Vertebral Augmentation: The Comprehensive Guide to Vertebroplasty, Kyphoplasty, and Implant Augmentation

9 Sacroplasty: Management of Sacral Insufficiency Fractures

Kieran Murphy

Summary

Sacral insufficiency fractures are relatively common but are often underdiagnosed and undertreated. These fractures are a frequent cause of low back pain in the elderly patient population but are frequently missed on X-ray and cross sectional evaluation of the lumbosacral spine. The typical sacral insufficiency fractures (SIFs) characteristically involve the sacral ala and the S2 vertebral body. When SIFs are suspected, MR imaging is the single best imaging modality for diagnosing these fractures but a combination of nuclear medicine bone scan and CT can be used in patients who cannot have an magnetic resonance imaging (MRI). The management of SIFs should consist of treatments that allow for early and sustained mobilization of the patient including sacroplasty if necessary. There are various techniques and different ways of performing sacroplasty including the short-axis technique, long-axis technique, lateral approach technique, and the three needle technique. All of these techniques have been shown to be safe and effective and studies of sacroplasty have confirmed its safety and efficacy out to as long as ten years. Providing the option of sacroplasty to those patients who do not or cannot undergo non-surgical management can lead to better mobility, improved function, dramatically decreased pain, and less mortality.

Keywords: sacroplasty, sacrum, osteoporosis, sacral insufficiency fractures, osseous augmentation

9.1 Introduction

First described by Lourie et al in 1982,¹ SIFs are a common but often underdiagnosed source of low back pain in the elderly and/or the osteoporotic patient. Insufficiency fractures of the pelvis are a consequence of undue stress onto a weakened bone or of increased stress on a bone with marginally adequate bone mineral density. Risks of SIFs are very similar to that of vertebral compression fractures and include risk factors of osteoporosis, osteopenia, osteomalacia, renal osteodystrophy, prior radiation therapy, Paget’s disease, previous lumbosacral fusion, total hip arthroplasty, and bone metabolic diseases known to weaken the skeletal system.¹^,² Osteoporosis is the most common cause of fractures of the pelvis and over 25 million people are affected in the United States. There is a strong female predominance for SIFs (10:1), and they can occur without an identifiable injury in someone with low bone mineral density and compromised bone strength.³ The incidence of SIFs comprises approximately 1 to 2% of the pathologic fractures involving the spine and pelvis. This incidence, however, may be an underestimate as the diagnosis is often delayed or does not happen due to the relatively poor sensitivity of plain radiographs and the lack of adequate recognition of SIFs on cross-sectional imaging including both MR and CT imaging.

9.2 Fractures of the Sacrum: Anatomy

Anatomically, the sacrum is comprised of five fused segments. Weight transfers can occur through the lumbar spine into the sacrum and then through the ilium into the proximal femora with regions of stress in the second sacral segment and in the pubic rami. This stress pattern can produce insufficiency fractures that can have a unique but often characteristic appearance of SIFs.⁴ In 1988, Denis et al classified the location of sacral fractures into three sacral zones (▶Fig. 9.1).⁵ Zone 1 fractures are laterally located fractures that involve the sacral ala but do not traverse the foramina or the central sacral canal. Zone 2 fractures involve the sacral foramina but do not involve the central spinal canal. Zone 3 fractures extend into and involve the central spinal canal. A fracture to the central portion of the sacrum is typically associated with a higher energy type injury and patients with zone 3 fractures can present with saddle anesthesia and loss of sphincter tone as a result of cauda equina injury or can present with varying degrees of injuries including neuropraxia or injury to a single nerve root.⁵ The most common location of SIFs are within zone 1, but a minority of the fractures can involve the sacral foramina. The SIFs typically run parallel to the sacroiliac joint along the entire sacral ala and can have a horizontal component that is usually located at the S2 level of the sacrum when present (▶Fig. 9.2). The most common fracture pattern is that of bilateral sacral alar fractures that primarily involve the S1 and S2 vertebrae. Unilateral fractures can also occur and can be present without a contralateral fracture or can progress to bilateral fractures. The appearance and

Fig. 9.1 Denis Fracture Classification. Zone 1 fractures are laterally located fractures that involve the sacral ala but do not traverse the foramina or central sacral canal. Zone 2 fractures involve the sacral foramina but do not involve the central spinal canal. Zone 3 fractures extend into and involve the central spinal canal. (Image created with BioRender.)

Fig. 9.2 The sacral insufficiency fractures typically run parallel to the sacroiliac joint along the entire sacral ala and can have a horizontal component that is usually located at the S2 level of the sacrum when present.

9.3 Sacral Insufficiency Fractures: Causes and Natural History

There are some studies that have examined the morbidity and mortality associated with SIFs. Park et al recently published their experience, looking at 325 patients with a mean follow-up of 51.5 months.⁶ The mean age at time of diagnosis was 69.4 years. There was a history of malignancy in 43.1% of patients and 21.8% had undergone pelvic irradiation prior to the fracture. The 6-month mortality rate was 9.8% and the 1-year mortality rate was 17.5%, while mortality increased to 25.5% at 3 years. The sex- and age-adjusted mortality ratio increased after these fractures, and the overall 3-month standardized mortality ratio (SMR) was 8.9.

The major cause of SIFs is normal stress on an osteoporotic or otherwise weakened bone. Traumas, both minor and severe, are also causes of sacral fractures, but SIFs are a low-velocity, low-energy type of fractures that develop due to normal or slightly increased stress on a weak bone. When sacral fractures are associated with some type of inciting event, it is typically a low-velocity injury such as a fall on the sacrum and coccyx from a standing height or a minimal axial load impact like stepping off a curb. Patients will often notice a severe and immediate pain in their back or buttock.⁷ The pain is often not severe and can be described as a dull ache that increases in severity over time. Other patients will feel pain primarily when sitting and will shift in their seats because their back and buttock hurts. Patients often develop an antalgic gait pattern due to the forces transmitted across the sacral ala that increase when the patient is walking. This pain may be quite debilitating and the patient may require a cane or walker to ambulate or may even be confined to a stretcher. Other patients with SIFs have severe localized pain in the low back or sacrum with a sciatica-type pain, usually in an S1 distribution.

9.4 History and Examination

Determining the cause and contributing factors to the SIFs is important and appropriate history taking is an essential element in identifying the risk factors as well as the inciting event. Important factors are whether the patient is on medications for osteoporosis,⁸ whether they have had a recent dual energy X-ray absorptiometry (DEXA) scan or quantitative CT (QCT) to determine bone density, and if they have had previous fractures of the wrist, hip, or spine. Appropriate imaging studies are also necessary to evaluate the fracture pattern and surrounding anatomy.⁴ A thorough laboratory evaluation should include a complete blood count and an extended blood chemistry along with measurements of ionized calcium, parathyroid hormone (PTH), and 1, 25-hydroxyvitamin D levels, alkaline phosphatase, albumin, free testosterone, thyroid-stimulating hormone, and serum protein electrophoresis. Other laboratory work for an osteoporosis should include urinary measurements of calcium and cortisol and a urinary protein electrophoresis. Obtaining a history of malignancy is also important and consideration should be given to whether the SIF may be related to a neoplastic process. If this is a concern, performing a biopsy during the process to treat the sacral fracture is warranted.

Physical examination techniques are also important in the diagnostic process and include the standing leg test and the presence of tenderness of the sacrum with compression of the pelvis. Typically, there is no muscle weakness or reflex changes and normal sphincter tone is most often present, but abnormalities of any of these must be documented. Patients with SIFs may be able to walk into the physician’s clinic independently or with the aid of a walker or wheelchair and on a stretcher in some cases. If they are walking without assist devices, they most often have a slow antalgic gait. It is not unusual for older patients or patients with more severe SIFs to be unable to walk. location of the fractures must be noted as well as the anatomic regions affected, as these factors can have significant implications in the repair of these fractures.

9.5 Imaging

If an SIF is suspected by history and/or physical examination, then the next step is to obtain the appropriate imaging. Spinal and/or pelvic radiographs have poor sensitivity and are of questionable value in the diagnosis of SIFs. The best imaging modality that yields the highest sensitivity and specificity is MR imaging ⁹. Fractures of the sacrum are best shown on dedicated studies of the sacrum and on the axial and coronal images. Traditionally, MR imaging examinations of the lumbar spine may miss a fracture of the sacrum as the axial images may not extend far enough inferiorly to see the fractures in this plane and the sagittal images may not optimally show the fractures or the fractures may be confused with the sacroiliac joint. They can be seen on lumbar imaging, however, if close attention is paid to the symptoms and the findings.⁹ Short tau inversion recovery (STIR) and non–fat saturated T1-weighted MR imaging sequences are the best imaging to diagnose these fractures as edema from the fractures are well seen on the STIR images and the fracture lines are most optimally demonstrated on the T1-weighted images (▶Fig. 9.3).

Fig. 9.3 Axial T1-weighted (a) and short tau inversion recovery (STIR; b) MR images show bilateral fracture lines (white arrows in a) that are well demonstrated on this T1-weighted image. The bilateral sacral insufficiency fractures are seen to be associated with considerable edema (white arrowheads in b) on the coronal STIR MR image.

Fig. 9.4 Nuclear medicine bone scan showing increase uptake of radiotracer in an H pattern (white lines) that resembles the shape of the H on the front of Honda automobiles.

Fig. 9.5 Axial CT image shows bilateral sacral fractures with fracture lines (white arrows) causing cortical and cancellous bone disruption. This disruption is seen without much surrounding sclerosis, thereby making these fractures more subtle than those with a large amount of sclerosis surrounding the fractures.

Traditionally, the most sensitive but not specific imaging modality is a nuclear medicine bone scan ¹⁰. A bone scan has increased activity of the radiotracer within the fracture and the pattern has classically been described as Honda’s sign, a typical H-shaped pattern on bone scan that is pathognomonic for SIFs (▶Fig. 9.4). The pattern of increased uptake on the bone scan represents increased activity that is vertically oriented in the sacral ala and is joined by horizontal activity in the mid to upper portion of the sacrum usually located at the S2 level of the sacrum.¹⁰ The H shape with the vertical components narrower at the inferior portion and wider at the superior portion resembles the shape of the H on the front of Honda automobiles (▶Fig. 9.4). A cross-sectional evaluation of a bone scan or a single-photon emission computed tomography (SPECT) scan may also be helpful in identifying and localizing SIFs. Despite the sensitivity of bone scans in detecting SIFs, MRI has replaced this modality in many departments, due largely to better availability of MR imaging.

If a patient has a pacemaker, cochlear implant, or something else that precludes from them getting an MRI, a CT scan is the necessary examination to compliment the bone scan. Any cross-sectional imaging examination may not highlight sacral fractures optimally and although CT scans can be more sensitive in detecting cortical breaks associated with SIFs, nondisplaced fractures without obvious reactive sclerosis may be missed¹¹ (▶Fig. 9.5).

9.6 Treatment

9.6.1 Conservative Treatment

The treatment of SIFs either can be interventional with a percutaneous approach, surgical, or can consist of nonsurgical management (NSM). Unstable fractures, especially high-velocity injuries with associated cauda equina syndrome, may require open reduction and internal fixation. As opposed to closed or percutaneous procedures, open procedures are associated with an increased risk of surgical and postsurgical complications including wound problems and infection.¹²

Historically, treatment has been limited to bed rest, oral narcotic medications, lumbosacral or pelvic corsets, and protected weight bearing with the patient using a walker in order to accomplish early mobilization.⁴^,¹³ If early mobilization is not possible, prolonged bed rest can lead to additional morbidities including deep venous thromboses, pulmonary emboli, reduced muscle strength, postural hypotension, impaired cardiac function, atelectasis, pneumonia, pressure ulcers, constipation, fecal impaction, depression, and side effects from opioids including altered sensorium, additional constipation, memory loss, and putting the patient at an increased risk for falling.¹⁴ These morbidities are profoundly impactful and are known complications of periods of inactivity. In addition to the substantial impact of the morbidities associated with SIFs, the associated mortality is also significant, with studies estimating the 1- to 3-year mortality at 20 to 25%.⁶^,¹⁵ When patients respond promptly to NSM, the initial clinical improvement may occur quickly, but it is important to know that compete resolution of symptoms may not occur for up to 9 to 12 months. All these factors contribute to a clinical scenario that can be arduous for the patient to tolerate with the goal being to prevent or limit the spiral of immobility, followed by bed rest, deconditioning, secondary events (e.g., infections, venous thromboembolism), and other sequelae of the initial event.¹⁶ In patients for whom the symptoms are sufficiently severe or debilitating, invasive treatments may benefit them and prevent the incapacitation that is often seen in patients with SIFs.

9.6.2 Osseous Augmentation

Chronic symptoms and disability related to osteoporotic insufficiency fractures are believed to be due to fracture nonunion, micro-motion, resultant deformity related to the original fracture deformity, or progressive deformity due to the inability of the weakened bone to promptly heal.¹⁷^,¹⁸ The percutaneous injection of polymethyl methacrylate (PMMA) into fractured vertebral bodies (osteoplasty or sacral vertebroplasty) has been safely performed to successfully treat painful osteoporotic vertebral fractures. A natural extension of the application of vertebroplasty is the percutaneous injection of PMMA into the fractured sacrum (sacroplasty) to treat persistent symptoms and disability associated with SIFs. Sacroplasty was first reported in the early 2000s as treatment for symptomatic sacral metastatic lesions,¹⁹^,²⁰ and subsequent reports have documented its safe and effective performance. The initial short follow-up intervals and small study cohorts led to more definitive studies evaluating the safety and efficacy of the procedure and the durability of initial results.²¹ More recently, studies with a greater number of patients and longer follow-up have clarified the treatment outcomes of sacroplasty regarding safety and long term efficacy.²²^,²³

9.7 Techniques

Various techniques have been described for performing percutaneous sacroplasty, and these include both short- and long-axis approaches. Routinely, sacroplasty is performed with fluoroscopy, but CT guidance or a combination of both may be used. Many interventional radiologists who are well trained in CT-guided procedures advocate for performing sacroplasty with CT guidance. While CT is a viable method of performing imaging guidance, it is slower and more expensive as compared with fluoroscopy, which is cheaper, faster, and technically straightforward (▶Table 9.1). Fluoroscopic guidance, however, typically requires more experience to identify untoward cement extravasation. More recently, the routine use of cone-beam CT has allowed a combination of both approaches to be used.

Whitlow et al looked at technical considerations and analyzed PMMA injection under fluoroscopic guidance.²⁴ Sacroplasty was performed on cadaveric specimens using biplane fluoroscopy. The cadaveric specimens were evaluated with CT that was performed both before and after sacroplasty to examine needle placement and to assess for PMMA extravasation. The CT imaging demonstrated that needle placement and PMMA delivery may be done safely and is facilitated by orienting the needle parallel to the L5–S1 interspace and ipsilateral sacroiliac joint and targeting the superolateral sacral ala within an area whose borders are formed by a line just lateral to the posterior sacral foramina and a line along the medial edge of the sacroiliac joint (▶Fig. 9.6). In another assessment of this technique, Betts published an article on fluoroscopic anatomy landmarks and associated these landmarks with their gross anatomic structures as seen with open dissection.²⁵

Table 9.1 Comparing the pros and cons of CT versus fluoroscopy when performing sacroplasty

	Fluoroscopic guidance	CT guided
Pros	Faster Cheaper Easier	Less steep learning curve Debatable reduction rate of complication
Cons	Require experience	Slower More expensive

Fluoroscopic guidance

CT guided

Pros

Faster

Cheaper

Easier

Less steep learning curve

Debatable reduction rate of complication

Cons

Require experience

Slower

More expensive

Fig. 9.6 (a, b) Short-axis target is shown on fluoroscopy with the left-sided needle (highlighted by yellow dashed line in a and b) targeting the superolateral left sacral ala between the outer border of the sacral foramina (thin black line in a) and the sacroiliac joint (black arrows in a). The short-axis technique involves placing the needle nearly parallel to the end plates of S1. The long-axis technique involves placing the needle (highlighted by red dashed line in a and b) between the outer border of the sacral foramina and the sacroiliac joint starting at the posteroinferior portion of S2 (white arrow in b) and advancing the needle anterosuperiorly to the midportion of the S1 vertebral body(white arrowhead in b).

9.7.1 Short-Axis Technique

In a 2007 manuscript reporting the results of sacroplasty in 37 patients, Frey et al described a variation of the short-axis technique for performing percutaneous sacroplasty.²⁶ All procedures were performed under fluoroscopic guidance using moderate sedation and every patient received preoperative antibiotics. The procedure time from the initial set up to the completion and patient recovery takes about an hour. At the start of the procedure, the patient is placed in a prone position and the image intensifier is placed in an oblique view along the axis of the ipsilateral sacroiliac joint (see ▶Fig. 9.6 and ▶Table 9.2 for details). This obliquity varies from patient to patient but is typically 5 to 20 degrees in mediolateral angulation. Next, two 13-gauge bone trocars were placed between the sacral foramina and the sacroiliac joint on the side of the fracture with an angle paralleling the sacroiliac joint (▶Fig. 9.7a,b). The needles were then inserted to approximately the midpoint of the sacrum on the lateral view, maintaining the initial angle. After mixing the cement, 3 to 5 mL of PMMA were injected through each trocars while monitoring the spread of the bone cement on the oblique anteroposterior fluoroscopic view. Care was taken when injecting the bone cement to avoid medial spreading of the cement toward the sacral nerve roots. Each patient was maintained in the prone position for 30 minutes after the procedure and prior to ambulation. The patients were then asked to stand on the affected leg to assess their pain improvement. If they had bilateral pain, they were asked to stand on each leg, one at a time to assess the level of pain they were having.

This study was a prospective, multicenter, observational cohort study of patients with a mean age of 76.6 years who had undergone and failed a trial of NSM for a mean of 34.4 days (range between 13 and 82 days). All patients were available at all follow-up intervals. The mean Visual Analog Scale (VAS) score at baseline was 7.7 and was 3.2 within 30 minutes after the procedure and 2.1 at 2 weeks, 1.7 at 4 weeks, 1.3 at 12 weeks, 1.0 at 24 weeks, and 0.7 at 52 weeks after the procedure¹⁶. Thirty minutes after the procedure, 5 patients reported complete pain relief, 10 patients reported no pain at 2 weeks, and 25 patients were pain free by 52 weeks after the procedure. Twenty patients were using narcotic analgesics at baseline and only 6 patients were using narcotics at 2 to 8 weeks following the procedure. One significant adverse event (SAE) was encountered during the procedure but none at any of the follow-up intervals. The single SAE involved a patient who developed S1 radicular pain during the procedure, necessitating termination of injection of the PMMA. Although the primary sacral pain was alleviated, the patient experienced persistent inferior buttock and posterior thigh pain that was completely relieved 7 days later by a selective nerve root injection consisting of 2.0 mL of preservative-free betamethasone (6 mg/mL) and 1.0 mL of 1.0% lidocaine injected in the epidural space around the S1 nerve root. Potential risks for sacroplasty include cement emboli, cement extravasation, sacral nerve root injury, and injury to the lumbosacral plexus. In February 2008, Frey et al published a subsequent study of 52 patients.²¹ In this study, using the short-axis technique, more than 75% of the patients had their pain reduced by half or more 30 minutes after the procedure. This study provided strong additional support for the safety and efficacy of sacroplasty.

Table 9.2 Short-axis technique

Sacroplasty using the short-axis technique: step by step
1	In the frontal plane, rotate the II cephalad to parallel the L5–S1 disk space. (This will usually require significant caudal angulation of the II)
2	Rotate the II so that the spinous processes are in the center of the vertebral body—a direct AP view
3	Rotate the II to the side opposite the treatment location, by about 25–30 degrees OR to an angle along the longitudinal axis of the SI joint that aligns the inferior portion of the joint
4	The starting position is chosen: halfway between the SIJ and a vertical line that joins the medial borders of the sacral neural foramina
5	Anesthetize the skin at the desired starting point and make a small incision
6	Insert the sacroplasty needle at the incision, advancing the needle parallel to the II
7	Using a mallet, slowly advance the needle tip just past the posterior sacral cortex and into the center one-third of the sacrum. It is important to keep the mediolateral angulation of the needle “as is,” to avoid deviating from the trajectory chosen
8	Rotate the II to get a lateral view of the sacrum, and the needle within the S1 vertebral body. (If using biplane equipment, the lateral II can be used for this purpose)
9	When the PMMA has been mixed and a toothpaste consistency achieved, inject it into the sacrum using both lateral and oblique AP views to monitor PMMA distribution. On the lateral view, watch for anterior extravasation (i.e., anterior to the anterior body of the sacrum), while on the oblique AP view there should be little or no extravasation into the neural exit foramina
10	Deposit the PMMA in the sacrum trying to fill the center portion of the sacral ala (i.e., between the SIJ and the neural foramina), intermittently retracting the needle and depositing PMMA along the needle tract, i.e., along the longitudinal axis of the sacrum
11	If necessary, insert a second needle into the inferior half of the sacrum using the same technique (and mediolateral positioning) as the first needle
12	When the PMMA has been deposited adequately, remove all needles and place appropriate bandages over the puncture sites
Abbreviations: AP, anteroposterior; II, image intensifier; PMMA, polymethylmethacrylate; SIJ, sacroiliac joint.

Fig. 9.7 (a, b) Anteroposterior fluoroscopic images show two needles place in sequence into the patient’s right sacral ala (black arrows) using the short-axis technique to inject bone cement (black arrowheads) into the sacral ala.

9.7.2 Long-Axis Technique

The long-axis technique can be used to access both the S1 and the S2 segments with one needle per side. The needle is placed between the sacroiliac joint and the lateral border of the neural foramen and directed superiorly at an oblique angle along the long axis of the sacrum (▶Fig. 9.6 and ▶Table 9.3). The long-axis technique can produce optimal cement distribution along the longitudinal axis of the fractures and can decrease the risk of violating the anterior border of the sacrum with the access needle. The starting point is at the posteroinferior portion of the S2 vertebral body between the lateral border of the sacral foramina and the sacroiliac joint. The needle is then advanced from the posteroinferior portion of S2 to the mid to superior portion of S1 (▶Fig. 9.6). The normal anatomy with the lordosis of the lumbosacral junction and the patient’s prone position makes this approach technically straightforward and can be accomplished without extreme angulation of the needle. As with the short-axis approach, care should be taken not to violate the anterior cortex of the sacrum as the lumbosacral plexus traverses the sacral ala from superior to inferior just anterior to the anterior sacral cortex. Anterior extravasation of the cement can also cause damage to the lumbosacral plexus and should also be avoided. The cement is best injected from distal to proximal using cement with a thick viscous consistency. The steps of the long-axis approach are listed in sequence in ▶Table 9.3.

A variation of the long-axis technique is to add a third needle placed in the center of the osseous sacrum directed in a similar orientation to the needles in the sacral ala with the starting point of the needle inferior to the thecal sac (▶Fig. 9.8). This technique can be used in fractures that have a prominent horizontal component that the treating physician believes needs additional dedicated stabilization in addition to stabilizing the fractures of the sacral ala. The three-needle long-axis technique will allow the injection of a substantial amount of bone cement into the center of the sacrum as well as the sacral ala (▶Fig. 9.9).

9.7.3 Lateral Approach Technique

An alternative approach involves placing the needles perpendicular to the sacrum and approaching it from lateral to medial (i.e., in a horizontal plane, extending from one side to the other; see ▶Fig. 9.10). The patient is positioned prone and sterilely prepped and draped taking into consideration the direct lateral-to-medial approach. In addition to fluoroscopic guidance, a cone-beam CT can be performed for planning purposes and to adequately visualize the sacral neural foramina. The most common skin-entry site is overlying the midportion of S1 as seen on a direct lateral view. The midportion of S2 may also be accessed in an identical manner to S1. Following local analgesia, a 15- to 18-cm-long Murphy needle is then inserted horizontally perpendicular to the long axis of the sacrum, targeting the fracture lines. One or more needles can be used.²⁷ Once the needle(s) has crossed the target fracture lines, cement is deposited first in the contralateral ala and then the needle is progressively withdrawn while injecting aliquots of cement in continuity under real-time fluoroscopic guidance (▶Fig. 9.11). Attention is paid to avoiding cement passing anterior to the cortex of the sacrum, and posteriorly to the inferior spinal canal.

Table 9.3 Long-axis technique

Sacroplasty using the long-axis technique: step by step
1	In the frontal plane, rotate the image intensifier cephalad to the AP plane
2	Rotate the II so that the spinous processes are in the center of the vertebral body—a direct AP view
3	Rotate the II to the side opposite the treatment location, by about 25–30 degrees OR to an angle along the longitudinal axis of the SIJ that aligns the inferior portion of the joint
4	The starting position is chosen: halfway between the SIJ and a vertical line that joins the medial borders of the sacral neural foramina
5	Anesthetize the skin at the desired starting point and make a small incision
6	Insert the sacroplasty needle at the incision, advancing the needle parallel to the II and angling the tip 20–40 degrees cranially
7	Using a mallet, slowly advance the needle tip just past the posterior sacral cortex. It is important to keep the mediolateral angulation of the needle “as is,” to avoid deviating from the trajectory chosen
8	Rotate the II to get a lateral view of the sacrum, adjusting the superoinferior angulation of the needle so that it advances to the level of the mid to superior portion of the S1 vertebral body. (If using biplane equipment, the lateral II can be used for this purpose. If so, the next two steps can be skipped as the biplane equipment allows you to adjust both angles as you go)
9	Return to the angled AP view and ensure that the mediolateral angulation of the needle is appropriate
10	Return to the lateral view, and advance the needle tip to the level of the superior portion of the S1 vertebral body
11	When the PMMA has been mixed and a toothpaste consistency achieved, inject it into the sacrum using both lateral and oblique AP views to monitor PMMA distribution. On the lateral view, watch for anterior extravasation (i.e., anterior to the anterior body of the sacrum), while on the oblique AP view, there should be little or no extravasation into the neural exit foramina
12	Deposit the PMMA in the sacrum trying to fill the center portion of the sacral ala (i.e., between the SIJ and the neural foramina), intermittently retracting the needle and depositing PMMA along the needle tract, i.e., along the longitudinal axis of the sacrum
13	When the PMMA has been deposited adequately, remove all needles and place appropriate bandages over the puncture sites
Abbreviations: AP, anteroposterior; II, image intensifier; PMMA, polymethyl methacrylate; SIJ, sacroiliac joint.

Fig. 9.8 Anteroposterior (a) and lateral (b) fluoroscopic views show the long-axis approach with a third needle (white arrows in a and b) placed in the center of the osseous sacrum directed in a similar orientation to the needles in the sacral ala with the starting point of the needle inferior to the thecal sac.

Fig. 9.9 Lateral (a) and anteroposterior (b) fluoroscopic images showing cement in the sacral ala (white arrows in b) and in the center portion of the sacrum (black arrows in b). Coronal CT reconstructed image (c) shows bone cement in the center of the sacrum as well as in the sacral ala.

Fig. 9.10 Lateral (a) and anteroposterior (b) fluoroscopic images showing the needle positioning and trajectory for the long-axis approach. The white arrow denotes an anterior osteophyte (not to be mistaken for cement extravasation on the postsacroplasty images). A longer needle is used in this case (e.g., an 18-cm Murphy needle) in order to reach the contralateral sacral ala.

9.8 Outcomes

Since initial publication of the technique, several more long-term studies have proven the safety, efficacy, and durability of the technique. For example, in 2012, Kortman et al ²⁸ published their experience. They looked at 243 patients who were experiencing severe pain unresponsive to NSM. Patients were followed for at least 1 year after their procedure. The average pretreatment VAS was 9.2 ± 1.1. Following sacroplasty, this improved to 1.9 ± 1.7 in those patients with SIFs. There were no major complications (such as hemorrhage, significant extravasation, pulmonary emboli, or procedure-related deaths). Similarly, in the Gupta et al publication in 2014,²^,³ 53 patients were followed for a mean of 27 (±3.7) days. The patients were 83% females and the mean VAS pretreatment pain score was 9.0. This decreased to 3.0 following the sacroplasty. This group also highlighted the safety of the technique as there were no procedural complications or procedure-related mortalities.

Fig. 9.11 Lateral (a) and anteroposterior (AP; b) fluoroscopic images showing polymethyl methacrylate (PMMA) deposition along the mediolateral axis of the S1 vertebrae. The AP view shows the sequential PMMA injection with injection of cement as the needle is being withdrawn. Coronal reformat (c) and axial (d) CT images showing PMMA distribution following the sacroplasty.

Most recently, Frey et al ¹ published a 10-year follow-up of the patients presenting for percutaneous sacroplasty beginning in 2004. Two hundred and forty-four patients with SIFs were evaluated. Two hundred and ten patients underwent sacroplasty and the 34 patients that were treated with NSM functioned as the control group. The patients’ gender, age, preprocedure pain duration, analgesic use, pain level, and patient satisfaction were recorded at the following post-op intervals: immediately post procedure, 2, 4, 12, 24, and 52 weeks, and 2 years. Ten years later, the patients in the experimental group were contacted. The experimental group was found to have a statistically significant drop in VAS score between follow-ups up to 1 year and opioid use was significantly less than in the control group. There was a progressive decrease in pain from year 1 to 10 and pain level remained low with a pain level of 0.5 on the VAS. In conclusion, these studies all have established that sacroplasty allows for a decrease in the use of opioid pain medications and produces significant pain relief, greater mobility, and improved patient satisfaction as compared with NSM. The long-term follow-up supports sacroplasty as being durable as well as safe and effective for patients suffering from SIFs. Other groups, such as Kamel et al, have documented significant increases in patient mobility. For example, in their group, 58% of patients returned to full mobility following the procedure.²⁹ This increase in postsacroplasty mobility has been confirmed by other authors such as Talmadge et al.³⁰

Where they occur, the main complications have been extravasation of cement into the neural foramina, primarily the S1 neural foramen. The extravasations occurred in only a few scattered cases (1–2% in most series), and most of the symptoms from the cement extravasation resolved with conservative management.³¹^,³² A minority of these patients needed either a therapeutic nerve root injection or surgical decompression of the neural foramen to adequately address their symptoms.

Overall, sacral and pelvic insufficiency fractures are a relatively common problem that can be very debilitating to patients, causing them a host of morbidities and even mortality as a result of their deconditioning and immobility. In the last decade, more aggressive and definitive treatments such as sacroplasty have been advocated for these patients.

The literature evaluating sacroplasty has evolved over time with several reports containing patient cohorts ranging up to more than 200 patients. The existing literature shows good efficacy and minimal complications and good durability of the procedure even in long-term follow-up. Importantly, improvements in patient condition are many and the treatment definitive in the appropriate patient. Providing sacroplasty to debilitated patients or patients who are not optimally responsive to NSM can thus lead to decreased pain, improved functionality, decreased morbidities, and most importantly a lower risk of mortality.