Radiofrequency-activated PMMA-augmentation through cannulated pedicle screws: A cadaver study to determine the biomechanical benefits in the osteoporotic spine

INTRODUCTION

PMMA-augmentation of pedicle screws strengthens the bone-screw-interface reducing cut-out risk. Injection of fluid cement bears a higher risk of extravasation, with difficulty of application because of inconsistent viscosity and limited injection time.

OBJECTIVE

To test a new method of cement augmentation of pedicle screws using radiofrequency-activated PMMA, which is suspected to be easier to apply and have less extravasations.

METHODS

Twenty-seven fresh-frozen human cadaver lumbar spines were divided into 18 osteoporotic (BMD ≤ 0.8 g/cm2) and 9 non-osteoporotic (BMD > 0.8 g/cm2) vertebral bodies. Bipedicular cannulated pedicle screws were implanted into the vertebral bodies; right screws were augmented with ultra-high viscosity PMMA, whereas un-cemented left pedicle screws served as negative controls. Cement distribution was controlled with fluoroscopy and CT scans. Axial pullout forces of the screws were measured with a material testing machine, and results were analyzed statistically.

RESULTS

Fluoroscopy and CT scans showed that in all cases an adequately big cement depot with homogenous form and no signs of extravasation was injected. Pullout forces showed significant differences (p < 0.001) between the augmented and non-augmented pedicle screws for bone densities below 0.8 g/cm2 (661.9 N ± 439) and over 0.8 g/cm2 (744.9 N ± 415).

CONCLUSIONS

Pullout-forces were significantly increased in osteoporotic as well as in non-osteoporotic vertebral bodies without a significant difference between these groups using this standardized, simple procedure with increased control and less complications like extravasation.

[PMMA augmentation of pedicle screws: results of a survey in Germany]

BACKGROUND

The anchorage of pedicle screws can be challenging in the osteoporotic spine. A promising technique are cement augumented pedicle screws. The goal of this study was to gain more information regarding application of pedicle screw augmentation in Germany.

MATERIALS AND METHODS

Participants of the National German Spine Congress 2009 were invited to participate in an internet-based anonymous survey regarding application of pedicle screw augmentation. The questionnaire was related to different aspects of materials and procedures for pedicle screw augmentation. The frequency of answers was divided according to the specialty state of the surgeons: orthopaedic and trauma surgeons vs. neurosurgeons. The Mantel-Haenszel test was applied to evaluate the differences between the groups.

RESULTS AND CONCLUSION

69 (64 %) orthopaedic and trauma surgeons and 39 (36 %) neurosurgeons participated (n = 108). Nearly 80 % of the participants use cement-augmented pedicle screws in their daily practice. Almost 2/3 of the specialists apply cannulated screws or other special screws. The Expedium (Company) screws are particularly preferred. The insertion of screws is combined with kyphoplasty or vertebroplasty in 20 % of the cases. The balloon kyphoplasty was applied most commonly. There was no statistical difference between the surgeon groups regarding the different techniques. The main indications for pedicle screw augmentation were osteoporosis, intraoperative findings as well as loosening of screws, and revision. The most frequently observed complication is cement extravasation into the spinal canal (28 %). The cost issue is considered as being important but unknown to most of the participants. It can be assumed that the use of pedicle screws in Germany is well established in spine surgery, without as yet a standard technique being established.