The Obturator Foramen "Safe Zone" for Anterior Pelvis Internal Fixation by Transobturator Cerclage.

OBJECTIVES

To quantify the morphology of an avascular "safe zone" within the obturator foramen to assess the risk of neurovascular injury with transobturator foramen cerclage.

DESIGN

Retrospective chart review.

SETTING

Level 1 trauma center and tertiary academic center.

PATIENT SELECTION CRITERIA: Adults ≥18 years without prior pelvic pathology and with pelvic computed tomography angiography demonstrating complete visualization of the obturator arteries.

OUTCOME MEASURES AND COMPARISONS: The minimum distance from the medial cranial border of the obturator foramen to the obturator artery (DOA) and the obturator foramen area (OFA) bounded by the obturator artery and pubis were measured on computed tomography angiography in the plane of the obturator foramen. Associations of OFA and DOA with demographic and anthropometric variables were analyzed by multivariable linear regression. The "safe zone" for passage of transobturator cerclage instrumentation was determined by the 5.0 mm outer diameter of a commercially available cable passer.

RESULTS

The sample included 60 adults, 35 men (58.3%), with a mean age of 56.2 ± 16.4 years. The mean DOA (left 6.8 ± 1.9 mm, right 6.9 ± 1.6 mm, P = 0.724) and OFA (left 195.1 ± 63.3 mm 2 , right 190.3 ± 55.4 mm 2 , P = 0.657) did not vary by laterality. DOA was >3.2 mm for all patients but <5.0 mm in 23.3% of patients. Multivariable analysis indicated that DOA was associated with patient height (β = 0.04, P = 0.019) but not sex (β = 0.01, P = 0.987) or weight (β = 0.01, P = 0.253).

CONCLUSIONS

A "safe zone" defined by the obturator artery and cranial and medial obturator foramina exists for internal fixation of the anterior pelvic ring by transobturator foramen cerclage. Although a cerclage device ≤3.2 mm in diameter seems safe, passage of a cerclage wire through the cranial and medial obturator foramina for internal fixation anterior pelvic ring disruption with typical instrumentation may injure the obturator neurovascular bundle without additional surgical dissection.

LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.