Article, Radiology

Incidence and clinical features of sacral insufficiency fracture in the emergency department

a b s t r a c t

Introduction: A sacral insufficiency fracture (SIF) often manifests as low back pain or sciatica in the absence of any antecedent trauma. These fractures may be missed because of lack of appropriate imaging. The purpose of this study was to clarify the incidence and clinical features of SIF as well as the characteristic findings on magnetic res- onance imaging (MRI) of the lumbar spine.

Materials and methods: The study participants comprised 250 patients (132 male, 118 female; mean age 58.6 years) with pelvic trauma. SIF was identified on computed tomography or MRI. The incidence, initial symp- toms, and time delay between the First visit and an accurate diagnosis of SIF were recorded.

Results: We detected 11 cases of SIF. Initial symptoms of SIF were low back pain (36.4%), gluteal pain (63.6%), and coxalgia (18.2%). Two patients complained of both low back pain and gluteal pain. The mean delay between the first visit and an accurate diagnosis of SIF was 23.9 days. This time interval was significantly longer than in pa- tients with other types of pelvic fracture. Four patients underwent MRI targeting the lumbar spine to investigate their symptoms. In all 4 patients, the signal intensity on T1-weighted and fat-suppressed images of the second sacral segment was low and high, respectively.

Conclusion: This study demonstrates that accurate diagnosis of SIF may be delayed because of difficulties in de- tecting this type of fracture on plain X-ray and the non-specific nature of the Presenting complaints. Emergency physicians should keep SIF in mind when investigating patients who complain of low back pain or gluteal pain. Findings at the second sacral segment on MRI targeting the lumbar spine may aid early diagnosis of this type of pelvic fracture.

(C) 2017

Introduction

Osteoporosis is a common disease in the elderly. Primary osteoporo- sis is found in 70%-80% of affected individuals and includes both post- menopausal and senile osteoporosis [1]. The clinical significance of osteoporosis lies in the fractures that occur. These include vertebral fractures, Colle fractures of the distal radius, and Hip fractures, as well as an increased risk of fractures at other sites when bone density is re- duced [2]. Burge et al. reported the incidence of osteoporosis-related fracture to be 27% for the vertebra, 19% for the wrist, 14% for the hip,

? Conflicts of interest: There is nothing to declare.Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

* Corresponding author at: Department of Orthopedics, Mitoyo General Hospital, Kagawa, 708 Himehama, Toyohama-cho, Kanonji, Kagawa 769-1695, Japan.

E-mail address: [email protected] (Y. Tamaki).

7% for the pelvis, and 33% for other sites [3]. Although almost all such fractures are easy to detect on X-ray, a fracture of the sacrum may be missed because it is difficult to visualize on X-ray because of overlying bowel gas. Sacral insufficiency fracture (SIF) in particular is often overlooked because dislocation is minimal (Fig. 1).

SIF was first reported by Lourie in 1982 [4]. The precise incidence of SIF is still unknown, but has been reported to be 1.0%-1.8% in at-risk pa- tient populations [5,6]. A patient with SIF most commonly presents with low back pain, buttock pain, hip pain, or other symptoms These clinical symptoms are frequently vague and non-specific, and can mimic a vari- ety of pathologic processes, including lumbar Spinal canal stenosis, a compression fracture of the lumbar vertebra, and metastatic disease [7]. There is often a Delay in diagnosis because initial imaging is often not targeted at the sacrum but rather at the lumbar spine and/or pelvis. The purpose of this study was to clarify the incidence and clinical fea- tures of SIF as well as the characteristic findings on magnetic resonance imaging (MRI) of the lumbar spine.

http://dx.doi.org/10.1016/j.ajem.2017.03.037

0735-6757/(C) 2017

Y. Tamaki et al. / American Journal of Emergency Medicine 35 (2017) 13141316 1315

Fig. 1. Representative computed tomography scans in patients with sacral insufficiency fracture. a) Axial view. b) Coronal view.

Materials and methods

We retrospectively identified 450 patients who visited the emergen- cy department in our hospital between January 2013 and November 2014 and were suspected to have a pelvic injury. Two hundred and fifty of these patients (132 male, 118 female; mean age 58.6 [range 4- 100] years) underwent computed tomography (CT) scans at our hospi- tal. We identified all pelvic fractures, including sacral fracture, iliac frac- ture, ischial fracture, and pubic fracture, seen on CT or MRI. Data on incidence, initial symptoms, and the time interval from the first visit to an accurate diagnosis of SIF were recorded. Four patients underwent MRI targeting the lumbar spine to investigate their presenting symptoms.

Results

Forty-six patients were diagnosed as having a pelvic fracture, 20 of which were caused by high-energy trauma, such as a road traffic acci- dent. Forty-two Insufficiency fractures were recorded in 26 patients and comprised 11 sacral fractures, 15 pubic fractures, 9 ischial fractures, and 7 iliac fractures. Twelve patients were diagnosed as having more than 2 fractures, such as a pubic fracture and an ischial fracture.

SIF was diagnosed in 11 patients (3 male, 8 female; mean age 80.9 [range 73-97] years). Initial symptoms of SIF were low back pain (4 pa- tients, 36.4%), gluteal pain (7 patients, 63.6%) and coxalgia (2 patients, 18.2%) (Table 1). Two patients complained of both low back pain and gluteal pain. The mean delay between the first visit and an accurate di- agnosis of SIF was 23.9 (range 1-92) days. The mean delay until diagno- sis was 7.1 (range 1-30) days for a pubic fracture, 2.8 (range 1-14) days for an ischial fracture, and 1.0 days [range 1 to 1] for an iliac fracture. The mean delay between the first visit and an accurate diagnosis of SIF was significantly longer than in patients with other types of pelvic fracture. Four of 11 patients with SIF underwent MRI targeting the lumbar

spine because of their symptoms. In all 4 patients, we could identify sig- nal changes in the second sacral segment on sagittal views. The signal intensity on T1-weighted and fat-suppressed images of the second sa- cral segment was low and high, respectively (Fig. 2).

Discussion

The true incidence of SIF is unknown but has been reported to be be- tween 1.0% and 1.8% in at-risk patient populations [5-7]. The incidence of SIF was 4.4% in our emergency department. One of the reasons for the slightly higher incidence in our study compared with previous re- ports could be that we detected SIF on CT and MRI. CT and MRI have higher resolution than X-ray. SIFs were observed in 11 (23.8%) of 46 pa- tients with pelvic fracture, which suggests that SIF is not a rare type of pelvic fracture.

In terms of the clinical features of SIF, Weber et al. reported that low back pain and bilateral buttock pain was present in all their 20 patients with SIF [5]. The initial symptoms in our study were low back pain, glu- teal pain, and coxalgia, which is similar to Weber et al.’s report. These symptoms are suggestive of lumbar spine disease, for example, Lumbar spinal canal stenosis or compression fracture of the lumbar vertebra. Lyder et al. reported that the initial imaging for SIF is often not targeted to the sacrum but rather to the lumbar spine and/or pelvis. It has also been reported that there is a delay of 40-55 days from symptom onset until dedicated sacral imaging is pursued [7]. The mean delay between initial presentation and an accurate diagnosis was 23.9 days in our study, which was significantly longer than that for other pelvic insuffi- ciency fractures. SIF should be kept in mind when investigating elderly patients with low back pain or buttock pain.

We believe that the main reason for delayed diagnosis of SIF is that X-ray and CT lack insensitivity for detection of this type of fracture. In a previous review article, Lyder et al. reported that only 20%-38% of SIF and pelvic ring fractures could be identified on plain films [7].

Table 1

Demographic and clinical data for 11 patients with sacral insufficiency fracture.

Patient

Age, year

Sex

Chief complaint

Delay until accurate diagnosis (days)

Diagnosis

1

73

F

Low back pain and gluteal pain

21

Sacral fracture

2

73

F

Gluteal pain

14

Sacral fracture

3

74

F

Low back pain

45

Sacral fracture

4

75

F

Gluteal pain

23

Sacral and pubic fracture

5

79

M

Low back pain and gluteal pain

33

Sacral fracture

6

80

F

Gluteal pain

7

Sacral fracture

7

81

F

Gluteal pain

22

Sacral and pubic fracture

8

83

M

Gluteal pain

92

Sacral fracture

9

85

F

Low back pain

1

Sacral fracture

10

90

M

Coxalgia

1

Sacral, pubic, iliac, ischial fracture

11

97

F

Coxalgia

4

Sacral, pubic, ischial fracture

1316 Y. Tamaki et al. / American Journal of Emergency Medicine 35 (2017) 13141316

Fig. 2. Magnetic resonance imaging of the lumbar spine in a representative case of sacral insufficiency fracture. There is no stenosis or compression fracture of the vertebra. However, signal changes are seen at the second sacral segment, comprising low intensity on a T1-weighted image and high intensity on short tau inversion recovery.

Further, CT is not sensitive for detection of SIF, with a reported sensitiv- ity of 60%-75% [7]. In contrast, MRI can detect early changes of SIF with a sensitivity of nearly 100% [7,8].

Patients with SIF often complain of low back pain and buttock pain, so it is natural for a physician to suspect lumbar disease. It would be very useful if SIF could be detected on lumbar MRI. In our study, 4 patients with SIF underwent MRI targeting the lumbar spine. In all 4 patients, the signal intensity of T1-weighted and fat-suppressed images of the second sacral segment on sagittal views was low and high, respectively. “H” pattern fractures have been reported to be the most common type of SIF [4]. Linstrom et al. reported an anatomical and biomechanical analysis showing that the horizontal component of the fracture seems to develop at a later stage after loss of support of the central sacrum from the laterally positioned vertical fracture in the sagittal plane, which progresses to the typical “H” pattern [9]. The loss of lateral sacral alar support causes the entire weight of the upper body to be longitudi- nally transferred down the central portion of the sacral bodies, which include the upper S2 or lower S1 levels. We consider that signal changes at S2 on lumbar MRI indicate an insufficiency fracture or bone marrow lesion caused by this mechanism.

Conclusions

The incidence of SIF was 4.4% in our emergency department. There- fore, SIF cannot be considered a rare fracture in elderly patients. Almost all patients with SIF in this retrospective study complained of low back

pain or gluteal pain, which led the physician to suspect lumbar disease. Emergency physicians should take care not to overlook SIF. Findings at the second sacral segment on MRI targeted to the lumbar spine may aid early diagnosis of SIF in patients who complain of low back pain or sciatica.

References

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