The indications for operative treatment of pelvic ring injuries include physiologic instability and deformity expected to cause functional problems.1 Anterior pelvic ring injury with unidentified instability can lead to substantial and significant morbidity for the patient. In particular, pain and activity limitations may occur with persistent instability or malunion.2,3 Accurate diagnosis of pelvic ring instability is the most effective strategy to prevent this. Malunion can also occur in the face of operative treatment; however, that scenario would most likely be attributed to inadequate initial treatment or noncompliance with weight-bearing instructions after fixation4 (Fig. 1).
The pelvic ring is formed by 3 bones; the right and left innominate bones and the sacrum. The sacroiliac joints are held in relative position by the “strongest” ligaments in the body, including the sacroiliac ligaments (anterior, posterior, and interosseous) and the sacrotuberous and sacrospinous ligaments. Anteriorly the pubis is held in position by interpubic ligaments. The strong ligamentous system of the posterior pelvis is well designed for stability but limits the amount of motion available.5 This motion is multiplanar, but includes only minute amounts of rotation (average < 4 degrees) and translation (average 1 mm or less) that is subclinically detectable.6,7 Over 30 muscles are attached to the pelvis, including very powerful muscle groups such as glutei, hip flexors, and essentially all of the abdominal and paraspinal muscles. These muscles impart substantial forces on the pelvis, and when the pelvis is injured, it certainly plays a role in creating deformity.
Traditional evaluation of pelvic ring stability has been based on static radiographs obtained at presentation: “trauma anteroposterior (AP)” pelvis x-ray and computed tomography (CT). Major deformity is managed with surgical intervention; however, most pelvic surgeons have encountered cases where mechanical instability based on static initial radiographs was unrecognized or under-appreciated.8–10 To improve the diagnostic acumen for pelvic ring injuries, authors have recently advocated examination under anesthesia or stress radiographs of the pelvic ring to more accurately diagnose subtle instability not recognized on static radiographs.8–10
The static pelvic x-ray or CT may simply be seen as a “snapshot” in time representing the positioning of the injured pelvis when the image(s) were obtained. Gardner et al11 presented a cadaver study that helps explain the phenomenon of normal or near-normal radiographs at presentation in a patient with pelvic ring instability. They stressed cadaver models with anterior posterior compression mechanisms and lateral compression mechanisms specifically looking at recoil of the pelvic ring after simulated injury. From a mechanical standpoint, this is analogous to elastic deformation. When a material is stressed with an applied load, it demonstrates the deformation. If the material returns to the predeformation state after the load is removed, the behavior is classified as elastic. The pelvic ring can behave in this manner as well; this mechanical behavior explains how a pelvic ring can sustain substantial deformity at injury and then recoil to a position that does not clearly demonstrate injury on plain radiographs (Fig. 2).
EXAMPLE: CASE 1
The patient is a 34-year-old woman injured in a high-speed motor vehicle accident, sustaining multiple injuries: at presentation, she was noted to have a left pneumothorax with a ruptured diaphragm and a ruptured spleen. She underwent emergent laparotomy for splenectomy and diaphragmatic repair. Trauma room radiographs of the pelvis demonstrated a minimally displaced sacral fracture on the left side and minimal anterior injury. At bedside, the pelvic ring acted stable with provocative AP and lateral compression-that is, the “rock-test.” Perioperative resuscitation restored hemodynamic stability. Based on “stable” static radiographs (x-rays and CT) and negative physical examination, the patient was assigned nonoperative treatment for the pelvic ring (Fig. 3). She was allowed toe-touch weight-bearing on the injured left side and weight-bearing as tolerated on the right. No further orthopaedic work-up or evaluation was performed. Examination under anesthesia was not believed to be required. The remaining hospital course was uncomplicated and she was discharged to home.
The patient returned to the clinic 2½ weeks after the injury. She was ambulating with partial weight-bearing on the left side using crutches and weight-bearing as tolerated on the right side. Physical examination revealed a stable pelvis, and her neurologic examination was intact. She reported that her pain was improving. AP, inlet, and outlet radiographs of the pelvis demonstrated increased, but mild displacement compared with injury x-rays. It was believed that continued nonoperative treatment was appropriate. The patient returned to the clinic in 4 weeks. She had advanced her weight-bearing on her own despite recommendations for no change, was obviously weight-bearing as tolerated, and no longer using assistive devices. Physical examination demonstrated what appeared to be a stable pelvic ring. She seemed relatively comfortable in gait while exhibiting a mild limp. Her neurologic examination was unchanged and intact. Pelvic radiographs demonstrated further (but mild) progression of the pelvic deformity with minimal internal rotation noted. At this point, it was believed that the pelvis was “healing with reasonable alignment.” The patient continued with nonoperative treatment and was recommended to follow-up in 1 month (Fig. 4A, B).
The patient did not return for follow-up as scheduled. Ultimately, the patient presented to the emergency department about 6 months after initial injury. She reported worsening low back pain and was given anti-inflammatories with early scheduled follow-up in the orthopaedic clinic. Ten days later, in the office, she complained of severe pain near the left sacroiliac joint and anterior pelvis. She specifically complained of pain with bowel movements, urination, and sexual intercourse. She was having difficulty in her job as a landscaper. The pelvis demonstrated moderate tenderness over the symphysis and the left sacroiliac joint. Range of motion demonstrated hip flexion of 110 degrees, full extension, abduction of 40 degrees internally, and 30 degrees external rotation; all with minimal to no pain on the anterior and posterior aspects of the right side and moderate pain on the left side, both at the symphysis as well as the sacroiliac joint. “Rock-test” showed no gross instability to the pelvis. From a neurologic standpoint, the patient had 5/5 motor strength in her lower extremities with no sensory deficits. Her gait was antalgic with a left-sided Trendelenburg sign. New pelvic radiographs demonstrated “substantially worse internal rotation and flexion deformity of the left hemi pelvis with osteolysis” at both the pubis and the left sacroiliac joint (Fig. 4C). A pelvic CT was ordered and demonstrated a healed malunion of the left sacrum with an internal rotation deformity and moderate osteolysis around the left sacroiliac joint. The CT of the pelvic ring confirmed substantial internal rotation and flexion and osteolysis of the parasymphyseal fracture (Fig. 5). The patient was substantially frustrated by pain and resultant limitations on her activity, and she was interested in surgical intervention.
Six and a half months after her injury, the patient went to surgery for pelvic ring reconstruction. Examination under anesthesia was performed and demonstrated no substantial or significant pelvic ring instability. Staged reconstructive effort was then performed. The first stage consisted of a posterior approach to the sacroiliac joint in the prone position. Osteotomy of the callus overlapping the sacroiliac joint of both the sacrum and the ilium was performed to mobilize the posterior pelvic ring. The wound was closed, and the patient was repositioned supine with the pelvis elevated on 2 folded blankets. A Pfannenstiel approach to access the left pubis was performed. Meticulous dissection in the space of Retzius was performed, and the urinary bladder was protected. Overlapping malunion of the pubic symphysis was osteotomized to mobilize the anterior pelvic ring. After the anterior and posterior pelvic ring osteotomies, the left hemipelvis was rendered mobile. A combination of a Jungbluth clamp placed in the symphysis with a Schanz pin placed in the left supra-acetabular region (anterior inferior iliac spine) allowed for adequate manipulation of the left hemipelvis and reduction of the pelvic ring. The pubis was stabilized with 2 orthogonal pelvic reconstruction plates. The anterior pubic wounds were surgically closed. Attention was then directed toward stabilizing the left posterior ring. The patient was repositioned prone and the posterior approach was again accessed. Sacroiliac screws were placed using a partially threaded screw first in the S1 corridor, followed by a fully threaded screw in the S2 corridor. Intraoperative fluoroscopy and plain radiographs demonstrated what was deemed acceptable reduction and stabilization of the pelvic ring (Fig. 6A).
The patient's postoperative course was unremarkable. Given her substantial malunion and subsequent pelvic reconstruction, the patient was maintained on strict non–weight-bearing on both lower extremities and was okay for standing transfers only at 10 weeks after surgery. At that point, she was advanced to weight-bearing as tolerated on both lower extremities. At 4-month follow-up, the patient had noted substantial improvement in pain and quickly returned to most activities. Radiographs of the pelvis demonstrated what appeared to be a consolidated anterior and posterior pelvic ring with intact hardware. Two years after pelvic ring reconstruction, the patient had returned to full activities including work as a landscaper. Pain with urination, bowel movements, or sexual activity had completely resolved. She did continue to have mild, “achy” cold weather-related pelvic pain; however, it did not inhibit her from activities of daily living, social activities, or work. Physical examination at the final follow-up demonstrated a trace antalgic gait and mild Trendelenburg sign on the left. Her pelvis was stable to AP and lateral compression. She had an intact neurologic examination. Radiographs obtained at that visit demonstrated a healed pelvic ring with restoration of alignment in both the AP and inlet and outlet radiographs of the pelvis (Fig. 6B).
Diagnosis of a mechanically unstable pelvic ring injury is frequently accomplished with history, physical examination, and static imaging studies including plain radiographs and pelvic CT. However, a subgroup of patients exists, for example, the patient described above, who seem to have a stable pelvic ring injury but demonstrate occult instability that can lead to unacceptable outcomes with nonoperative treatment. Thus, the goal is to accurately identify those patients with a mechanically unstable pelvic ring injury and provide stability via operative fixation. This is reliably accomplished with the addition of dynamic examination under anesthesia of the pelvic ring as outlined by Sagi et al.9 The utilization of this modality increases the diagnostic acumen of the pelvic surgeon. Conversely, if examination under anesthesia does not demonstrate pelvic ring instability, the physician can be confident that the patient will heal the injury without further deformity.10 In summary, the authors strongly recommend the utilization of dynamic examination under anesthesia for patients with pelvic ring injuries of unclear stability to reduce the occurrence of late pelvic ring deformity.
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10. Whiting PS, Auston D, Avilucea FR, et al. Negative stress examination under anesthesia reliably predicts pelvic ring union without displacement. J Orthop Trauma. 2017;31:189–193.
11. Gardner MJ, Krieg JC, Simpson TS, et al. Displacement after simulated pelvic ring injuries: a cadaveric model of recoil. J Trauma. 2010;68:159–165.