Month: October 2024

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How Accurate Is Frameless Fiducial—Free Deep Brain Stimulation?

Operative Neurosurgery 27:431–439, 2024

Frameless deep brain stimulation (DBS) offers advantages in terms of patient comfort and reduced operative time. However, the need for bony fiducial markers for localization remains a drawback due to the time-consuming and uncomfortable procedure. An alternative localization method involves the direct tracking of an intraoperative 3-dimensional scanner. This study aims to assess the accuracy of the NexFrame frameless DBS system in conjunction with the O-Arm (Medtronic Inc.), both with and without fiducial markers.

METHODS: The locations of 100 DBS leads were determined, with 50 cases using fiducial-free localization and 50 involving fiducial markers. The coordinates were compared with the expected intraoperative targets. Absolute errors in the X, Y, and Z coordinates (ΔX, ΔY, and ΔZ) were calculated, along with the vector error (Euclidean) (vector error square root Δx 2 + Δy 2 + Δz 2 ).

RESULTS: The vector error averaged 1.61 ± 0.49 mm (right) and 1.52 ± 0.60 mm (left) for the group without fiducial bone markers and 1.66 ± 0.69 (right) and 1.44 ± 0.65 mm (left) for the other cohort (P = .76 right; P = .67 left). Absolute errors in the X, Y, and Z coordinates for the fiducial-free group were 0.88 ± 0.55, 0.79 ± 0.45, and 0.79 ± 0.57 mm (right) and 0.72 ± 0.37, 0.78 ± 0.56, and 0.77 ± 0.71 mm (left). For the group with fiducial markers, these errors were 0.87 ± 0.72, 0.92 ± 0.39, and 0.86 ± 0.50 mm (right) and 0.75 ± 0.33, 0.80 ± 0.51, and 0.73 ± 0.64 mm (left) with no statistically significant difference.

CONCLUSION: Our analysis of the accuracy of NexFrame DBS, both with and without fiducial markers, using an intraoperative navigable cone-beam computed tomography, demonstrates that both techniques provide sufficient and equivalent 3-dimensional accuracy.

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Transforaminal lumbar interbody fusion subsidence

J Neurosurg Spine 41:463–472, 2024

The aims of this study were to 1) define the incidence of transforaminal lumbar interbody fusion (TLIF) interbody subsidence; 2) determine the relative importance of preoperative and intraoperative patient- and instrumentation-specific risk factors predictive of postoperative subsidence using CT-based assessment; and 3) determine the impact of TLIF subsidence on postoperative complications and fusion rates.

METHODS All adult patients who underwent one- or two-level TLIF for lumbar degenerative conditions at a multi-institutional academic center between 2017 and 2019 were retrospectively identified. Patients with traumatic injury, infection, malignancy, previous fusion at the index level, combined anterior-posterior procedures, surgery with greater than two TLIF levels, or incomplete follow-up were excluded. Interbody subsidence at the superior and inferior endplates of each TLIF level was directly measured on the endplate-facing surface of both coronal and sagittal CT scans obtained greater than 6 months postoperatively. Patients were grouped based on the maximum subsidence at each operative level classified as mild, moderate, or severe based on previously documented < 2-mm, 2- to 4-mm, and ≥ 4-mm thresholds, respectively. Univariate and regression analyses compared patient demographics, medical comorbidities, preoperative bone quality, surgical factors including interbody cage parameters, and fusion and complication rates across subsidence groups.

RESULTS A total of 67 patients with 85 unique fusion levels met the inclusion and exclusion criteria. Overall, 28% of levels exhibited moderate subsidence and 35% showed severe subsidence after TLIF with no significant difference in the superior and inferior endplate subsidence. Moderate (≥ 2-mm) and severe (≥ 4-mm) subsidence were significantly associated with decreases in cage surface area and Taillard index as well as interbody cages with polyetheretherketone (PEEK) material and sawtooth surface geometry. Severe subsidence was also significantly associated with taller preoperative disc spaces, decreased vertebral Hounsfield units (HU), the absence of bone morphogenetic protein (BMP) use, and smooth cage surfaces. Regression analysis revealed decreases in Taillard index, cage surface area, and HU, and the absence of BMP use predicted subsidence. Severe subsidence was found to be a predictor of pseudarthrosis but was not significantly associated with revision surgery.

CONCLUSIONS Patient-level risk factors for TLIF subsidence included decreased HU and increased preoperative disc height. Intraoperative risk factors for TLIF subsidence were decreased cage surface area, PEEK cage material, bullet cages, posterior cage positioning, smooth cage surfaces, and sawtooth surface designs. Severe subsidence predicted TLIF pseudarthrosis; however, the causality of this relationship remains unclear.

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Feasibility, Clinical Potential, and Limitations of Trans-Burr Hole Ultrasound for Postoperative Evaluation of Chronic Subdural Hematoma: A Prospective Pilot Study

Neurosurgery 95:924–931, 2024

Chronic subdural hematoma (CSDH) is commonly managed through burr hole surgery. Routine follow-up using computed tomography (CT) imaging is frequently used at many institutions, contributing to significant radiation exposure. This study evaluates the feasibility, safety, and reliability of trans-burr hole sonography as an alternative postoperative imaging modality, aiming to reduce radiation exposure by decreasing the frequency of CT scans.

METHODS: We conducted a prospective pilot study on 20 patients who underwent burr hole surgery for CSDH. Postoperative imaging included both CT and sonographic examinations through the burr hole. We assessed the ability to measure residual subdural fluid thickness under the burr hole sonographically compared with CT, the occurrence of complications, and the potential factors affecting sonographic image quality. The Pearson correlation coefficient was used to demonstrate relationships between CT and ultrasound and axial and coronal ultrasound.

RESULTS: Sonography through the burr hole was feasible in 73.5% of cases, providing measurements of residual fluid that closely paralleled CT findings, with an average discrepancy of 1.2 mm for axial and 1.4 mm for coronal sonographic views. A strong positive correlation was found between axial and coronal ultrasound (r = 0.955), CT and axial ultrasound (r = 0.936), and CT and coronal ultrasound (r = 0.920). The primary obstacle for sonographic imaging was the presence of air within the burr hole or the subdural space, which typically resolved over time after surgery.

CONCLUSION: Trans-burr hole sonography emerges as a promising technique for postoperative monitoring of CSDH, with the potential to safely reduce reliance on CT scans and associated radiation exposure in selected patients. Our results support further investigation into the extended use of sonography during the follow-up phase. Prospective multicenter studies are recommended to establish the method’s efficacy and to explore strategies for minimizing air presence postsurgery.

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