Interventional Spine

Susan M Renner, PhD,
Avinash G Patwardhan, PhD, Non ASSR Member
Chris Carson, MS, Non ASSR Member
Braden McIntosh, BS, Non ASSR Member
Robert M Havey, BS, Non ASSR Member
Anastasios Dimitriadis, MD, Non ASSR Member

Scientific Paper

Mentor Award: No

Institution where work was conducted

Edward Hines Jr. VA Hospital

Affiliation and Department

Musculoskeletal Biomechanics Laboratory, Edward Hines Jr. VA Hospital

Address

5000 South 5th Ave
Bldg1 RmA201
Hines, Illinois
60141
Phone: 312-420-9722, Fax: 708-202-7938
Email: susan.renner@va.gov

Purpose

Recent studies suggest endplate fracture incurred during vertebral compression fracture (VCF) alters intervertebral disc mechanics at the adjacent levels [1]. The deformity created by the endplate fracture leads to increased nucleus volume, which does not allow the nucleus to pressurize, and thus alters disc behavior. This altered disc behavior has recently been theorized to increase fracture risk adjacent to an endplate deformity. This study tested the hypothesis that reduction of endplate deformity after both endplate fracture and subsequent vertebral compression fracture will restore disc mechanics.

Methods & Materials

Six thoraco-lumbar spine segments (T10-L2, T12-L4, or L1-L5 age:72.2±6.4yrs) were tested. A void was created under the upper endplate of the middle vertebra. The specimen was compressed via follower load until the weakened endplate fractured and a notable endplate deformity was observed on digital fluoroscopy. The specimen was then compressed further to create a vertebral compression fracture. The compression fracture was corrected, as observed radiographically, taking special care to correct the endplate deformity as much as possible using the StaXx® FX Structural Kyphoplasty device (Spine Wave, Inc., Shelton, CT). Specimens were tested in flexion-extension (±6Nm) under 400N preload before and after endplate and vertebral fractures and after endplate deformity reduction. Lateral radiographs were taken in neutral posture under 400N preload to measure maximum endplate deformity. Intradiscal-pressure (IDP) in flexion-extension was recorded in the discs above and below the fractured body and normalized so pressure in neutral position was taken to zero.

Results

Vertebral height after endplate and vertebral fracture was significantly less than intact (73.3±9.1% and 67.7±6.0% of intact respectively, p<0.001) (Figure 1A-B). Vertebral height was significantly increased after endplate fracture reduction (p<0.001), but remained significantly less than intact (89.0±9.3% of intact, p=0.014) (Figure 1C).
Intact IDP increased 0.12±0.13MPa during flexion under 400N preload. After endplate and vertebral fractures the disc with endplate fracture developed significantly less IDP at maximum flexion in the disc with endplate fracture than intact (32±19% and 34±7.8% of intact respectively, p<0.004). After endplate fracture reduction IDP during flexion was restored to 73±47% of intact (p=0.162), and was significantly improved compared to after endplate and vertebral fractures (p<0.03) (Figure 2A). The IDP during flexion was not significantly affected in the disc below the fractured vertebra, where the endplates remained intact throughout testing (Figure 2B).

Conclusion

The inability of the disc with a damaged endplate to develop normal intradiscal pressure during flexion was previously shown to increase loading of the anterior cortex of the adjacent vertebra and may increase the risk of subsequent fracture. Although reduction of the endplate fracture with StaXx FX did not fully restore the endplate to its intact condition, enough correction of the endplate deformity was achieved to improve the disc’s load sharing ability. Further studies are needed to investigate whether the reduction of endplate fracture will alleviate the risk of adjacent fractures.

References

1. Tzermiadianos, MN, Renner, SM, Phillips, FM, Hadjipavlou, AG, Zindrick, MR, Havey, RM, Voronov, M, Patwardhan, AG. Altered disc pressure profile after an osteoporotic vertebral fracture is a risk for adjacent vertebral body fracture. Eur Spine J. 2008; Sept. 16. (EPub ahead of print).

Financial Disclosures: Chirs Carson-Employee of Spine Wave, Inc. Avinash G. Patwardhan institutional research grant Department of Veterans Affairs and Spine Wave, Inc.

This abstract has not been previously presented.

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