity and sensitivity for revealing areas of injury and edema. Hence, they are the recommended diagnostic imaging test for stress injuries. These sequences are commonly applied in evaluation of sports-related injury to allow for detection of injuries not seen with other MRI sequences or imaging modalities. However, MSK-MRI fluid-sensitive sequences have only recently been applied to reveal the scope of childbirth-related pelvic injuries.
Soon after beginning a study of levator ani (LA) muscle injury following vaginal birth, it became evident we should add these standard MSK-MRI fluid-sensitive sequences to our existing protocol of anatomical MRI sequences to better characterize the full scope of possible injuries and pattern of recovery.
The purpose of this study is to report on the occurrence and severity of bony and LA muscle injuries observed and how magnitude of tissue trauma relates to clinical consequences in the first 8 months’ postpartum. Fluid-sensitive sequences are necessary for 3 of 4 indicators of bone and muscle injury evaluated in our study. The sequences show: (1) increased signal that indicates edema (extracellular fluid) in bone; (2) matched linear signal changes in bone that indicate a fracture; or (3) increased signal that indicates edema in muscle. The fourth indicator of injury, visual discontinuity of muscle seen with muscle tear, does not require fluid-sensitive sequences. However, use of fluid-sensitive sequences makes detection of tears and their magnitude much easier. The precision of these measures offered opportunity to assess more precisely the relationship between injury magnitude and relative consequences seen clinically in the first 8 months’ postpartum.
Materials and Methods
Study design
The parent study Evaluating Maternal Recovery from Labor and Delivery (EMRLD) is an institutional review board–approved (University of Michigan Institutional Review Board HUM00051193) longitudinal cohort study following up primiparous women with recent history of childbirth. In this article, we report on those with higher-risk factors for LA injury. The first published reports from this work included: (1) details on EMRLD’s sampling strategies and a Strengthening the Reporting of Observational Studies in Epidemiology diagram; (2) specifics of using MSK-MRI methods; (3) ensuing anatomical detail of pelvic floor structures at rest, during dynamic activity, and by LA muscle subdivision and line of action; and (4) predominant demographic or obstetric variables associated with LA tear when evaluated early postpartum. EMRLD data collection occurred from June 13, 2005, through March 14, 2012, collecting data at approximately 7 weeks after a first vaginal birth and again at about 8 months after first vaginal birth. In this article, we report the 7 weeks to 8 months’ postpartum longitudinal findings.
Sample
The enriched sampling relied on inclusion criteria of heuristically determined risk factors for LA tear (eg, prolonged second stage, anal sphincter tear, higher maternal age, forceps delivery) suggestive in 2005, the time of the study’s start. Women were excluded from EMRLD if aged <18 years, spoke a primary health care language other than English, delivered at <36 weeks’ gestation, birthed >1 infant, or if the infant was admitted to neonatal intensive care.
Of the 90 women originally recruited into EMRLD, 22 women did not have a second MRI at 8 months’ postpartum. Our analysis was based on the 68 women with MRI data at both 7 weeks and 8 months’ postpartum.
MRI
MRIs were completed on a 3-T Philips Achieva (Philips Medical System, Eindhoven, The Netherlands) with an 8-channel cardiac coil positioned over the pelvis. The lower pelvis was imaged in the coronal, axial, and sagittal planes with proton density-weighted (PD) sequences; repeat time (TR) = 2107 milliseconds; echo time (TE) = 30 milliseconds; number sequence averages = 2; slice thickness = 4 mm, gap = 1 mm; and field of view (FOV) = 20 cm, matrix = 256 × 256. For better definition of the anterior pelvic floor anatomy, additional tailored imaging (slice thickness = 2 mm, gap = 0.2 mm; FOV = 18 cm, matrix = 256 × 256) included 3 planes of PD sequences and axial and coronal planes, either PD fat saturation (TR = 2355 milliseconds; TE = 30 milliseconds) or short tau inversion recovery (STIR) (TR = 5987 milliseconds; TE = 60 milliseconds; number sequence averages = 2) sequences. A single sacral PD fat saturation sequence was obtained in the axial plane (slice thickness = 4 mm, gap = 1 mm; FOV = 20 cm, matrix = 256 × 256).
The complete MRI protocol has been discussed in previously published reports. MRIs were reviewed by 2 board-certified, fellowship-trained MSK radiologists who were blinded to details of an individual woman’s birth data and risk category. They were aware if the woman was having her initial 7 weeks or 8 months’ postpartum visit since the postpartum uterus was obvious in the pelvic MRI study.
We used standard MSK-MRI radiology grading categories to evaluate edema and fractures in bone and muscle injuries so our data could be compared across time and studies in the radiology literature. When there was a difference in scoring between the 2 radiologists, the scans were reviewed together and graded by consensus, consistent with standard procedures in radiology. The radiologists measured and scored 4 sites of likely MSK injury.
Pubic bone marrow evaluation for edema
Bone marrow edema was assessed by grading signal intensity (none, mild, moderate, or intense) within the bone marrow of each pubic bone (right, left) as compared with the ischial tuberosity and other bones in the FOV. The spectrum of bone stress injuries has been correlated with clinical findings in athletes and military recruits and is graded 0-4, based on the degree of bone marrow edema according to the MSK-MRI scale with STIR or fat-suppressed sequences. Grade 0 is no abnormal signal. Grades 1-3 are mild, moderate, and intense bone marrow edema. Grade 4 is a true stress fracture with a line of increased signal (STIR or fat-suppressed sequences) with matching linear decreased signal on T1.
Pubic bone evaluation for fracture
Evidence of pubic bone fractures in the cortical or trabecular bone was assessed as matching lines of increased and decreased signal on the fluid-sensitive and standard T1 sequences visible in 2 imaging planes. Fractures were recorded as none, subcortical, or cortical fractures for both pubic bones.
LA evaluation for edema
The LA was evaluated for the presence and location of increased signal, indicating edema consistent with stress or injury, as compared with other pelvic muscles, including the obturator internus. Grading classification categories were none, mild, moderate, or intense for each side.
LA evaluation for tear
The LA was evaluated for discontinuity of muscle observed as loss of visible muscle in an area where it is known to occur, indicating muscle tear. Grading classifications were: 0% to <20% (none to subtle), 20% to <50% (low grade), or ≥50% (high grade) for each side. Based on previous pelvic floor imaging experience, it was assumed that normal muscles should be symmetric and that each should have the same morphological configuration as muscles seen in nulliparous controls reported in other studies.
Clinical symptoms and pelvic floor function evaluation
Participants completed standardized questionnaires on symptoms of urinary and fecal incontinence at 7 weeks and 8 months’ postpartum. Strength of the LA was evaluated at both time points by measuring the vagina closure force at rest and during maximal pelvic muscle contraction (average of 3 attempts) using an instrumented speculum modified to not be influenced by changes in abdominal pressure. Pelvic organ support was assessed during Valsalva in the lithotomy position using the pelvic organ prolapse quantification system. Demonstrable stress incontinence was documented in the standing position and measures made of volume of urine loss by the quantified paper towel standing stress test. A urethral pressure profile was obtained at 8 months’ postpartum only, due to its invasive nature. These measures were made by a nurse practitioner with >5 years of experience in clinical examinations. She was blinded to the MRI findings.
To standardize rehabilitation during the study period, at the examination, the same nurse practitioner instructed each woman in Knack technique and individually prescribed home pelvic muscle exercises per the graduated strength-training protocol.
Statistical analysis
Of the 68 women with MRIs at 7 weeks and 8 months’ postpartum, 59 had fluid-sensitive sequences, and the remaining 9 women had only nonfluid-sensitive sequences. Discovery of the importance of these sequences occurred after study initiation. The missing sequences were due to early enrollment before the MSK-MRI protocol was in use. Since LA tear is readily observable without fluid-sensitive sequences, the full 68 women were retained for that analysis, but the 9 were not included in analysis of pubic bone edema, fracture, and LA edema.
A composite score for the degree of injury for each individual was derived by collapsing “left,” “right” sides to yield ordinal-level data: for the LA tears, a composite score of “0” indicated no or subtle tear on both sides, “1” indicated a low-grade unilateral tear, “2” indicated a bilateral low-grade or unilateral high-grade tear, and a score of “3” indicated a bilateral high-grade tear. Similar composite scores were constructed for pubic bone marrow edema, pubic bone fracture, and LA edema ( Tables 1-4 ).
| Demographic | Total | Mean (SD) or frequency | Range or % |
|---|---|---|---|
| Maternal age, y | 68 | 30.38 (5.48) | 19–46 |
| Maternal age >31 y | 27 | 40 | |
| Race | 66 | ||
| Black | 2 | 3 | |
| White | 58 | 88 | |
| Asian | 3 | 5 | |
| Other | 3 | 5 | |
| Non-Hispanic/Non-Latino | 66 | 100 | |
| Education | 66 | ||
| High school graduate or less | 6 | 9 | |
| Some college | 13 | 20 | |
| College/technical school graduate | 17 | 26 | |
| Graduate school | 29 | 44 | |
| Birth variables | |||
| Infant weight, g | 67 | 3411.90 (507.12) | 2100–4550 |
| Infant head circumference, cm | 66 | 34.19 (1.62) | 30–38 |
| Second stage, min | 67 | 154.91 (126.58) | 6–518 |
| Second stage >150 min | 31 | 46 | |
| Active pushing, min | 56 | 113.75 (84.65) | 6–312 |
| Passive second stage, min | 56 | 44.45 (72.40) | 0–307 |
| Anal tear | 68 | 22 | 32 |
| Episiotomy | 68 | 14 | 21 |
| Vacuum | 68 | 4 | 6 |
| Forceps | 68 | 2 | 3 |
| Clinical variables ∼8 mo postpartum | Total | Mean (SD) or frequency | Range or % |
|---|---|---|---|
| LA resting force on instrumented speculum, newtons | 62 | 1.92 (0.48) | 1–4 |
| LA volitional contraction (average of 3 repetitions) on instrumented speculum, newtons | 62 | 4.16 (1.93) | 1–10 |
| POP-Q anterior vaginal wall, cm | 63 | −2.13 (0.70) | −3 to 1 |
| POP-Q posterior vaginal wall, cm | 63 | −2.28 (0.63) | −3 to 0 |
| POP-Q cervix descent, cm | 62 | −7.71 (0.60) | −8 to −6 |
| POP-Q genital hiatus, cm | 63 | 4.69 (0.91) | 2–7 |
| POP-Q perineal body measure, cm | 63 | 2.29 (0.66) | 1–4 |
| POP-Q total vaginal length, cm | 62 | 11.98 (1.16) | 9–14 |
| Maximum urethral pressure, cm H 2 O | 55 | 66.95 (19.71) | 24–128 |
| Quantified standing stress test | 63 | ||
| No leakage | 57 | 90 | |
| Drops (<10 cm 3 ) | 3 | 5 | |
| Some leakage (10–11 cm 3 ) | 0 | 0 | |
| A lot of leakage (>33 cm 3 ) | 3 | 5 | |
| Antonakos urinary incontinence (points, 0 = none, 8 = high) | 64 | 3.30 (2.57) | 0–8 |
| Sandvik urinary incontinence (points, 0 = none, 8 = high, as frequency multiplied by amount) | 62 | 1.24 (1.10) | 0–3 |
| Wexner fecal incontinence (points, 0 = none, 20 = high) | 64 | 1.58 (1.54) | 0–6 |
| Variable | MRI score | 7 wk postpartum, n (%) | 8 mo postpartum, n (%) | n (%) with different score 8 mo postpartum | n (%) with same score 8 mo postpartum | Stuart-Maxwell statistic ( P value) |
|---|---|---|---|---|---|---|
| Pubic bone marrow edema (n = 59) | None | 20 (34) | 51 (86) | 0 (0) | 20 (100) | 27.2 (< .0001) |
| I = Diffuse mild | 6 (10) | 1 (2) | 5 (83) | 1 (17) | ||
| II = Focal mild or diffuse intense | 21 (36) | 5 (8) | 19 (90) | 2 (10) | ||
| III = Focal intense | 12 (20) | 2 (3) | 10 (83) | 2 (17) | ||
| Total | 59 (100) | 59 (100) | 34 (58) | 25 (42) | ||
| Pubic bone fracture (n = 59) | None | 42 (71) | 57 (97) | 0 (0) | 42 (100) | 11.2 (.011) |
| I = <5 mm unilateral or bilateral | 5 (8) | 2 (3) | 3 (60) | 2 (40) | ||
| II = ≥5 mm unilateral or bilateral | 10 (17) | 0 (0) | 10 (100) | 0 (0) | ||
| III = Cortical unilateral or bilateral | 2 (3) | 0 (0) | 2 (100) | 0 (0) | ||
| Total | 59 (100) | 59 (100) | 15 (25) | 44 (75) | ||
| Levator ani edema (n = 59) | None | 6 (10) | 55 (93) | 0 (0) | 6 (100) | 45.1 (< .0001) |
| I = Mild unilateral or bilateral | 2 (3) | 1 (2) | 2 (100) | 0 (0) | ||
| II = Moderate unilateral or bilateral | 40 (68) | 3 (5) | 39 (98) | 1 (3) | ||
| III = Intense unilateral or bilateral | 11 (19) | 0 (0) | 11 (100) | 0 (0) | ||
| Total | 59 (100) | 59 (100) | 52 (88) | 7 (12) | ||
| Levator ani tear (n = 68) | None or subtle | 40 (59) | 42 (62) | 0 (0) | 40 (100) | 0.74 (.86) |
| I = Low-grade (<50%) unilateral | 8 (12) | 6 (9) | 2 (25) | 6 (75) | ||
| II = Low-grade (<50%) bilateral or high-grade (≥50%) unilateral | 13 (19) | 14 (21) | 0 (0) | 13 (100) | ||
| III = High-grade (≥50%) bilateral | 7 (10) | 6 (9) | 1 (14) | 6 (86) | ||
| Total | 68 (100) | 68 (100) | 3 (4) | 65 (96) |
| Variable | LA tear severity | 7 wk postpartum | 8 mo postpartum | ANOVA P value a | ||
|---|---|---|---|---|---|---|
| n | Mean (SD) | n | Mean (SD) | |||
| LA strength | ||||||
| Force at rest, newtons | None | 38 | 1.75 (0.34) | 34 | 1.93 (0.53) | .432 |
| I | 8 | 1.93 (0.26) | 8 | 1.88 (0.21) | ||
| II | 9 | 1.59 (0.53) | 13 | 1.91 (0.61) | ||
| III | 6 | 1.81 (0.36) | 7 | 1.98 (0.16) | ||
| Force at volitional contraction, newtons | None | 38 | 3.99 (1.68) | 34 | 4.90 (2.04) | .008 |
| I | 8 | 3.19 (2.02) | 8 | 3.51 (1.96) | ||
| II | 9 | 2.46 (0.85) | 13 | 3.09 (1.20) | ||
| III | 6 | 2.82 (1.21) | 7 | 3.29 (0.78) | ||
| Pelvic organ prolapse quantification | ||||||
| Anterior vaginal wall descent, cm | None | 39 | −2.12 (0.64) | 35 | −2.19 (0.56) | .190 |
| I | 8 | −2.19 (0.26) | 8 | −2.25 (0.38) | ||
| II | 12 | −2.26 (0.48) | 13 | −2.08 (0.76) | ||
| III | 7 | −1.57 (0.93) | 7 | −1.86 (1.35) | ||
| Posterior vaginal wall descent, cm | None | 39 | −2.37 (0.60) | 35 | −2.33 (0.54) | .005 |
| I | 8 | −2.56 (0.18) | 8 | −2.50 (0.38) | ||
| II | 12 | −2.29 (0.45) | 13 | −2.31 (0.69) | ||
| III | 7 | −1.57 (1.10) | 7 | −1.71 (0.95) | ||
| Cervix descent, cm | None | 39 | −7.64 (0.79) | 35 | −7.66 (0.67) | .369 |
| I | 8 | −7.88 (0.35) | 8 | −7.75 (0.46) | ||
| II | 12 | −8.00 (0.00) | 12 | −7.88 (0.43) | ||
| III | 7 | −7.71 (0.49) | 7 | −7.64 (0.63) | ||
| Genital hiatus, cm | None | 39 | 4.51 (0.98) | 35 | 4.70 (0.96) | .706 |
| I | 8 | 4.50 (0.60) | 8 | 4.63 (0.52) | ||
| II | 12 | 4.29 (0.84) | 13 | 4.46 (1.05) | ||
| III | 7 | 4.57 (1.06) | 7 | 5.14 (0.75) | ||
| Perineal body, cm | None | 39 | 2.40 (0.65) | 35 | 2.31 (0.69) | .921 |
| I | 8 | 2.56 (0.73) | 8 | 2.13 (0.69) | ||
| II | 12 | 2.46 (0.66) | 13 | 2.42 (0.61) | ||
| III | 7 | 2.57 (1.06) | 7 | 2.07 (0.61) | ||
| Total vaginal length, cm | None | 39 | 11.56 (1.63) | 34 | 11.96 (1.28) | .900 |
| I | 8 | 12.00 (1.16) | 8 | 11.81 (1.46) | ||
| II | 12 | 11.75 (1.20) | 13 | 12.19 (0.88) | ||
| III | 7 | 11.36 (0.90) | 7 | 11.93 (0.61) | ||
| Urethral function/incontinence | ||||||
| Maximum urethral pressure, cm H 2 O b | None | – | – | 32 | 66.13 (20.89) | .945 |
| I | – | – | 6 | 65.83 (14.91) | ||
| II | – | – | 12 | 67.67 (16.84) | ||
| III | – | – | 5 | 71.80 (27.70) | ||
| Quantified standing stress test, cm 3 c | None | 39 | 0.24 (1.51) | 36 | 3.46 (14.76) | .696 |
| I | 8 | 27.52 (64.38) | 8 | 0.00 (0.00) | ||
| II | 12 | 0.00 (0.00) | 13 | 3.33 (9.47) | ||
| III | 7 | 7.09 (18.77) | 6 | 0.92 (2.24) | ||
| Antonakos urine leakage (potential 8 points based on “yes = 1” “no = 0” across 8 items) | None | 39 | 3.08 (2.51) | 36 | 3.06 (2.48) | .488 |
| I | 8 | 4.25 (3.06) | 8 | 4.00 (3.02) | ||
| II | 13 | 3.85 (3.21) | 13 | 4.00 (2.58) | ||
| III | 7 | 3.43 (3.74) | 7 | 2.43 (2.57) | ||
| I | 8 | 16.50 (8.12) | 8 | 15.50 (6.80) | ||
| II | 13 | 15.85 (7.07) | 13 | 15.54 (5.59) | ||
| III | 7 | 15.29 (8.58) | 7 | 12.29 (4.92) | ||
| Sandvik urinary incontinence (points) | None | 39 | 1.00 (1.19) | 34 | 1.09 (0.97) | .276 |
| I | 8 | 2.00 (2.56) | 8 | 1.50 (1.20) | ||
| II | 13 | 2.00 (2.00) | 13 | 1.54 (1.20) | ||
| III | 7 | 1.14 (1.46) | 7 | 1.14 (1.46) | ||
| Wexner fecal incontinence (points) | None | 36 | 1.89 (1.91) | 36 | 1.78 (1.64) | .599 |
| I | 7 | 2.57 (3.99) | 8 | 1.00 (0.93) | ||
| II | 13 | 2.15 (1.63) | 13 | 1.85 (1.63) | ||
| III | 7 | 3.29 (3.77) | 7 | 0.71 (1.11) | ||
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