Failure of human cervical endplates: a cadaveric experimental model.

STUDY DESIGN

An in vitro biomechanical study using a servohydraulic testing machine on cadaveric endplates.

OBJECTIVES

To characterize the effects of bone mineral density, endplate geometry, and preparation technique on endplate failure load.

SUMMARY OF BACKGROUND DATA

The effects of endplate preparation methods on failure loads are only partly characterized in the literature. Endplate burring has been recommended to increase fusion rates. However, graft subsidence may complicate anterior reconstruction procedures.

METHODS

After radiographic screening, 21 cadaveric cervical spines underwent dual-energy x-ray absorptiometry scanning to quantify mineral content. Endplate geometry was calculated in 55 randomly selected endplates from the inferior C2 to the superior T1 levels. These vertebrae were embedded in polyester resin and randomly left intact, perforated, or burred. The cervical endplates were loaded at a rate of 0.2 mm/s on an Instron materials tester with an attached 9 mm diameter polycarbonate rod (an area of 64 mm2). A stepwise, univariate linear regression was used to compare the point of endplate failure with the vertebral level, endplate area, gender, age, bone mineral density, and preparation technique.

RESULTS

Mean bone mineral density, as measured by dual-energy x-ray absorptiometry, was 0.713 g/cm2 (+/- 0.173 g/cm2). Mean endplate area was calculated at 323 mm2. A mean compressive force of 754 N (+/- 445 N) was required before endplate failure. Trends toward increasing compressive loads were noted with decreasing endplate area and increasing bone mineral density. Increasing age (P = 0.0203), caudal vertebral level (P < 0.0001), endplate burring (P = 0.0068), and female gender (P = 0.0452) were associated with significantly lower endplate fracture loads in compression.

CONCLUSIONS

Bone quality was predictive of endplate compressive failure loads. Intact endplates failed at significantly higher loads than their perforated or burred counterparts.