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Jeffrey J. Laurent, K. Michael Webb, Elisa J. Beres, Kevin McGee, Jinzhong Li, Bert van Rietbergen, and Gregory A. Helm

Object. Fusion procedures in the lumbar spine have been performed in the US since 1911. Since that time, the indications and techniques for spinal fusion have evolved. Despite technical advancements, spinal fusion remains a major operation, and fusion nonunion rates of up to 35% are still reported. In this study, the authors were able to induce intertransverse process fusions in immune-competent New Zealand White rabbits by percutaneous administration of an adenoviral vector containing the bone morphogenetic protein (BMP-6) gene (Ad-BMP-6). The results represent an important step forward in finding new methods to increase the success and decrease the morbidity associated with spinal fusion.

Methods. Five New Zealand White rabbits were used. Injection of the adenoviral construct was performed at multiple levels (bilaterally) in each animal while using fluoroscopic guidance. Injection consisted of either Ad-BMP-6 or Ad—β-galactosidase (β-gal) (control). Because multiple levels were injected, each animal served as an internal control. The animals underwent postinjection computerized tomography (CT) scanning at 7 and 14 weeks. After undergoing final CT scanning, the animals were killed and the spines were harvested. The fusion sites were analyzed by gross inspection, histopathological methods, and micro—CT studies.

Conclusions. The results of this study show that an anatomically precise fusion can be accomplished by percutaneous administration of gene therapy. The next step in these studies will be extension of the technique to nonhuman primates and eventually to human clinical studies.

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Remco J. P. Doodkorte, Ricardo Belda, Alex K. Roth, Bert van Rietbergen, Jacobus J. Arts, L. M. Arno Lataster, Lodewijk W. van Rhijn, and Paul C. Willems

OBJECTIVE

Complications after adult spinal deformity surgery are common, with implant-related complications occurring in up to 27.8% of cases. Sublaminar wire fixation strength is less affected by decreasing trabecular bone density in comparison to pedicle screw (PS) fixation due to the predominant cortical bone composition of the lamina. Sublaminar fixation may thus aid in decreasing implant-related complications. The goal of this study was to compare fixation characteristics of titanium sublaminar cables (SCs), ultra–high-molecular-weight polyethylene (UHMWPE) tape, PSs, and PSs augmented with UHMWPE tape in an ex vivo flexion–bending setup.

METHODS

Thirty-six human cadaver vertebrae were stratified into 4 different fixation groups: UHMWPE sublaminar tape (ST), PS, metal SC, and PS augmented with ST (PS + ST). Individual vertebrae were embedded in resin, and a flexion–bending moment was applied that closely resembles the in vivo loading pattern at transitional levels of spinal instrumentation.

RESULTS

The failure strength of PS + ST (4522 ± 2314 N) was significantly higher compared to the SC (2931 ± 751 N) and PS (2678 ± 827 N) groups, which had p values of 0.028 and 0.015, respectively (all values expressed as the mean ± SD). Construct stiffness was significantly higher for the PS groups compared to the stand-alone sublaminar wiring groups (p = 0.020). In contrast to SC, ST did not show any case of cortical breach.

CONCLUSIONS

The higher failure strength of PS + ST compared to PS indicates that PS augmentation with ST may be an effective measure to reduce the incidence of screw pullout, even in osteoporotic vertebrae. Moreover, the lower stiffness of sublaminar fixation techniques and the absence of damage to the cortices in the ST group suggest that ST as a stand-alone fixation technique in adult spinal deformity surgery may also be clinically feasible and offer clinical benefits.