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Michelle J. Clarke, James Guzzo, Jean-Paul Wolinsky, Ziya Gokaslan and James H. Black III

Iatrogenic aortic injuries are a potentially devastating complication of spine surgery. In instrumented cases, injuries may occur in the perioperative period due to iatrogenic vessel injury, or they may occur years later as prominent implants erode or penetrate major vessels. The authors present a case of a 71-year-old man in whom a thoracic pedicle screw was found perforating the thoracic aorta during routine follow-up 6 months after surgery. Due to the risk of future complications, the screw was removed while simultaneously delivering an endovascular aortic stent to gain vascular control. Surgical considerations and potential technical limitations are discussed.

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Wesley Hsu, Ahmed Mohyeldin, Sagar R. Shah, Colette M. ap Rhys, Lakesha F. Johnson, Neda I. Sedora-Roman, Thomas A. Kosztowski, Ola A. Awad, Edward F. McCarthy, David M. Loeb, Jean-Paul Wolinsky, Ziya L. Gokaslan and Alfredo Quiñones-Hinojosa

Object

Chordoma is a malignant bone neoplasm hypothesized to arise from notochordal remnants along the length of the neuraxis. Recent genomic investigation of chordomas has identified T (Brachyury) gene duplication as a major susceptibility mutation in familial chordomas. Brachyury plays a vital role during embryonic development of the notochord and has recently been shown to regulate epithelial-to-mesenchymal transition in epithelial-derived cancers. However, current understanding of the role of this transcription factor in chordoma is limited due to the lack of availability of a fully characterized chordoma cell line expressing Brachyury. Thus, the objective of this study was to establish the first fully characterized primary chordoma cell line expressing gain of the T gene locus that readily recapitulates the original parental tumor phenotype in vitro and in vivo.

Methods

Using an intraoperatively obtained tumor sample from a 61-year-old woman with primary sacral chordoma, a chordoma cell line (JHC7, or Johns Hopkins Chordoma Line 7) was established. Molecular characterization of the primary tumor and cell line was conducted using standard immunostaining and Western blotting. Chromosomal aberrations and genomic amplification of the T gene in this cell line were determined. Using this cell line, a xenograft model was established and the histopathological analysis of the tumor was performed. Silencing of Brachyury and changes in gene expression were assessed.

Results

The authors report, for the first time, the successful establishment of a chordoma cell line (JHC7) from a patient with pathologically confirmed sacral chordoma. This cell line readily forms tumors in immunodeficient mice that recapitulate the parental tumor phenotype with conserved histological features consistent with the parental tumor. Furthermore, it is demonstrated for the first time that silencing of Brachyury using short hairpin RNA renders the morphology of chordoma cells to a more differentiated-like state and leads to complete growth arrest and senescence with an inability to be passaged serially in vitro.

Conclusions

This report represents the first xenograft model of a sacral chordoma line described in the literature and the first cell line established with stable Brachyury expression. The authors propose that Brachyury is an attractive therapeutic target in chordoma and that JHC7 will serve as a clinically relevant model for the study of this disease.

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Scott L. Parker, Anubhav G. Amin, S. Harrison Farber, Matthew J. McGirt, Daniel M. Sciubba, Jean-Paul Wolinsky, Ali Bydon, Ziya L. Gokaslan and Timothy F. Witham

Object

Pedicle screws provide efficient stabilization along all 3 columns of the spine, but they can be technically demanding to place, with malposition rates ranging from 5% to 10%. Intraoperative electromyographic (EMG) monitoring has the capacity to objectively identify a screw breaching the medial pedicle cortex that is in proximity to a nerve root. The purpose of this study is to describe and evaluate the authors' 7-year institutional experience with intraoperative EMG monitoring during placement of lumbar pedicle screws and to determine the clinical utility of intraoperative EMG monitoring.

Methods

The authors retrospectively studied 2450 consecutive lumbar pedicle screws placed in 418 patients from June 2002 through June 2009. All screws were inserted using a free-hand technique and anatomical landmarks, stimulated at 10.0 mA, and evaluated with CT scanning within 48 hours postoperatively. Medial pedicle screw breach was defined as having greater than 25% of the screw diameter extend outside of the pedicle, as confirmed on CT scanning or intraoperatively by a positive EMG response indicating a medial breach. The sensitivity and specificity of intraoperative EMG monitoring in detecting the presence of a medial screw breach was evaluated based on the following definitions: 1) true positive (a positive response to EMG stimulation confirmed as a breach intraoperatively or on postoperative CT scans); 2) false positive (positive response to EMG stimulation confirmed as a correctly positioned screw on postoperative CT scans); 3) true negative (no response to EMG stimulation confirmed as a correctly positioned screw on postoperative CT scans); or 4) false negative (no response to EMG stimulation but confirmed as a breach on postoperative CT scans).

Results

One hundred fifteen pedicle screws (4.7%) showed positive stimulation during intraoperative EMG monitoring. At stimulation thresholds less than 5.0, 5.0–8.0, and > 8.0 mA, the specificity of a positive response was 99.9%, 97.9%, and 95.9%, respectively. The sensitivity of a positive response at these thresholds was only 43.4%, 69.6%, and 69.6%, respectively. At a threshold less than 5.0 mA, 91% of screws with a positive EMG response were confirmed as true medial breaches. However, at thresholds of 5.0–8.0 mA or greater than 8.0 mA, a positive EMG response was associated with 89% and 100% false positives (no breaches), respectively.

Conclusions

When using intraoperative EMG monitoring, a positive response at screw stimulation thresholds less than 5.0 mA was highly specific for a medial pedicle screw breach but was poorly sensitive. A positive response to stimulation thresholds greater 5.0 mA was associated with a very high rate of false positives. The authors' experience suggests that pedicle screws showing positive stimulation below 5.0 mA warrants intraoperative investigation for malpositioning while responses at higher thresholds are less reliable at accurately representing a medial breach.

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Hormuzdiyar H. Dasenbrock, Courtney Pendleton, Aaron A. Cohen-Gadol, Jean-Paul Wolinsky, Ziya L. Gokaslan, Alfredo Quinones-Hinojosa and Ali Bydon

Although Harvey Cushing was a neurosurgical pioneer, his work on the spine remains largely unknown. In fact, other than his own publications, Cushing's patients with pathological lesions of the spine who were treated while he was at the Johns Hopkins Hospital, including those with spinal cord tumors, have never been previously described. The authors report on 7 patients with spinal cord tumors that Cushing treated surgically between 1898 and 1911: 2 extradural, 3 intradural extramedullary, and 2 intramedullary tumors. The authors also describe 10 patients in whom Cushing performed an “exploratory laminectomy” expecting to find a tumor, but in whom no oncological pathological entity was found. Cushing's spine surgeries were limited by challenges in making the correct diagnosis, lack of surgical precedent, and difficulty in achieving adequate intraoperative hemostasis. Other than briefly mentioning 2 of the 4 adult patients in his landmark monograph on meningiomas, these cases—both those involving tumors and those in which he performed exploratory laminectomies—have never been published before. Moreover, these cases illustrate the evolution that Harvey Cushing underwent as a spine surgeon.

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C. Rory Goodwin, Pablo F. Recinos, Ibrahim Omeis, Eric N. Momin, Timothy F. Witham, Ali Bydon, Ziya L. Gokaslan and Jean-Paul Wolinsky

Sacral neoplasm resection is managed via partial or total sacrectomy that is performed via the Kraske approach. The combination of the patients positioning and the relatively long operative time required for this procedure increase the risk of pressure ulcers. Facial pressure ulcers can cause tissue necrosis and/or ulceration in a highly visible area, leading to a cosmetically disfiguring lesion. Here, the authors report the use of a Mayfield clamp in the positioning of patients undergoing sacral tumor resection to prevent facial pressure ulceration. After the patient is placed prone in the Kraske or Jackknife position, the hips and knees are flexed with arms to the side. Then while in the prone position, the patient is physically placed in pins, and the Mayfield clamp is fixated at the center of the metal arch via the Mayfield sitting adapter to the Andrews frame, suspending the head (and face) over the table. The authors find that this technique prevents the development of facial pressure ulcers, and it has the potential to be used in patients positioned in the Kraske position for other surgical procedures.

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Oren N. Gottfried, Ibrahim Omeis, Vivek A. Mehta, Can Solakoglu, Ziya L. Gokaslan and Jean-Paul Wolinsky

Object

Pelvic incidence (PI) directly regulates lumbar lordosis and is a key determinant of sagittal spinal balance in normal and diseased states. Pelvic incidence is defined as the angle between the line perpendicular to the S-1 endplate at its midpoint and the line connecting this point to a line bisecting the center of the femoral heads. It reflects an anatomical value that increases with growth during childhood but remains constant in adulthood. It is not altered by changes in patient position or after traditional lumbosacral spinal surgery. There are only 2 reports of PI being altered in adults, both in cases of sacral fractures resulting in lumbopelvic dissociation and sacroiliac (SI) joint instability. En bloc sacral amputation and sacrectomy are surgical techniques used for resection of certain bony malignancies of the sacrum. High, mid, and low sacral amputations result in preservation of some or the entire SI joint. Total sacrectomy results in complete disruption of the SI joint. The purpose of this study was to determine if PI is altered as a result of total or subtotal sacral resection.

Methods

The authors reviewed a series of 42 consecutive patients treated at The Johns Hopkins Hospital between 2004 and 2009 for sacral tumors with en bloc resection. The authors evaluated immediate pre- and postoperative images for modified pelvic incidence (mPI) using the L-5 inferior endplate, as the patients undergoing a total sacrectomy are missing the S-1 endplate postoperatively. The authors compared the results of total versus subtotal sacrectomies.

Results

Twenty-two patients had appropriate images to measure pre- and postoperative mPI; 17 patients had high, mid, or low sacral amputations with sparing of some or the entire SI joint, and 5 patients underwent a total sacrectomy, with complete SI disarticulation. The mean change in mPI was statistically different (p < 0.001) for patients undergoing subtotal versus those undergoing total sacrectomy (1.6° ± 0.9° vs 13.6° ± 4.9° [± SD]). There was no difference between patients who underwent a high sacral amputation (partial SI resection, mean 1.6°) and mid or low sacral amputation (SI completely intact, mean 1.6°).

Conclusions

The PI is altered during total sacrectomy due to complete disarticulation of the SI joint and discontinuity of the spine and pelvis, but it is not changed if any of the joint is preserved. Changes in PI influence spinopelvic balance and may have postoperative clinical importance. Thus, the authors encourage attention to spinopelvic alignment during lumbopelvic reconstruction and fixation after tumor resection. Long-term studies are needed to evaluate the impact of the change in PI on sagittal balance, pain, and ambulation after total sacrectomy.

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Risheng Xu, Matthew J. McGirt, Edward G. Sutter, Daniel M. Sciubba, Jean-Paul Wolinsky, Timothy F. Witham, Ziya L. Gokaslan and Ali Bydon

Object

The aim of this study was to conduct the first in vitro biomechanical comparison of immediate and postcyclical rigidities of C-7 lateral mass versus C-7 pedicle screws in posterior C4–7 constructs.

Methods

Ten human cadaveric spines were treated with C4–6 lateral mass screw and C-7 lateral mass (5 specimens) versus pedicle (5 specimens) screw fixation. Spines were potted in polymethylmethacrylate bone cement and placed on a materials testing machine. Rotation about the axis of bending was measured using passive retroreflective markers and infrared motion capture cameras. The motion of C-4 relative to C-7 in flexion-extension and lateral bending was assessed uninstrumented, immediately after instrumentation, and following 40,000 cycles of 4 Nm of flexion-extension and lateral bending moments at 1 Hz. The effect of instrumentation and cyclical loading on rotational motion across C4–7 was analyzed for significance.

Results

Preinstrumented spines for the 2 cohorts were comparable in bone mineral density and range of motion in both flexion-extension (p = 0.33) and lateral bending (p = 0.16). Lateral mass and pedicle screw constructs significantly reduced motion during flexion-extension (11.3°–0.26° for lateral mass screws, p = 0.002; 10.51°–0.30° for pedicle screws, p = 0.008) and lateral bending (7.38°–0.27° for lateral mass screws, p = 0.003; 11.65°–0.49° for pedicle screws, p = 0.03). After cyclical loading in both cohorts, rotational motion over C4–7 was increased during flexion-extension (0.26°–0.68° for lateral mass screws; 0.30°–1.31° for pedicle screws) and lateral bending (0.27°–0.39° and 0.49°–0.80°, respectively), although the increase was not statistically significant (p > 0.05). There was no statistical difference in postcyclical flexion-extension (p = 0.20) and lateral bending (0.10) between lateral mass and pedicle screws.

Conclusions

Both C-7 lateral mass and C-7 pedicle screws allow equally rigid fixation of subaxial lateral mass constructs ending at C-7. Immediately and within a simulated 6-week postfixation period, C-7 lateral mass screws may be as effective as C-7 pedicle screws in biomechanically stabilizing long subaxial lateral mass constructs.

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Oral Presentations

2010 AANS Annual Meeting Philadelphia, Pennsylvania May 1–5, 2010

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Oren N. Gottfried, Scott L. Parker, Ibrahim Omeis, Ali Bydon, Ziya L. Gokaslan and Jean-Paul Wolinsky

Cervical spondylolysis is an uncommon disorder involving a cleft at the pars interarticularis. It is most often found at the C-6 level, and clinical presentations have included incidental radiographic findings, neck pain, and rarely neurological compromise. Although subaxial cervical spondylolysis has been described in 150 patients, defects at the C-2 pedicles are rare.

The authors present 2 new cases of C-2 spondylolysis in athletically active young persons who did not demonstrate instability or neurological deficits, were able to remain active, and are being managed conservatively with serial examinations and imaging. They also discuss the results of 22 previously reported cases of C-2 spondylolysis. Based on the literature and their own experience, the authors conclude that most patients with C-2 spondylolysis remain neurologically intact, maintain stability despite the bony defect, and can be managed conservatively. Surgery is reserved for patients who demonstrate severe instability or spinal cord compromise due to stenosis.