Konstantinos Kafchitsas

Dual-Energy CT–based Phantomless in Vivo Three-dimensional Bone Mineral Density Assessment of the Lumbar Spine

PURPOSE To evaluate the feasibility of phantomless in vivo dual-energy computed tomography (CT)-based three-dimensional (3D) bone mineral density (BMD) assessment in comparison with dual x-ray absorptiometry (DXA). MATERIALS AND METHODS This retrospective study was approved by the institutional review board, and the requirement to obtain informed consent was waived. Data from clinically indicated dual-energy CT and DXA examinations within 2 months, comprising the lumbar spine of 40 patients, were included. By using automated dedicated postprocessing dual-energy CT software, the trabecular bone of lumbar vertebrae L1-L4 were analyzed and segmented. A mixed-effects model was used to assess the correlations between BMD values derived from dual-energy CT and DXA. RESULTS One hundred sixty lumbar vertebrae were analyzed in 40 patients (mean age, 57.1 years; range, 24-85 years), 21 male (mean age, 54.3 years; range, 24-85 years) and 19 female (mean age, 58.5 years; range, 31-80 years). Mean BMD of L1-L4 determined with DXA was 0.995 g/cm(2), and 18 patients (45%) showed an osteoporotic BMD (T score less than -2.5) of at least two vertebrae. Mean dual-energy CT-based BMD of L1-L4 was 0.254 g/cm(3). Bland-Altman analysis with mixed effects demonstrated a lack of correlation between dual-energy CT-based and DXA-based BMD values, with a mean difference of 0.7441 and 95% limits of agreement of 0.7441 ± 0.4080. CONCLUSION Dedicated postprocessing of dual-energy CT data allows for phantomless in vivo BMD assessment of the trabecular bone of lumbar vertebrae and enables freely rotatable color-coded 3D visualization of intravertebral BMD distribution.

Insertion of the artificial disc replacement: a cadaver study comparing the conventional surgical technique and the use of a navigation system.

Study Design. Comparison of total disc replacement (TDR) with and without computer-assisted surgical navigation. Objective. To test and evaluate the accuracy of computer-assisted navigation for the lumbar spine by comparing the traditional C-arm-aided insertion of an arthroplasty device to the navigation-aided insertion of the implant. Summary of Background Data. Previous studies have shown that poor placement of the CHARITÉ disc can be correlated to worse clinical results. Because of parallax effect, exclusive use of fluoroscopy could make placement of the artificial disc less accurate. False positioning may also lead to spondylolisthesis, disc degeneration of the adjacent segment, subsidence of the disc, and failure of the implant. Methods. Ten human cadaver spine specimens were used at 3 lumbar segments (L3–L4, L4–L5, and L5–S1). Before implantation, all artificial discs were planned for “ideal” placement on a digital computed tomography image. Fifteen lumbar intervertebral disc prostheses (Depuy, Raynham, MA) were placed using Vector Vision image guidance (BrainLAB AG, Munich, Germany), by an inexperienced TDR-surgeon. Fifteen lumbar intervertebral disc prostheses were placed with exclusive use of fluoroscopy by an experienced TDR-surgeon. After insertion, DICOM computed tomography scans were analyzed using computer software to assess placement accuracy of each disc prosthesis. Results. The navigated placement of the disc was significantly more accurate. Only 3 navigated disc prostheses were suboptimal and none was poorly placed. Conclusion. Surgical computer-assisted navigation may be a useful tool in the hands of a spine surgeon to achieve more accurate placement of the disc prosthesis. Because of the parallax effect, computer-assisted navigation offers more placement accuracy than stan- dard fluoroscopy. Because the accurate placement of total disc prosthesis has been correlated with better clinical outcome, further study regarding the navigation of the TDR is essential.

CAD of osteoporosis in vertebrae using dual-energy CT

The assessment of bone mineral density (BMD) in vertebrae is critical for the diagnosis of osteoporosis. Recent developments in dual-source CT allow for the simultaneous acquisition of two image data sets with different X-ray tube energies — dual-energy CT (DECT). We present a comprehensive approach for assessing the density of the trabecular bone in vertebrae of the spine based on DECT image data. For this, we apply and combine methods from different areas: the deformation of a template mesh for delineating the structures of interest, a biophysical model of the trabecular bone for the computation of BMD values, and different visualization approaches for the display of the results. In addition, we investigate the correlation between the computed BMD values with concurrently measured pull-out forces for pedicle screws. We show that there is a linear correlation between both measures and thus, DECT provides correct BMD values for the trabecular bone. We conclude that our approach enables the radiologist to diagnose osteoporosis based on DECT image data which has the potential to replace the current gold standard dual-energy X-ray absorp-tiometry.

Cement distribution in vertebroplasty pedicle screws with different designs

ZusammenfassungDie Auswirkungen der verminderten Knochendichte machen sich im Falle einer Spondylodese besonders bemerkbar. Zur besseren Fixierung der Schrauben im Knochen wurde die Zementaugmentation zum Gegenstand vieler Studien, die die biomechanische Überlegenheit und den erhöhten Auszugswiderstand der zementaugmentierten Schrauben nachgewiesen haben. Aufgrund inadäquater, aber auch gefährlicher Zementverteilungen im Wirbelkörper, bestand die Notwendigkeit zur Entwicklung alternativer Applikationsformen im Vergleich zu der konventionellen Technik. Pedikelschrauben mit seitlichen Öffnungen und einem zentralen Bohrloch wurden eigens für diese Anwendung entwickelt. Diese neuen Schrauben erlauben eine gute Zementaugmentation und vergrößern den Schraubendurchmesser, aber auch die Oberflächenkohäsion zwischen den drei Komponenten (Schraube-Zement-Knochen). Die Zementverteilung kann durch die Auswahl der seitlichen Öffnungen (Größe und Lage) entsprechend beeinflusst werden. Schrauben mit konisch zulaufendem Kerndurchmesser und distal gelegenen weiten Öffnungen führen zur Entstehung einer uniformen Zementwolke.AbstractThe effects of deteriorated bone density become particularly apparent in cases where spinal instrumentation is needed. Cement augmentation of pedicle screws for better bone purchase became the subject of many studies, which proved the biomechanical superiority and the increased pullout strength of cement augmented screws. Inadequate, and sometimes dangerous, cement distribution made the need for development of special implants inevitable. Pedicle screws with side openings and a central drill hole allow cement augmentation through the implant and increase not only the screw diameter but also the interfacial strength between the three components (screw-cement-bone). Accordingly cement distribution can be affected by the selection of the side openings (size and position). Screws with conical core and distally situated side openings facilitate the development of uniform cement dough.The effects of deteriorated bone density become particularly apparent in cases where spinal instrumentation is needed. Cement augmentation of pedicle screws for better bone purchase became the subject of many studies, which proved the biomechanical superiority and the increased pullout strength of cement augmented screws. Inadequate, and sometimes dangerous, cement distribution made the need for development of special implants inevitable. Pedicle screws with side openings and a central drill hole allow cement augmentation through the implant and increase not only the screw diameter but also the interfacial strength between the three components (screw-cement-bone). Accordingly cement distribution can be affected by the selection of the side openings (size and position). Screws with conical core and distally situated side openings facilitate the development of uniform cement dough.

Kümmell's Disease: Clarifying the Mechanisms and Patients' Inclusion Criteria.

The three major causes of vertebral body collapse include infection, malignant neoplasia, and trauma and it may be difficult to distinguish between them, particularly in the presence of severe osteoporosis. In 1891, however, Dr Hermann Kümmell, further added another possibility of vertebral body crush; the delayed posttraumatic collapse. As originally described, this rare clinical entity includes patients, who after a trivial trauma and an asymptomatic clinical course they develop a progressive vertebral body collapse and a painful kyphosis. Although more than a century has passed from its initial description, only few cases have been reported in the literature, whereas the main pathologic eliciting event is still under investigation. As a consequence, great controversy exists regarding the discrete features of the clinical course, its radiographic appearance and the histopathological findings. To explain the time lag between the initial trauma and the occurrence of the vertebral collapse, the hypothesis of ischemic necrosis was advanced. Equation of Kümmell’s disease with vertebral osteonecrosis, however, has wrongly led many authors to report cases of Kümmell’s disease, even in the absence of history of spinal trauma. On the other hand, high coincidence of vertebral osteonecrosis and the pathognomonic radiographic finding of intravertebral vacuum cleft, has further added to the confusion. In this review we present an overview of the literature on Kümmell’s disease, focusing on the different proposed eliciting mechanisms. We also highlight controversial subjects on clinical course, diagnosis and treatment of this entity, in an attempt to further clarify patients’ inclusion criteria.

Navigation of artificial disc replacement: evaluation in a cadaver study

Introduction: Previous studies have shown that total disc replacement (TDR) resulted in significantly better restoration of disc-space height and significantly less subsidence than anterior interbody fusion with BAK cages. Clinical outcomes and flexion/extension range of motion correlated with the accuracy of surgical placement of the CHARITÉ™ artificial disc. False positioning of the artificial disc leads to spondylarthrosis and disc degeneration of the adjacent segment, and exclusive use of a C-arm could cause such false positioning (due to the parallax effect). The objective of this study was to test and evaluate the accuracy of navigated artificial disc replacement as performed by a spine surgeon without a prior learning curve. In each case, the placement position achieved by the surgeon was compared with the preoperatively planned position for that specimen. Materials and Methods: Lumbar intervertebral disc prostheses (CHARITÉ™, DePuy Spine) were placed using an image guidance technique (BrainLAB VectorVision system) in ten human cadaveric spine specimens. A total of 15 such disc replacements were performed using navigation. Post-instrumentation accuracy was assessed by a computer on the basis of CT scans. Results: The placement of the disc was assessed as ideal (<3 mm from the planned position), suboptimal (3–5 mm from the planned position) or poor (>5 mm from the planned position). Only three disc prostheses were placed suboptimally, and none was poorly placed. Placement in the coronal plane was significantly better than in the other planes. Discussion: Navigation is a useful instrument in the hands of the spine surgeon, enabling an ideal placement of the disc prosthesis. Navigation offers greater accuracy and less inter-procedural variation than standard fluoroscopy (due to the parallax effect). As accurate (ideal or suboptimal) placement correlates with good clinical outcome, further clinical studies on the navigation of TDR are essential. In this present study, the disc replacement was performed by a surgeon without experience in total disc replacement, indicating that prior completion of a learning curve was not essential.

Direct visualization of regions with lowered bone mineral density in dual-energy CT images of vertebrae

Dual-energy CT allows for a better material differentiation than conventional CT. For the purpose of osteoporosis diagnosis, a detection of regions with lowered bone mineral density (BMD) is of high clinical interest. Based on an existing biophysical model of the trabecular bone in vertebrae a new method for directly highlighting those low density regions in the image data has been developed. For this, we combine image data acquired at 80 kV and 140 kV with information about the BMD range in different vertebrae and derive a method for computing a color enhanced image which clearly indicates low density regions. An evaluation of our method which compares it with a quantitative method for BMD assessment shows a very good correspondence between both methods. The strength of our method lies in its simplicity and speed.

[Sintering prophylaxis of a vertebral body replacement: anterior cement augmentation of vertebral end plates].

Due to the increasing number of elderly patients with osteoporosis, the incidence of more complex operations demanding a vertebral body replacement is increasing in this population. Cement augmentation of pedicle screws helps to prevent screw pullout. Similarly it is possible to augment the end plates in anterior spine surgery in order to prevent cage subsidence. The technique is simple, quick and safe, as needles can be placed under visual control. In a series of 20 patients neither surgery-related complications nor aseptic loosening were found.

The Prevalence of Vitamin D deficiency in Elective Spine Surgery: A Study in Three Orthopaedic Centers

Introduction Decreased bone mineral density due to osteoporosis and osteomalacia pose a significant risk for instrumentation failure and adjacent fractures in elective spinal surgery. The purpose of this study was to evaluate serum levels of 25hydroxyvitamin D (25OH D) in patients presenting for elective spine surgery and to determine whether patients with degenerative spinal disease and spinal instability need a perioperative treatment with Vitamin D substitution. Material and Methods Serum 25-OH vitamin D levels were evaluated postoperatively (<72 hours) in patients undergoing elective spinal fusion in three orthopaedic centers, in Germany and in Greece. Patients with diagnosis of spinal instability as well as with degenerative spine disease were treated with spinal fusion. Results 369 consecutive patients (mean, 68.3 ± 15.4 years) were admitted for elective spine surgery. Mean 25-OH vitamin D level was 19,44 ± 11,52 ng/mL (range, 4–71,8 ng/ mL). 228 (62.0%) patients were diagnosed with vitamin D deficiency and 87 (38.9%) were diagnosed with vitamin D insufficiency (20–30 ng/mL). There was no statistically significant difference between men and women. There was also no significant difference between the patients of the three centers. Conclusion Vitamin D deficiency is very common in patients with spinal instability as well as with degenerative spine disease. Therefore an algorithm of treatment as well as a preoperative control of the Vitamin D values is required before spine fusion surgery is performed, to enhance bone mineral density and thus better pedicle screw fixation.

First Clinical Experience with BMD Assessment in Vertebrae Using Dual-Energy CT

Dual-energy CT (DECT) can be performed with state-of-the-art dual-source CT (DSCT) scanners and allows for assessing bone mineral density (BMD). In this work, we present first clinical experience with in vivo BMD assessment of vertebrae based on DECT data which has been acquired with a state-of-the-art DSCT scanner in the clinical routine. In contrast to previous work where we did in vitro tests of our method, we apply it her for the first time to in vivo data and prove the feasibility of our technique in a clinical setting. For \(25\) patients, DXA as well as DECT data have been acquired and BMD of vertebrae was assessed. Advantages of DECT are its 3D capabilities allowing to compute the spatial BMD distribution and to focus the examination on the trabecular bone. Correlation between both imaging techniques regarding the averaged BMD values per vertebra are only moderate.