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Vernard S. Fennell, Sheri Palejwala, Jesse Skoch, David A. Stidd and Ali A. Baaj

Object

Experience with freehand thoracic pedicle screw placement is well described in the literature. Published techniques rely on various starting points and trajectories for each level or segment of the thoracic spine. Furthermore, few studies provide specific guidance on sagittal and axial trajectories. The goal of this study was to propose a uniform entry point and sagittal trajectory for all thoracic levels during freehand pedicle screw placement and determine the accuracy of this technique.

Methods

The authors retrospectively reviewed postoperative CT scans of 33 consecutive patients who underwent open, freehand thoracic pedicle-screw fixation using a uniform entry point and sagittal trajectory for all levels. The same entry point for each level was defined as a point 3 mm caudal to the junction of the transverse process and the lateral margin of the superior articulating process, and the sagittal trajectory was always orthogonal to the dorsal curvature of the spine at that level. The medial angulation (axial trajectory) was approximately 30° at T-1 and T-2, and 20° from T-3 to T-12. Breach was defined as greater than 25% of the screw diameter residing outside of the pedicle or vertebral body.

Results

A total of 219 thoracic pedicle screws were placed with a 96% accuracy rate. There were no medial breaches and 9 minor lateral breaches (4.1%). None of the screws had to be repositioned postoperatively, and there were no neurovascular complications associated with the breaches.

Conclusions

It is feasible to place freehand thoracic pedicle screws using a uniform entry point and sagittal trajectory for all levels. The entry point does not have to be adjusted for each level as reported in existing studies, although this technique was not tested in severe scoliotic spines. While other techniques are effective and widely used, this particular method provides more specific parameters and may be easier to learn, teach, and adopt.

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David A. Stidd, Joshua Wewel, Ali J. Ghods, Stephan Munich, Anthony Serici, Kiffon M. Keigher, Heike Theessen, Roham Moftakhar and Demetrius K. Lopes

Object

Cerebrovascular lesions can have complicated abnormal anatomy that is not completely characterized by CT or MR angiography. Although 3D rotational angiography provides superior spatial and temporal resolution, catheter angiograms are not easily registered to the patient, limiting the use of these images as a source for neuronavigation. However, 3D digital subtraction angiography (DSA) contains not only vascular anatomy but also facial surface anatomy data. The authors report a novel technique to register 3D DSA images by using only the surface anatomy contained within the data set without having to fuse the DSA image set to other imaging modalities or use fiducial markers.

Methods

A cadaver model was first created to assess the accuracy of neuronavigation based on 3D DSA images registered by facial surface anatomy. A 3D DSA scan was obtained of a formalin-fixed cadaver head, with acquisitions of mask and contrast runs. The right common carotid artery was injected prior to the contrast run with a 45% contrast solution diluted with water-soluble red liquid latex. One week later, the head was registered to a neuronavigation system loaded with the 3D DSA images acquired earlier using facial surface anatomy. A right pterional craniotomy was performed and 10 different vascular landmarks were identified and measured for accuracy using the neuronavigation system. Neuronavigation based only on 3D DSA was then used to guide an open clipping procedure for a patient who presented with a ruptured distal lenticulostriate aneurysm.

Results

The accuracy of the measurements for the cadaver model was 0.71 ± 0.25 mm (mean ± SE), which is superior to the 1.8–5 mm reported for neuronavigation. The 3D DSA–based navigation-assisted surgery for the distal lenticulostriate aneurysm aided in localization, resulting in a small craniotomy and minimal brain dissection.

Conclusions

This is the first example of frameless neuronavigation based on 3D catheter angiography registered by only the surface anatomy data contained within the 3D DSA image set. This is an easily applied technique that is beneficial for accurately locating vascular pathological entities and reducing the dissection burden of vascular lesions.