Increased pedicle screw pullout strength with vertebroplasty augmentation in osteoporotic spines

2002 ◽  
Vol 96 (3) ◽  
pp. 309-312 ◽  
Author(s):  
John S. Sarzier ◽  
Avery J. Evans ◽  
David W. Cahill
Keyword(s):  
Pedicle Screw ◽  
Pedicle Screws ◽  
Pullout Strength ◽  
Mineral Density ◽  
Content Type ◽  
Pullout Force ◽  
Grade Ii ◽  
The Mean ◽  
Grade Iii ◽  
Fine Print

Object. The authors conducted a biomechanical study to evaluate pedicle screw pullout strength in osteoporotic cadaveric spines. Nonaugmented hemivertebrae were compared with pressurized polymethylmethacrylate (PMMA)—augmented hemivertebrae. Methods. Six formalin-fixed cadaveric thoracolumbar spines at least two standard deviations below the mean bone mineral density (BMD) for age were obtained. Radiographic and BMD studies were correlated to grades I, II, and III osteoporosis according to the Jekei scale. Each of the 21 vertebrae underwent fluoroscopic placement of 6-mm transpedicular screws with each hemivertebra serving as the control for the contralateral PMMA-augmented hemivertebra. Pedicle screws were then evaluated for biomechanical axial pullout resistance. Augmented hemivertebrae axial pullout forces were increased (p = 0.0005). The mean increase in pullout force was 181% for Grade I, 206% for Grade II, and 213% for Grade III osteoporotic spines. Augmented Grade I osteoporotic spines demonstrated axial pullout forces near those levels reported in the literature for nonosteoporotic specimens. Augmented Grade II osteoporotic specimens demonstrated increases to levels found in nonaugmented vertebrae with low-normal BMD. Augmented Grade III osteoporotic specimens had increases to levels equal to those found in nonaugmented Grade I vertebrae. Conclusions. Augmentation of osteoporotic vertebrae in PMMA-assisted vertebroplasty can significantly increase pedicle screw pullout forces to levels exceeding the strength of cortical bone. The maximum attainable force appears to be twice the pullout force of the nonaugmented pedicle screw for each osteoporotic grade.

Three-dimensional fluoroscopy-guided percutaneous thoracolumbar pedicle screw placement

2003 ◽  
Vol 99 (3) ◽  
pp. 324-329 ◽  
Author(s):  
Langston T. Holly ◽  
Kevin T. Foley
Keyword(s):  
Pedicle Screw ◽  
Three Dimensional ◽  
Pedicle Screws ◽  
Screw Placement ◽  
Content Type ◽  
Image Guided ◽  
Spinal Navigation ◽  
Mean Diameter ◽  
The Mean ◽  
Fine Print

✓ The authors sought to evaluate the feasibility and accuracy of three-dimensional (3D) fluoroscopic guidance for percutaneous placement of thoracic and lumbar pedicle screws in three cadaveric specimens. After attaching a percutaneous dynamic reference array to the surgical anatomy, an isocentric C-arm fluoroscope was used to obtain images of the region of interest. Light-emitting diodes attached to the C-arm unit were tracked using an electrooptical camera. The image data set was transferred to the image-guided workstation, which performed an automated registration. Using the workstation display, pedicle screw trajectories were planned. An image-guided drill guide was passed through a stab incision, and this was followed by sequential image-guided pedicle drilling, tapping, and screw placement. Pedicle screws of various diameters (range 4–6.5 mm) were placed in all pedicles greater than 4 mm in diameter. Postoperatively, thin-cut computerized tomography scans were obtained to determine the accuracy of screw placement. Eighty-nine (94.7%) of 94 percutaneous screws were placed completely within the cortical pedicle margins, including all 30 lumbar screws (100%) and 59 (92%) of 64 thoracic screws. The mean diameter of all thoracic pedicles was 6 mm (range 2.9–11 mm); the mean diameter of the five pedicles in which wall violations occurred was 4.6 mm (range 4.1–6.3 mm). Two of the violations were less than 2 mm beyond the cortex; the others were between 2 and 3 mm. Coupled with an image guidance system, 3D fluoroscopy allows highly accurate spinal navigation. Results of this study suggest that this technology will facilitate the application of minimally invasive techniques to the field of spine surgery.

Thoracic pedicle screws: postoperative computerized tomography scanning assessment

2004 ◽  
Vol 100 (4) ◽  
pp. 325-331 ◽  
Author(s):  
Robert F. Heary ◽  
Christopher M. Bono ◽  
Margaret Black
Keyword(s):  
Computerized Tomography ◽  
Pedicle Screws ◽  
Ct Scanning ◽  
Screw Placement ◽  
Grading System ◽  
Content Type ◽  
Thoracic Pedicle Screws ◽  
Grade Ii ◽  
Grade Iii ◽  
Fine Print

Object. The authors evaluated the accuracy of placement of thoracic pedicle screws by performing postoperative computerized tomography (CT) scanning. A grading system is presented by which screw placement is classified in relation to neurological, bone, and intrathoracic landmarks. Methods. One hundred eighty-five thoracic pedicle screws were implanted in 27 patients with the assistance of computer image guidance or fluoroscopy. Postoperative CT scanning was conducted to determine a grade for each screw: Grade I, entirely contained within pedicle; Grade II, violates lateral pedicle but screw tip entirely contained within the vertebral body (VB); Grade III, tip penetrates anterior or lateral VB; Grade IV, breaches medial or inferior pedicle; and Grade V, violates pedicle or VB and endangers spinal cord, nerve root, or great vessels and requires immediate revision. Based on anatomical morphometry, the spine was subdivided into upper (T1–2), middle (T3–6), and lower (T7–12) regions. Statistical analyses were performed to compare regions. The mean follow-up period was 37.6 months. The following postoperative CT scanning—documented grades were determined: Grade I, 160 screws (86.5%); Grade II, 15 (8.1%); Grade III, six (3.2%); Grade IV, three (1.6%); and Grade V, one (0.5%). Among cases involving screw misplacements, Grade II placement was most common, and this occurred most frequently in the middle thoracic region. Conclusions. The authors' grading system has advantages over those previously described; however, further study to determine its reliability, reproducibility, and predictive value of clinical sequelae is warranted. Postoperative CT scanning should be considered the gold standard for evaluating thoracic pedicle screw placement.

Using lamina screws as a salvage technique at C-7: computed tomography and biomechanical analysis using cadaveric vertebrae

2009 ◽  
Vol 11 (1) ◽  
pp. 28-33 ◽  
Author(s):  
Mario J. Cardoso ◽  
Anton E. Dmitriev ◽  
Melvin D. Helgeson ◽  
Frederick Stephens ◽  
Victoria Campbell ◽  
...  
Keyword(s):  
Bone Mineral Density ◽  
Cervical Spine ◽  
Pedicle Screw ◽  
Bone Mineral ◽  
Pedicle Screws ◽  
Pullout Strength ◽  
Mineral Density ◽  
The Mean ◽  
The Right ◽  
Pedicle Width

Object Transpedicular instrumentation at C-7 has been well accepted, but salvage techniques are limited. Lamina screws have been shown to be a biomechanically sound salvage technique in the proximal thoracic spine, but have not been evaluated in the lower cervical spine. The following study evaluates the anatomical feasibility of lamina screws at C-7 as well as their bone-screw interface strength as a salvage technique. Methods Nine fresh-frozen C-7 cadaveric specimens were scanned for bone mineral density using dual energy x-ray absorptiometry. Prior to testing, all specimens were imaged using CT to obtain 1-mm axial sections. Caliper measurements of both pedicle width and laminar thickness were obtained. On the right side, pedicle screws were first inserted and then pulled out. Salvage intralaminar screws were inserted into the left lamina from the right spinous process/lamina junction and then pulled out. All screws were placed by experienced cervical spine surgeons under direct fluoroscopic visualization. Pedicle and lamina screws were 4.35- and 3.5-mm in diameter, respectively. Screws sizes were chosen based on direct and radiographic measurements of the respective anatomical regions. Insertional torque (IT) was measured in pounds per inch. Tensile loading to failure was performed in-line with the screw axis at a rate of 0.25 mm/sec using a MiniBionix II system with data recorded in Newtons. Results Using lamina screws as a salvage technique generated mean pullout forces (778.9 ± 161.4 N) similar to that of the index pedicle screws (805.3 ± 261.7 N; p = 0.796). However, mean lamina screw peak IT (5.2 ± 2.0 lbs/in) was significantly lower than mean index pedicle screw peak IT (9.1 ± 3.6 lbs/in; p = 0.012). Bone mineral density was strongly correlated with pedicle screw pullout strength (r = 0.95) but less with lamina screw pullout strength (r = 0.04). The mean lamina width measured using calipers (5.7 ± 1.0 mm) was significantly different from the CTmeasured mean lamina width (5.1 ± 0.8 mm; p = 0.003). Similarly, the mean pedicle width recorded with calipers (6.6 ± 1.1 mm) was significantly different from the CT-measured mean pedicle width (6.2 ± 1.3 mm; p = 0.014). The mean laminar width measured on CT at the thinnest point ranged from 3.8 to 6.8 mm, allowing a 3.5-mm screw to be placed without difficulty. Conclusions These results suggest that using lamina screws as a salvage technique at C-7 provides similar fixation strength as the index pedicle screw. The C-7 lamina appears to have an ideal anatomical width for the insertion of 3.5-mm screws commonly used for cervical fusions. Therefore, if the transpedicular screw fails, using intralaminar screws appear to be a biomechanically sound salvage technique.

Insertion torque and pullout force of rescue screws for anterior cervical plate fixation in a fatigued initial pilot hole

2004 ◽  
Vol 1 (2) ◽  
pp. 198-201 ◽  
Author(s):  
Tobias Pitzen ◽  
Frederick Franta ◽  
Dragos Barbier ◽  
Wolf-Ingo Steudel
Keyword(s):  
Strong Correlation ◽  
Peak Torque ◽  
Insertion Torque ◽  
Mineral Density ◽  
Content Type ◽  
Pullout Force ◽  
Pilot Hole ◽  
The Mean ◽  
Rescue Screw ◽  
Fine Print

Object. The purpose of this study was to investigate whether thicker-core-diameter screws increase fixation strength in the cervical spine. Methods. Bone mineral density (BMD) was determined for each vertebral body (VB) obtained in six human C4–7 segments. Based on their BMD, the specimens were assigned to one of two groups in which torque and pullout force were tested. Two initial pilot holes were drilled into the VBs and tests were first performed using a standard screw. The test was repeated using a thicker rescue screw inserted into the same initial pilot hole. The mean value of peak torque and pullout force resulting from the single left/right measurements was used for statistical analysis. A t-test was performed to determine the effect of screw design on peak torque and pullout force. Moment correlation coefficients were calculated to determine the effect of BMD on peak torque and pullout force. Mean insertional peak torque for the standard screw was 82.1 N/cm and that for the rescue screw was 47.6 Ncm (p < 0.001). There was a strong correlation between insertional peak torque and BMD for both standard screws (r = 0.71, p = 0.02) and rescue screws (r = 0.59, p = 0.07). The mean pullout force for standard screws was 464.7 N, whereas it was 164.5 N for rescue screws (p < 0.001). There was a strong correlation between pullout force and BMD for both standard (r = 0.75, p = 0.0081) and rescue screws (r = 0.7, p = 0.025). Conclusions. Uncemented rescue screws that have been inserted into a fatigued hole in the cervical VB do not strengthen the screw—bone interface compared with the strength initially conferred by a standard screw.

Frameless stereotaxy for anterior spinal procedures

2001 ◽  
Vol 95 (2) ◽  
pp. 196-201 ◽  
Author(s):  
Langston T. Holly ◽  
Orin Bloch ◽  
Chinyere Obasi ◽  
J. Patrick Johnson
Keyword(s):  
Pedicle Screw ◽  
Pedicle Screws ◽  
Optical Tracking ◽  
Frameless Stereotaxy ◽  
Anatomical Landmarks ◽  
Content Type ◽  
Registration Error ◽  
The Mean ◽  
K Wires ◽  
Fine Print

Object. Intraoperative image guidance provides real-time three-dimensional visualization and has been successfully applied in many posterior spinal procedures. The feasibility of applying these techniques to anterior spinal surgery has not been studied systematically because the anterior spine, in contrast to the posterior spine, lacks distinct anatomical landmarks for registration. The authors sought to evaluate the practicality of performing stereotaxy in the anterior spine in a cadaveric model. Methods. Unilateral C4—L4 pedicle screws were placed posteriorly in three cadaveric specimens to serve as unknown markers within each vertebral body. The specimens then underwent computerized tomography (CT) scanning, and the CT data were transferred to an optical tracking system. The anterior surface of the spine was registered for use with the stereotactic system by using a paired point—matching technique. Attached to a surgical drill, K-wires were placed under stereotactic guidance in a tip-to-tip orientation with the posterior pedicle screws. A second postoperative CT scan was obtained, and accuracy was determined by measuring the distance between the tips of the K-wire and pedicle screw. The K-wires were placed tip to tip with pedicle screw markers in 57 vertebral levels. The mean registration error was 1.47 ± 0.04 mm, and when combined with the universal instrument registration error of 0.7 mm yielded an overall registration error of 2.17 ± 0.04 mm. The mean tip-to-tip distance for all K-wires placed was 2.46 ± 0.23 mm. The difference between the mean tip-to-tip distance and overall registration error was not statistically significant (p > 0.05), indicating that the K-wires were placed within the expected range of error. Conclusions. The results of this study confirmed the feasibility of performing anterior stereotactic procedures throughout the spine. The accuracy of the findings in this study indicates that anterior stereotaxy should be applicable in clinical practice.

Anatomical data on the craniocervical junction and their correlation with degenerative changes in 30 cadaveric specimens

2005 ◽  
Vol 3 (5) ◽  
pp. 379-385 ◽  
Author(s):  
Stefan A. König ◽  
Axel Goldammer ◽  
Hans-Ekkehart Vitzthum
Keyword(s):  
Articular Cartilage ◽  
Articular Surface ◽  
Craniocervical Junction ◽  
Degenerative Changes ◽  
Content Type ◽  
Articular Surfaces ◽  
Anatomical Data ◽  
Grade Ii ◽  
Grade Iii ◽  
Fine Print

>Object. The goal of this project was to measure vertebral dimensions at the craniocervical junction and to investigate degenerative changes in this region and their correlations with the anatomical data. These studies will assist in an understanding of biomechanical conditions in this region, which are clinically relevant in cases of cervicogenic headaches and vertigo. Methods. The authors examined 30 cadaveric specimens obtained from patients ranging in age from 24 to 88 years at death. Measurements of angles of the vertebrae were conducted using an imprint method. Microsections of osseous endplates and articular cartilage were graded according to their degrees of degeneration by using the Petersson classification (0, no sign of degeneration; I, superficial degeneration with several fragmentations; II, deeper degeneration with cartilaginous disintegration and penetrating ulceration; or III, complete cartilaginous degeneration with the appearance of subchondral bone in > 50% of the articular surface). The authors found Grade I changes in 100% of the occiput specimens. In the superior articular cartilage of C-1 no changes (Grade 0) were found in two specimens, whereas 6% of the specimens exhibited Grade II changes and 89% exhibited Grade I changes. In the inferior articular cartilage of C-1, 57% of the specimens displayed Grade I changes, 14% Grade II, and 20% Grade III changes. In the superior articular cartilage of C-2, 62.5% of the specimens displayed Grade I changes and 25% Grade II changes. At the occiput—C1 level the authors found a higher frequency of degeneration at the upper left articular surface of the atlas (Quadrants 1 and 3), and at the C1–2 level they found a higher frequency of degeneration at the upper left and upper right articular surfaces of the axis (Quadrants 2 and 3, respectively). Using the McNemar test, the authors investigated the frequency of affection of single quadrants in a left—right side comparison (lateral reversal). Significant differences were identified for Quadrant 2 of the upper left articular surface of C-2 and Quadrant 3 of the upper right articular surface of C-2. These results correlate with the analysis of single articular surfaces of the axis, but contradict the results for the atlas, in which no significant difference in the left—right side comparison was found. Conclusions. Severe degeneration in the atlantooccipital joints appears to be a rare condition, with no Grade II or III degeneration found in the occipital condyles and 6% Grade I, 89% Grade II, but no Grade III changes in the superior articular cartilage of the atlas. Degeneration of the inferior articular cartilage of C-1 and the superior articular cartilage of C-2 indicates that the atlantoaxial joint faces more intense mechanical exposure, which is increased at the upper joint surfaces.

Minimally invasive transforaminal lumbar interbody fusion with ipsilateral pedicle screw and contralateral facet screw fixation

2005 ◽  
Vol 3 (3) ◽  
pp. 218-223 ◽  
Author(s):  
Jee-Soo Jang ◽  
Sang-Ho Lee
Keyword(s):  
Minimally Invasive ◽  
Pedicle Screw ◽  
Interbody Fusion ◽  
Transforaminal Lumbar Interbody Fusion ◽  
Lumbar Interbody Fusion ◽  
Content Type ◽  
The Mean ◽  
Level Fusion ◽  
Fine Print

Object. The purpose of this study was to introduce a minimally invasive transforaminal lumbar interbody fusion (TLIF) technique that involves ipsilateral pedicle screw (PS) and contralateral facet screw (FS) fixation. Methods. Eight men and 15 women (mean age 59.5 years, range 48–68) underwent the aforementioned TLIF procedure for degenerative spondylolisthesis and uni- or bilateral radiculopathy. Twenty-two patients underwent one-level fusion and one patient two-level fusion (L4—S1). In all cases the various procedures were undertaken via one small incision. There were no intraoperative complications. The mean estimated blood loss (EBL) was 310 ml, and the mean operative time was 150 minutes in cases of one-level fusion. The follow-up period ranged from 13 to 28 months (mean 19 months). The mean Numeric Rating Scale score reflected improvement-reductions from 7.5 (back pain) and 7.4 (leg pain) to 2.3 and 0.7, respectively (p < 0.0001). The mean Oswestry Disability Index (ODI) scores also reflected improved status (ODI of 33.1 before the surgery to 7.6 after the surgery; p < 0.0001). Examination indicated that 22 of 24 fusion sites exhibited osseous union. At the last follow-up examination, satisfactory outcomes were observed in 21 out of 23 patients. Conclusions. The TLIF with ipsilateral PS and contralateral FS fixation has the advantages over the conventional TLIF of reduced EBL and diminished soft-tissue injury.

Surgery for cerebral arteriovenous malformation: risks related to lenticulostriate arterial supply

1997 ◽  
Vol 86 (5) ◽  
pp. 801-805 ◽  
Author(s):  
Michael K. Morgan ◽  
Katharine J. Drummond ◽  
Verity Grinnell ◽  
William Sorby
Keyword(s):  
Cerebral Arteriovenous Malformation ◽  
Arterial Supply ◽  
Content Type ◽  
Increased Risk ◽  
Complications Of Surgery ◽  
Grade Ii ◽  
Martin Grade ◽  
Grade Iii ◽  
Fine Print

✓ The aim of this study was to compare complications of surgery in arteriovenous malformations (AVMs) supplied by the middle cerebral artery (MCA) with and without a lenticulostriate arterial contribution. Ninety-two consecutive surgical resections of AVMs with an angiographically demonstrated MCA supply were performed between January 1989 and July 1996. Ten of these cases had a significant lenticulostriate arterial contribution. The cases were graded according to the Spetzler—Martin classification. There were no deaths and 4.3% of cases developed new major neurological deficit by the 3-month follow-up examination. All cases had angiographically confirmed obliteration of the AVM. There were no complications in 16 patients with Spetzler—Martin Grade I AVMs, one case of complications in 40 patients with Grade II AVMs, eight cases of complications in 26 patients with Grade III AVMs, and seven cases of complications in 10 patients with Grade IV and V AVMs. The supply of blood from lenticulostriate branches was associated with complications in eight of the 10 cases. The effect of the presence of a lenticulostriate arterial supply was most apparent in cases of Grade III AVMs: complications were experienced in three of 20 patients whose AVMs were not supplied by the arteries and in five of six patients whose AVMs were fed by the lenticulostriate arteries. This difference is significant (p < 0.0001). The conclusions drawn from this study are that for Grade III AVMs, the presence of a lenticulostriate arterial supply can be considered a factor predictive of an increased risk of surgical complications.

Percutaneous pedicle screw fixation of the lumbar spine: preliminary clinical results

2002 ◽  
Vol 97 (1) ◽  
pp. 7-12 ◽  
Author(s):  
Kevin T. Foley ◽  
Sanjay K. Gupta
Keyword(s):  
Lumbar Spine ◽  
Pedicle Screw ◽  
Screw Fixation ◽  
Pedicle Screws ◽  
Pedicle Screw Fixation ◽  
Posterior Fixation ◽  
Content Type ◽  
Insertion Device ◽  
Lumbar Pedicle ◽  
Fine Print

Object. Standard techniques for pedicle screw fixation of the lumbar spine involve open exposures and extensive muscle dissection. The purpose of this study was to report the initial clinical experience with a novel device for percutaneous posterior fixation of the lumbar spine. Methods. An existing multiaxial lumbar pedicle screw system was modified to allow screws to be placed percutaneously by using an extension sleeve that permits remote manipulation of the polyaxial screw heads and remote engagement of the screw-locking mechanism. A unique rod-insertion device was developed that linked to the screw extension sleeves, allowing for a precut and -contoured rod to be placed through a small stab wound. Because the insertion device relies on the geometrical constraint of the rod pathway through the screw heads, minimal manipulation is required to place the rods in a standard submuscular position, there is essentially no muscle dissection, and the need for direct visual feedback is avoided. Twelve patients (six men and six women) who ranged in age from 23 to 68 years underwent pedicle screw fixation in which the rod-insertion device was used. Spondylolisthesis was present in 10 patients and osseous nonunion of a prior interbody fusion was present in two. All patients underwent successful percutaneous fixation. Ten patients underwent single-level fusions (six at L5—S1, three at L4–5, and one at L2–3), and two underwent two-level fusions (one from L3–5 and the other from L4—S1). The follow-up period ranged from 10 to 19 months (mean 13.8 months). Conclusions. Although percutaneous lumbar pedicle screw placement has been described previously, longitudinal connector (rod or plate) insertion has been more problematic. The device used in this study allows for straightforward placement of lumbar pedicle screws and rods through percutaneous stab wounds. Paraspinous tissue trauma is minimized without compromising the quality of spinal fixation. Preliminary experience involving the use of this device has been promising.

The Ki-67 labeling index as a prognostic factor in Grade II oligoastrocytomas

2005 ◽  
Vol 102 (6) ◽  
pp. 1033-1039 ◽  
Author(s):  
Mark E. Shaffrey ◽  
Elana Farace ◽  
David Schiff ◽  
James M. Larner ◽  
Melike Mut ◽  
...  
Keyword(s):  
Labeling Index ◽  
World Health ◽  
Ki 67 ◽  
Content Type ◽  
Prognostic Utility ◽  
Grade Ii ◽  
Health Organization ◽  
The University ◽  
Grade Iii ◽  
Fine Print

Object. This study was conducted to determine whether proliferative tumor activity, as assessed using the Ki-67 immunohistochemical labeling index (LI), has prognostic utility for patients with Grade II oligoastrocytomas. Methods. The study period spans the years 1988 to 2000. In a retrospective analysis, the authors selected cases with biopsy-proven diagnoses of Grade II oligoastrocytomas on initial presentation. The authors added new patients to this group and followed all patients prospectively at the University of Virginia Neuro-Oncology Center. Twenty-three adult patients were followed for at least 1 year (median 40.3 months). Eleven patients with Grade II tumors and initial Ki-67 LIs less than 10% had a significantly longer median time to tumor progression (TTP, 51.8 months compared with 9.9 months) and a longer median survival (93.1 months compared with 16.1 months) than 12 patients with initial Ki-67 LIs of 10% or greater. Twelve patients with Grade III oligoastrocytomas had a mean TTP that was similar to the TTP of patients with Grade II tumors and high Ki-67 LIs (mean 4 months compared with 9.9 months) and duration of survival (13.3 months compared with 16.1 months). Conclusions. Patients with a Grade II oligoastrocytoma and a Ki-67 LI of 10% or greater have a much shorter TTP and potentially a poorer disease prognosis than expected—more similar to patients with a Grade III oligoastrocytoma. These results indicate that in the future a measure of proliferative activity should be taken into consideration along with the World Health Organization grading criteria for oligoastrocytomas.

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