Fig. 6.1
Two cases of sacral fragment dislocation related to misdiagnosis. In patient on the left (a), the S4–S5 body of the sacrum has been dislocated anteriorly, due to the patient being allowed to sit in a chair without precautions. In the patient on the right (b, c), S1 and S2 anterior root compression related to sacral foramina narrowing secondary to a body-to-left wing dislocation
Historically, treatment has relied on a short period bed rest and analgesics, which is appropriate for most patients. However, a small number of patients may be refractory to medical management and require prolonged bed rest and escalating opioid analgesia. This may generate the well-known problems associated with bed rest in an elderly debilitated population, such as pneumonia, urinary tract infections, muscle wasting, and thrombophlebitis, and may also exacerbate underlying osteoporosis [13]. In addition, some patients may experience opioid side effects such as change in mental status, respiratory depression, constipation, and medication dependence.
Several alternatives for treatment exist. These include open surgical fixation, which is generally reserved for patients with displaced fractures or fracture/dislocations, as well as percutaneous cement fixation [12, 14–20]. This chapter will focus on treatment of sacral fractures with percutaneous sacroplasty using either fluoroscopic or CT guidance. While no randomized controlled trials have been performed to assess sacroplasty, multiple cohort studies have reported reductions in pain scores and analgesic requirements, with minimal associated morbidity [7, 14, 17, 21, 22].
Although there is a vast clinical experience using cement to treat fractured vertebrae, the anatomy of the sacrum is far more complex which creates special challenges for treatment. The bone has a somewhat curved pyramidal appearance and is traversed by a central canal as well as neural foramina. Fracture lines in osteoporotic cases are typically of two varieties: parallel to the sacroiliac joints and traversing the horizontal bridges between the parallel columns of the neural foramina. [23] The fracture lines can be symmetrical (Figs. 6.2 and 6.3) or asymmetrical (Fig. 6.4). There may be multiple interconnected fractures or several distinct areas of fracture. The cortex may not be disrupted, or there may be frank cortical disruption or extensive tumor-related bone destruction. This is important to appreciate as cortical or bone destruction is a risk factor for cement leakage. All extraosseous cement extravasation, in particular into the central canal, sacral neural foramina, sacroiliac joint, and vascular structures, should be avoided. Moreover, as well as for the rest of the spine, the sacrum can be affected by primary or secondary malignancies, with anarchic osteolysis of the wings and/or the body of the sacrum, increasing the risk of extra-sacral leakage.
Fig. 6.2
Sacral osteoporotic symmetric fractures at the body-to-wing area S1–S2. On coronal T1SE (a) and T2STIR (b) images, abnormal signal intensity can be depicted through the joining area between the wing and the body of S1, while a crossover fracture line is appreciated at S1 body, just above the foramina area. Sacroplasty was performed introducing the needles bilaterally (c), and complete cementation of the fracture was performed (d)
Fig. 6.3
Complete symmetrical fracture of the sacrum. On conventional midline sagittal T2STIR image, the fracture can be missed as small focal signal abnormality can be appreciated only inside the sacral body (a). Coronal T1SE sacral MR pictures show dramatic complete symmetrical fractures of the sacral wings (b). Bilateral fragment dislocation appreciated on 2D recon CT image demonstrates severe bilateral foraminal stenosis (c)
Fig. 6.4
Asymmetrical fracture of the sacrum. On coronal CT recon image on the left (a) and coronal bone scanning on the right (b), complete sacral fracture on the left side and small right-sided fracture can be appreciated
In addition to sacral-related pain, pain originating from the coccyx is sometimes hard to delineate from that arising from the sacrum. Coccydynia accounts for less than 1% of all the causes of low back pain. A coccygeal fracture and/or subluxation can be extremely hard to diagnose, and even harder to tolerate for patients, causing drug abuse and psychological consequences (Figs. 6.5 and 6.6). Local anesthetic and steroid infiltration can solve the pain temporarily in 59% of cases, while manipulation and injection in 85%: unfortunately approximately 1/3 of the patients do not experience a stable pain solution [24]. Surgical coccygectomy can be proposed, but complications have been reported in ¼ of patients. [25]
Fig. 6.5
Coccygeal subluxation in a 34-year-old woman. On sagittal 2D CT scan (top left), detachment of the coccyx from the sacrum is appreciated. To perform coccygeoplasty, a 13G Jamshidi needle has been introduced through the S4–S5 body directly into the coccyx (top middle, left down), and 2–3 cc of PMMA has been injected, re-attaching the coccyx to the sacrum (top right and down right images)
Fig. 6.6
Severe coccyx subluxation of very long coccygeal bone. On the left, several subluxation of coccygeal vertebra can be appreciated. On the right, complete PMMA bridge reconnecting the coccyx to the sacrum can be appreciated on sagittal (middle) and (right) scans
6.2 Patient Selection
Sacroplasty is indicated for the treatment of symptomatic/painful sacral fractures in the subset of patients where medical management has failed to provide pain relief [17]. Sacroplasty may be performed for primary or metastatic neoplasms of the sacrum or benign cystic lesions of the sacrum such as aneurysmal bone cysts failing to respond to medical management [17, 26, 27]. Overall, 4 weeks is a reasonable trial of medical management, although earlier intervention is often considered for patients who are hospitalized for severe pain requiring intravenous analgesia.
Patient selection is critical in planning any image-guided intervention. It is important to recall that the natural history of most sacral fractures is benign and they tend to heal on their own. The population at risk for sacral fractures typically has severe or focal osteoporosis and is therefore at risk for delayed or failed healing. Treatment with appropriate osteoporotic therapy is essential. The practitioner must consider a particular patient’s pain duration and intensity when considering treatment options. This decision becomes most straightforward for a patient who was able to ambulate independently and can no longer enjoy this freedom due to pain limitations. For patients who are able to ambulate but have new limitations on their ability to ambulate, the decision becomes less clear. As all procedures may generate complications, pain medication, time, and the hopes of healing may be the best option for some patients. However, if the pain medication requirements are too significant, or the patient’s pain limits their ability to perform their daily activities, or pain persists beyond a tolerable time span, these patients may also be appropriate candidates for cement augmentation therapy. In those patients with persistent coccygodynia, with no significant improvement after conservative therapy, coccygeoplasty is an option (Figs. 6.5 and 6.6).
6.3 Considering Additional Pain Generators
It is important to note that patients with painful sacral fractures typically have multiple additional underlying pain generators [28]. The intense pain from the fracture may mask chronic pain or other new pains caused by the event that incited the initial sacral fracture. It is possible that a patient will have residual pain even with the most technically successful procedure. Additional interventions may be required to treat underlying spondylosis symptoms when unmasked after a successful sacral fracture treatment.
6.4 Pre-procedure Planning
6.4.1 History and Physical
Planning begins with a complete history and physical examination. As with all image-guided pain interventions, it is important to correlate the imaging findings with the patient’s pain symptoms. This can be challenging for patients with intense pain, as they will have limited ability to cooperate for an examination. It is not unusual for a patient to resist any movement with a complete sacral fracture.
6.4.2 Clinical/Laboratory Assessment
Thorough review of clinical data is also important to exclude concurrent infection such as pneumonia or urinary tract infection. Identification of coagulopathy, thrombocytopenia, or metabolic abnormalities that would increase the risks of the planned procedures is also important. Thorough evaluation for the use of anticoagulants is a discussion that should be had with the care team in order to weigh the risks and benefits of discontinuing certain agents should this become necessary. As the use of prophylactic antibiotics periprocedurally is a best practice to limit the risk of infection, it is important to elicit an allergy history. There are only a few absolute contraindications to sacroplasty: active systemic infection, uncorrectable bleeding diathesis, insufficient cardiopulmonary health to safely tolerate sedation or general anesthesia, and known allergy to bone cement. Information relevant to each of these should be obtained during patient selection.
6.4.3 Imaging
Most patients being considered for sacroplasty have had plain X-rays. Although of limited use to detect sacral fractures, they should be reviewed to detect additional pelvic or hip fractures that may be overlooked in bedbound patients with distracting injuries. The gold standard test used to detect acute fractures of the spinal axis is MRI with T1-weighted sequences and short-tau inversion recovery (STIR) or T2-weighted fat saturation sequences that identify bone marrow edema, fracture lines, and neoplastic lesions. In osteoporotic fractures, MRI scan generally demonstrates diffuse signal abnormalities along the wing-to-body joining line (JL), in an “H” (when symmetrical fracture occurs) or “half-H” (asymmetrical fracture) shape, suggesting the diagnosis of sacral insufficiency fracture (Figs. 6.2, 6.3, and 6.4). CT scan may show nondisplaced fractures, and occasionally fractures that are weeks old may show sclerotic changes around fracture lines. Although CT is less sensitive than MRI in demonstrating acute sacral fracture, it remains crucial for a pre-op planning by demonstrating fracture dislocation and sacral foramina involvement which is a condition increasing the risk of PMMA extravasation (Figs. 6.1b and 6.3c). CT enhances the ability to delineate blastic from lytic masses identified on MRI. If an MRI is not possible, bone scans may demonstrate recent fractures with increased radiotracer uptake. Correlation with history is important to avoid missing a fracture if the bone scan is performed too early in the course of healing in a severely osteoporotic patient. SPECT or SPECT-CT imaging is useful to confirm anatomic localization of radiotracer uptake in the complex sacral anatomy.
6.5 Technique
6.5.1 Consent
Ideally an informed consent conversation should take place with the patient and their involved family. This is a good opportunity to fully explain and set expectations regarding pain relief and the potential of additional underlying pain generators that may be unmasked after a successful procedure [28]. The standard risks of bleeding or infection apply to all patients. Particular attention should be paid to those with underlying diabetes. A thorough clinical review to exclude common infection sources such as pneumonia and UTI is required. The use of periprocedural antibiotics as prophylaxis is a recognized best practice.
The possible complication of nontarget cement deposition with liquid agents is perhaps more likely in the sacrum than with vertebral augmentation. The complex anatomy can make nontarget cement deposition more difficult to detect. It is not unusual for overall cement volumes to be higher than those for lumbar vertebra as it is common to use multiple needles for cement injection. In frail patients, the subcutaneous tissues overlying the sacrum are quite thin, and the risk of a cement tail causing irritation is higher than in the lumbar spine. This unusual outcome should be anticipated as a potential complication and explained in advance [29].
6.6 Technique
6.6.1 CT vs. Fluoroscopic Guidance
When using fluoroscopy as a guidance modality, the complex sacral anatomy provides challenges for the operator [30]. The AP view is most clear. This allows for the operator to avoid the sacral neural canal as well as the neural foramina and sacroiliac joints. However, the lateral view can be troublesome in the pelvis. In larger patients, limited X-ray penetration may prevent adequate visualization of ventral cement. A small cement aliquot entering a venous structure may be difficult to detect. The contours of the sacrum may also make detection of extraosseous cement confusing or difficult. The benefits of real-time visualization of cement injection are to be balanced with the patient anatomy, the planned approach, and the limitations of the specific fluoroscopic equipment. If there is adequate visualization of the ventral surface of the sacrum, the procedure can be performed safely with fluoroscopic guidance.
CT guidance can help overcome the limits of fluoroscopy for optimal visualization of sacral anatomy during access with needle trocars and while injecting cement [30]. The canal and foramina as well as surrounding vascular structures can be readily seen. This is balanced by the need to limit radiation dose and procedure time with limited anatomic coverage and intermittent scanning that can limit the detection of nontarget cement deposition out of the field of imaging. Utilizing small cement aliquots between images and thicker cement can mitigate this limitation. CT guidance provides the most flexibility with needle positioning and targeting visible fractures, centering needles in the midportion of lytic areas, and may be optimal for patients with complex cancer-related fractures and tumor deposits. Many metastatic lesions destroy the standard bony anatomy that guides safety and accuracy on plane films and makes CT beneficial for use in patients with infiltrating lesions.
6.7 Technique
6.7.1 Patient Positioning
For procedures using both CT guidance and fluoroscopic guidance, the patient is placed in the prone position on the table. This may be the most difficult and painful portion of the procedure. If available, partnering with an anesthesiologist and administration of intravenous analgesia and sedation may allow safe and comfortable patient transfer from supine to prone position with minimal physiologic stress. Proper cushioning and support is important for the safety and comfort of the patient. Thorough prepping and skin cleansing with antimicrobial scrubs is particularly important in this procedure given the proximity to the perineum. Sacroplasty can be performed using general anesthesia, monitored anesthesia care, intravenous anesthesia, intravenous sedation, and analgesia. Accurate and copious local anesthetic administration is vital to minimize pain during the procedure as to maximize post-procedure comfort. Collaboration among the operator, the anesthesiologist, and the patient helps determine the best anesthesia plan.
6.8 Technique
6.8.1 Cement and Needles
The minimum tools that are required for sacroplasty include bone needles (13, 11, 10.5, or 10 gauge) and medical-grade barium-opacified (at least 28% by weight) acrylic bone cement. The bone needles are usually 10 cm in length, but the approach may warrant the use of a longer needle (such as a 15-cm-length bone needle) [31]. The cement can be injected with small 1 mL handheld syringes, pre-filled cement delivery cannulas designed for coaxial use with the bone needle, or a commercially available cement delivery system. Recently, new biomaterials have been tested for bone regeneration, looking for the ideal tool to repair the human bone: new osteoconductive materials have been used to fix bone defects in osteoporotic patients and in neoplastic fractures (Fig. 6.7).
