Percutaneous Sacroplasty : Effectiveness and Long-Term Outcome Predictors

Study group

This study was approved by the Institutional Review Board of Seoul National University Bundang Hospital (IRB No. B-1902-522-103). Considering the use of anonymized patient data, the requirement for informed consent was waived. From April 2006 to March 2018, we enrolled 43 patients who were referred for PSP to our spinal intervention center at a single tertiary hospital. All patients complained of very severe low back or buttock pain without a definite neurologic deficit. Since the aim of our study was to investigate the long-term outcomes of PSP, three patients were excluded because they had metastatic sacral fractures related to an underlying malignancy (lung cancer, cervical cancer, and renal cell carcinoma). Finally, a total of 40 patients (male : female, 4 : 36; mean age, 75.6±7.9 years; range, 59–89 years) with benign SIFs were enrolled (Fig. 1). Our institution basically followed the procedure guidelines of percutaneous vertebroplasty, which applied to the patients with acute sacral fracture (evident on magnetic resonance imaging [MRI]) with severe pain, despite enough conservative treatment for more than 2 weeks. However, the procedure was performed quickly in three cases, when the pain was too severe despite the conservative management in short-term. For pain relief, our institution used drugs or steroid injection treatment before the procedure. Most patients tried pain control with opioid drugs (n=24) or non-opioid drugs (n=10), but five patients received steroid injection therapy (transforaminal epidural steroid injection [n=2] and caudal injection [n=3]).

Fig. 1.

Flow chart depicting the process of patient selection. NASS : North American Spine Society.

Clinical assessment

The review of the patients’ medical records was performed by one of the authors who was not involved in the patients’ treatment. Information regarding each patient’s age, sex, dual-energy X-ray absorptiometry (DEXA) score, cause of sacral fracture, hospital stay, short-term follow-up with overall pain relief, and any comorbidities that could be related to the patient’s prognosis was collected.

Short-term outcomes were assessed either by the orthopedic surgeon who initially interviewed the enrolled patients or by the radiologist who performed the PSP. Follow-up assessments were performed at least within 1 month after the procedure. The grade of satisfaction was categorized considering the patients’ subjective responses or the visual analog scale (VAS) score. A reduction of more than 3 points or 30% symptom relief was categorized as much improved, reductions of less than 3 points or 30% symptom relief were categorized as slightly improved, and others were categorized under the no-change or aggravated groups. Analgesic use was described as opioid use. If opioids were used before the procedure, we checked whether the opioid was continued or not at the time of discharge.

Interviews to assess long-term outcomes were conducted with all patients approximately at 1 year to 13 years (mean, 6.7 ±3.4 years; range, 1.1–13.2 years) after the end of the procedure; in these interviews, the degree of pain relief and response associated with the procedure were evaluated. On the basis of the 4-point North American Spine Society (NASS) patient satisfaction index1), patients were asked to recall their overall level of pain improvement as follows : 1, the sacroplasty met my expectations; 2, I experienced less improvement than I had hoped, but I would undergo the same procedure again for the same result; 3, the sacroplasty helped, but I would not undergo the same procedure again for the same result; and 4, my condition is the same or worse than that before the sacroplasty. Then, we categorized the four possible responses as a “good response” (scored with 1 or 2 points) or “poor response” (scored with 3 or 4 points). We also investigated any re-visit history and other comorbidities during the long-term follow-up. If the patient’s pain recurred, the number of visits to the hospital and the treatment (conservative, medical treatment, or steroid injection) they received were also checked. If the patient had died, the above-mentioned items were confirmed by the family members.

PSP with C-arm flat-panel detector computed tomography (CT)

Each sacroplasty was performed by two radiologists with 7 and 16 years’ experience in spine intervention. Before PSP, MRI images were carefully reviewed to decide the appropriate needle target site and needle tract. In the angiography room, all patients were positioned prone on the table and were conscious under local anesthesia with 2% lidocaine (Huons, Hwaseong, Korea). Using fluoroscopic guidance with an oblique trajectory, real-time positioning of one trocar needle (Cook : osteo-site bone biopsy needle, 11-gauge) was performed at the fracture site at one side of the sacral ala along the short axis of the sacrum parallel to the sacroiliac joint (Fig. 2).

Fig. 2.

A 72-year-old woman with sacral insufficiency fracture extension to both sacral ala, treated with the short-axis approach. A : Axial T2-weighted image shows fracture gaps with perilesional edema of the bilateral alae. We planned to place a needle at the fracture gap along the short axis of the sacrum parallel to the sacroiliac joint (arrows : the direction of the trocar needle, line : sacroiliac joint). B and C : A needle was inserted into the target site under fluoroscopy. D : C-arm flat-panel detector CT (C-arm CT) can check the precise needle position at a fracture site. The needle tip is shown within the sacrum with no violation of the anterior cortex of the sacrum. E and F : Each CT image demonstrates cement distribution. It shows near total cement filling at both SIF sites (arrows), without any cement leakage. CT : computed tomography.

C-arm CT was then performed by rotating the angiographic (fluoroscopic) tube 240° to check the needle tip position. If the needle was placed at the fracture site and did not penetrate the anterior cortex, liquid and powder PMMA (DePuy International, Leeds, UK) mixed with 500 mg of cefazolin were used as bone cement. The cement was then injected under real-time fluoroscopic guidance, as in conventional vertebroplasty. The injection was stopped if the cement spread near the sacral foramen or outside the anterior cortex. C-arm CT was then performed to check the cement distribution. If cement distribution was appropriate, the same method was also performed for the contralateral sacral ala. After cement injection, C-arm CT was performed again to check the cement distribution. The amounts of cement injected were recorded [12].

Image analysis

Two radiologists (one with a 1-year fellowship in musculoskeletal imaging and an attending radiologist with 7 years’ experience in musculoskeletal imaging) who were blinded to the clinical outcome reviewed the pre-procedural patients’ MR images taken within one month of the occurrence of symptoms. We reached a consensus regarding the types and locations of sacral fractures, whether there was an anterior cortex breakage, neural foraminal extension, sagittal malalignment, visible fracture gap, and other compression fractures at the T–L spine levels. The types and locations of sacral fractures were categorized according to the AOSpine Sacral Fracture Classification (Table 1) [3,20].

Table 1.

AO sacral fracture classification system

For evaluation of factors that can affect the patient's outcome, we also evaluated the degree of degenerative changes in the lower lumbar spine. Based on the recent radiographic grading systems for the lumbar spine [16,17], we analyzed whether the patients showed moderate to severe central or neural foraminal stenosis at the L4–5 or L5–S1 levels. Evaluation of facet joint arthrosis was based on the radiographic methods reported by Pathria et al. [18], Grogan et al. [9], and Weishaupt et al. [21]. We reviewed whether the patient had lumbar scoliosis and sagittal malalignments such as spondylolisthesis or retrolisthesis.

Assessment of technical success with CT was performed immediately after PSP and was defined by the following criteria: good cement filling (more than 75%) at the fracture site and no evidence of major symptomatic cement leakage [12]. After the procedure, we confirmed that there was no complication, including cement extravasation (anteriorly through the nutritional vessels, posteriorly into the spinal canal, medially into the neuroforamina, laterally into the sacroiliac joint, cephalad into the intervertebral space or at least into the fracture), infections, hemorrhages, pulmonary emboli, or procedure-related deaths during any period of follow-up [2,10].

Statistical analysis

No formal statistical analysis was performed to analyze the prognostic value of the clinical or imaging characteristics. Improvements in the VAS scores and reductions in opioid use on short-term follow-up were analyzed using the Wilcoxon Rank Sum Test. The percentage of the effect of the predicted factors in the good and bad response groups was presented. All statistical analyses were performed using SPSS version 21.0. (SPSS Inc., IBM Company, Chicago, IL, USA). Two-sided p-values <0.05 were considered statistically significant.

Clinical and imaging characteristics

Clinical characteristics of the included 40 patients (mean age±standard deviation [SD], 75.6±7.9 years; female : male, 36 : 4) and the number of cases that could be observed for improvement of pain are summarized in Table 2. Most patients had a fracture without any specific cause (n=17, 42.5%), but some patients had minor trauma such as slips (n=22, 55%) or a blunt trauma from the traffic accident (n=1, 2.5%). The mean±SD of the duration of hospitalization after the procedure was 1.66±1.27 days. Only 29 of the 40 patients had result of DEXA exam according to our institutional chart. T-scores of each 29 patients were all below -2.5 (mean±SD, -3.88±0.92) and met the diagnosis for osteoporosis.

Table 2.

Baseline characteristics and short-term clinical outcomes in patients who received sacroplasty for sacral insufficiency fractures (n=40)

Imaging findings of the patients who received sacroplasty are summarized in Table 3. According to the AOSpine Sacral Fracture Classification [3,20], type C0 was seen most frequently (33 of 40 patients, 82.5%), followed by type C2 (four of 40 patients, 10%), and type B2 (three of 40 patients, 7.5%). Anterior cortex breakage was noted in 26 of 40 patients (65%). Neural foraminal extension was seen in six of 40 patients (15%). Sagittal malalignment was visible in eight of 40 patients (20%). Fracture gap was seen in 37 of 40 patients (92.5%). Combined compression fractures of the T–L spine level were seen in 14 of 40 patients (35%).

Table 3.

Imaging findings in 40 patients who received sacroplasty by using the short-axis technique

Technical success

Sacroplasties were performed on unilateral (n=3) or bilateral sacral alae (n=37) in all patients, and an average of 2.6 mL (range, 1–5) of cement was injected at each sacral fracture site. Technical success was achieved in almost all patients (n=39, 97.5%) without any significant complication. Only one patient reported left radicular pain after the procedure. Mild cement leakage over the fractured anterior cortex led to irritation of the left L5 nerve root. The patient received epidural steroid injection through an extraforaminal targeting approach at the L5/S1 level (Fig. 3). The patient’s pain successfully improved after injection without symptom recurrence on final follow-up.

Fig. 3.

An 81-year-old woman complaining of left side radicular pain after the procedure. A-C : Axial image of pelvis computed tomography shows mild cement leakage (arrowhead) over the fractured anterior cortex led to irritation of the left L5 nerve root (arrows). D : The patient received transforaminal epidural steroid injection through the extraforaminal targeting approach at the L5/S1 level. Anteroposterior fluoroscopic image shows that injected contrast (arrowheads) flows along the medial margin of the pedicle.

Short-term treatment outcomes

Thirty-seven patients (92.5%) were available for short-term follow-up assessments. Among these patients, 28 (75.7%) reported a much improved and seven patients (18.9%) reported a slightly improved status after sacroplasty. Only two patients (5.4%) had persistent symptoms. The mean VAS score was 9.11±1.23 pre-treatment, which decreased to 2.53±1.91 posttreatment (p<0.001). The number of patients requiring opioid treatment decreased from 37 (64.8%) to three (8.1%) postoperatively (p<0.001).

Long-term clinical outcomes

The long-term outcomes are summarized in Table 4. Of the 40 patients, telephone interviews were possible with 12 patients. Among the remaining 28 patients, death was confirmed in 18 patients and follow-up loss in 10 patients.

Table 4.

Long-term clinical outcomes in patients who received sacroplasty for sacral insufficiency fractures (n=40)

Of the 12 patients for whom long-term clinical outcome data were obtained, nine (75%) replied that they had experienced positive satisfaction (NASS patient-satisfaction index 1 or 2). The negative satisfaction group (NASS patient-satisfaction index 3 or 4) showed a higher incidence of compression fractures at the T–L-spine level on initial MR imaging and a greater re-visit rate than the positive satisfaction group : 66.7% vs. 22.2% for compression fracture incidence and 66.7% vs. 33.3% for the re-visit rate.

The death group showed a higher incidence of comorbidity than the survival group : 83.3% vs. 25.0%. Chronic medical diseases such as hypertension, chronic kidney disease, dyslipidemia, myocardial infarction, stroke, liver cirrhosis, rheumatic disease, and chronic obstructive pulmonary disease were the most frequent comorbidities (n=14), followed by malignancy (n=8) and infection (n=3).

For the additional items in the questionnaire, nine patients (75%) replied that they would undergo a repeat PSP if they experienced a similar attack of low back pain (LBP) and all 12 patients replied that they would recommend the same procedure to others.

Among the 30 patients with available long-term follow-up medical data (NASS 1 or 2, NASS 3 or 4, or death), 15 (50%) re-visited the hospital after the procedure. The frequency of re-visits to the hospital was higher in the poor response group than in the good response group : 67% vs 44%. The causes of re-visits were not related to the previous sacral fracture or PSP, but were mostly new-onset LBP due to degeneration (n=12, 80%) and new compression fractures in another vertebral segment (n=3, 20%). The patients were treated conservatively with modalities including spinal injections (n=8, 60%), medication (n=2, 13%), and observation (n=5, 33%) (Table 5).

Table 5.

Comorbidity, cause, and treatment during re-visits in the good response group (NASS 1 or 2), poor response group (NASS 3 or 4), and death group in the long-term follow up (n=30)

In terms of degenerative changes in pre-procedural MRI, the poor response group showed a higher incidence of facet joint arthrosis (100% vs. 55.6%), central canal stenosis (100% vs. 22.2%), neural foraminal stenosis (33.3% vs. 22.2%), scoliosis (100% vs. 33.3%), and sagittal malalignment (100% vs. 44.4%) than the good response group (Table 6).

Table 6.

Imaging findings related to fractures or degeneration in the good response group (NASS 1 or 2) and poor response group (NASS 3 or 4) in long-term follow-up (n=12)