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Single-Leg-Stance (Flamingo) Radiographs to Assess Pelvic Instability: How Much Motion Is Normal?
David N. Garras, MD1; Joshua T. Carothers, MD1; Steven A. Olson, MD1
1 Division of Orthopaedic Surgery, Duke University Medical Center, Box 3389, Durham, NC 27710. E-mail address for S.A. Olson: olson016@mc.duke.edu
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Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
Investigation performed at Duke University Medical Center, Durham, North Carolina

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Oct 01;90(10):2114-2118. doi: 10.2106/JBJS.G.00277
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Background: Chronic pelvic instability is a relatively uncommon cause of pelvic and low-back pain. Patients present with feelings of instability and mechanical symptoms. Static radiographs are often inadequate to detect abnormal relative motion between the hemipelves consistent with chronic pelvic instability; dynamic views of the pelvis are required. We assessed the amount of physiologic motion present at the pubic symphysis in normal adult men and nulliparous and multiparous women with alternating-single-leg-stance radiographs.

Methods: Forty-five asymptomatic adult volunteers (fifteen in each group) were evaluated with a standing anteroposterior pelvic radiograph as well as with anteroposterior pelvic radiographs made with the subjects assuming both right and left single-leg stance. The subjects completed a questionnaire to determine their eligibility for participation in the study, and an examination was performed to exclude certain physical anomalies that might alter the radiographic findings.

Results: The mean total translation (and standard deviation) at the pubic symphysis, as measured by three blinded observers, was 1.4 ± 1.0, 1.6 ± 0.8, and 3.1 ± 1.5 mm for the men, nulliparous women, and multiparous women, respectively. With the numbers available, we found no significant difference between the translation in the men and that in the nulliparous women (p = 0.63). The multiparous women had significantly more translation than did either the nulliparous women (p = 0.002) or the men (p = 0.0005). There was a significant positive association between the number of pregnancies and the total translation (p < 0.0001).

Conclusions: The use of anteroposterior pelvic radiographs made with the subject alternating between right and left single-leg stance demonstrated, with high interobserver reliability, that multiparous women had a significantly different physiologic range of pubic translation as compared with men and nulliparous women. The ranges of physiologic motion at the pubic symphysis measured on the single-leg-stance radiographs in this study can be used to identify pathologic amounts of motion at this site.

Clinical Relevance: This investigation suggests that up to 5 mm of physiologic motion can occur at the pubic symphysis in asymptomatic individuals, as demonstrated by alternating-single-leg-stance radiographs.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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