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Seoung Woo Park, T. Jesse Lim and Jon Park

Object

Interspinous process implants are becoming more common for the treatment of lumber disc degeneration. The authors undertook this study to evaluate the effect of the In-Space interspinous spacer on the biomechanics of the lumbosacral spine.

Methods

Seven L2–S1 cadaver spines were physiologically loaded in extension, flexion, lateral bending, and axial rotation modes. The range of motion (ROM) and intervertebral disc pressure (DP) at the level implanted with an In-Space device and at adjacent levels were measured under 4 experimental conditions. Biomechanical testing was carried out on 7 sequentially prepared specimens in the following states: 1) the intact L2–S1 cadaver spine and 2) the L2–S1 cadaver specimen implanted with an In-Space interspinous spacer at L3–4 (Group 1), 3) after an additional L3–4 discectomy (with the In-Space interspinous spacer still in place) (Group 2), and finally, 4) after removal of the In-Space interspinous spacer, leaving only the discectomized (that is, destabilized) spine model (Group 3).

Results

The extension ROM at the implanted level after experimental conditions 2 and 3 above was statistically significantly reduced. An increase of ROM at the adjacent levels compensated for the reduction at the implanted level. However, there was no statistically significant change in ROM in any of the other modes of motion at any of the levels studied. Likewise, the DP reduction at L3–4 during extension was statistically significant, but in all other modes of motion, there was no statistically significant change in DP at any measured level. The In-Space interspinous spacer statistically significantly reduced the ROM of the L3–4 motion segment in Groups 1 and 2 (extension: 67%, p = 0.018 and 70%, p = 0.018; flexion: 72%, p = 0.028 and 80%, p = 0.027). After placement of the In-Space interspinous spacer, the DP was decreased at L3–4 in extension for Groups 1 and 2 in the posterior anular region (63%, p = 0.028; 59%, p = 0.043), Group 2 in the center region (73%, p = 0.028), and Groups 1 and 2 in the anterior anular region (57%, p = 0.018; 60%, p = 0.018).

Conclusions

The In-Space interspinous spacer both stabilizes the spine and reduces the intervertebral DP at the instrumented level during extension. The biomechanics for other modes of motion and at the adjacent levels are not affected statistically significantly, however. The device thus performed as intended. It significantly stabilized the motion segments at the instrumented level, but not at the segment adjacent to the instrumented level.

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Jack R. Engsberg, Kenneth S. Olree, Sandy A. Ross and T. S. Park

Object. The goal of this investigation was to quantify changes in hamstring muscle spasticity and strength in children with cerebral palsy (CP) as a function of their having undergone a selective dorsal rhizotomy.

Methods. Nineteen children with CP (CP group) and six children with able bodies (AB group) underwent testing with a dynamometer. For the spasticity measure, the dynamometer measured the resistive torque of the hamstring muscles during passive knee extension at four different speeds. Torque—angle data were processed to calculate the work done by the machine to extend the knee for each speed. Linear regression was used to calculate the slope of the line of best fit for the work—velocity data. The slope simultaneously encompassed three key elements associated with spasticity (velocity, resistance, and stretch) and was considered the measure of spasticity. For the strength test, the dynamometer moved the leg from full knee extension to flexion while a maximum concentric contraction of the hamstring muscles was performed. Torque—angle data were processed to calculate the work done on the machine by the child. Hamstring spasticity values for the CP group were significantly greater than similar values for the AB group prior to surgery; however, they were not significantly different after surgery. Hamstring strength values for the CP group remained significantly less than those for the AB group after surgery, but were significantly increased relative to their presurgery values.

Conclusions. The results of spasticity testing in the present investigation agreed with those of previous studies, indicating a reduction in spasticity for the CP group. The results of strength testing did not agree with those in the previous literature; a significant increase in strength was observed for the CP group.

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M. Sean Grady, Robert F. Bedford and T. S. Park

✓ Air embolism is a potential hazard during craniotomy whenever intracranial venous pressure is subatmospheric. In order to better understand both the risk of air embolism and its treatment in neurosurgical patients, the authors have investigated the relationship of superior sagittal sinus pressure (SSP) to head position in 15 children and examined the effects of both jugular venous compression and positive end-expiratory airway pressure (PEEP) on SSP. Progressive head elevation significantly decreased mean SSP and, in five patients, SSP was less than 0 mm Hg at 90° torso elevation. A PEEP of 10 cm H2O was ineffective in significantly increasing SSP at any degree of head elevation, whereas bilateral internal jugular compression always caused a significant increase in SSP. The authors conclude that children are at risk for venous air embolism when undergoing suboccipital craniectomy in the sitting position because intracranial venous pressure is often subatmospheric when the head is elevated. Furthermore, maintaining PEEP does not appear to be a reliable treatment for increasing SSP, whereas bilateral internal jugular compression is effective.

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Michael R. Chicoine, T. S. Park and Bruce A. Kaufman

✓ If the spasticity of cerebral palsy (CP) is reduced in children at a young age by selective dorsal rhizotomy, the incidence of lower-extremity deformities requiring orthopedic surgery may be reduced; however, this has never been investigated in detail. The authors examined the effects of selective dorsal rhizotomy on rates of lower-extremity orthopedic surgery in 178 children with CP. Age at selective dorsal rhizotomy ranged from 2 to 19.3 years (mean 5.5 years) with follow-up intervals ranging from 24 to 70 months (mean 44 months). Spastic CP was classified as quadriplegia (33%), diplegia (65%), and hemiplegia (2%). To assess the effects of early versus late rhizotomy on rates of orthopedic surgery, patients were grouped as follows: Group I underwent rhizotomy between 2 and 4 years of age (54 patients), and Group II underwent rhizotomy between 5 and 19 years of age (124 patients). Comparison of Kaplan—Meier plots of lifetime orthopedic surgery rates revealed that Group II underwent orthopedic surgery at a higher rate than Group I (p = 0.037). Analysis by procedure type revealed higher orthopedic surgery rates in Group II than Group I for heel cord releases (p = 0.0025), adductor releases (p = 0.018), and hamstring releases (p = 0.02). Orthopedic surgery rates were no higher for Group II compared to Group I for ankle/foot operations (p = 0.023), femoral osteotomy (p = 0.25), iliopsoas releases (p = 0.35), and “other” operations (p = 0.013). The data indicate that early rhizotomy reduces the need for orthopedic surgery for heel cord, hamstring, and adductor releases.

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Tord D. Alden, Jeffrey G. Ojemann and T. S. Park

Chiari I malformation is a well-described entity characterized by hindbrain herniation through the foramen magnum. Although the exact origin of congenital Chiari I malformation is unknown, it appears to be caused by a mismatch between the volume of the posterior fossa neural elements and the posterior fossa cranial content. Several theories have been proposed to describe the resultant pathophysiology of this mismatch. It is clear, however, that abnormal cerebrospinal fluid flow and velocity play a role in the symptoms and signs associated with this disorder. The authors will review the pathophysiology, clinical presentation, and treatment options for patients with Chiari I malformation.

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T. S. Park, Wayne S. Cail, Johnny B. Delashaw and John Kattwinkel

✓ A 2-day-old neonate with a spinal cord arteriovenous malformation developed severe paraparesis. The abrupt neurological deterioration was not associated with hemorrhage or aneurysmal dilatation. Ischemic damage of the spinal cord is suggested as the cause of the clinical manifestation.

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Progressive spasticity and scoliosis in children with myelomeningocele

Radiological investigation and surgical treatment

T. S. Park, Wayne S. Cail, William M. Maggio and Diane C. Mitchell

✓ Seventeen myelodysplastic patients with progressive extremity spasticity and scoliosis underwent radiological evaluation and surgical treatment. All but one were under 18 years of age at the time of surgical treatment. Duration of the clinical presentation ranged from 1½ to 7 years. Metrizamide was instilled into the subarachnoid space in 12 patients, the lateral ventricle in two, and the hydromyelic cavity in three. Sequential computerized tomography scanning after intrathecal instillation of the contrast material clearly demonstrated hydromyelia in nine patients and compression of the brain stem in five. Posterior fossa decompression with plugging of the obex was performed in 12 patients, posterior fossa decompression alone in three, and ventriculoperitoneal (VP) shunting procedures in two. Of the 12 patients who underwent the obex plugging procedures, eight have shown partial or complete resolution of spasticity and an increase in motor strength with no significant postoperative complications. In contrast, posterior fossa decompression or VP shunting procedures alone have not led to a favorable neurological outcome. Hydromyelia may occur more commonly among myelodysplastic patients than previously recognized and may be treated most effectively by the obex plugging procedure.