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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, Matthew J. McGirt, Daniel M. Sciubba, Ziya L. Gokaslan, Alfredo Quiñones-Hinojosa and Ali Bydon

At the beginning of the 20th century, the development of safer anesthesia, antiseptic techniques, and meticulous surgical dissection led to a substantial decrease in operative risk. In turn, the scope of surgery expanded to include elective procedures performed with the intention of improving the quality of life of patients. Between 1908 and 1912, Harvey Cushing performed 3 dorsal rhizotomies to improve the quality of life of 3 patients with debilitating neuralgia: a 54-year-old man with “lightning” radicular pain from tabes dorsalis, a 12-year-old boy cutaneous hyperesthesia and spasticity in his hemiplegic arm, and a 61-year-old man with postamputation neuropathic pain. Symptomatic improvement was seen postoperatively in the first 2 cases, although the third patient continued to have severe pain. Cushing also removed a prominent spinous process from each of 2 patients with debilitating headaches; both patients, however, experienced only minimal postoperative improvement. These cases, which have not been previously published, highlight Cushing's views on the role of surgery and illustrate the broader movement that occurred in surgery at the time, whereby elective procedures for quality of life became performed and accepted.

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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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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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Editorial

Pedicle versus lateral mass screws

Alexander R. Vaccaro

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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.

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Nasir A. Quraishi, Jean-Paul Wolinsky, Ali Bydon, Timothy Witham and Ziya L. Gokaslan

Myxopapillary ependymomas rarely present as a primary intrasacral lesion, and extensive sacral osteolysis is unusual. The authors report a case series of 6 patients with these complex tumors causing extensive sacral destruction, who underwent resection, lumbopelvic reconstruction, and fusion. The operative procedure, complications, and outcome are summarized after a mean follow-up of 3.55 years (range 18–80 months).

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Scott L. Parker, Risheng Xu, Matthew J. McGirt, Timothy F. Witham, Donlin M. Long and Ali Bydon

Object

The most common spinal procedure performed in the US is lumbar discectomy for disc herniation. Longterm disc degeneration and height loss occur in many patients after lumbar discectomy. The incidence of mechanical back pain following discectomy varies widely in the literature, and its associated health care costs are unknown. The authors set out to determine the incidence of and the health care costs associated with mechanical back pain attributed to segmental degeneration or instability at the level of a prior discectomy performed at their institution.

Methods

The authors retrospectively reviewed the data for 111 patients who underwent primary, single-level lumbar hemilaminotomy and discectomy for radiculopathy. All diagnostic modalities, conservative therapies, and operative treatments used for the management of postdiscectomy back pain were recorded. Institutional billing and accounting records were reviewed to determine the billed costs of all diagnostic and therapeutic measures.

Results

At a mean follow-up of 37.3 months after primary discectomy, 75 patients (68%) experienced minimal to no back pain, 26 (23%) had moderate back pain requiring conservative treatment only, and 10 (9%) suffered severe back pain that required a subsequent fusion surgery at the site of the primary discectomy. The mean cost per patient for conservative treatment alone was $4696. The mean cost per patient for operative treatment was $42,554. The estimated cost of treatment for mechanical back pain associated with postoperative same-level degeneration or instability was $493,383 per 100 cases of first-time, single-level lumbar discectomy ($4934 per primary discectomy).

Conclusions

Postoperative mechanical back pain associated with same-level degeneration is not uncommon in patients undergoing single-level lumbar discectomy and is associated with substantial health care costs.