Does 2.5 cm of Symphyseal Widening Differentiate
APC I from APC II Pelvic Ring Injuries?
Christopher J. Doro MD 1; Daren P. Forward FRCS 1 ; Hyunchul Kim MS 2 ; Jason W. Nascone MD 1 ; Marcus F. Sciadini MD 1 ;
Adam H. Hsieh PhD 2 ; Greg Osgood MD 1 ; Robert V. O’Toole MD 1
1. R Adams Cowley Shock Trauma Center, Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, MD, USA
2. Orthopaedic Mechanobiology Lab, Department of Bioengineering, University of Maryland, College Park, MD, USA
RESULTS
Although the average symphysis pubis distance at the point at
which the anterior sacroiliac ligaments failed was 22.3 mm (n = 20;
range, 10.25 to 44.8 mm), 80% of the values were outside the range
of 2.0 to 3.0 cm. The distance at rupture in male specimens
averaged 25.3, whereas female specimens averaged 17.8 mm (p =
0.06).
INTRODUCTION
It has been proposed that 2.5 cm of diastasis of the
symphysis pubis corresponds with injury to the anterior
sacroiliac ligament and differentiates Young-Burgess
anteroposterior compression I (APC I) pelvic ring injury,
which is treated nonoperatively, from anteroposterior
compression II (APC II) pelvic ring injury, which often is
treated operatively.
Our hypothesis was that if a pelvis has >2.5 cm of symphysis
pubis diastasis, the anterior sacroiliac ligaments are
disrupted and the pelvic floor has failed. Our goal was to test
this amount of diastasis and correlate it to pelvic ligament
injury.
Figure 1 Experimental setup showing the unconstrained (left) and constrained (right)
testing modes. The servohydraulic biaxial testing machine was mounted to the sacrum and
was rotated to create the displacement torque. The unconstrained samples could slide
vertically, whereas the constrained samples were prevented from having vertical
displacement by rods, as shown. The blue arrows indicate the directions of rotation.
(MTS = servohydraulic biaxial testing machine; SI = sacroiliac joint;
SP = symphysis pubis; A = acetabulum.)
METHODS
We modeled the anteroposterior compression pelvic ring
disruption by sectioning the symphysis pubis and mounting
fresh cadaveric human pelves on a servohydraulic biaxial
testing machine. A pure torsional moment was applied about
the axis of the sacrum, with the hemipelvis either
unconstrained (n=10) or constrained to move only in the
plane of rotation (n=10).
The position of the hemipelvis was recorded with a three
dimensional motion capture system and video. We recorded
the displacement of the symphysis pubis, the displacement of
the anterior aspect of the sacroiliac joint, and the applied
torque to determine the symphysis pubis distance that
corresponded with failure of the anterior sacroiliac
ligaments.
Figure 2 Range of symphysis pubis (SP) diastasis at the point of anterior sacroiliac
ligament (SI) rupture for all specimens. Eighty percent of the values were outside the range
of 2.0 to 3.0 cm.
Figure 3 Failure after testing. The long black
arrow indicates the right side hemipelvis with
intact sacrospinous and sacrotuberous ligaments
after the sample had been tested in unconstrained
external rotation. All ten specimens tested had
intact sacrospinous and sacrotuberous ligaments
at the completion of testing. The red arrow points
to the ruptured sacrospinous and sacrotuberous
ligaments on the left side after testing in
constrained external rotation. Three of the ten
constrained samples experienced rupture, such as
this rupture of the sacrospinous and
sacrotuberous ligaments. SI, sacroiliac joint; SS/
ST, sacrospinous and sacrotuberous ligaments;
SP, symphysis pubis.
Symphysis pubis distance was similar in the unconstrained and
constrained groups (p = 0.57). The sacrospinous and sacrotuberous
ligaments were not injured in the unconstrained testing but were at
least attenuated in all constrained tests.
CONCLUSIONS
Significant morphological variation is seen in anterior sacroiliac
tolerances. Our data support that anterior sacroiliac ligament
disruption is likely for displacement >4.5 cm and may or may not
be disrupted for values between 1.0 and 4.5 cm. Additionally, our
study suggests that the sacrospinous and sacrotuberous ligaments
might not rupture prior to the anterior sacroiliac ligament.
Clinicians should therefore use caution when basing treatment
decisions on the assumption that 2.5 cm of symphyseal
displacement corresponds to disruption of the anterior sacroiliac
and pelvic floor ligaments.
SELECTED REFERENCES
Pennal GF, Tile M, Waddell JP, Garside H. Pelvic disruption: assessment and classification. Clin Orthop Relat
Res. 1980;151:12-21.
Burgess AR, Eastridge BJ, Young JW, Ellison TS, Ellison PS Jr, Poka A, Bathon GH, Brumback RJ. Pelvic ring
disruptions: effective classification system and treatment protocols. J Trauma. 1990;30:848-56.
Tile M, Helfet DL, Kellam JF, eds. Fractures of the pelvis and acetabulum. 3rd ed. Philadelphia: Lippincott
Williams & Wilkins; 2003.
Young JW, Burgess AR, Brumback RJ, Poka A. Pelvic fractures: value of plain radiography in early assessment
and management. Radiology. 1986;160:445-51.