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Patrick W. Hitchon, Vijay Goel, Thomas Rogge, Andrew Dooris, John Drake and James Torner

Object. The authors conducted a study to determine if the rigidity supplied to the spine by posterior placement of the Ray threaded fusion cage (TFC) is further enhanced by the placement of pedicle screws and, additionally, if bilateral anteriorly placed TFCs render the spine more rigid than a single anteriorly placed TFC.

Methods. Ten human cadaveric spinal specimens (L2—S1) were affixed within a testing frame. Loads of 1.5, 3, 4.5, and 6 Nm were applied to the spine in six degrees of freedom: flexion—extension, right and left lateral bending, and right and left axial rotation. Motion in an x, y, and z cartesian axis system was tracked using dual video cameras following light-emitting diodes attached to the spine and base plate. Load testing of the spines was performed in the intact mode, following which the spinal segments were randomized to receive anterior or posterior instrumentation. In five spine specimens we performed posterior discectomy, posterior lumbar interbody fusion (PLIF) with placment of femoral rings and pedicle screws, PLIF with bilateral TFCs, and bilateral TFCs with pedicle screws. Five other spines underwent anterior-approach discectomy, followed by implantation of a unilateral cage and bilateral cages. Load testing was performed after each step.

Conclusion. Spines in which PLIF with pedicle screws and TFCs with pedicle screws were placed were more rigid than after discectomy in all directions of motion except flexion. Anterior discectomy provided significantly (p ≤ 0.05) less stability in left and right axial rotation than the intact spines and following posterior discectomy. Following anterior implantation of bilateral TFCs, spines were significantly more rigid than after discectomy in all directions except extension.

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Patrick W. Hitchon, Vijay K. Goel, Thomas N. Rogge, James C. Torner, Andrew P. Dooris, John S. Drake, S. J. Yang and Koji Totoribe

Object. The goal of this study was to evaluate the comparative efficacy of three commonly used anterior thoracolumbar implants: the anterior thoracolumbar locking plate (ATLP), the smooth-rod Kaneda (SRK), and the Z-plate.

Methods. In vitro testing was performed using the T9—L3 segments of human cadaver spines. An L-1 corpectomy was performed, and stabilization was achieved using one of three anterior devices: the ATLP in nine spines, the SRK in 10, and the Z-plate in 10. Specimens were load tested with 1.5-, 3-, 4.5-, and 6-Nm in flexion and extension, right and left lateral bending, and right and left axial rotation. Angular motion was monitored using two video cameras that tracked light-emitting diodes attached to the vertebral bodies. Testing was performed in the intact state in spines stabilized with one of the three aforementioned devices after the devices had been fatigued to 5000 cycles at ± 3 Nm and after bilateral facetectomy.

There was no difference in the stability of the intact spines with use of the three devices. There were no differences between the SRK- and Z-plate—instrumented spines in any state. In extension testing, the mean angular rotation (± standard deviation) of spines instrumented with the SRK (4.7 ± 3.2°) and Z-plate devices (3.3 ± 2.3°) was more rigid than that observed in the ATLP-stabilized spines (9 ± 4.8°). In flexion testing after induction of fatigue, however, only the SRK (4.2 ± 3.2°) was stiffer than the ATLP (8.9 ± 4.9°). Also, in extension postfatigue, only the SRK (2.4 ± 3.4°) provided more rigid fixation than the ATLP (6.4 ± 2.9°). All three devices were equally unstable after bilateral facetectomy. The SRK and Z-plate anterior thoracolumbar implants were both more rigid than the ATLP, and of the former two the SRK was stiffer.

Conclusions. The authors' results suggest that in cases in which profile and ease of application are not of paramount importance, the SRK has an advantage over the other two tested implants in achieving rigid fixation immediately postoperatively.

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Abhaya V. Kulkarni, James M. Drake and Maria Lamberti-Pasculli

Object. Hydrocephalus is a common condition of childhood that usually requires insertion of a cerebrospinal fluid (CSF) shunt. Infection is one of the most devastating complications that may arise from the presence of CSF shunts. In this study, the authors prospectively analyzed perioperative risk factors for CSF shunt infection in a cohort of children.

Methods. Between 1996 and 1999, 299 eligible patients underwent CSF shunt operations (insertions and revisions) that were observed by a research nurse at a tertiary care pediatric hospital. Several perioperative variables were recorded. All cases were followed postoperatively for 6 months to note any development of CSF shunt infection. A Cox proportional hazards model was used to analyze the relationship between the variables and the development of shunt infection.

Thirty-one patients (10.4%) experienced shunt infection. Three perioperative variables were significantly associated with an increased risk of shunt infection: 1) the presence of a postoperative CSF leak (hazard ratio [HR] 19.16, 95% confidence interval [CI] 6.96–52.91); 2) patient prematurity (< 40 weeks' gestation at the time of shunt surgery: HR 4.72, 95% CI 1.71–13.06); and 3) the number of times the shunt system was inadvertently exposed to breached surgical gloves (HR 1.07, 95% CI 1.02–1.12).

Conclusions. Three variables associated with an increased incidence of shunt infection have been identified. Changes in clinical practice should address these variables, as follows. 1) Great care should be taken intraoperatively to avoid a postoperative CSF leak. 2) Alternatives to placement of a CSF shunt in premature infants should be studied. 3) Surgeons should minimize manual contact with the shunt system and consider the use of double gloves.

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Hugh J. L. Garton, John R. W. Kestle and James M. Drake

Object. In evaluating pediatric patients for shunt malfunction, predictive values for symptoms and signs are important in deciding which patients should undergo an imaging study, whereas determining clinical findings that correlate with a low probability of shunt failure could simplify management.

Methods. Data obtained during the recently completed Pediatric Shunt Design Trial (PSDT) were analyzed. Predictive values were calculated for symptoms and signs of shunt failure. To refine predictive capability, a shunt score based on a cluster of signs and symptoms was derived and validated using multivariate methods.

Four hundred thirty-one patient encounters after recent shunt insertions were analyzed. For encounters that took place within 5 months after shunt insertion (early encounters), predictive values for symptoms and signs included the following: nausea and vomiting (positive predictive value [PPV] 79%, likelihood ratio [LR] 10.4), irritability (PPV 78%, LR 9.8), decreased level of consciousness (LOC) (PPV 100%), erythema (PPV 100%), and bulging fontanelle (PPV 92%, LR 33.1). Between 9 months and 2 years after shunt insertion (late encounters), only loss of developmental milestones (PPV 83%, LR 36.7) and decreased LOC (PPV 100%) were strongly associated with shunt failure. However, the absence of a symptom or sign still left a 15 to 29% (early encounter group) or 9 to 13% (late encounter group) chance of shunt failure. Using the shunt score developed for early encounters, which sums from 1 to 3 points according to the specific symptoms or signs present, patients with scores of 0, 1, 2, and 3 or greater had shunt failure rates of 4%, 50%, 75%, and 100%, respectively. Using the shunt score derived from late encounters, patients with scores of 0, 1, and 2 or greater had shunt failure rates of 8%, 38%, and 100%, respectively.

Conclusions. In children, certain symptoms and signs that occur during the first several months following shunt insertion are strongly associated with shunt failure; however, the individual absence of these symptoms and signs offers the clinician only a limited ability to rule out a shunt malfunction. Combining them in a weighted scoring system improves the ability to predict shunt failure based on clinical findings.

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Patrick W. Hitchon, Vijay Goel, John Drake, Derek Taggard, Matthew Brenton, Thomas Rogge and James C. Torner

Object. Polymethylmethacrylate (PMMA) has long been used in the stabilization and reconstruction of traumatic and pathological fractures of the spine. Recently, hydroxyapatite (HA), an osteoconductive, biocompatible cement, has been used as an alternative to PMMA. In this study the authors compare the stabilizing effects of the HA product, BoneSource, with PMMA in an experimental compression fracture of L-1.

Methods. Twenty T9—L3 cadaveric spine specimens were mounted individually on a testing frame. Light-emitting diodes were placed on the neural arches as well as the base. Motion was tracked by two video cameras in response to applied loads of 0 to 6 Nm. The weight-drop technique was used to induce a reproducible compression fracture of T-11 after partially coring out the vertebra. Load testing was performed on the intact spine, postfracture, after unilateral transpedicular vertebroplasty with 7 to 10 ml of PMMA or HA, and after flexion—extension fatiguing to 5000 cycles at ± 3 Nm.

No significant difference between the HA- and PMMA cemented—fixated spines was demonstrated in flexion, extension, left lateral bending, or right and left axial rotation. The only difference between the two cements was encountered before and after fatiguing in right lateral bending (p ≤ 0.05).

Conclusions. The results of this study suggest that the same angular rigidity can be achieved using either HA or PMMA. This is of particular interest because HA is osteoconductive, undergoes remodeling, and is not exothermic.

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Patrick A. Lo, James M. Drake, Douglas Hedden, Pradeep Narotam and Peter B. Dirks

✓ Neck injuries in children most commonly affect the upper cervical spine. Injuries of the transverse ligament and its attachments may result in C1–2 instability, but the optimum form of treatment is unknown.

Three patients, who ranged in age from 5 to 11 years, sustained transverse atlantal ligament injuries with unilateral avulsion fracture of the osseous tubercle of C-1. One child was injured in a fall and two were involved in motor vehicle accidents. Although all patients presented with neck pain, none exhibited neurological deficits. Plain radiography demonstrated no evidence of osseous injury, but an increased predental interval was noted in each case. Computerized tomography (CT) scanning demonstrated the avulsion fractures, and magnetic resonance imaging revealed evidence of soft-tissue injuries in the occipital—C2 ligamentous complex. All children were managed with external immobilization (halo vest in two and a Sterno-Occipito-Mandibular Immobilizer brace in one), for 6 to 12 weeks. Follow-up CT scanning demonstrated reattachment of the avulsed osseous tubercle, and dynamic cervical spine radiographs revealed the absence of C1–2 instability.

The results of these cases suggest a role for external immobilization in the treatment of osseous avulsion injuries of the transverse atlantal ligament in children.

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Walter J. Hader, James Drake, Douglas Cochrane, Owen Sparrow, Edward S. Johnson and John Kestle

✓ Late failure following successful third ventriculostomy for obstructive hydrocephalus is rare, and death caused by failure of a previously successful third ventriculostomy has been reported only once. The authors present three patients who died as a result of increased intracranial pressure (ICP) after late failure of a third ventriculostomy.

Through a collaborative effort, three patients were identified who had died following third ventriculostomy at one of the authors' institutions. A 13-year-old girl with neurofibromatosis Type 1 underwent third ventriculostomy for obstructive hydrocephalus caused by a tectal lesion. Three years later her condition deteriorated rapidly over the course of 6 hours and she was found dead at home. A 4-year-old boy treated with third ventriculostomy for aqueductal stenosis presented 2 years postoperatively with symptoms of increased ICP. This patient suffered a cardiorespiratory arrest while under observation and died despite external ventricular drainage. A 10-year-old boy with previous ventriculoperitoneal (VP) shunt placement underwent conversion to a third ventriculostomy and shunt removal. Eight months after the procedure his condition deteriorated, with evidence of raised ICP, and he underwent emergency insertion of another VP shunt, but remained in a vegetative state and died of complications. Neuropathological examinations in two cases demonstrated that the third ventriculostomy was not patent, and there was also evidence of increased ICP.

Late failure of third ventriculostomy resulting in death is a rare complication. Delay in recognition of recurrent ICP symptoms and a false feeling of security on the part of family and caregivers because of the absence of a shunt and the belief that the hydrocephalus has been cured may contribute to fatal complications after third ventriculostomy. Patients with third ventriculostomies should be followed in a manner similar to patients with cerebrospinal fluid shunts.

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John R. W. Kestle, James M. Drake, D. Douglas Cochrane, Ruth Milner, Marion L. Walker, Rick Abbott III, Frederick A. Boop and the Endoscopic Shunt Insertion Trial Participants

Object. Endoscopically assisted ventricular catheter placement has been reported to reduce shunt failure in uncontrolled series. The authors investigated the efficacy of this procedure in a prospective multicenter randomized trial.

Methods. Children younger than 18 years old who were scheduled for their first ventriculoperitoneal (VP) shunt placement were randomized to undergo endoscopic or nonendoscopic insertion of a ventricular catheter. Eligibility and primary outcome (shunt failure) were decided in a blinded fashion. An intention-to-treat analysis was performed. The sample size offered 80% power to detect a 10 to 15% absolute reduction in the 1-year shunt failure rate.

The authors studied 393 patients from 16 pediatric neurosurgery centers between May 1996 and November 1999. Median patient age at shunt insertion was 89 days. The baseline characteristics of patients within each group were similar: 54% of patients treated with endoscopy were male and 55% of patients treated without endoscopy were male; 30% of patients treated with and 26% of those without endoscopy had myelomeningocele; a differential pressure valve was used in 51% of patients with and 49% of those treated without endoscopy; a Delta valve was inserted in 38% of patients in each group; and a Sigma valve was placed in 9% of patients treated with and 12% of those treated without endoscopy. Median surgical time lasted 40 minutes in the group treated with and 35 minutes in the group treated without endoscopy. Ventricular catheters, which during surgery were thought to be situated away from the choroid plexus, were demonstrated to be in it on postoperative imaging in 67% of patients who had undergone endoscopic insertion and 61% of those who had undergone nonendoscopic shunt placements. The incidence of shunt failure at 1 year was 42% in the endoscopic insertion group and 34% in the nonendoscopic group. The time to first shunt failure was not different between the two groups (log rank = 2.92, p = 0.09).

Conclusions. Endoscopic insertion of the initial VP shunt in children suffering from hydrocephalus did not reduce the incidence of shunt failure.

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Sagun Tuli, Jayshree Tuli, James Drake and Julian Spears

Object. Despite improved therapeutic strategies and better diagnostic techniques in the management of pediatric hydrocephalus there continues to be a significant mortality rate associated with cerebrospinal fluid (CSF) shunts. The goal of this study was to determine the long-term outcome and predictors of death in these patients.

Methods. Data were collected in all patients requiring a CSF shunt presenting to a single tertiary care pediatric institution during a 10-year period. Patients with neoplasms were excluded because their deaths were predominantly related to the tumor. Descriptive statistics were obtained on the patient characteristics, surgical features, and shunt characteristics. The time and cause of death were determined. Kaplan—Meier survival estimates were used to determine overall survival of patients. Univariate analysis was performed using the log-rank test. Multivariate analysis included use of Cox regression model to determine the significance of age (at the time of initial shunt insertion), the number of shunt-related failures and infections, and whether the shunts were complex or multiple in nature in predicting death. Hazard ratios, 95% confidence intervals and probability values were calculated.

Of 907 patients, 124 died. The most common causes were myelomeningocele (191 cases), intraventricular hemorrhage (114 cases), and tumor (190 cases) with 7.9, 3.5, and 32.6% dying, respectively, during the study period. Restricting all analyses to cases without neoplasms, the incidence of shunt-related failures was 58.1% in patients who died and 55.3% in those who survived, with an incidence of shunt-related infection of 19.4% in the former and 18.5% in the latter. The overall mortality rates in all patients at 1, 5, and 10 years were 4.5, 8.9, and 12.4%, respectively, from time of initial shunt insertion to death or last follow-up visit. The infection rate per procedure (that is, following the first shunt insertion) was 10.9% (78 of 717 cases). Evaluation of predictors of death revealed a statistically significant effect of infection with a hazard ratio of 1.66 (p = 0.04).

Conclusions. The mortality rate in shunt-treated pediatric patients with hydrocephalus remains high, dependent on the underlying reason for CSF shunt insertion and the subsequent development of infection of the shunt apparatus.