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

17 Additional and Adjacent Level Fractures after Vertebral Augmentation

Scott Kreiner

Summary

Vertebral compression fractures (VCFs) are common as are the occurrence of additional vertebral fractures that happen after the incident level fracture. There are several reasons that predispose patients to additional vertebral fractures including the anatomy of the fracture and the use of corticosteroids but the primary determinate factors are low bone mineral density and spinopelvic imbalance. Prior vertebral compression fractures also increase the risk of an additional fracture substantially with an increased risk up to 75 times higher for patients with three or more fractures. There is ample data showing no increased risk of additional fractures after vertebral augmentation but certain procedural features may predispose to adjacent level fractures such as cement extravasation into the disk.

Keywords: vertebral augmentation, adjacent level fractures, bone mineral density, spinopelvic balance, kyphotic deformity

17.1 Introduction

Compression fractures of the spine are a large problem, affecting between 700,000 and a million persons in the United States annually, and 25% of women in their lifetime.¹^,² Treatment of these compression fractures should not only focus on the index fracture but also on preventing further fractures in the future. To better understand how to prevent future fractures, it is imperative that we know what puts patients at risk for developing new fractures.

17.2 Risk Factors for Additional or Adjacent-Level Fractures

There are several risk factors associated with the development of additional or adjacent-level fractures. These risk factors are similar to the risk of initial fractures discussed in Chapter 4. Decreased bone mineral density (BMD) is the primary determinant in the development of additional or adjacent fractures whether they are treated or untreated.³^–¹⁵ In fact a prominent decline in BMD of 2 SD is associated with a fourfold to sixfold increase in risk of additional fracture.¹⁵^,¹⁶ In addition, the use of chronic corticosteroids has been associated with a propensity for developing VCFs and recurrent compression fractures¹¹^,¹⁷ via their effects promoting osteoclastic activity, inhibiting osteoblastic activity, and the interference on the small intestine’s ability to absorb calcium. The presence of prior fracture is also predictive of future fractures. A single compression fracture increases the risk of another fracture by 3.2 to 5 times, the presence of two or more fractures increases the risk of another fracture by a multiple of 10 to 12, and the presence of three or more fractures increases the risk of another fracture by a very substantial 23 to 75 times.¹⁵^,¹⁸^,¹⁹ A combination of low BMD and more than two prior fractures increases the risk of a new vertebral fracture to at least a factor of 75-fold, relative to women with a BMD in the top 67th percentile and no prior fracture.¹⁵

However, it is not just the presence of a prior fracture that increases the risk of future fracture; there are biomechanical effects directly related to the index fracture that are associated with the increased risk of future fracture. End plate fracture itself affects the biomechanics of the spine by disrupting the ability of the intervertebral disk to pressurize, which increases the compressive loading on the anterior wall of the adjacent vertebrae, predisposing it to fracture.²⁰ The correction of end plate deformity by reducing the end plate and stabilizing it with polymethyl methacrylate (PMMA) decreases this force and is an important factor in decreasing adjacent-level fractures.²⁰ An even more important factor in causing additional and adjacent-level fractures is the kyphotic angle formed by the index fracture. This kyphotic deformity causes the body mass from above the fracture to deviate anterior to the typical center of balance, thereby increasing the effective pressure on adjacent vertebrae.²¹ Additionally, to maintain equilibrium, the paraspinal muscles must supply a force equal and opposite to this anterior mass movement in direct proportion to the lever arm. So, as the kyphotic deformity increases, so do the downward forces on the spine especially on the anterior portion of the vertebral body.

Clinically, these biomechanical factors have been shown to be directly related to the occurrence of additional and adjacent-level fractures. Lunt et al¹⁹ showed that the shape of the fracture (▶Table 17.1) strongly influences the risk of future fracture, with more kyphotic deformity increasing the risk of fracture by a factor of 5.9 as compared with a compression fracture without kyphotic deformity that increases the risk of future fracture by a factor of only 1.6. In addition to the focal anatomic changes caused by a VCF, Baek et al²² further defined the relationship between postfracture spinopelvic balance and the development of new fractures. The presence of a segmental kyphotic angle (SKA; ▶Fig. 17.1) of over 11 degrees is associated with increased risk of fracture regardless of whether the vertebral body has undergone augmentation. Other spinopelvic parameters associated with increased fracture risk include a sagittal vertical axis (SVA; ▶Fig. 17.2) of greater than 6 cm, sacral slope (SS; ▶Fig. 17.3) less than 25 degrees, and a lumbar lordosis (LL) of less than 25 degrees.

17.3 Possible Influences of Vertebral Augmentation Technique

There has been some concern that the placement of PMMA in the spine, adjacent to osteoporotic vertebrae, increases the risk of adjacent-level fracture.²³ This perception is likely because, as discussed earlier, these patients are at higher risk than patients without a fracture history. Additionally, there is some evidence to support that additional and adjacent-level fractures are more likely to occur sooner after vertebral augmentation than with nonsurgical management, though the rate of adjacent-level fractures is similar.²⁴

Table 17.1 Risk of future fracture based on shape of incident fracture

Shape of deformity		Relative risk of future fracture
Central fracture with global/posterior flattening		1.6
Anterior fracture central		5.9

Fig. 17.1 Measurement techniques for assessment of regional deformity (RKA/SKA). (IVA, intervertebral angle; VW, vertebral wedging; SKA, segmental kyphosis angle; RKA, regional kyphosis angle.) IVA + VW = SKA. (Reproduced with permission of Koller H, Acosta F, Hempfing A, et al. Long-term investigation of nonsurgical treatment for thoracolumbar and lumbar burst fractures: an outcome analysis in sight of spinopelvic balance. Eur Spine J 2008;17:1073.)

A systematic review by Papanastassiou et al ²⁵ compared the available evidence, which showed that when comparing rates of additional or adjacent fracture, balloon kyphoplasty and vertebroplasty have rates of 11.7 and 11.5%, respectively, as compared with a rate of 22.7% for nonsurgical management. Additionally, fracture reduction, or increasing the height of a previously fractured vertebral body with kyphoplasty, does not increase the risk of adjacent-level fracture when compared with vertebroplasty.²⁶

Fig. 17.2 Sagittal vertical axis (SVA) is the most common measurement of global alignment. (Reproduced with permission of Diebo BG, Varghese JJ, Lafage R, et al. Sagittal alignment of the spine: what do you need to know? Clin Neurol Neurosurg 2015;139:295–301.)

Fig. 17.3 Pelvic parameters also play a role in stresses on the spine and influence the risk of future fracture. (Reproduced with permission of Diebo BG, Varghese JJ, Lafage R, et al. Sagittal alignment of the spine: what do you need to know? Clin Neurol Neurosurg 2015;139:295–301.)

The data available suggest that the risk of additional and adjacent-level fractures is essentially the same whether or not the incident fracture has undergone vertebral augmentation.²⁶ However, certain factors associated with vertebral augmentation may increase the risk of fracture adjacent to the index fracture. In particular, the leakage of intradiskal cement during the procedure has been associated with an increased risk of fracture. Nieuwenhuijse et al⁸ prospectively followed 115 patients with 216 VCFs for recurrent fracture after vertebroplasty. Both patient and vertebra-specific risk factors were assessed. While a number of risk factors of additional fracture were found, the only independent risk fracture related to vertebral augmentation was the presence of intradiskal cement leakage. This finding has been corroborated by other authors.²⁷^–²⁹