Article
A novel technique for cement augmentation of pedicle screws reduces cement leakage rates. A prospective, controlled, clinical trial in osteoporotic bone
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Authors
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T.R. Blattert
- Wirbelsäulenchirurgie und Traumatologie, Orthopädische Fachklinik Schwarzach
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H.J. Riesner
- Orthopädie und Unfallchirurgie, Bundeswehrkrankenhaus Ulm
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C. Josten
- Unfall-, Wiederherstellungs- und Plastische Chirurgie, Wirbelsäulenzentrum, Universitätsklinikum Leipzig
| Published: | June 4, 2012 |
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Outline
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Objective: Cement augmentation techniques have been developed to increase purchase of pedicle screws in osteoporotic bone. Different augmentation techniques are being used based on screw types and surgical methods. For solid screws, vertebral bodies can be prefilled with cement in a vertebroplasty technique before screws are inserted. In a modification, pretapped voids can be filled with cement before screw insertion. As an alternative, fenestrated screws have been developed for in situ injection of cement through the screw itself. Extravertebral, epidural, and endovascular leakage of cement, however, remains a problem in either technique. To reduce leakage rates, a novel augmentation technique was developed.
Methods: Inclusion criteria: fracture type A3 or higher; t-score ≤ 2.5. Exclusion criteria: non-traumatic fractures. Fenestrated screws measuring 6.5 mm in diameter were used (CD Horizon® Legacy FNSTM, Medtronic). In the trial group (TG), screw beds were pretapped. The tap used has a regular diameter of 5.5 mm and can be expanded to 8.0 mm after pedicle passage. For the vertebral body, this results in an overtapping of 1.5 mm for the screw bed in comparison to the screw itself. After screw insertion, cement augmentation with 1.5cc of PMMA (KyphX® HV-RTM, Medtronic) was performed. Leakage rates were evaluated with post op CT scans. In the control group (CG), the screw bed was probed, but not tapped. FU time was 24 months.
Results: In TG, 20 patients with 96 augmented pedicle screws were included. Leakage rate was 8/96 (8.3%). CG consisted of 52 patients with 208 screws. Leakage rate was 41/208 (19.7%). This difference is statistically significant (p < 0.005). At 2 years FU, 17/18 patients in TG showed no signs of implant loosening. 1/18 patient suffered from secondary loss of correction with screw cut out. For CG, there were 2/47 cases with implant loosening (p > 0.05).
Conclusions: Use of the novel technique described here results in a significant reduction of cement leakage rates if compared to the control group. We found no difference, however, for the rate of secondary implant loosening. Obviously, the cement leaving the screw is being distributed reliably within the void created around the screw shaft, rather than being directed into unwanted regions of less resistance. On the other hand, implant purchase is not being compromised by this technique.
