The appearance of dural sealants under MR imaging.

Dural sealants are an adjunct to obtain watertight closure after intradural procedures. This study aims to characterize the appearance on MR imaging of 3 commonly employed dural sealants: fibrin glue, PEGH, and BSAG. To this end, patients who underwent spinal intradural procedures that included the use of dural sealant during closure were identified retrospectively. Post-operative data on 15 patients, including complications such as pseudomeningocele formation and infection, were gathered. The appearance of dural sealants on follow-up MR imaging scans within 3 days of surgery was analyzed. Fifteen patients were identified (5 with fibrin glue, 5 with PEGH, and 5 with BSAG applied during closure) with appropriately timed post-operative MR imaging scans. All 3 substances were identifiable based on anatomic location and imaging characteristics on post-operative MR imaging in standard T1, T1 PGFS, and T2 FSE. Definite differentiation between CSF and fibrin glue or PEGH was not possible with the T1 or T1 PGFS, or with the T2 FSE. Differences in intensity between CSF and BSAG were also not significant on either T1 sequence, but they were statistically significant on the T2 FSE. All patients had an uneventful post-operative course, and no patients developed post-operative pseudomeningocele at 30 days. This study concludes that water-based dural sealants such as fibrin glue and PEGH are difficult to differentiate from CSF on standard T1, T1 PGFS and T2 FSE, while BSAG is easily recognized on the T2 FSE. Recognition of water-based sealants therefore requires communication between the neurosurgeon and the neuroradiologist to avoid post-operative misidentification.

An improved metric for quantifying the stiffnesses of intact human vertebrae.

Accurately quantifying the compressive stiffnesses of whole human vertebrae is important in the development of new treatment regimes for fractures due to osteoporosis or metastatic involvement. Two methods are commonly used to quantify compressive stiffnesses of whole vertebrae: first, the maximum slope of the force-deformation curve over a 0.2 per cent strain window; second, the slope of the best-fit line to the load-deflection curve over a specified loading range. Because the whole bone load-displacement response is non-linear, these two measurement systems yield different stiffness values for the same set of experimental data. Thus, the goal of this study was to develop and validate a standard method for deriving the whole bone stiffnesses of human vertebrae. Data from uniaxial compression tests on isolated human thoracic vertebrae (N=30 from 24 donors; T7-T10; age, 84 +/- 10, seven male, and 17 female) were analysed using the two aforementioned stiffness measurement techniques. A sensitivity analysis was also conducted whereby stiffness values were calculated for strain windows ranging from 0.05 per cent to 10 per cent. The results showed that the whole vertebra stiffness was sensitive to the calculation method. Using strain window approaches, the calculated stiffness was erratic at small strain ranges (less than 0.75 per cent), but it began to stabilize at 1 per cent strain. Comparing the historical measurement techniques versus the new standard, it was found that the 1 per cent and 0.2 per cent strain window techniques were well correlated (R2 = 0.91; p < 0.01); however, compared with the 1 per cent strain window method, the 0.2 per cent technique consistently overestimated stiffness and had five times the sensitivity to small changes in strain window magnitude. In conclusion, it is recommended that the 1 per cent strain window technique is adopted as a new standard for measuring the whole bone compressive stiffnesses of human vertebrae based on this method's superior level of accuracy and repeatability when compared with current techniques. The adoption of such a standard in the biomechanics field is important because it allows for inter-study comparisons of new orthopaedic treatments, such as vertebroplasty products.

Percutaneous axial lumbar interbody fusion (AxiaLIF) of the L5-S1 segment: initial clinical and radiographic experience.

INTRODUCTION: Anterior access to the L5-S1 disc space for interbody fusion can be technically challenging, frequently requiring the use of an approach surgeon for adequate exposure. We reviewed our experience with a novel minimally invasive technique for L5-S1 interbody fusion that exploits the presacral space and its relative dearth of critical structures. METHODS: 35 patients (20 F:15 M, mean age 54 years) were included in this analysis. Average follow-up was 17.5 months. Back pain was secondary to lumbar degenerative disc disease (DDD), degenerative lumbar scoliosis, or lytic spondylolisthesis. All patients had radiographic evidence of L5-S1 degeneration and underwent percutaneous paracoccygeal axial fluoroscopically-guided interbody fusion (axiaLIF) with cage, local bone autograft, and rhBMP. RESULTS: Mean operative time for the L5-S1 axiaLIF procedure was 42 minutes. Twenty-one patients underwent axiaLIF followed by percutaneous L5-S1 pedicle screw-rod fixation. Two patients underwent axiaLIF followed by percutaneous L4-L5 extreme lateral interbody fusion (XLIF) and posterior instrumentation. Ten patients had a stand-alone procedure. Unfavorable anatomy precluded access to the L5-S1 disc space during open lumbar interbody fusion in 2 patients who subsequently underwent axiaLIF at this level as part of a large construct. Thirty-two patients (91%) had radiographic evidence of stable L5-S1 interbody cage placement and fusion at the last follow-up. CONCLUSIONS: The percutaneous paracoccygeal approach to the L5-S1 interspace provides a minimally invasive corridor through which discectomy and interbody fusion can safely be performed. It can be used alone or in combination with minimally invasive or traditional open fusion procedures. It may provide an alternative route of access to the L5-S1 interspace in those patients who may have unfavorable anatomy for or contraindications to the traditional open anterior approach to this level.