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DOES VERTEBROPLASTY CAUSE STRESS PEAKS IN ADJACENT VERTEBRAE?
Presentation 1151 − Topic 40. Spine biomechanics
S597
DOES VERTEBROPLASTY CAUSE STRESS PEAKS IN ADJACENT VERTEBRAE? René Aquarius (1), Jasper Homminga (2), Bo Willems (1), Nico Verdonschot (1,2), Esther Tanck (1)
1. Radboud University Nijmegen Medical Centre, The Netherlands; 2. Twente University, The Netherlands
Introduction Vertebral fractures are associated with pain and a decreased quality of life. One method of treatment is the injection of bone cement into the vertebra (vertebroplasty). Some studies, however, suggest that the relatively stiff bone cement results in stress peaks in the adjacent vertebrae, thereby inducing new fractures (Berlemann 2002, Polikeit 2003). The goal of this study is to determine whether vertebroplasty is capable of causing stress peaks in adjacent vertebrae.
Methods Ten vertebral bodies were obtained from four fresh frozen spines. The upper endplates were cast in bone cement and contained in a metal cup. The lower endplates were cast in dental vinylpolysiloxane (Zhermack, Italy), to mimic intervertebral disc properties, and subsequently placed onto a pressure sensor (Tekscan, USA). In the first part of the test, each vertebra was crushed axially with a displacement driven loading condition of 2 mm/min. In the second part of the test the vertebrae were augmented with bone cement (3.5 - 5 ml, Buchbinder 2009, Klazen 2010) and crushed again. In between the augmentation and the second crush test, X-rays were made to determine the location of the cement. Tekscan data was analyzed qualitatively: pressure profiles of both parts of the test were compared and related to the location of the bone cement as determined by X-ray. Strength and stiffness before and after augmentation were compared using a paired T-test. (significance: p<0.05).
Results There was no clear relationship between the location of the bone cement and the registered stress distribution: stress peaks often occurred in areas with (almost) no bone cement (Figure 1). The mean compressive strength after augmentation (2857N (SD 2018N)) was significantly lower than the strength of the intact, unaugmented vertebra (4070N (SD 2018N, p=0.002)). The stiffness after augmentation (3059 N/mm (SD 1276 N/mm)) was also significantly lower than the stiffness before augmentation (940 N/mm (SD 793 N/mm), p<0.001).
Figure 1. A: Example of a pressure map before (left) and after (right) augmentation. B: The 3 X-rays of the same vertebra (l to r: axial, anterior, and lateral view) show the cement filling.
Discussion There was no clear relationship between the bone cement locations in the vertebrae and the pressure distributions beneath the lower endplates. It therefore seems unlikely that vertebral augmentation in itself can cause adjacent vertebral fractures. Unlike previous in vitro studies, we found a large reduction in both strength and stiffness after augmentation. In the current study we used a clinically relevant amount of bone cement (~3.5ml), whereas others used higher volumes (Berlemann 2002, Polikeit 2003). Given the large reductions in both strength and stiffness that we found, our results suggest that vertebroplasty may not give enough initial mechanical support to the fractured vertebra. Our study shows that there is no relationship between vertebroplasty and stress peaks which could lead to adjacent level fractures. Hence, it is unlikely that vertebroplasty executed with a clinically relevant amount of bone cement accelerates fracture of adjacent vertebrae after vertebroplasty.
References Berlemann et al, J Bone Joint Surg Br, 84-B: 748752,2002. Buchbinder et al, N Eng J Med, 361: 557-568,2009. Klazen et al, Lancet, 376: 1085-1092, 2010. Polikeit et al, Spine, 28: 991-996, 2003.
ESB2012: 18th Congress of the European Society of Biomechanics
Journal of Biomechanics 45(S1)
S597
DOES VERTEBROPLASTY CAUSE STRESS PEAKS IN ADJACENT VERTEBRAE? René Aquarius (1), Jasper Homminga (2), Bo Willems (1), Nico Verdonschot (1,2), Esther Tanck (1)
1. Radboud University Nijmegen Medical Centre, The Netherlands; 2. Twente University, The Netherlands
Introduction Vertebral fractures are associated with pain and a decreased quality of life. One method of treatment is the injection of bone cement into the vertebra (vertebroplasty). Some studies, however, suggest that the relatively stiff bone cement results in stress peaks in the adjacent vertebrae, thereby inducing new fractures (Berlemann 2002, Polikeit 2003). The goal of this study is to determine whether vertebroplasty is capable of causing stress peaks in adjacent vertebrae.
Methods Ten vertebral bodies were obtained from four fresh frozen spines. The upper endplates were cast in bone cement and contained in a metal cup. The lower endplates were cast in dental vinylpolysiloxane (Zhermack, Italy), to mimic intervertebral disc properties, and subsequently placed onto a pressure sensor (Tekscan, USA). In the first part of the test, each vertebra was crushed axially with a displacement driven loading condition of 2 mm/min. In the second part of the test the vertebrae were augmented with bone cement (3.5 - 5 ml, Buchbinder 2009, Klazen 2010) and crushed again. In between the augmentation and the second crush test, X-rays were made to determine the location of the cement. Tekscan data was analyzed qualitatively: pressure profiles of both parts of the test were compared and related to the location of the bone cement as determined by X-ray. Strength and stiffness before and after augmentation were compared using a paired T-test. (significance: p<0.05).
Results There was no clear relationship between the location of the bone cement and the registered stress distribution: stress peaks often occurred in areas with (almost) no bone cement (Figure 1). The mean compressive strength after augmentation (2857N (SD 2018N)) was significantly lower than the strength of the intact, unaugmented vertebra (4070N (SD 2018N, p=0.002)). The stiffness after augmentation (3059 N/mm (SD 1276 N/mm)) was also significantly lower than the stiffness before augmentation (940 N/mm (SD 793 N/mm), p<0.001).
Figure 1. A: Example of a pressure map before (left) and after (right) augmentation. B: The 3 X-rays of the same vertebra (l to r: axial, anterior, and lateral view) show the cement filling.
Discussion There was no clear relationship between the bone cement locations in the vertebrae and the pressure distributions beneath the lower endplates. It therefore seems unlikely that vertebral augmentation in itself can cause adjacent vertebral fractures. Unlike previous in vitro studies, we found a large reduction in both strength and stiffness after augmentation. In the current study we used a clinically relevant amount of bone cement (~3.5ml), whereas others used higher volumes (Berlemann 2002, Polikeit 2003). Given the large reductions in both strength and stiffness that we found, our results suggest that vertebroplasty may not give enough initial mechanical support to the fractured vertebra. Our study shows that there is no relationship between vertebroplasty and stress peaks which could lead to adjacent level fractures. Hence, it is unlikely that vertebroplasty executed with a clinically relevant amount of bone cement accelerates fracture of adjacent vertebrae after vertebroplasty.
References Berlemann et al, J Bone Joint Surg Br, 84-B: 748752,2002. Buchbinder et al, N Eng J Med, 361: 557-568,2009. Klazen et al, Lancet, 376: 1085-1092, 2010. Polikeit et al, Spine, 28: 991-996, 2003.
ESB2012: 18th Congress of the European Society of Biomechanics
Journal of Biomechanics 45(S1)