Special Articles
Original Research
Sacrum and Coccyx Radiographs Have Limited Clinical Impact in the Emergency Department
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OBJECTIVE. The purpose of this study was to determine the yield and clinical impact of sacrum and coccyx radiographs in the emergency department (ED).
MATERIALS AND METHODS. Consecutive sacrum and coccyx radiographs obtained in the EDs of four hospitals over a 6-year period were categorized as positive for acute fracture or dislocation, negative, or other. Five follow-up metrics were analyzed: follow-up advanced imaging in the same ED visit, follow-up advanced imaging within 30 days, new analgesic prescriptions, clinic follow-up, and surgical intervention within 60 days.
RESULTS. Sacrum and coccyx radiographs from 687 patients (mean age, 48.1 years; 61.6% women and 38.4% men) obtained at level-1 (n = 335) and level-2 (n = 352) trauma centers showed a positivity rate of 8.4% ± 2.1% (n = 58/687). None of the 58 positive cases had surgical intervention. At the level-1 trauma centers, there was no significant association between sacrum and coccyx radiograph positivity and analgesic prescription or clinical follow-up (p = 0.12; odds ratio [OR], 2.3; 95% CI, 0.81–6.20). At the level-2 trauma centers, 97.1% (n = 34/35) of patients with positive sacrum and coccyx radiographs received analgesic prescriptions or clinical referrals, whereas negative cases were at 82.9% (OR, 7.0; 95% CI, 0.94–52.50). Of all cases, 5.7% (n = 39) and 4.3% (n = 29) had advanced imaging in the same ED visit and within 30 days, respectively. Sacrum and coccyx radiography results had no significant correlation with advanced imaging in the same ED visit (level-1, p = 0.351; level-2, p = 0.179). There was no significant difference in 30-day advanced imaging at the level-1 trauma centers (p = 0.8), but there was at the level-2 trauma centers (p = 0.0493).
CONCLUSION. ED sacrum and coccyx radiographs showed a low positivity rate and had no quantifiable clinical impact. We recommend that sacrum and coccyx radiographs be eliminated from ED practice and patients treated conservatively on the basis of clinical parameters.
Keywords: coccygodynia, coccyx, emergency department radiographs, sacrum
The diagnosis of sacral and coccygeal fractures can be challenging, with missed or delayed diagnoses in 24–70% of cases [1–5]. Factors that complicate radiographic interpretations include a combination of intrinsic sacral tilt, kyphotic curvature of the coccyx, overlying fecal material or bowel, variants in coccygeal anatomy, obesity, and poor technical quality [1, 3]. Fractures of the sacrum often occur with high-energy trauma in young adults and lower-energy trauma in the elderly or osteoporotic [6]. They may be associated with other pelvic ring fractures and approximately 25% can present with neurologic symptoms, including ipsilateral leg weakness, bladder dysfunction, or bowel dysfunction [2, 7, 8]. However, in the modern emergency department (ED), high-energy trauma or neurologic deficits usually lead to advanced imaging with CT—often after pelvic radiography in accordance with the Advanced Trauma Life Support protocols [1].
ED visits have increased sharply [9], which, combined with health care reform, has increased emphasis on patient turnaround time and ED workflow metrics [10]. We hypothesize that, in current practice, patients who continue to undergo sacrum and coccyx radiography have a lower pretest clinical probability for injury because of low-impact trauma, pain without known trauma, or benign clinical examination. Because of this hypothesized pretest selection bias, ED sacrum and coccyx radiographs may be obsolete and an unnecessary cause of increased patient length of stay, health care costs, and patient radiation exposure. In this article we examine ED patients who undergo sacrum and coccyx radiography to determine the positivity rate as well as clinical impact. We investigate the costs of sacrum and coccyx radiographs in terms of dollars charged.
| Materials and Methods |   |
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This study was approved by our institutional review board and was compliant with HIPAA. The requirement for written informed consent was waived due to the retrospective nature of our study.
Using the institutional clinical data warehouse, we retrospectively identified consecutive sacrum and coccyx radiographic examinations performed in the ED of four university-affiliated hospitals between January 1, 2009, and December 31, 2014. The 6-year period was chosen to include sufficient patients and achieve statistical significance. The only exclusion criterion was age less than 18 years. All patients in our study presented with pain, but not all had a documented history of trauma. We combined traumatic and nontraumatic causes of pain because minor trauma can be undocumented or unrecognized. Additionally, insufficiency or stress fractures can present without a history of trauma.
The four university hospitals included in this study have the following characteristics: Hospital 1 is an urban hospital with a level-2 trauma designation and 60,000 annual ED visits. Hospital 2 is a suburban quaternary care center with a level-2 trauma designation and 40,000 annual ED visits. Hospital 3 is a suburban hospital with a level-2 trauma designation and 35,000 annual ED visits. Hospital 4 is an urban level-1 trauma center with 115,000 annual ED visits and approximately 9000 annual trauma activations or consults.
For each patient encounter, the sacrum and coccyx radiography reports were recorded as positive or negative for fracture or other. Any cases of equivocal interpretations (e.g., “possible fracture, correlate with point tenderness”) were included as positive. This was done to maximize capture of impressions that may have altered clinical care. A musculoskeletal fellowship trained radiologist with 3 years of emergency radiology experience performed the categorization of the radiology reports. The “other” category was used to document nontraumatic findings that may be clinically relevant (e.g., lytic lesions, erosions, etc.).
Five follow-up metrics were extracted from the electronic medical records.
Cross-sectional imaging, either CT or MRI, performed during the same ED visit. Follow-up imaging was recorded if it included any or all of the sacrum or coccyx. In this regard CT or MRI of the pelvis, sacrum and coccyx, and lumbar spine were included
Cross-sectional imaging performed within 30 days of initial ED presentation
New analgesic prescriptions
Scheduled or recommended clinical follow-up
Surgical interventions involving the bony pelvis, sacrum, or coccyx within 60 days of sacrum and coccyx radiography
Professional, technical, and global charges for sacrum and coccyx radiography were obtained from the radiology billing department for our study population over the 6-year study period.
Continuous variables were expressed as mean ± SD, and categoric variables were expressed as frequency. Significance was assessed at two-sided α-error of 0.05 except in the case of multiple hypothesis testing, in which significance was assessed using an α-error of 0.025. Equal variance was assumed for t tests when the ratio of the variances of the two groups was between 0.5 and 2.0, otherwise nonequal variance was assumed. The Fisher exact test was used on independent variables to assess the significance of associations. All calculations were performed in MATLAB 2015a with the Statistics and Machine Learning Toolbox (Mathworks).
| Results | |
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Over the 6-year period, 687 patients (mean age, 48.1 years; 61.6% women and 38.4% men) met the inclusion criteria. Three hundred fifty-two patients (mean age, 51.3 years, 69.4% women and 30.6% men) were at the level-2 trauma centers. Three hundred thirty-five cases (mean age, 44.8 years, 53.4% women and 46.4% men) occurred at the level-1 trauma center.
A pooled independent two-sample t test revealed that the positivity rates at the level-1 and level-2 trauma sites were not significantly different (p = 0.15), enabling us to combine the data for this analysis. In the total population, 91.3% of radiographs were reported as negative, 8.4% ± 2.1% (n = 58/687) were positive for acute findings, and 0.3% (n = 2/687) of cases had other findings. Due to the low rate of other findings, a Wilson score interval correction yielded a 95% CI of 0.6% ± 0.5%, adjusting the middle of the interval from 0.3%. Table 1 presents follow-up metrics for both positive and negative sacrum and coccyx radiographs.
Of the 687 patients, 65.8% underwent recommended follow-up in the clinic and 47.9% were prescribed new pain medications. In none of the 58 positive cases on radiography was there surgical intervention within 60 days (95% CI, 0–0.6%).
At the level-2 trauma centers, a majority of patients are recommended clinical follow-up, whereas this is not true at the level-1 trauma center (significance confirmed with a Fisher exact test). Because of this inherent difference in practice, the data from the level-1 trauma center was analyzed separately from the level-2 trauma centers. Because these groups were not independent (i.e., some patients who had fractures received both clinical follow-up recommendation and pain medication), we dichotomized the results into contingency tables with clinical follow-up, pain medication administration, or both to see whether there was an association with sacrum and coccyx radiograph positivity (Tables 2 and 3 for the level-2 and level-1 centers, respectively) and subsequently performed a Fisher exact test. The two cases with a finding of other at the level-2 trauma centers were not included in this analysis.
At the level-2 trauma centers, the Fisher exact test yields were p = 0.026. Because of the performance of multiple hypotheses testing, we corrected our significance level to p < 0.025. This implies no significant association of sacrum and coccyx radiograph positivity with pain medication or clinical follow-up metrics, although there was a trend that patients with positive sacrum and coccyx radiographs were more likely to receive pain medication, clinical follow-up, or both. Additionally, the odds ratio (OR) was 7.0 (95% CI, 0.94–52.5); the OR includes 1.0, implying that sacrum and coccyx radiograph positivity and receiving pain medication or clinical follow-up were independent. At the level-2 trauma centers, 97.1% (n = 34/35) patients with positive sacrum and coccyx radiographs received pain medications, clinical referrals, or both, whereas the rate for negative cases was 82.9%.
At the level-1 trauma center, the Fisher exact test was p = 0.12. This implied no significant association between sacrum and coccyx radiograph positivity and receiving pain medication or clinical follow-up. Additionally, the OR was 2.3 (95% CI, 0.81–6.2), including 1.0. Descriptively, 78.3% of level-1 trauma patients with positive sacrum and coccyx radiographs received either pain medications or clinical referral versus 61.5% with negative sacrum and coccyx radiographs who received the same. However, this was not statistically significant.
In the total population, 5.7% (n = 39) underwent follow-up CT or MRI in the same ED visit, and 4.3% (n = 29) underwent advanced imaging within 30 days. On an equal variance two-tailed independent t test, follow-up imaging rates (both in the same visit and within 30 days) showed no significant difference between the level-1 and level-2 trauma centers (p = 0.23). The rates of follow-up imaging for positive versus negative sacrum and coccyx radiographs were analyzed using the t test with unequal variance. At the level-1 trauma center, there was no significant difference in follow-up imaging in the ED (positive sacrum and coccyx radiographs, 3/23; negative sacrum and coccyx radiographs, 19/312; p = 0.351) or within 30 days (positive sacrum and coccyx radiographs, 1/23; negative sacrum and coccyx radiographs, 10/312; p = 0.8). At the level-2 trauma centers, there was no significant difference in follow-up imaging in the ED (positive sacrum and coccyx radiographs, 4/35; negative sacrum and coccyx radiographs, 12/315; p = 0.179). At the level-2 trauma centers, there was a difference in 30-day follow-up imaging (positive sacrum and coccyx radiographs, 6/35; negative sacrum and coccyx radiographs, 12/315; p = 0.0493). Figure 1 is a flowchart detailing the results of advanced imaging with respect to the initial sacrum and coccyx radiographic results. Figure 2 provides examples of sacrum and coccyx radiographs with concordant and discordant advanced imaging findings.
 View larger version (43K) | Fig. 1 —Flowchart shows patients who underwent sacrum and coccyx radiography and advanced imaging in either emergency department (ED) or within 30 days after ED visit. |
 View larger version (439K) | Fig. 2A —Concordant and discordant CT and radiography. A, 75-year-old woman with low back pain. Lateral sacrococcygeal radiograph (A) shows anterior buckling at S2 level (arrow). CT image (B) confirms bilateral sacral fractures (arrows), with pattern suggesting insufficiency fractures. |
 View larger version (299K) | Fig. 2B —Concordant and discordant CT and radiography. B, 75-year-old woman with low back pain. Lateral sacrococcygeal radiograph (A) shows anterior buckling at S2 level (arrow). CT image (B) confirms bilateral sacral fractures (arrows), with pattern suggesting insufficiency fractures. |
 View larger version (419K) | Fig. 2C —Concordant and discordant CT and radiography. C, 69-year-old woman after fall. Lateral sacrococcygeal radiograph (C) and corresponding same-day CT image (D) show anterior cortical discontinuity at S5 (arrow, C), which was questioned on radiograph but not substantiated on CT image. |
 View larger version (255K) | Fig. 2D —Concordant and discordant CT and radiography. D, 69-year-old woman after fall. Lateral sacrococcygeal radiograph (C) and corresponding same-day CT image (D) show anterior cortical discontinuity at S5 (arrow, C), which was questioned on radiograph but not substantiated on CT image. |
The professional, technical, and global charges for sacrum and coccyx radiography over the study period are summarized in Table 4. At our institution, the average global charge for sacrum and coccyx radiography over the study period was $230 ($201–$263); $24 for professional fees and $206 for technical charges. Total charges over the study period were $158,010.
| Discussion | |
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In our study, ED sacrum and coccyx radiographs were positive in 8.4% of patients, but none of these patients underwent surgical intervention within 60 days. There was no significant change in pain medication administration, clinical follow-up recommendations, or ED advanced imaging on the basis of positive sacrum and coccyx radiographs. At the level-2 trauma centers, there was a higher rate of 30-day follow-up imaging in patients with positive sacrum and coccyx radiographs. Additionally, there was a trend toward increased pain medication administration and clinical follow-up if sacrum and coccyx radiographs were positive. However, this delayed follow-up imaging, and these conservative follow-up metrics could be determined on clinical grounds. Indeed, this may be correlative rather than causative: Patients with fractures may have increased pain and thus be more likely to receive analgesics or follow-up appointments. The subset of patients who underwent advanced imaging after positive sacrum and coccyx radiographs did not show a high correlation between radiographic and CT or MRI results: three positive findings were confirmed, there was one new positive finding, and seven of 11 cases were negative on advanced imaging. Given our four-hospital population, with inherent practice differences, our data provide strong evidence to curtail or eliminate the use of ED sacrum and coccyx radiography in the setting of known or suspected trauma, which may decrease ED length of stay, decrease costs, and decrease patient radiation exposure.
Sacral fractures can be unstable or stable and operative or nonoperative. Of all acute injuries detectable on sacrum and coccyx radiographs, sacral fractures necessitating surgery are the most clinically important. Instability implies that fractures are likely to change position with physiologic loading and is most likely to occur in cases of displacement or disruption of the sacroiliac joints, vertical fractures, and sacrotuberous or sacrospinous ligament avulsion [6, 11]. Inappropriately treated or untreated sacral fractures may result in increased pain, immobility, or even neurologic compromise [12]. In practice, isolated fractures occurring below S2 are rarely unstable [6]. It was for this reason that we captured surgical intervention up to 60 days—to determine whether any of the patients with positive sacrum and coccyx radiographs had unstable or operative fractures. The fact that none of our patients with positive sacrum and coccyx radiograph results underwent surgical intervention implies that in our practice high-risk patients are already being triaged to pelvic radiography and subsequently CT. As an illustrative metric of our ED population, at only the level-1 trauma center, our trauma registry documents 294 pelvic ring fractures in the final year of the study (2014), implying more than 1500 at all hospitals during the entire study period.
We hypothesize that over the previous decades, the patient populations undergoing acute sacrum and coccyx radiography has changed significantly with the widespread application of CT. This temporal change in CT usage, the changing patient population undergoing sacrum and coccyx radiography, and literature studies that have isolated only specific types of sacral fractures combine to result in the high degree of variability in the reported detection of sacral fractures on radiography [3, 5, 13, 14]. However, even in the earlier CT era, there was variability, with Resnik et al. [14] reporting that they missed only 16% of sacral fractures on radiography and stating that experience may play a role in decreasing missed sacral fractures on radiography. It is interesting to note that if at four busy hospitals over a 6-year period, we captured 687 ED sacrum and coccyx radiography studies, the individual radiologist's exposure to acute sacrum and coccyx radiographs is probably limited. On the basis of these results, we speculate that individual radiologist experience with these studies is decreasing, which may be another argument against their use.
Regarding coccygeal injury or pain, one of the earliest studies by Duncan [15] circa 1937 confirmed no radiologic difference between patients with coccygodynia and control subjects who were asymptomatic. Indeed, both traumatic and nontraumatic coccygodynia are initially treated conservatively with hot or cold packs, foam seat pads or donut cushions, analgesics, and avoiding hard seats [16]. Conservative treatment should be pursued for 3–8 months before surgical intervention is considered [17, 18]. In cases that are refractory to conservative treatment, resection of the coccyx may be considered in both traumatic and nontraumatic cases [16, 17]. In certain situations, dynamic coccygeal radiographs or lateral radiographs in the seated position may be illustrative of ligament luxation or hypermobility [19, 20], but this is not applicable in the ED setting.
Finally, sacrum and coccyx radiography results in patient radiation exposure (including gonadal radiation dose) and costs. Additionally, there is an ongoing effort to decrease ED length of stay (LOS) because decreasing LOS helps in controlling costs as well as increasing patient satisfaction with ED care [21]. In certain situations, decreasing sacrum and coccyx radiography use may result in ED LOS time savings. An estimated 250 million diagnostic radiographic examinations are performed each year in the United States, with aggregate costs in the billions of dollars [22]. A reduction in unnecessary imaging enables optimal allocation of health care resources. In our study, sacrum and coccyx radiography resulted in aggregate charges of $158,010 across the study period, with zero surgical interventions in positive sacrum and coccyx radiography cases. Although the actual amount collected would have been less, these charges represent an overall health system cost and possibly a financial burden to patients in terms of self-payers or copay. With an added emphasis on cost control, we make the case for better use of these health care dollars. This study adds to recent work documenting the inefficiency of some traditional radiographic examinations in the ED [23, 24].
Our work has limitations. First, we capture only certain medical interventions that may result from sacrum and coccyx radiographic findings, namely, follow-up imaging, pain medication administration, clinical follow-up, and surgical intervention. We do not capture other medical interventions, such as chemo-therapy or antibiotic administration; we chose not to collect this data because the spectrum of possible medical interventions was broad and connecting them directly to sacrum and coccyx radiographic results was difficult. Regional practice differences in the patients who undergo sacrum and coccyx radiography may affect the utility and positivity rate.
We capture whether or not clinical follow-up was recommended; however, it is possible that the results of sacrum and coccyx radiography impacted the advice the patients were given at clinical follow-up. This would not be captured in our data. However, conservative management can be triaged on the basis of clinical symptoms and tolerance without the results of sacrum and coccyx radiography. For the 30-day follow-up imaging, we cannot confirm that new trauma or change in the clinical situation did not occur between the ED visit and the follow-up imaging. Finally, we captured all sacrum and coccyx radiographs obtained in the study period; from our chart review, we can state that the vast majority of these cases were for pain after acute or subacute trauma. However, a few cases were pain without documented prior trauma. Because our clinical indication often documents “pain,” it was not possible to reliably exclude these cases. Nonetheless, we created the category of other to capture these positive noninjury cases that may have clinical impact; however, we note that these cases were surprisingly limited.
| Conclusion | |
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Because of low yield and limited clinical impact in the ED, we recommend that sacrum and coccyx radiography be eliminated from ED practice in the setting of known or suspected trauma and that patients be treated conservatively or receive advanced imaging on the basis of clinical parameters. Failure of conservative treatment could prompt delayed sacrum and coccyx radiography or delayed cross-sectional imaging (as already happens in a subset of patients). A prospective pilot study may be necessary to ensure that elimination of sacrum and coccyx radiography does not unintentionally lead to higher rates of CT or MRI in the ED.
F. Khosa is the ARRS Scholar (2013–2015).
F. Khosa receives salary support from National Institutes of Health grant 1R56HL126558-01.
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