Percutaneous vertebral augmentation techniques comprise minimally invasive, imaging-guided procedures that aim for the stabilization or restoration of the damaged vertebral body. Treatment goals of percutaneous vertebral augmentation techniques are pain relief, kyphosis reduction and prevention of progression of vertebral collapse, and decreased morbidity and mortality. Rationale for vertebral augmentation includes failure of conservative management and conditions that are inappropriate for open surgery. The general underlying principle of percutaneous vertebral augmentation techniques is the percutaneous placement of vertebral implants with or without prior manipulation of the vertebral body. An implant material that is commonly used is the polymeric bone substitute polymethylmethacrylate (PMMA). The following text is intended to provide an overview of the two most common techniques, vertebroplasty and kyphoplasty, and the more recently described technique of vertebral body stenting.

Metastatic lesions are the most common bone tumors but seldom they are candidates for surgery due to advanced disease and comorbidities. Palliative therapy consists mainly of radiation therapy, and various percutaneous methods are available as well. Traditionally the endovascular embolization has been the most commonly used percutaneous method when applicable.

Recently, cementoplasty [59], ethanol injection [60], laser ablation (LITT) [61], cryotherapy [62], and radiofrequency ablation (RFA) [63] have become a part of a treatment paradigm towards better control and effect in palliative therapy. Microwave therapy [64], focused ultrasound (FUS) [65], and irreversible electroporation (IRE) [66] are emerging techniques.

When malignant primary bone tumors are considered, surgery is the primary treatment of choice. However, benign bone tumors are often small, and curative treatment result is possible using percutaneous techniques. The most common entity treated this way is osteoid osteoma. Palliative treatment of primary bone tumors using percutaneous techniques is also possible.

Cementoplasty refers to percutaneous injection of cement into the bone. The procedure is called also vertebroplasty or osteoplasty when performed in spine. Cementoplasty is used increasingly to treat bone metastases. The primary indication is pain control but preservation of structural integrity of bone is equally important. Polymethylmethacrylate (PMMA) is the most common cement used as it has best mechanical properties and possible direct effect on tumor tissue and nociceptors [67]. Treatment is usually mediated under fluoroscopy (also 3D fluoroscopy) or CT guidance. Careful monitoring during cement injection is mandatory in order to avoid cement leakage into the vascular structures and neural spaces. Typical targets are acetabular and sacral lesions and generally areas subject to compression forces (Fig. 48.7). Bone biopsy or vertebroplasty sets are used to gain lesion access and to inject cement. Cementoplasty can be used in combination as a stabilizing procedure before or with other therapies such as radiation therapy and radiofrequency ablation [68]. Initial results with the combination therapy of cementoplasty and RFA have been promising [69].

Ethanol injection is a simple and cost-effective method to achieve tumor necrosis [60]. The necrotizing effect is due to direct toxic effect, dehydration, and thrombosis. A thin (18–25 g) needle is advanced to the tumor, and 95 % ethanol is carefully administered according to the tumor volume but not exceeding 25 ml. Prior to alcohol injection, fluoroscopy control of contrast spread at the injection site is recommended in order to minimize the effects of extravasation. The problem with ethanol injection is the inability to monitor the ethanol spread directly under fluoroscopy; therefore, CT is the preferred method of guidance.

Laser ablation is an ablation technique frequently used to treat malignant soft tissue tumors [70]. LITT uses optical fibers to mediate light energy to tumor tissue thus ensuing coagulation necrosis. Powerful Nd:YAG or infrared lasers can be used. Along with FUS, LITT is ideally suited for MRI guidance and thermal monitoring due to lack of MRI interference. Using cooled laser catheters, larger tumors can be successfully treated. Bone access is through drill or trocar, and treatment is conducted in coaxial manner while making sure that the active part of the laser probe is freely situated in the lesion.

The advent of new-generation thin cryoprobes has increased the use of cryoablation in the treatment of malignant tumors. The cellular death occurs due to freezing of cytoplasm, and the freezing cycle is based on Joule-Thompson effect. The advantage of cryotherapy is the visualization of the ice ball in MRI or in CT that makes the local therapy control straightforward. The treatment is also better tolerated than heat-distributing methods. The downside of cryoablation is the lengthy treatment time due to the fact that typically several freeze-thaw cycles are needed to obtain desired effect. Prolonged treatment may also initialize transient hemolysis. Initial results of the use of cryotherapy in treating bone tumors are encouraging [62, 71].

Radiofrequency ablation is the most commonly used ablation method and is widely accepted as part of clinical paradigm in treating hepatic metastases. Similarly to LITT, RFA effect is based on ensuing tissue coagulation. The mechanism here is alternating electrical current that oscillates in high frequency. Most applicators are based on monopolar technology although bipolar technique is also used [72]. In bone, the electrode insertion to tumor tissue is through trocar or drill, if the cortical bone remains intact. CT and fluoroscopy are the most common guidance methods, but also MRI with certain restrictions may be used. In skeletal metastatic disease, the pain palliation results of RFA therapy are good to excellent [73]. The problem with RFA is that the monitoring of treatment effect during ablation is often not possible, but instead, the treatment effect relies primarily to accurate probe placement and pre-procedural planning. To generalize, this is true with all methods. Radio-frequency ionization is a low-temperature bipolar method that is more local in its effect and is used to achieve tumor decompression by vaporizing tumor tissue with the touch of the probe. It is particularly well suited to be used as combination therapy with cementoplasty.

Of benign tumors, the osteoid osteoma (OO) or lesions mimicking OO are best suited for curative percutaneous therapy. The tumors are typically small, well delineated, and readily diagnosed with imaging. Both laser and RFA can be used to obtain similar results. CT/3D fluoroscopy and MRI are used to guide therapy [61, 74–76] (Fig. 48.8).

Both OO and metastatic lesions frequently involve spine. Care must be practiced when treating lesions adjacent to critical neural structures with thermal techniques. Thermal protective measures can also be utilized; these include CO₂ and saline injection or infusion to insulate critical structures from the heat [77–79].

Percutaneous methods for tumor management provide a minimally invasive means to achieve tumor palliation in malignant invasion of bone. The primary intention is not the complete removal of tumor tissue but that of tumor reduction, pain management, and restoring/maintaining structural integrity. In the case of selected benign entities, such as osteoid osteoma, curative results can be obtained.

Cystic and reactive bone lesions are a heterogeneous entity with few common particulars but perhaps the increased osteoclastic activity resulting in bone resorption leading to cyst and cyst-like as well as other reactive changes, such as edema, in bone. These lesions include tumor-like, vascular lesions of aneurysmal bone cysts (ABC) and simple unicameral bone cysts (UBC) as well as more reactive conditions with cystic elements, such as osteochondritis dissecans (OCD), post-traumatic bone cysts, herniation pits, and osseous ganglia.

Aneurysmal bone cyst is an expanding bone lesion with vascular components [80]. It can arise as de novo lesion (70 %) or as a secondary lesion (30 %). The exact etiology is unknown, but ABC may concede with reactive vascular malformation, post-trauma, and genetic alterations ultimately thought to lead to an increase of local intraosseous venous pressure and consequent development of the lesion [81–85]. Active ABCs necessitate therapy and surgical resection, and curettage is the standard approach but not applicable to all lesions [86, 87]; other treatment methods are curettage with or without bone grafting [88] and percutaneous techniques. Radiation therapy is effective but with side effects, and steroid injections are ineffective [89, 90]. The most widely used percutaneous techniques are selective embolization, which is mainly used as temporary measure to facilitate surgery and application of direct intralesional sclerotherapy and/or demineralized bone particles [91, 92] (Fig. 48.9). Different sclerosing agents can be used, Ethibloc^® is common, but use of polidocanol is reported [93], and authors have used also sodium tetradecyl sulfate (STS, Fibro-vein^®); these drugs are not FDA approved for described use. The authors use dual puncture technique in order to minimize possible extravasation of sclerosing agent to surrounding tissue or venous structures. Possible complications include pulmonary embolism via venous drainage and local irritation and subcutaneous fistulae [94]. Spinal lesions should be treated with utmost care. Experience and fluoroscopy control upon sclerosant injection is mandatory. Due to this, the majority of ABC sclerotherapy is done under fluoroscopy guidance, although CT or MRI can be used for initial cyst puncture to facilitate better accuracy and selective therapy (Fig. 48.9). Results of sclerotherapy in treating ABCs are promising with high success rate [95, 96].

Simple unicameral bone cyst is a benign, usually self-limiting entity [97] mostly encountered among pediatric patients. Therapy is conservative if the cyst is not active, not symptomatic or does not pose fracture threat. In therapy, minimally invasive surgery or percutaneous techniques are preferred; invariably the therapy is performed under fluoroscopy. Surgery involves percutaneous curettage, which can be mechanical and/or chemical (alcohol, Ethibloc^®, corticosteroids,), and consequent filling of the defect with bone substitutes. Combined use of mechanical and chemical curettage (sclerosing agents) and bone substitutes seems to allow best results [98]. As an access method, dual puncture technique is recommended.

Reactive conditions may cause cystic transformation of bone [99, 100]. Traumatic cysts, when present, often affect subchondral bone and may occasionally be treated with percutaneous decompression drilling and bone substitute filling (Fig. 48.10). Similarly to trauma, chronic overuse or mechanical stress may cause degenerative or reactive bone lesions. These include intraosseous ganglion cysts and herniation pits [101–104] that can be treated with percutaneous trepanation when small. Due to the inconspicuous fluoroscopy visualization of these lesions, 3D fluoroscopy, CT, and MRI are optional guidance methods for therapy.

Osteochondritis dissecans is a subchondral lesion of bone associated with microtrauma [105]. Conservative therapy is preferred, but operative treatment is often necessary to treat this condition mostly affecting pediatric patients. Percutaneous retrograde drilling presents as a minimally invasive therapy method [105–107]; with proper navigation guidance, fluoroscopy, CT, or MRI can be used as guidance modalities.

Femoral head osteonecrosis is a devastating reactive condition often leading to destruction of the joint. Femoral head decompression drilling is a procedure that alleviates symptoms and may halt the progression of the condition. Especially lesions that are of Ficat I or II stage and small are more likely to respond to decompression [108, 109]. Here several small drill channels are made to the necrotic lesion through femoral neck, using the greater trochanter as a starting point. The authors use a 3-mm drill and flexible Kirschner wires.

Percutaneous reduction or/and fixation of fractures is a minimally invasive treatment option in a situation where there is little inherent dislocation or instability associated with trauma. Standard operative approach typically provides superior exposure, allowing access and manipulation of fractures leading to satisfactory positioning and fixation; however, with this traditional regime, there is an increased risk of complications, and some patients simply are not candidates for surgery due to poor physical condition or underlying comorbidity.

Similarly to open techniques, percutaneous fracture reduction and fixation can be achieved via instrumentation and bone cement injection or both. Cement injection is used when there is poor prognosis of healing, especially considering the usage of instrumentation, most often these cases are due to insufficiency fractures or tumors.

Image guidance is frequently used in conjunction with percutaneous fracture fixation. As a rule, a preceding helical thin slice CT and MRI, if necessary, are performed to facilitate procedural planning and possible image fusion for navigation purposes.

Fluoroscopy is by far the most commonly used for procedural guidance but CT is an option as well. The advent of new cone-beam CT devices with inbuilt navigation protocols and large field of view is probably going to widen the indications for percutaneous fixation of fractures [110]. Currently the most frequent targets for instrumented image-guided percutaneous fixation are scaphoid, calcanear, vertebral, and sacroiliac fractures.

Traumatic scaphoid fractures determined as acute B2 type can be treated conservatively with cast fixation or with percutaneous screw fixation [111–113]. Here a reduction is achieved first with an inserted Kirschner wire, and subsequent screw fixation follows. Percutaneous fixation may be associated with better overall outcome [113].

Traumatic calcanear fractures, although rare (2 % of all fractures), are common in young age groups (90 % of patients), and thus, their satisfactory treatment is economically important. Calcanear fractures have been frequently treated with percutaneous fixation, particularly those of type C2 (AO83), and there is evidence that percutaneous technique is associated with considerably less morbidity than traditional lateral approach open surgery [114, 115]; also more complicated fractures of calcaneus can be treated with percutaneous technique with initial overall results being similar to open surgery. Cement injection as a solo treatment method is infrequent but used as a method in treating calcanear joint depression type of fracture. Cement can be applied using open approach or percutaneous technique [116].

Traumatic events involving pelvic fractures are mostly of high impact of nature; this often results to significant injury, frequently extending beyond bony structures [117, 118]. Pelvic fractures consist 0.3–8 % of all fractures [119, 120]. Surgical treatment paradigm remains challenging due to technical difficulty, hemodynamic instability, and associated trauma, which may postpone pelvic surgery. Surgical treatment is performed with unstable pelvic ring fracture types B and C (AO class). Assessment of instability remains a problem, the preferred closed reduction should be performed within 2 days from initial trauma, and later attempt may fail due to ensuing fibrosis and hematoma organization. Percutaneous reduction involves clamps or handles that are attached to the fragments [121]. Open reduction is done with standard surgical technique and exposure.

Percutaneous fixation of pelvic fractures relies completely on image guidance and navigation. The operative technique does not follow standard access routes or dissection planes and due to the atraumatic nature of fixation screw placement, a most straightforward course of approach for the fixation instrumentation is chosen according to the preceding imaging (CT). With this approach, critical structures are avoided. Typically a coaxial technique is used; first, a guide wire is inserted to the intended fixation position followed with over-the-wire screws [122, 123]. External fixation of pelvic fractures is used predominantly as a temporary measure to facilitate later conclusive fixation.

Pelvic anatomy is complex and with risk of neurovascular complications associated with surgical fracture repair; navigation tools are increasingly used to minimize risk of misplacement of fixation material. Navigation can be achieved either with direct real-time (online) systems working in conjunction with imaging devices and/or data (fluoroscopy, CT, cone-beam CT [3D fluoro], MRI) or with offline systems, or both [110, 123–126]. With offline systems, there is no active image registration during the procedure thus exposing the situation to error due to faulty positional registration (external or internal patient movement or reference base movement).

In the management of pelvic fractures, a typical case involves a combination of surgical techniques due to sequential nature of treatment; percutaneous methods and image guidance are part of the established paradigm.

Traumatic thoracolumbar vertebral fractures are common, and invariably the most common fracture type is that of burst fracture (AO class A). These fractures present as potential targets for image-guided open or percutaneous image-guided fixation due to preserved posterior components of the vertebrae facilitating transpedicular introduction of fixation material. The rationale for posterior fixation is functional and procedural. Posterior fixation can make the fixation more stable and prevent the excess loss of reduction; furthermore, percutaneous procedure is minimally invasive with less traumatic consequences to paraspinal musculature, nerves, and vasculature. Most experience from percutaneous fixation is with Sextant system [127] (Fig. 48.11).

The percutaneous fixation appears to be as effective as open fixation with minor inefficiency in restoring anterior height of the vertebra [114, 127]; this could be compensated with simultaneous kyphoplasty or vertebral stenting [52]. Similarly to pelvic region, image guidance and navigation are in the key role in performing vertebral fracture fixation. There is evidence that active, real-time navigation should be preferred over static offline registration due to registration mismatch that generated inaccuracy in thoracic region [128, 129].