Vertebral Augmentation for Osteoporotic Compression Fractures

11 Vertebral Augmentation for Osteoporotic Compression Fractures Daisuke Togawa, MD, PhD and Isador H. Lieberman, MD, MBA, FRCS(C) INTRODUCTION Osteoporosis is a systemic disease currently afflicting approx 44 million Americans; this figure will increase as the population ages. It results in progressive bone mineral loss and concurrent changes in bony architecture that leave bone vulnerable to fracture, often after minimal or no trauma. The spine is the most common site of osteoporotic fracture, with vertebral compression fracture (VCF) occurring in 20% of people over the age of 70 yr, and up to 50% of women 80 yr and older (1,2). Overall, 700,000 people per year in the United States suffer a VCF, exceeding even the frequency of hip fractures (3). Osteoporotic VCFs have been shown to be associated with up to a 30% age-adjusted increase in mortality (4). The cost to society of managing osteoporotic VCF patients in the United States in 1995 was $746 million (5). Possible acute complications of vertebral fracture include cord compression, urinary retention, and ileus (6). Long-term consequences include considerable pain (reported in 35% of detectable VCFs) (7) as well as pulmonary compromise (a 9% loss in predicted forced vital capacity with each vertebral fracture) (8). Other chronic sequelae include deconditioning, deformity, insomnia, and depression, resulting in substantial physical, functional, and psychosocial impairment (8,9). Nonoperative Management of VCFs Two-thirds of patients with acute, painful VCFs experience pain improvement regard- less of the treatment applied. Traditional, nonoperative management includes bed rest, analgesics, and bracing. This type of medical management, however, fails to restore spinal alignment, and the lack of mobility itself can result in secondary complications, including worsening osteoporosis, atelectasis, pneumonia, deep vein thrombosis, decubitus ulcer, and pulmonary embolism. An alternative approach is supervised ambulatory mobility by a physiotherapist plus hydrotherapy (10). In one-third of patients, severe pain, limited mobility, and poor quality of life persist despite appropriate nonoperative management. Whether the pain has resolved or not, no patient after a VCF spontaneously achieves a realigned spine, corrected sagittal contour, or restoration of vertebral height. From: Arthroscopic and Endoscopic Spinal Surgery: Text and Atlas: Second Edition Edited by: P. Kambin © Humana Press Inc., Totowa, NJ 239 240 Togawa and Lieberman Operative Management of VCFs Historically, the only alternative to nonoperative management of symptomatic vertebral fractures was open surgical decompression (anterior or posterior decompression and stabilization via internal fixation hardware and bone grafting), and this was usually reserved for those patients with gross spinal deformity or neurological impairment (<0.5%) (6). This surgical caution came about because of the adverse risk/benefit ratio in this elderly population with poor bone quality and multiple comorbid conditions. Percutaneous vertebroplasty (PVP) is a minimally invasive method that involves the percutaneous injection of polymethyl methacrylate (PMMA) into a collapsed vertebral body to stabilize the vertebra. Originally developed for osteolytic metastasis, myeloma, and hemangioma, the procedure resulted in quick, effective pain relief and a low complication rate (11–13). PVP is now also increasingly used for the treatment of osteoporotic vertebral fractures (9). However, PVP does not expand the collapsed vertebra, potentially locking the spine in a kyphotic posture. In addition, the PMMA bone filler has associated problems (epidural leakage, thermal necrosis, inability to integrate with bone, handling difficulties, toxicity to patient and operator) (2,14). Kyphoplasty is an advanced minimally invasive technique with a number of potential advantages over PVP, including lower risk of cement extravasation and better restoration of vertebral body height (15). A cannula is introduced into the vertebral body, followed by insertion of an inflatable bone tamp, which, when deployed, reduces the compression fracture and restores the vertebral body toward its original height, while creating a cavity to be filled with bone cement. The cement augmentation is therefore done with more control into the low-pressure environment of the preformed cavity with viscous, partially cured cement. PERCUTANEOUS VERTEBROPLASTY Background Percutaneous vertebral augmentation (vertebroplasty, or PVP) was first reported by Galibert and colleagues in 1984 and initially involved augmentation of the vertebral body with PMMA to treat a hemangioma. PVP was reportedly not performed in the United States until 1994. Originally targeted for osteolytic metastasis, myeloma, and hemangioma, PVP resulted in early appreciable pain relief and a low complication rate (13,16). Its indications subsequently expanded to osteoporotic vertebral collapse with chronic pain, and then further to include treatment of asymptomatic vertebral collapse and even prophylactic intervention for at-risk vertebral bodies (17). Nevertheless, the treatment of acute fractures in ambulatory patients and prophylactic treatment remain controversial (18). In fact, vertebral augmentation itself is somewhat controversial, with questions concerning a lack of defined indications, expected complications, outcome mea- sures, and the need for long-term follow-up data (2). An open question in PVP is the mechanism of pain relief. The most intuitive expla- nation involves simple mechanical stabilization of the fracture. However, another pos- sibility is the analgesic result from local chemical, vascular, or thermal effects of PMMA on nerve endings in surrounding tissue (9,19). Supporting this concept is the lack of correlation between cement volume and pain relief (20,21). Further evidence against an effect resulting solely from mechanical stabilization is the fact that PVP Vertebral Augmentation 241 typically does not restore lost vertebral body height and therefore does not correct altered biomechanics (1,18). Technique Injection of opacified PMMA is performed via a transpedicular or paravertebral approach under continuous fluoroscopic guidance to obtain adequate filling and to avoid PMMA leakage. For complex or high-risk cases, computed tomography (CT) and fluoroscopic guidance are sometimes combined (11,18). In routine cases, PVP can be performed under local anesthesia with slight sedation in less than 1 h (1), although general anesthesia is sometimes required because pain may intensify during cement injection (9). Preceding PMMA injection, intraosseous venography is often used to determine the filling pattern and identify sites of potential PMMA leakage (outline the venous drainage pattern, confirm needle placement within the bony trabeculae, and delineate fractures in the bony cortex). However, some clinicians have dispensed with routine venography (1). Contraindications to vertebroplasty include coagulopathy, absence of facilities to perform emergency decompressive surgery in the event of a complication, and extreme vertebral collapse (>65–70% reduction in vertebral height) (9). Results From 1985 to March 2004, 329 articles on PVP were published in peer-reviewed journals. Vertebroplasty data from more than 1000 patients have been reported in sev- eral case series (1,11,13,18,22–34). The longest reported follow-up is 3 yr, although the first article on vertebroplasty was published in 1987. Reportedly, pain has been reduced in 70–90% of patients. There have been no reported cement failures, and only two reported cases of fracture progression in the treated vertebral bodies (caused by inadequate cement fill). Barr et al. (18) reported the results of 47 patients treated with vertebroplasty with an average follow-up of 18 mo. Their article outlines marked to complete pain relief in only 63% of patients with osteoporotic VCFs. Vertebroplasty, however, does not address the spinal deformity. In addition, this technique requires a high-pressure cement injection using low-viscosity cement, thus increasing the risk of cement leaks through the fracture clefts or the venous sinuses. Evans et al. (26) reported their retrospective results of 245 cases with an average follow-up of 7 mo. In thier study, pain score was significantly decreased and the ability to participate in an active daily lifestyle was significantly improved following vertebroplasty (26). Complications The principal risk of PVP, which involves the forced injection of low-viscosity PMMA cement into the closed space of the collapsed vertebral body, is cement extravasation. Extravasation rates are as high as 65% when used to treat osteoporotic fractures (13,28). The likelihood is greater when using cement with a liquid rather than paste consistency, or with higher PMMA volume (25). However, in most settings, the majority of extrava- sations have no clinical relevance, at least in the short term (1). The consequence of an extravasation depends on its location. In epidural or foraminal extravasation, nerve root compression and radiculopathy is the major risk. This occurred in 11 of 274 patients (4%) treated by Deramond et al. (11). Three of those patients required surgical nerve root decompression. Other clinicians have described a 242 Togawa and Lieberman 5% rate of radiculopathy as well (6,20,35). Extravasation into perivertebral veins can cause cement embolism to the lungs; deaths attributed to cement embolism have been documented. However, two reported deaths

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