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When do anterior external or internal fixators provide additional stability in an unstable (Tile C) pelvic fracture? A biomechanical study



This study aimed at evaluating the additional stability that is provided by anterior external and internal fixators in an unstable pelvic fracture model (OTA 61-C).


An unstable pelvic fracture (OTA 61-C) was created in 27 synthetic pelves by making a 5-mm gap through the sacral foramina (posterior injury) and an ipsilateral pubic rami fracture (anterior injury). The posterior injury was fixed with either a single iliosacral (IS) screw, a single trans-iliac, trans-sacral (TS) screw, or two iliosacral screws (S1S2). Two anterior fixation techniques were utilized: external fixation (Ex-Fix) and supra-acetabular external fixation and internal fixation (In-Fix); supra-acetabular pedicle screws connected with a single subcutaneous spinal rod. The specimens were tested using a nondestructive single-leg stance model. Peak-to-peak (P2P) displacement and rotation and conditioning displacement (CD) were calculated.


The Ex-Fix group failed in 83.3 % of specimens with concomitant single-level posterior fixation (Total: 15/18–7 of 9 IS fixation, 8 of 9 TS fixation), and 0 % (0/9) of specimens with concomitant two-level (S1S2) posterior fixation. All specimens with the In-Fix survived testing except for two specimens treated with In-Fix combined with IS fixation. Trans-sacral fixation had higher pubic rotation and greater sacral and pubic displacement than S1S2 (p < 0.05). Rotation of the pubis and sacrum was not different between In-Fix constructs combined with single-level IS and TS fixation.


In this model of an unstable pelvic fracture (OTA 61-C), anterior fixation with an In-Fix was biomechanically superior to an anterior Ex-Fix in the setting of single-level posterior fixation. There was no biomechanical difference between the In-Fix and Ex-Fix when each was combined with two levels of posterior sacral fixation.

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No funds were received in support of this work. Implants were kindly donated by Stryker and Zimmer corporations.

Conflict of interest

Erik Mcdonald, BS: no conflict of interest. Alexander A. Theologis, MD: no conflict of interest. Patrick Horst, MD: no conflict of interest. Utku Kandemir, MD: Payment for lectures on speaker’s bureaus (AO North America). Murat Pekmezci, MD: Grants (Stryker, Biomet).

Ethical standards

No funds were received in support of this work. As this is a biomechanical study utilizing foam models, approval by the appropriate ethics committee and patient consent were not applicable.

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Correspondence to A. A. Theologis.

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Mcdonald, E., Theologis, A.A., Horst, P. et al. When do anterior external or internal fixators provide additional stability in an unstable (Tile C) pelvic fracture? A biomechanical study. Eur J Trauma Emerg Surg 41, 665–671 (2015).

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  • Pelvic fracture
  • External fixation
  • Internal fixation
  • Biomechanical analysis