Can a modified anterior external fixator provide posterior compression of AP compression type III pelvic injuries?

Abstract

Background: Current anterior fixators can close a disrupted anterior pelvic ring. However, these anterior constructs cannot create posterior compressive forces across the sacroiliac joint. We explored whether a modified fixator could create such forces.

Questions/purposes: We determined whether (1) an anterior external fixator with a second anterior articulation (X-frame) would provide posterior pelvic compression and (2) full pin insertion would deliver higher posterior compressive forces than half pin insertion.

Methods: We simulated AP compression Type III instability with plastic pelvis models and tested the following conditions: (1) single-pin supraacetabular external fixator (SAEF) using half pin insertion (60 mm); (2) SAEF using full pin insertion (120 mm); (3) modified fixator with X-frame using half pin insertion; (4) modified fixator using full pin insertion; and (5) C-clamp. Standardized fracture compression in the anterior and posterior compartment was performed as in previous studies by Gardner. A force-sensitive sensor was placed in the symphysis and posterior pelvic ring before fracture reduction and the fractures were reduced. The symphyseal and sacroiliac compression loads of each application were measured.

Results: The SAEF exerted mean compressions of 13 N and 14 N to the posterior pelvic ring using half and full pin insertions, respectively. The modified fixator had mean posterior compressions of 174 N and 222 N with half and full pin insertions, respectively. C-clamp application exerted a mean posterior load of 407 N.

Conclusions: Posterior compression on the pelvis was improved using an X-frame as an anterior fixation device in a synthetic pelvic fracture model.

Clinical relevance: This additive device may improve the initial anterior and posterior stability in the acute management of unstable and life-threatening pelvic ring injuries.

Fig. 1A–C

(A) A single X-frame is shown with the reversed-threaded rod (top) providing compression (red arrow) and distraction (green arrow). (B) The first X-frame applied to the SAEF facilitates a symphyseal compression by the use of the reversed-threaded rod on the top of the frame, (C ) while the second X-frame enables a compression force across the sacroiliac joint by distraction of the Schanz pin tips.

Fig. 2

Force-sensitive sensors are positioned in the symphyseal and sacroiliac (SI) joints to detect load transmission.