Currently, vertebroplasty and kyphoplasty are increasingly popular percutaneous techniques used for the treatment of symptomatic spine metastasis, multiple myeloma, and hemangiomas. Both procedures involve percutaneous injection of polymethylmethacrylate (PMMA) bone cement into the affected vertebra. This approach has demonstrated efficient pain relief as pain receptors are destroyed by the exothermic reaction of the cement polymerization.¹ Despite the lack of mechanical studies, it is logical to conclude that cement would also provide increased strength to a vertebral body partially destroyed by tumor and may therefore be a reasonable treatment or prevention for pathologic vertebral fracture. Vertebroplasty involves direct injection of the PMMA cement into the vertebral body under fluoroscopic guidance. With kyphoplasty, the cement is injected after a cavity is created into the affected vertebra by the inflation of a balloon, with the aim of reducing any collapse of the bone that has occurred, also allowing a reduced risk of cement leakage, as the cement is introduced with less pressurization. The relative indications for kyphoplasty must be carefully considered because of the increased cost of this treatment relative to vertebroplasty. Both techniques have risks including cement leakage in about 10% to 70% of cases on radiograph, and up to 93% of cases on assessment of CT scans.² While most cases are reported to be asymptomatic, cement leakage into the vertebral canal can induce mechanical compression and exothermic damage to the neural structures.² The limitations of these techniques must be known and respected in order to avoid these complications. Symptomatic spinal cord compression and overt instability are major contraindications for both vertebroplasty and kyphoplasty. Some cases present technical difficulties, rather than contraindications, such as the rupture of the posterior cortex with epidural involvement.³,⁴ There are also controversies regarding vertebroplasty for tumors of the upper cervical spine, with regard to multidirectional forces applied in this region.⁵ The lack of biomechanical studies and reported experiences have led some teams to consider open procedures such occipitocervical fixation as more desirable.⁵ We opine that MIS treatment is a valuable option in a frail cancer patient with limited life expectancy who would not be a candidate for conventional open procedures (Fig. 31.1). Respecting these limitations, many series have reported excellent results with low morbidity, as demonstrated by randomized controlled trials.¹,⁶

Bony destruction associated with spine tumors increases the risk of intractable mechanical pain and vertebral fracture that can cause sudden and irreversible damage of the neurologic structures. In such cases, surgical stabilization must be discussed systematically prior to radiation therapy.⁷ Many stabilization techniques have been developed to improve outcomes of patients with instability related to spine tumors. These techniques require wide exposure, resulting in increased blood loss, the frequent need for blood transfusion, increased postoperative pain, and longer hospital stay.⁸ Moreover, these aggressive strategies require delaying the initiation of adjuvant therapies for many weeks until complete healing. These strategies may be not suitable for patients in poor medical condition and those with limited life expectancy. Indeed, cancer patients often suffer from malnourishment and diminished immunity and are at an increased risk for postoperative complications.⁹

Moreover, as stated previously, vertebroplasty is not suitable when bony destruction and deformation predispose to cement leak, endangering the nearby neurovascular sturctures. Thus, the percutaneous pedicle screw-rod fixation technique, originally introduced for the treatment of degenerative conditions, has increased popularity as a treatment for instability related to spine tumors. Under general anesthesia, the patient is positioned prone on a radiolucent table, allowing anteroposterior (AP) and lateral fluoroscopic control. The pedicles are identified first, and screws are then introduced under strict fluoroscopic guidance. The rods are bent to the spinal curvature and introduced percutaneously. From a biomechanical point of view, long-segment instrumentation seems to be safer as distraction forces are applied over the whole length of the instrumented spine.¹⁰ Restoring the weightbearing properties of the
spinal column often relieves the mechanical pain (Fig. 31.2). Indeed, many studies have reported very good clinical results and a low complication rate.¹⁰, ¹¹, ¹², ¹³ However, this technique has some limitations. First, although the safety of percutaneous screw placement has been largely demonstrated in the literature,¹⁰,¹¹ the visualization of the pedicles on fluoroscopic control can be altered by lysis of the pedicle in certain cases of metastatic spread. Navigation systems can help overcome this limitation. Second, as long-segment instrumentation is often required, the immediate postoperative course can still be painful and require a hospital stay of 3 to 4 days. This transient pain is related to muscle splitting and should be considered during decision making. Third, although this technique treats mechanical instability, it has no direct effect on the tumor. Therefore, adjuvant treatment is required to achieve local tumor control. In practice, irradiation can be performed from the seventh postoperative day.¹²,¹³ This allows treatment of local pain related to the tumor and prevents tumor growth, which could lead to compression of neurologic structures. Finally, the absence of bone fusion must be systematically considered. This is not an important concern for patients with limited life expectancy, because the patient is likely to die before the hardware failure occurs. However, with the improvement of anticancer therapies, many patients with primitive or metastatic tumors are expected to have prolonged survival. Such patients could potentially benefit from a fusion procedure (open), as the longterm efficacy of percutaneous fixation has not been adequately assessed.