General Session: Tumor, Trauma, Infection, Image

Presented by: E. Jazini - View Audio/Video Presentation (Members Only)

Author(s):

E. Jazini(1), N. Klocke(2), O. Tannous(1), H. Johal(1), J. Hao(2), D. Gelb(1), J. Nascone(1), R. O'Toole(1), B. Bucklen(2), S. Ludwig(3)

(1) University of Maryland, Department of Orthopaedics at Shock Trauma, Baltimore, MD, United States
(2) Musculoskeletal Education and Research Center (MERC) , A Division of Globus Medical, Inc., Audubon, PA, United States
(3) University of Maryland, Baltimore, MD, United States

Abstract

Purpose: To determine whether an anterior pubis symphysis plate is biomechanically necessary to provide full pelvic ring stabilization when lumbopelvic fixation is used to treat zone II sacral fractures with anterior symphysis disruption, or if a posterior-only approach can be used in lieu of a 360° procedure.

Methods: A “floating hip model” was used to simulate bilateral stance during flexion-extension moments (≤8Nm) applied to fresh-frozen cadaveric lumbopelvic specimens, which had been previously cleaned and potted at L4 and at the left ischium. This model allowed the Optotrak motion capture system to assess relative Eulerian motion between left and right iliac crests for the pelvic ring and across the intended sacral fracture zone, while the right hemipelvis was permitted 5 degrees-of-freedom. Following intact motion collection, the pubis symphysis was transected with a scalpel, and a small gap fracture model was simulated (< 1mm) by an oscillating saw used to create a vertical fracture through the sacral foramen. Next, bilateral cannulated iliac screws were placed in the pelvic wings, and rods (with cross-connectors) were used to connect the pedicle screws placed in L4 and L5. The motion profile was then captured both with (L4-P+Ant: Small Gap) and without (L4-P: Small Gap) an anterior pubis symphysis plate (n=7). A larger fracture gap model (1cm) was created with rongeurs along the previously created fracture line. Use of an anterior plate was also tested in this model of a larger comminution (L4-P+Ant: Large Gap and L4-P: Large Gap, n=4). Sacral fracture zone motion (SFM), pelvic ring motion (PRM), and total lumbopelvic motion (LPM) were normalized on a per-specimen basis, and were evaluated with student t-tests (p< 0.05) (Figure).

Results: Average motion was always greater than that observed within intact, regardless of anterior plate use, across SFM and PRM. However, the anterior plate always reduced overall motion; the only instance of statistical significance was found within the SFM of the small gap model, although findings approached significance (p=0.078) within the SFM large gap model.

Conclusions: Use of an anterior plate leads to reduced motion when the pubis symphysis is disrupted in conjunction with zone II sacral fractures of varying complexities. Although most findings of comparisons between motion with and without the anterior plate proved to be non-significant, standard deviations of motion were high when the anterior plate was not added to the surgical construct. This demonstrates that among specimens, permissible motion was much more variable and in some instances was substantially greater with this construct. Although this small cadaveric study did not include the surrounding musculature to provide further motion restraint, findings indicate that a 360° approach may be necessary with such complex and traumatic injuries.

Figure