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Michael Y. Wang and Barth A. Green

Object

Cervical stenotic myelopathy can be treated via anterior or posterior approaches. In anterior cervical decompression and fusion (ACDF), because the risks and likelihood of pseudarthrosis increase with the number of treated segments, attempts are typically made to limit the number of treated levels. Thus, postoperative recurrence of myelopathy following ACDF may occur because stenotic levels were not treated or because adjacent segments have degenerated. Revision decompressive surgery via an anterior approach is one solution; however, if the stenosis involves multiple levels a posterior decompressive laminoplasty can be performed as an alternative.

Methods

Twenty-four cases treated over an 8-year period were identified and data were retrospectively reviewed. In 15 cases posterior decompressive surgery was necessary because of progressive spinal degeneration and stenosis (five cases following initial treatment for radiculopathy, seven after initial treatment for spondylotic myelopathy, and three due to spreading of an ossified posterior longitudinal ligament). In nine cases revision surgery was undertaken because the initial decompression was inadequate.

The mean follow-up period after the second surgery was 16 months. Improvements in myelopathy were seen in 83% of patients (mean improvement of 1.25 points on the Nurick Scale). Preoperative severe gait disorders were associated with poor recovery. Complications included two cases of transient C-5 nerve root palsy and two cases of new persistent axial neck pain.

Conclusions

Laminoplasty is a straightforward and effective treatment for failed ACDF due to inadequate decompression or progressive degeneration of the spinal column, avoiding reentry through scar tissue. In terms of myeolpathic pain, the recovery rate is comparable with that related to revision ACDF.

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Blair Calancie, K. John Klose, Sylvia Baier and Barth A. Green

✓ Dysfunction of spinal motor conduction during surgical procedures may not be reflected by changes in somatosensory evoked potential waveforms. A method of monitoring that allows direct and continuous assessment of motor function within the central nervous system during surgery would be useful. This paper describes one such method utilizing noninvasive electric cortical stimulation to evoke muscle activity (the motor evoked potential, or MEP) during surgery. The effect of isoflurane (superimposed on a baseline of N2O/narcotic anesthesia) on MEP's in response to cortical stimulation is specifically examined.

Eight patients undergoing elective neurosurgical operations were included in the study. All patients received a background of general anesthesia and partial nondepolarizing neuromuscular blockade. The motor cortex was stimulated electrically via self-adhesive scalp electrodes. Electromyographic responses from multiple muscles were measured with subdermal electroencephalograph-type needle electrodes. Motor responses to stimulation were continually recorded on magnetic tape for off-line analysis. Once closing of the surgical incision was begun, a series of four to five stimuli of constant magnitude were applied to obtain “baseline” MEP responses. Patients were then ventilated with isoflurane for up to 8 minutes, during which time stimuli were continued every 15 to 20 seconds. Comparison was made of MEP responses for trials before, 1 minute after, and 5 minutes after the addition of isoflurane.

All patients demonstrated reproducible motor responses to cortical stimulation during surgery. Addition of isoflurane ((isoflurane)exp, ≤ 0.5%) to pre-existing anesthesia caused marked attenuation of MEP amplitudes in all patients within 5 minutes of its application, without affecting neuromuscular transmission as judged by direct peripheral nerve stimulation. It is concluded that: 1) monitoring motor system integrity and function with electric transcranial cortical stimulation during surgery is feasible when utilizing an N2O/narcotic anesthetic protocol; and 2) the quality of data obtained will likely suffer with the addition of isoflurane.

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Thomas T. Lee, Glen R. Manzano and Barth A. Green

✓ Twenty-five patients underwent an expansive cervical laminoplasty for nontraumatic cervical spondylosis with myelopathy during the period from June 1990 to November 1994, and all had a minimum of 18 months of follow-up review. The open-door laminoplasty procedure presently reported consisted of the same approach evaluated by Hirabayashi in 1977, except that the authors of this report used three rib allografts to anchor the “open door,” rather than spinous process sutures or autologous bone grafts. Posterior foraminotomies and decompression were performed in patients with clinical radiculopathy and radiographic evidence of foraminal stenosis.

Preoperatively, gait disturbance was present in all patients. All 25 patients (100%) had long-tract signs on presentation. Nondermatomal upper-extremity symptoms (numbness, tingling, weakness, and pain) were quite common in this group of patients. Bowel, bladder, and/or sexual dysfunction was found in 13 (52%) of 25 patients. Preoperative radiographic studies showed a mean midline anteroposterior diameter spinal canal/vertebral body (SC/VB) ratio of 0.623 and a mean compression ratio (sagittal/lateral diameter ratio × 100%) of 37%.

This procedure was quite successful in relieving preoperative symptoms and few complications occurred. Gait disturbance was improved in 21 (84%) of 25 patients and hand numbness and tingling were improved in 13 (87%) of 15 patients. Bowel or bladder function improved in 10 (77%) of 13 patients. Radiculopathy, when present, was alleviated in all four patients after the decompressive procedure. The postoperative SC/VB ratio, as measured by plain lateral radiographs and/or computerized tomography scans, was improved to 0.871, a 38% improvement. In a comparison with the preoperative SC/VB ratio using the two-tailed t-test, alpha was less than 0.001. The compression ratio improved to 63% postoperatively, which yielded an alpha of less than 0.005 according to the two-tailed t-test. Only one postoperative complication, an anterior scalene syndrome, was encountered.

Various predictors of surgical outcome based on gait improvement were evaluated. Age greater than 60 years at the time of presentation, duration of symptoms more than 18 months prior to surgery, preoperative bowel or bladder dysfunction, and lower-extremity dysfunction were found to be associated with poorer surgical outcome. Even when these conditions were present, gait improvement was noted in at least 70% of the patients.

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Thomas T. Lee, Glen R. Manzano and Barth A. Green

Twenty-five patients underwent an expansive cervical laminoplasty for nontraumatic cervical spondylosis with myelopathy during the period from June 1990 to November 1994, and all had a minimum of 18 months of follow-up review. The open-door laminoplasty procedure presently reported consisted of the same approach evaluated by Hirabayashi in 1977, except that the authors of this report used three rib allografts to anchor the “open door,” rather than spinous process sutures or autologous bone grafts. Posterior foraminotomies and decompression were performed in patients with clinical radiculopathy and radiographic evidence of foraminal stenosis.

Preoperatively, gait disturbance was present in all patients. All 25 patients (100%) had long-tract signs on presentation. Nondermatomal upper-extremity symptoms (numbness, tingling, weakness, and pain) were quite common in this group of patients. Bowel, bladder, and/or sexual dysfunction was found in 13 (52%) of 25 patients. Preoperative radiographic studies showed a mean midline anteroposterior diameter spinal canal/vertebral body (SC/VB) ratio of 0.623 and a mean compression ratio (sagittal/lateral diameter ratio X 100%) of 37%.

This procedure was quite successful in relieving preoperative symptoms and few complications occurred. Gait disturbance was improved in 21 (84%) of 25 patients and hand numbness and tingling were improved in 13 (87%) of 15 patients. Bowel or bladder function improved in 10 (77%) of 13 patients. Radiculopathy, when present, was alleviated in all four patients after the decompressive procedure. The postoperative SC/VB ratio, as measured by plain lateral radiographs and/or computerized tomography scans, was improved to 0.871, a 38% improvement. In a comparison with the preoperative SC/VB ratio using the two-tailed t-test, alpha was less than 0.001. The compression ratio improved to 63% postoperatively, which yielded an alpha less than 0.005 according to the two-tailed t-test. Only one postoperative complication, an anterior scalene syndrome, was encountered.

Various predictors of surgical outcome based on gait improvement were evaluated. Age greater than 60 years at the time of presentation, duration of symptoms more than 18 months prior to surgery, preoperative bowel or bladder dysfunction, and lower-extremity dysfunction were found to be associated with poorer surgical outcome. Even when these conditions were present, gait improvement was noted in at least 70% of the patients.

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Photochemically induced graded spinal cord infarction

Behavioral, electrophysiological, and morphological correlates

Ricardo Prado, W. Dalton Dietrich, Brant D. Watson, Myron D. Ginsberg and Barth A. Green

✓ Neurological and morphological outcome was evaluated in a rat model of graded spinal cord infarction initiated by a photochemical reaction. In this model, light-dye interactions induce primary microvascular stasis, resulting in consistent patterns of tissue necrosis. Four groups of rats underwent photoinduction times ranging from 30 seconds to 10 minutes. Neurological and electrophysiological functions were assessed starting 1 week after irradiation and continuing for 8 weeks. A functional neurological score was obtained by combining results from sensory and motor tasks, and electrophysiological function was evaluated from the somatosensory evoked potential recordings. In rats irradiated for short periods (30 seconds and 1 minute) mild behavioral deficits were documented. In contrast, electrical conduction was suppressed acutely in both groups; this recovered by 8 weeks to baseline or near baseline in the 30-second group but not in the 1-minute group. In rats irradiated for longer periods (5 and 10 minutes), severe behavioral and conduction abnormalities were detected at both the subacute and chronic testing periods. Although no significant difference in behavior was documented between the 5- and 10-minute groups acutely, the rats with 5-minute photoinduction time demonstrated a significant improvement in behavior over time whereas the group with 10-minute photoinduction time showed no improvement. A severe conduction block was present in both animal groups during the course of the study. Histopathological examination combined with morphometric measurements of the lesion area in cross section revealed four different degrees of spinal cord necrosis which correlated significantly with photoinduction times and neurological scores at 8 weeks. Reproducible degrees of ischemic damage to spinal cord parenchyma following primary microvascular occlusion result in a predictable sequence of behavioral and functional abnormalities, which in some cases recover with time.

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Nariyuki Hayashi, Barth A. Green, Mayra Gonzalez-Carvajal, Joseph Mora and Richard P. Veraa

✓ A reliable and reproducible microelectrode technique provided consistent simultaneous measurements of local spinal cord blood flow (local SCBF), tissue oxygen tension (TO2), and tissue oxygen consumption (TO2C) in the rat. Local SCBF was measured by the hydrogen clearance technique, local TO2 was measured polarographically, and local TO2C was calculated from the declining slope of local TO2 following temporary arrest of local SCBF. Mean local TO2 values varied only slightly between gray and white matter, while local TO2C and SCBF maintained a 3 to 1 ratio between gray and white matter areas. Measurements were also made of these parameters in specific white matter tracts and laminae of Rexed. Local white matter SCBF was relatively homogeneous throughout the ventral, lateral, and dorsal funiculi. Gray matter blood flow was more variable with topography. The highest local SCBF was recorded in areas rich in internuncial neurons. The somatic motor regions had values slightly higher than recorded in sensory regions.

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Nariyuki Hayashi, Barth A. Green, Mayra Gonzalez-Carvajal, Joseph Mora and Richard P. Veraa

✓ Using a reliable and reproducible microelectrode technique, consistent simultaneous measurements of local spinal cord blood flow (SCBF), tissue oxygen tension, and tissue oxygen consumption were made at cervical, thoracic, and lumbar levels in the rat spinal cord. These observations showed that the metabolic state is maintained constant along the cord, despite significant variations in vasculature. The physiological and anatomical aspects of these findings are discussed.

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Postoperative fibrosis after surgical treatment of the porcine spinal cord: a comparison of dural substitutes

Invited submission from the Joint Section Meeting on Disorders of the Spine and Peripheral Nerves, March 2004

Iftikharul Haq, Yenisel Cruz-Almeida, Edir B. Siqueira, Michael Norenberg, Barth A. Green and Allan D. Levi

Object. Postoperative adhesion- and fibrosis-induced spinal cord tethering is not uncommon and may be associated with delayed clinical sequelae. Multiple dural substitutes have been used in surgery without a full appreciation of the grafts' adverse effects. The authors conducted a comparative animal experimental study to evaluate the degree of chronic inflammatory reactions, adhesions, and fibrosis caused by the use of four dural substitutes—Surgicel, Durasis, DuraGen, and Preclude.

Methods. Twenty-six pigs weighing 30 to 40 kg underwent a two-level lumbar laminectomy (a midline durotomy, implantation of a 2-cm dural substitute in the subarachnoid space, and watertight dural closure). After 8 weeks the animals were killed, and two independent neuropathologists blinded to the dural substitute group evaluated several sites along the implants, providing descriptions and quantitative scoring of fibrosis, chronic inflammatory reactions, foreign-body reactions, and spinal cord changes. Kruskal—Wallis one-way analysis of variance for ranks corrected for multiple comparisons was used to examine differences among the materials.

Conclusions. The DuraGen dural substitute produced the least amount of inflammation in the subarachnoid space and Preclude generated the most (p < 0.001). Surgicel and DuraGen were completely resorbed on histological sections, but both produced some inflammation, which diminished gradually from the dural implant center. Histological evaluation of the nonresorbed grafts demonstrated that Durasis caused the least degree of inflammatory cell infiltration (p < 0.001). The Preclude dural substitute consistently demonstrated encapsulation and arachnoidal reaction. There was no evidence of implant-related adverse effects on the underlying pia mater and white matter regardless of the substitute type.

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Michael Y. Wang, Barth A. Green, Sachin Shah, D.O. Steven Vanni and Allan D. O. Levi

Object

An aging population will require that surgeons increasingly consider operative intervention in elderly patients. To perform this surgery safely will require an understanding of the factors that predict successful outcomes as well as complications.

Methods

Records of patients older than the age of 75 years who underwent lumbar spinal stenosis surgery were retrospectively reviewed. Preexisting medical illnesses were analyzed using the Charlson Weighted Comorbidity Index. Ambulatory function was rated on a four-point scale. Statistical analysis was performed using a one-tailed t-test with unpaired variance.

Eighty-eight patients treated between 1994 and 2001 were identified. Forty-five percent were women and 52 patients underwent spinal fusion. The follow-up period averaged 21 months. Back pain was present preoperatively in 89%; after surgery 43% experienced complete relief and 33% partial improvement. Leg pain was present preoperatively in 98%; after surgery 43% experienced complete relief and 42% partial improvement. Of the 33 patients with preoperative gait disturbances, 61% improved at least one point on the ambulatory scale. Wound complications and systemic complications were demonstrated in 24 and 16 patients, respectively. There were no deaths. Age (p = 0.322), number of fused levels (p = 0.371), and the number of laminectomy levels (p = 0.254) were not predictive of complications. Length of operative time (p = 0.003) and the CharlsonWeighted Comorbidity Index score (p = 0.088) were associated with both systemic and wound complications.

Conclusions

Surgery in patients older than age 75 years can be conducted safely and with similar outcome rates as in younger patients. The CharlsonWeighted Comorbidity Index score and operative time were predictive of the risk of complications.

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Thomas T. Lee, Gustavo J. Alameda, Erika B. Gromelski and Barth A. Green

Object. Progressive posttraumatic cystic myelopathy (PPCM) can occur after an injury to the spinal cord. Traditional treatment of PPCM consists of inserting a shunt into the cyst. However, some authors have advocated a more pathophysiological approach to this problem. The authors of the present study describe their surgical treatment protocol and outcome in a series of patients with syringomyelia.

Methods. Medical records of 34 patients undergoing surgical treatment for PPCM were reviewed. Laminectomies and intraoperative ultrasonography were performed. In patients without focal tethering of the spinal cord and in whom only a confluent cyst had been revealed on ultrasonography, a syringosubarachnoid shunt was inserted; in those with both tethering and a confluent cord cyst, an untethering procedure was performed first. When a significant reduction (> 50%) in the size of the cyst was shown after the untethering procedure, no shunt was inserted. When no changes in cyst size were demonstrated on ultrasonography, a short syringosubarachnoid shunt was used. The mean follow-up period was 28.7 months (range 12–102 months).

The interval between the mechanism of injury and the operation ranged from 5 months to 37 years (mean 11 years). Pain was the most frequent symptom, which was followed by motor deterioration and spasticity. Postoperative improvement was noted in 55% of patients who experienced motor function deterioration and in 53% of those who demonstrated worsening spasticity. In 14 of 18 patients with an associated tethered spinal cord, tethering alone caused significant collapse of the cyst. Postoperative magnetic resonance imaging demonstrated cyst collapse in 92% of patients who had undergone untethering alone and in 93% of those who underwent syringosubarachnoid shunt placement. Treatment failure was observed in 7% of the former group and in 13% of the latter.

Conclusions. Posttraumatic cystic myelopathy can occur with or without the presence of tethered cord syndrome. Intraoperative ultrasonography can readily demonstrate this distinction to aid in surgical decision making. Untethering alone in patients with tethered cord syndrome and cyst formation can reduce the cyst size and alleviate symptoms and signs of posttraumatic cystic myelopathy in the majority of these cases. Untethering procedures in which duraplasty is performed to expand the subarachnoid space may be a more physiologically effective way of treating tethered cord with associated syringomyelia.