Vertically unstable fractures of the pelvic ring are uncommon high-energy injuries, usually caused by falls from a height or motor vehicle accidents. By definition, the injury pattern is rotationally and vertically unstable, with complete disruption of the posterior osseous ligamentous structure of the pelvis. The anterior injury consists of disruption of the symphysis pubis or unilateral or bilateral fractures of the pubic rami. Posteriorly the injury may comprise a dislocation or fracture-dislocation of the sacroiliac joint; a vertical fracture of the sacrum, frequently transforaminal; or an iliac wing fracture. These are severe injuries, with high mortality and frequent morbidity due to pain and malunion.1,2
Initial treatment of vertically unstable fractures may include traction, closed reduction, and anterior external fixation during resuscitation. For definitive treatment, anterior fixation alone is not sufficient to maintain reduction of the posterior injury.3
If the posterior injury is primarily of the sacroiliac joint, this may be approached from the front, reduced, and fixed with plates.4 Alternatively a posterior approach can be used to reduce and fix the sacroiliac joint with interfragmentary screws5 or to place sacral bars or internal fixation systems.6 A similar posterior approach has been described to reduce and fix sacral fractures with small plates.7 Sacral fractures are not accessible through an anterior approach because the L5 and sacral nerve roots are at risk.6 Posterior approaches require a frequently multiply injured patient to be turned prone and have been associated with prominence of fixation devices and wound breakdown.6 An alternative technique is to perform a closed reduction with the patient supine, then to fix the posterior injury with percutaneous iliosacral screws.8,9 Fixation of the anterior injury also should be performed,8 usually by plating the symphysis or by applying an anterior external fixator.
At our institution, percutaneous iliosacral screw fixation has become the treatment of choice for the posterior component of many pelvic ring injuries, including injuries thought to be vertically unstable. Our experience and some anecdotal reports from others using similar techniques suggested, however, that the technical results in patients with vertically unstable fractures might not be as good as hoped, particularly in patients with a vertical sacral fracture. Percutaneous iliosacral screws have a developing role in the management of pelvic fractures, but little evidence has been reported to guide their use in vertically unstable injuries.
This study was performed to measure the technical failure rate of percutaneous sacroiliac screw fixation of vertically unstable pelvic fractures (OTA type 61-C) and particularly to test the hypothesis that fixations in which the posterior injury is a vertical fracture of the sacrum (OTA type 61-C1.2) are more likely to fail after closed reduction and percutaneous iliosacral screw fixation than fixations with dislocations or fracture-dislocations of the sacroiliac joint (OTA type 61-C1.3).
MATERIALS AND METHODS
The institutional review board approved this study. All patients with pelvic fractures admitted to Parkland Memorial Hospital between January 1, 1993, and December 31, 1998, were identified from the trauma registry. Hospital records and operative reports were examined to identify patients treated with iliosacral screws. Of these patients, initial anteroposterior, inlet, and outlet radiographs and computed tomography (CT) scans were examined to identify patients with vertically unstable injuries.
Patients were included in the study if they had an unequivocal vertically unstable pelvic fracture that was treated with closed reduction and percutaneous iliosacral screws. An unequivocal vertically unstable fracture was defined as at least 1 cm of combined vertical displacement on initial inlet and outlet views or sacroiliac dislocation with at least 1 cm of separation of the entire sacroiliac joint on initial CT scan (Fig. 1) or a complete vertical sacral fracture with at least 1cm of separation over the whole fracture surface on initial CT scan (Fig. 2). Criteria for exclusion were any evidence of a lateral compression component to the injury, defined as a sacral impaction fracture (Fig. 3) or internal rotation of the affected hemipelvis on CT scan; a treatment delay of more than 3 weeks; H-shaped sacral fractures; patients whose initial posterior stabilization used a method other than iliosacral screws; or patients whose initial posterior surgery was performed at another hospital.
Demographic and injury information was collected from the trauma registry. Immediate postoperative anteroposterior, inlet, and outlet radiographs and similar follow-up views from a minimum of 12 months postinjury were examined. Position, length, and numbers of iliosacral screws and any evidence of metalwork failure (eg, bending or breakage) were recorded. Two observers independently measured residual postoperative displacement and late displacement of the posterior pelvis. One observer (A.J.S.) had contributed to the care of patients included in the study; the other (D.R.G.) had not. The observers measured vertical displacement on each radiograph by constructing horizontal reference lines through bony landmarks10; displacement of the innominate bone in a posterior or superior direction was taken as positive. Each observer calculated a “combined vertical displacement” by adding the measurements for inlet and outlet views. Differences between the observers of 0.5 cm or more of combined vertical displacement were resolved by consensus; when there was a small difference (<0.5 cm) or the observers could not agree, the greater value was chosen.
The main outcome measure was failure, defined as at least 1 cm of combined vertical displacement of the posterior pelvis compared with immediate postoperative position. The main analysis was for association between fracture pattern and failure. Patient demographic data, iliosacral screw position, and anterior pelvic fixation methods also were studied. Fisher exact test was used to identify association between variables, and P < 0.05 was considered significant.
A total of 816 pelvic fracture patients were identified, of which 95 included widely separated or vertically displaced posterior injuries. Twenty-one had evidence of lateral compression and were excluded. Two patients had double vertical or H-shaped sacral fractures, and one had an unclassifiable complex sacral and pelvic fracture. Six patients died (five on the day of injury and one 36 hours after surgery). Surgery was delayed more than 3 weeks in one patient (posterior open reduction and plate fixation 5 weeks postinjury), and one patient was referred from another hospital after failed anterior sacroiliac joint plating. The radiographic record was incomplete for one patient. The cohort comprised 62 surviving patients with unequivocally vertically unstable pelvic fractures in whom the posterior injury was treated with closed reduction and percutaneous iliosacral screw fixation. Of these cases, 32 were dislocations or fracture-dislocations of the sacroiliac joint (OTA type 61-C1.2), and 30 were vertical fractures of the sacrum (OTA type 61-C1.3). Sixteen of the 62 patients were women; mean age was 34 (range 17 to 59), and mean ISS was 20 (range 9 to 50).
Pelvic surgery was performed within 5 days in 53 of the 62 patients. Patients were placed supine on a radiolucent table, and an image intensifier was moved frequently between inlet, outlet, and lateral views. Closed reduction was performed by longitudinal traction and closed manipulation. Reduction was to within 1 cm or less of combined vertical displacement on inlet and outlet views in all but four patients. Reduction was held manually, while cannulated, percutaneous iliosacral screws were placed. All screws were partially threaded and used with washers. Moderate compression was applied across the sacroiliac joint, but in the case of vertical sacral fractures, screws were tightened only until the fracture surfaces were approximated. Two patients were fixed with a single screw in S1, 3 with two screws in S2, 56 with a screw in each of S1 and S2, and 1 with two screws in S1 and one in S2. The longest screw reached the sacral body in 18 patients, the level of the far foraminae in 15, the far ala in 22, and across the far sacroiliac joint in 7. Anterior fixation was by symphysis plate in 27 patients, percutaneous superior ramus or anterior column screw in 19, and external fixation in 10 and was not performed in 6. Patients were mobilized non-weight bearing (allowed to place the ipsilateral foot on the floor, but not to bear any body weight) for 3 months after surgery, then were allowed to advance to full weight bearing.
Fixation failed in 4 patients (see example in Figure 4), all with vertical sacral fractures (Table 1). All four patients required revision fixation. None of these failures occurred in the patients with more than 1 cm of combined vertical displacement at initial reduction or in patients who were noted to be noncompliant with postoperative instructions.
In two further cases with vertical sacral fractures, there was evidence that the fracture had only barely been held by the fixation. In each patient, one screw had bent and the other loosened, but these fractures had healed, and the follow-up radiographs did not meet the displacement criteria for failure. The remaining 56 patients had no evidence of redisplacement or implant failure at a minimum of 12 months follow-up.
A vertical sacral fracture pattern was significantly associated with failure (Fisher exact test, P = 0.04); the excess risk of failure compared with sacroiliac joint injury was 13% (95% confidence interval 1% to 25%). Failure was not associated significantly with anterior fixation method, accuracy of posterior reduction, iliosacral screw arrangement or length, or any demographic or injury variable (Table 2).
It is generally accepted that operative treatment of unstable pelvic ring fractures allows early rehabilitation and reduces morbidity.11 It seems likely that this applies to vertically unstable fractures as well as other injury patterns, although the long-term benefits of accurate and maintained reduction of the posterior injury are controversial.12,13 Nevertheless, any surgeon performing a reduction and fixation strives for maintenance of that reduction until healing.
Biomechanical studies have shown that anterior internal fixation, external fixation, or a combination of these is insufficient to maintain reduction of vertically unstable posterior injuries of the pelvic ring.6,14 Percutaneous sacroiliac screws are an attractive option for direct fixation of the posterior lesion. This technique has well- recognized risks of nerve or vessel injury,15,16 but when performed with high-quality image intensification and due regard to the anatomy of the sacrum,17 complication rates have been low.8,9
In this study, stringent criteria were used for selection of the sample to ensure that all fractures were vertically unstable and a fair test of this aspect of the performance of iliosacral screws. In particular, injuries with any characteristics of a lateral compression fracture, in which a sacral fracture might be secondarily stable due to impaction, or the posterior ligaments or pelvic floor might be intact to prevent vertical displacement, were excluded. These stringent criteria and the relatively large size of the series strengthen the study. The study is retrospective, and it is possible that some relevant patients have been missed. Because patients were identified from the trauma registry and hospital management records, however, there is no reason to suspect that failed fixations or specific fracture patterns were less likely to be included, so selection bias is unlikely. Sufficient data were obtained on all but one eligible patient, and measurements were performed independently by two observers, so significant information bias is also unlikely.
The choice of 1 cm of combined vertical redisplacement as the principal outcome measure requires some discussion. Other studies have used 1 cm of superior displacement on a single anteroposterior radiograph as a definition of failure,8 but we thought that posterior re- displacement should not be ignored, particularly as posterior displacement is often a major component of these injuries. The routine use of inlet and outlet views allowed us to assess redisplacement in both vectors, and calculation of combined vertical redisplacement provided a simple measure of loss of reduction. We acknowledge that measurement of displacement on routine radiographs is difficult and unlikely to be precise. The value 1 cm of redisplacement was chosen as the minimum that could be detected reliably. Smaller, real displacements may have been missed, but all fractures had healed at assessment, so these could not be progressive, and it is unlikely that such small malunions would be clinically significant. Redisplacement of 1 cm may or may not be clinically important, but it provided a measurable and appropriately sensitive threshold for technical failure.
All outcome data were collected from radiographs: This study addressed only the technical success of fracture fixation. No attempt has been made to infer clinical outcome, which would require other, patient-based, outcome measures.
It is not surprising that percutaneous iliosacral screws performed differently in the settings of sacroiliac joint dislocation and sacral fractures. In sacroiliac joint dislocations, the screw passes through both cortices of the ilium on one side of the injury, then the cortical and subchondral bone of the articular surface of the sacrum and a substantial depth of uninjured cancellous bone of the sacral ala and body on the other side. When a vertical sacral fracture is fixed, the screw has strong hold lateral to the fracture but passes through no cortical bone and only a relatively shorter length of cancellous bone medial to the fracture. Vertical shear forces are converted easily to rotational forces around the poorly fixed tip of the screw in soft bone. The use of a longer screw is limited anatomically, and even if the tip reaches the hard bone of the far articular surface, fixation at the tip is subject to the large moment resulting from a long screw. Finally, although the irregularities of a dislocated sacroiliac joint can be reduced, interdigitated, and compressed to resist shear forces, the cancellous surfaces of a sacral fracture collapse under compression, and the surgeon must be cautious to minimize compression to avoid additional damage to nerve roots exiting the injured forminae.
Several measures can be taken to prevent fixation failure in the case of vertical sacral fractures. Vertical forces across the pelvis might be reduced by maintaining a period of bed rest, but this is often contraindicated in these patients with severe or multiple injuries. Alternative methods of fixation can be considered, such as the long transsacral plate used to revise one of our patients, a combination of iliosacral screws and a vertebropelvic fixator,18 or open reduction internal fixation.7
This study has shown the technical results of percutaneous iliosacral screw fixation of the posterior component of a vertically unstable pelvic fracture when combined with appropriate anterior fixation. In patients in whom the posterior injury was primarily a sacroiliac joint dislocation, the technique was particularly successful, with no cases of redisplacement. Where the posterior injury was a vertical sacral fracture, the technique was still successful in most cases, but redisplacement occurred in 13%. Across the whole group, failure was not associated with anterior fixation technique, iliosacral screw arrangement, or screw length, but only with the presence of a vertical sacral fracture. This study has shown that percutaneous iliosacral screw fixation is a useful technique in the management of vertically unstable pelvic fractures but suggests that a vertical sacral fracture should make the surgeon more wary of fixation failure and loss of reduction.
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Vertically Unstable Pelvic Fractures Fixed with Percutaneous Iliosacral Screws: Does Posterior Injury Pattern Predict Fixation Failure?
David Templeman, MD
Wayzata Orthopedics, Plymouth, MN
Griffin and colleagues have documented that vertical sacral fractures are prone to redisplacement when stabilized with percutaneous iliosacral screws. This is a valuable article that will help define appropriate indications for closed reduction and percutaneous iliosacral screw fixation of pelvic ring injuries.
Important facts to consider in reading of the article are the author's description of the technique of reduction, placement of screws, and degree of interfragmentary compression that was achieved. They describe redis- placement in 4 of 26 vertical sacral fractures; but an overall success rate of 90% (56/62) which is commendable in the treatment of these severe injuries. Despite this, debate continues concerning the indications for the use of closed reductions and percutaneous iliosacral screws for the fixation of sacral fractures. Arguments to support the use of open reduction are:
- Reilly found that malreductions of experimentally created sacral fractures compromised the area available for the insertion of iliosacral screws by narrowing the “safe zone” for the insertion of the screws.
- As Griffin and his co-authors note when using percutaneous iliosacral screws “the surgeon will be cautious to minimize compression in order to avoid additional damage to nerve roots exiting the injured foramina.” I believe this is especially the case when there is uncertainty as to the accuracy of the reduction of transforaminal fractures. An open reduction permits direct visualization of the fracture line.
- The use of iliosacral screws inserted into the body of S1; where there is better bone density, allows for interfragmentary compression, with the screws threads achieving purchase in the dense bone of the sacral body.
- Tornetta & Matta, Cole et al, and others have achieved higher success rates after performing open reductions and iliosacral screw fixation of sacral fractures.
In conclusion, this is a valuable article that will help us to continue to define the appropriate indications for closed reduction and percutaneous iliosacral screw fixation of pelvic fractures.
1. Matta JM, Tornetta P III. Internal fixation of unstable pelvic ring injuries. Clin Orthop
2. Cole JD, Blum DA, Ansel LJ. Outcome after fixation of unstable posterior pelvic ring injuries. Clin Orthop
3. Templeman D, Goulet J, Duwelius PJ, Olson S, Davidson M. Internal fixation of displaced fractures of the sacrum. Clin Orthop
4. Reilly MC, Bono CM, Litkouhi B, Sirkin M, Behrens FF. The effect of sacral fracture malreduction on the safe placement iliosacral screws. J Orthop Trauma