J Korean Neurosurg Soc.  2012 Nov;52(5):435-440. 10.3340/jkns.2012.52.5.435.

Effect of Bone Cement Volume and Stiffness on Occurrences of Adjacent Vertebral Fractures after Vertebroplasty

• Kim JM
• Shin DA
• Byun DH
• Kim HS
• Kim S
• Kim HI

• KMID: 2018248
• DOI: http://doi.org/10.3340/jkns.2012.52.5.435

Abstract

OBJECTIVE
The purpose of this study is to find the optimal stiffness and volume of bone cement and their biomechanical effects on the adjacent vertebrae to determine a better strategy for conducting vertebroplasty.
METHODS
A three-dimensional finite-element model of a functional spinal unit was developed using computed tomography scans of a normal motion segment, comprising the T11, T12 and L1 vertebrae. Volumes of bone cement, with appropriate mechanical properties, were inserted into the trabecular core of the T12 vertebra. Parametric studies were done by varying the volume and stiffness of the bone cement.
RESULTS
When the bone cement filling volume reached 30% of the volume of a vertebral body, the level of stiffness was restored to that of normal bone, and when higher bone cement exceeded 30% of the volume, the result was stiffness in excess of that of normal bone. When the bone cement volume was varied, local stress in the bony structures (cortical shell, trabecular bone and endplate) of each vertebra monotonically increased. Low-modulus bone cement has the effect of reducing strain in the augmented body, but only in cases of relatively high volumes of bone cement (>50%). Furthermore, varying the stiffness of bone cement has a negligible effect on the stress distribution of vertebral bodies.
CONCLUSION
The volume of cement was considered to be the most important determinant in endplate fracture. Changing the stiffness of bone cement has a negligible effect on the stress distribution of vertebral bodies.

Keyword

Finite element analysis; Bone cements; Vertebroplasty

MeSH Terms

Bone Cements
Finite Element Analysis
Spine
Sprains and Strains
Vertebroplasty
Bone Cements

Figure

• 

  Fig. 1 Geometry of multilevel spinal units with customized volume mesh used in the finite element analysis. The unit consists of three segments (T11, T12, & L1) and bone cement is inserted into T12.

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  Fig. 2 Stiffness change with different bone cement volumes. When bone cement volume of 30% is used, stiffness is restored from osteoporotic bone state to the condition of normal bone and further increase in bone cement volume results in stiffness value beyond that of normal bone.

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  Fig. 3 Sagittal plane of the studied spine segments with contours showing von Mises stress distribution for different bone cement filling volumes. Changes in both magnitude and distribution of stress in each vertebral body can be observed with more apparent changes in upper vertebra (T11) than lower one (L1).

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  Fig. 4 Percentile difference in maximal principal strains in structures when bone cement stiffness is increased from 1000 MPa to 3000 MPa with 50% bone cement volume. Negligible changes are observed in all structures but in cortical shell and trabecular core of T11 and T12 segment.

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