Abstract
Background
While the biomechanical properties of trans-pedicular screws have proven to be superior in the lumbar spine, little is known concerning pullout strength of trans-pedicle screws in comparison to different distal terminal constructs like sublaminar hooks alone, trans pedicular screws with sublaminar hooks and clow hooks alone in the thoracolumbar spine surgery. In vitro biomechanical pullout testing was performed to evaluate the axial pullout strength of four different distal terminal constructs in thoracolumbar spine surgery.
Methods
32 fresh-frozen lamb spines were used. The lamb spines were divided into four groups, each group is composed of eight lamb spine cadavers with a different distal fixation pattern was used to terminate the construct at L1. (Group 1) trans-pedicular screws alone, (Group 2) sublaminar hooks alone, (Group 3) trans-pedicular screws augmented with a sublaminar hooks via a domino connector and (Group 4) clow hooks alone.
Results
The average pullout strength of group 1 was 927N, group2 was 626N, group 3 was 988N and group 4 was 972N. Group 3 and 4 showed the most significant pullout forces when compared to group 1 and group 2. However Group 3 and group 4 didn't show any significant statistical difference when compared to each others.
Conclusion
Our study thus suggests that the strongest construct that may reduce the pullout phenomina in the distal fixation constructs are the trans-pedicular screw with laminar hooks. It is strongly advised to be used in osteoporotic bones and in conditions where pullout strength is required to be enhanced. But farther prospective clinical studies are needed to clearly demonstrate the beneficial effect of a trans-pedicular screw augmented with a laminar hooks in reducing the risk of distal instrumentation pullout.
Level of Evidence
Level 5
Disclosure
The authors declare that no conflict of interests were associated with the present study.
