Revision of the failed pedicle screw in osteoporotic lumbar spine: biomechanical comparison of kyphoplasty versus transpedicular polymethylmethacrylate augmentation.

OBJECTIVES

In this study, we aimed to compare of kyphoplasty versus transpedicular polymethylmethacrylate (PMMA) augmentation biomechanically in the revision of the failed pedicle screw in osteoporotic lumbar spine.

MATERIALS AND METHODS

Bone mineral density (BMD) of lumbar vertebrae collected from four bovines were measured. Each vertebra was decalcified with hydrochloric acid solution to obtain osteoporotic specimens. Primary polyaxial pedicle screws were inserted into the pedicles and pulled out until they failed. The pullout strength results of all specimens were recorded. Revision pedicle screws were randomly inserted into the same pedicles by either pedicle hole PMMA augmented (group 1) or kyphoplasty (Xvoid™) PMMA augmented pedicle screws (group 2). The pullout strength results of all specimens were re-recorded.

RESULTS

The mean BMD significantly decreased from 1.686 ± 227.9 g/cm(2) to 1.432 ± 157.1 g/cm(2) following decalcification (p<0.001). In group 1, the mean pullout strength of primary screws significantly decreased from 3443 ± 1086 N/m(2) to 2088 ± 924 N/m(2) following pedicle screw augmentation (p=0.006). In group 2, the mean pullout strength of primary screws decreased from 3702 ± 1063 N/m(2) to 3664 ± 1057 N/m(2) following kyphoplasty augmentation (p=0.934). Pedicle screw augmentation group achieved significantly lower pullout strength values than kyphoplasty pedicle hole augmentation group (p=0.002).

CONCLUSION

Although pedicle hole PMMA augmentation is the gold standard for the failed screws in an osteoporotic bone, kyphoplasty augmented pedicle screw seems to be more effective method increasing the pullout strength.