Dental Cement Augmentation Increases Pullout Strength with Comparable Removal Torque for Lateral Mass Screws.

STUDY DESIGN

Biomechanical/basic science.

OBJECTIVE

To evaluate efficacy of dental cement augmentation of lateral mass screws in the cervical spine.

SUMMARY OF BACKGROUND DATA

Premature loosening and fixation failure is a known problem of screw fixation of the spine, especially in cases of poor bone quality. Cement augmentation of screws with PMMA has limited utility in the cervical spine due to the small size of the bone and high risk of extravasation. Augmentation with dental cement may present a viable solution for posterior cervical spinal screw fixation.

METHODS

15 cadaveric cervical vertebra were prepared. Lateral mass screw fixation (3.5×12 mm) was performed bilaterally with standard freehand technique by an attending spine surgeon. For augmented screws, dental composite was applied into the screw hole before placement of the screw. 9 vertebrae were used for pull-out testing. Screws were attached to a material testing machine and axially loaded until failure. In the remaining 6 vertebrae, peak torque required to remove the screws from bone was measured via a digital torque driver. A t-test was used to analyze the results between the augmented and non-augmented groups with significance set to P<0.05.

RESULTS

Augmented lateral mass screws exhibited significantly higher pullout strength (263.8±79.4N) compared to non-augmented screws (127.7±21.2N). (P=0.0005) There was no significant difference in the mean torque required for screw removal between the augmented (4.20±2.83 lb-in) and non-augmented groups (4.49±2.09 lb-in) (P=0.9). The dental composite was radio-opaque and observable on xray.

CONCLUSION

Augmentation with dental composite enhanced pullout strength without altering removal torque of cervical lateral mass screws in human bone. Dental cement augmentation of lateral mass screws during subaxial cervical spine fusion may be a safe and effective method of improving fixation strength without affecting ease of revision.