The myth of 2.5 cm symphyseal diastasis

Abstract

Detection of disruption of the pubic symphysis and resulting anterior pelvic ring instability primarily depends on the symphyseal widening on standard anterior-posterior X-rays. Based on biomechanical and clinical analyses from the 80 to 90's, a cut-off value of 2.5 cm widening distinguished between stable and unstable lesions. A relevant debate developed concerning minor (< 2.5 cm displacement), moderate (> 2.5 cm displacement) and severe disruptions (> 2.5 cm displacement + posterior complete pelvic ring instability) of the pubic symphysis. Analysis of anatomic, biomechanical, physiological and clinical literature showed, that an exact value does not allow this differentiation. Thus, symphyseal posttraumatic disruptions with displacements > 10 mm should be treated surgically, while in minor displacements (5-10 mm) stress examination can guide adequate treatment.

Keywords: Consequences; Instability; Pubic symphysis; Symphyseal physiology; Symphyseal width.

Fig. 1

Axial CT view of a pelvis with an uninjured pubic symphysis with anterior physiological widening compared to the posterior symphyseal part

Fig. 2

Anterior–posterior compression (APC) injury with small diastasis of the pubic symphysis (approximately 1 cm) in all three standard views (ap. View (a), Inlet-view (b) and Outlet view (c)). Potential involvement of the left SI-joint with slight anterior widening

Fig. 3

Anterior–posterior pelvic view showing parallel symphyseal widening (a). Flamingo views with left (b) and right (c) weight bearing show some minor vertical displacement

Fig. 4

Patient with a typical displacement of a pure right transverse acetabular fracture with classical internal rotation of the obturator segment around a vertical axis through the pubic symphysis (a). The Inlet view shows some anterior symphyseal widening compared to the posterior symphyseal axial surface while the Outlet view presents with anatomic symphyseal position (c), corresponding to symphyseal strain or to a normal anatomy (see. Figure 1)

Fig. 5

Minor displacement with vertical incongruity of the pubic symphysis after a frontal motor vehicle collision (a). Already, Inlet- (b) and Outlet-views (c) show larger symphyseal displacement with suspected injury to the right SI-joint

Fig. 6

Borderline view of a symphyseal separation of 2–2.5 cm. Based on the existing literature, it remains unclear if this corresponds to instability

Fig. 7

The anterior–posterior pelvic view shows symphyseal widening/separation with parallel displacement (a). No clear anterior SI-joint opening can be observed (a). External rotation stress views show a significant more displaced symphyseal disruption (b)