Examination Under Anesthetic for Occult Pelvic Ring Instability

Objective: To describe the technique and results of stress examination with fluoroscopy under anesthesia (EUA) to determine stability and the need for operative stabilization of traumatic pelvic ring injuries. Design: Retrospective chart and radiographic review. Setting: Level I trauma center. Subjects: Skeletally mature patients with traumatic incomplete posterior pelvic ring injuries. Methods: Patients were consented for EUA if preoperative radiographs and computed tomographic scanning of the pelvis demonstrated an incomplete injury to the posterior pelvic ring (Orthopaedic Trauma Association [OTA] 61-B type injuries). Patients with nondisplaced anterior compression fractures of the sacral ala without internal rotation or a fracture line exiting the posterior cortex were excluded from this analysis. Similarly, skeletally immature patients or those with complete instability of the pelvic ring (OTA 61-C type injuries) were excluded. All patients meeting inclusion criteria were taken to the operating room, anesthetized, and placed in the supine position for stress examination (EUA) of the pelvic ring using intraoperative dynamic fluoroscopy. Examination consisted of a resting static film followed by internal rotation, external rotation, and push-pull maneuvers of both lower extremities. Each of these maneuvers was performed using the anteroposterior, inlet, and outlet projections, providing a total of 15 distinct images for each patient's examination. The preoperative classification of the pelvic ring injury was then accepted or redefined based on the amount of rotational and translational instability in the axial, coronal, and sagittal planes. The decision to proceed with anterior and/or posterior operative reduction and stabilization was subsequently based on the degree of pelvic ring instability noted during the EUA. Results: A total of sixty-eight patients underwent an EUA of their pelvis by the senior author. Fifty males and 18 females with an average age of 35 years comprised the study group. In all, 37 anteroposterior compression (APC or OTA 61-B1) injuries and 31 lateral compression (LC or OTA 61-B2) injuries were evaluated. Of the 14 pelvic ring injuries initially classified as an APC-1, seven (50%) were deemed stable and treated nonsurgically, whereas seven (50%) were felt to have sufficient instability (an occult APC-2) to warrant treatment with anterior fixation based on EUA. Of the 23 injuries initially classified as an APC-2, all but one required surgical fixation: 13 (57%) were treated with anterior fixation alone (APC-2a), whereas nine (39%) were treated with anterior fixation and supplemental iliosacral screw placement (APC-2b) based on the degree of instability noted during the EUA. Of the 20 injuries initially classified as an LC-1, 13 (65%) were stable and treated nonsurgically (LC-1a), whereas seven (35%) were treated with anterior and/or posterior stabilization (LC-1b) based on the degree of instability noted during the EUA. Conclusions: The reported incidence of poor functional outcomes associated with pelvic fracture may be attributable, in part, to inadequate treatment of misdiagnosed injuries and chronic instability and/or malunion. Performing an examination under anesthesia with dynamic stress fluoroscopy as described in this series revealed occult instability in 50% of presumed APC-1 injuries, 39% of APC-2 injuries, and 37% of LC-1 injuries. We propose a modification to the Young-Burgess Classification system to reflect the dynamic component of pelvic ring instability disclosed on EUA as follows: APC-2a for those injuries requiring anterior only fixation, APC-2b for those injuries that may require treatment with anterior and posterior fixation, LC-1a for those injuries that are stable and do not require internal fixation, and LC-1b for those lateral compression injuries that may require treatment with internal fixation. We conclude that pelvic EUA merits further analysis as an important diagnostic tool that may provide additional information regarding instability of the pelvic ring.