OBSTETRIC PUBIC SYMPHYSEAL DIASTASIS: IMAGING SUPPORT OF A
NOVEL BIOMECHANICAL MODEL
Hesch, J
Hesch Institute, Henderson NV, USA
Introduction
In pregnancy pelvic joint and pelvic outlet widening occurs in response to
ligamentous softening, fetal growth, and parturition. Obstetric pubic symphyseal
diastasis (OPSD) is widening of the symphysis at mid-joint of 10mm or more.
Progressive widening can provoke severe pain and functional impairment. Most
recover with conservative care; surgical stabilization is typical for 25mm or
greater. Chronic painful pubic dysfunction due to OPSD is a poorly understood
disabilitywth chronic widening of less than 10mm, pain and functional
limitations. MRI and CT images undergird novel biomechanical interpretation,
suggesting treatment modification.
Purpose
To present a novel hypothesis that OPSD involves a distinctly different
biomechanical trajectory rather than simply a traumatic escalation of peripartum
pelvic mechanics.
Materials and Methods
Articles gathered from www.PubMed.org and general web searches using key words
symphyseal diastasis, pubic joint instability, obstetric instability, and pubic
instability, covering 1997-2012. MRI and CT images were evaluated in cases of
acute OPSD with gapping of anterior-superior SI joint (SIJ).
Results
Several images demonstrated SIJ gapping with a peculiar previously unreported,
inferior-posterior retroarticular approximation; provoking further inquiry.
Testing with ligamented pelvis and flexible anatomical models was performed to
simulate obstetric joint and outlet widening. This included sacral nutation,
medial infolding of the ilia, and spreading of the ischial bones, lower pubic
and SIJ, as described in the literature. A distinct compressive end-point was
encountered in the superior-anterior SIJ and superior pubic joint, where no
further expansi on could occur. Diastasis was introduced by cutting and separating the
joint.
Relevance
Replicating the gapping of the superior SIJ, congruent with the OPSD x-ray, MRI and CT images, actually reduced pelvic outlet dimension. Only by moving the pubes and ilia in a cam-like manner, coupled with posteromedial glide at the SIJ’s,
primarily in the transverse plane, was pelvic outlet maximized. No other
trajectory was able to enhance outlet dimension to this degree.
Conclusions
Imaging and mechanical testing support the hypothesis of novel biomechanics with OPSD. Research using this hypothesis may identify optimal intervention for acute and
chronic cases.
Discussion
The unique properties of the axial ligament; size, location and decreased elastin, suggest that in the presence of OPSD it may function as a mechanical stop during
parturition, maintaining optimal pelvic outlet dimension. In chronic cases,
muscular and ligamentous recoil may be absent or insufficient, preventing
form-closure. The chronic pubic dysfunction and OPSD populations are especially
in need of improved care. In vivo biomechanical research during parturition is
improbable. Computer modeling and pre/post intervention imaging and functional
metrics seem reasonable.
Implications
A diagnostic tool may already exist in the form of CT or MRI images in the
medical record. Passive external forces directed at reducing the unique
cam-like transverse plane movement of the ilia prior to or during application
of a pelvic binder at the trochanters, an orthopedic standard of care may have
merit.
Keywords: obstetric pubic symphyseal diastasis, SIJ, axial ligament, pelvic
binder.
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