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Regina Eymann, Wolf-Ingo Steudel and Michael Kiefer

Object

The authors' goal in this paper was to evaluate prospectively the efficacy and safety of a new pediatric gravitational shunt to determine whether it warrants inclusion in a randomized, controlled trial with other shunts.

Methods

A total of 55 children between the ages of 0 and 6 years (median age 0.5 years, average age 4 ± 6 years) underwent primary shunt implantation; all received the Miethke Paedi-GAV. The follow-up period ranged between 12 and 77 months (mean 47 ± 21 months). The primary end point of the study was the first shunt failure necessitating revision.

The 1- and 2-year shunt survival rates were 75 and 68%, respectively. The average failure-free shunt survival duration was 1423 ± 641 days. Based on imaging findings, no slitlike ventricles occurred. The complication rate was 33%, and the median time to shunt failure was 45 days. Underdrainage occurred in one child (1.8%) and overdrainage in two children (3.6%).

Conclusions

These preliminary results prove the Miethke Paedi-GAV to be a safe and effective pediatric shunt worthy of inclusion in a randomized comparison with other shunts in the pediatric population.

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Martin Strowitzki, Michael Kiefer and Wolf-Ingo Steudel

✓ The authors present a newly designed device for ultrasonic guidance of neuroendoscopic procedures. It consists of a puncture adapter that attaches to a rigid endoscope having an outer diameter of 6 mm and is mounted on a small, bayonet-shaped ultrasound probe. This adapter directs the movement of the endoscope precisely within the ultrasonic field of view. The targeted region is identified by transdural insonation via an enlarged single burr-hole approach, and the endoscope is tracked in real time throughout its approach to the target. The procedure has been performed in 10 patients: endoscopic ventriculocystostomy in four cases; removal of a colloid cyst of the third ventricle in two cases; and intraventricular tumor biopsy, intraventricular tumor resection, third ventriculostomy, and removal of an intraventricular hematoma in one case each. The endoscope was depicted on ultrasonograms as a hyperechoic line without disturbing echoes and, consequently, the target (cyst, ventricle, or tumor) was safely identified in all but one case, in which intraventricular air hid a colloid cyst in the foramen of Monro.

The method presented by the authors proved to be very effective in the guidance and control of neuroendoscopic procedures. Combining this method with image guidance is recommended to define the entry point of the endoscope precisely.

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Tobias Pitzen, Frederick Franta, Dragos Barbier and Wolf-Ingo Steudel

Object. The purpose of this study was to investigate whether thicker-core-diameter screws increase fixation strength in the cervical spine.

Methods. Bone mineral density (BMD) was determined for each vertebral body (VB) obtained in six human C4–7 segments. Based on their BMD, the specimens were assigned to one of two groups in which torque and pullout force were tested. Two initial pilot holes were drilled into the VBs and tests were first performed using a standard screw. The test was repeated using a thicker rescue screw inserted into the same initial pilot hole. The mean value of peak torque and pullout force resulting from the single left/right measurements was used for statistical analysis. A t-test was performed to determine the effect of screw design on peak torque and pullout force. Moment correlation coefficients were calculated to determine the effect of BMD on peak torque and pullout force.

Mean insertional peak torque for the standard screw was 82.1 N/cm and that for the rescue screw was 47.6 Ncm (p < 0.001). There was a strong correlation between insertional peak torque and BMD for both standard screws (r = 0.71, p = 0.02) and rescue screws (r = 0.59, p = 0.07). The mean pullout force for standard screws was 464.7 N, whereas it was 164.5 N for rescue screws (p < 0.001). There was a strong correlation between pullout force and BMD for both standard (r = 0.75, p = 0.0081) and rescue screws (r = 0.7, p = 0.025).

Conclusions. Uncemented rescue screws that have been inserted into a fatigued hole in the cervical VB do not strengthen the screw—bone interface compared with the strength initially conferred by a standard screw.

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Tobias Rainer Pitzen, Jörg Drumm, Bernhard Bruchmann, Dragos Doru Barbier and Wolf-Ingo Steudel

Object

Among the various ways to optimize the fixation of bone implants is to use bone cement, for example, in a total hip prosthesis. No data exist, however, concerning the effectiveness of cemented rescue screws for anterior cervical plate fixation. The aim of this study was to investigate whether cemented rescue screws increase fixation strength in comparison with uncemented standard screws.

Methods

Six cervical spine segments (C4–7) were explanted during routine autopsy studies from fresh human cadavers. Bone mineral density (BMD) was measured for each vertebral body (VB) using quantitative computerized tomography scanning, and 24 VBs were dissected from the segments. Two initial pilot holes were drilled into each VB parallel to the sagittal plane. Based on their BMD, the specimens were assigned to one of two groups in which torque and pullout force were tested. The test was begun with standard screws and was repeated with cannulated slotted rescue screws into which bone cement was injected. The mean values of peak torque and pullout forces resulting from the left and right measurements were used for statistical analysis. A t-test was performed to determine the effect of screw type on peak torque and pullout force. Moment correlation coefficients were calculated to determine the effect of BMD on peak torque and pullout force for each type of screw.

The mean insertional peak torque was 67.1 N/cm for the standard screw and 102.6 N/cm for the cemented screw (p < 0.05). The mean pullout force was 526.9 N for standard osteoporosis screws and 531.5 N for cemented screws (p > 0.05). The effect of increased holding strength as measured by peak torque and pullout force was more pronounced in the presence of low bone density.

Conclusions

Cemented rescue screws that have been inserted into a fatigued pilot hole in the cervical VB strengthen the screw–bone interface compared with the strength initially conferred by a standard screw.

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Regina Eymann, Somar Chehab, Martin Strowitzki, Wolf-Ingo Steudel and Michael Kiefer

Object

The authors evaluated the safety and efficacy of antibiotic-impregnated shunt catheters (AISCs) and determined the cost–benefit ratio related to the fact that AISCs increase the implant costs of a shunt procedure by ~ $400 per patient.

Methods

The control group comprised 98 adults with chronic hydrocephalus and 22 children, who were treated without AISCs (non-AISCs). In the treatment group, AISCs (Bactiseal, Codman, Johnson & Johnson) were implanted in 171 adults and 26 children. The minimum follow-up period was 6 months.

Results

Important risk factors for shunt infections (such as age, comorbidity, cause of hydrocephalus, operating time, and duration of external cerebrospinal fluid drainage prior to shunt placement) did not differ between the study and control groups. In the pediatric AISC group, the frequency of premature, shunt-treated infants and the incidence of external ventricular drainage prior to shunt insertion were actually higher than those in the non-AISC group. When using AISCs, the shunt infection rate dropped from 4 to 0.6% and from 13.6 to 3.8% in the adult and the pediatric cohort, respectively. Overall the infection rate decreased from 5.8 to 1%, which was statistically significant (p = 0.0145). The average costs of a single shunt infection were $17,300 and $13,000 in children and adults, respectively. The cost–benefit calculation assumed to have saved shunt infection–related costs of ~ $50,000 in 197 AISC–treated patients due to the reduction in shunt infection rate in this group compared with costs in the control group. Despite the incremental implant costs associated with the use of AISCs, the overall reduction in infection-related costs made the use of AISCs cost beneficial in the authors' department.

Conclusions

From clinical and economic perspectives, AISCs are seemingly a valuable addition in hydrocephalus therapy.

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Tobias R. Pitzen, Dieter Matthis, Dragos D. Barbier and Wolf-Ingo Steudel

✓ The purpose of this study was to generate a validated finite element (FE) model of the human cervical spine to be used to analyze new implants. Digitized data obtained from computerized tomography scanning of a human cervical spine were used to generate a three-dimensional, anisotropic, linear C5–6 FE model by using a software package (ANSYS 5.4). Based on the intact model (FE/Intact), a second was generated by simulating an anterior cervical fusion and plate (ACFP) C5–6 model in which monocortical screws (FE/ACFP) were used. Loading of each FE model was simulated using pure moments of ± 2.5 Nm in flexion/extension, axial left/right rotation, and left/right lateral bending. For validation of the models, their predicted C5–6 range of motion (ROM) was compared with the results of an earlier, corresponding in vitro study of six human spines, which were tested in the intact state and surgically altered at C5–6 with the same implants. The validated model was used to analyze the stabilizing effect of a new disc spacer, Cenius (Aesculap AG, Tuttlingen, Germany), as a stand-alone implant (FE/Cenius) and in combination with an anterior plate (FE/Cenius+ACFP). In addition, compression loads at the upper surface of the spacer were investigated using both models.

As calculated by FE/Intact and FE/ACFP models, the ROM was within 1 standard deviation of the mean value of the corresponding in vitro measurements for each loading case. The FE/Cenius model predicted C5–6 ROM values of 5.5° in flexion/extension, 3.1° in axial rotation (left and right), and 2.9° in lateral bending (left and right). Addition of an anterior plate resulted in a further decrease of ROM in each loading case. The FE/Cenius model predicted an increase of compression load in flexion and a decrease in extension, whereas in the FE/Cenius+ACFP model an increase of graft compression in extension and unloading of the graft in flexion were predicted.

The current FE model predicted ROM values comparable with those obtained in vitro in the intact state as well as after simulation of an ACFP model. It predicted a stabilizing potential for a new cage, alone and in combination with an anterior plate system, and predicted the influence of both loading modality and additional instrumentation on the behavior of the interbody graft.

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Abdullah Nabhan, Wolf-Ingo Steudel, Lutfi Dedeman, Jehad Al-Khayat and Basem Ishak

Object

This study compares the effectiveness of subcutaneous infiltration of a local anesthetic agent (LA) versus intravenous regional anesthesia (IVRA) during endoscopic carpal tunnel release.

Methods

Forty-four patients suffering from severe symptoms restricting normal daily activities—such as persistent loss of feeling in the fingers or hand, or no strength in the thumb in spite of prolonged nonsurgical treatment—and with electromyographically proven carpal tunnel syndrome were enrolled in this study. All underwent endoscopic carpal tunnel release. Twenty-two patients had an endoscopic release of the median nerve under LA (LA Group). The other 22 patients underwent the surgery after intravenous induction of regional anesthesia (IVRA Group). The operating room in-out time and tourniquet time were evaluated in both groups. The patients were also asked to evaluate the pain associated with the tourniquet during surgery using a visual analog scale.

The Michigan Hand Outcomes Questionnaire was used to assess the functional outcome preoperatively and at both 2 weeks and 6 months postoperatively.

Results

One patient in the LA Group needed an additional application of prilocaine, whereas 3 patients in the IVRA Group needed additional LA and 1 of these required propofol. The tourniquet time and operating room time were significantly lower in the LA Group (p = 0.01 for both). There were no complications related to the endoscopic surgery. The Michigan Hand Outcomes Questionnaire did not show significant differences between the groups at either postoperative follow-up examination.

Conclusions

Endoscopic carpal tunnel release with subcutaneous infiltration of LA was well tolerated and effective. Injection-associated problems such as increased thickness of the synovial layer or impaired endoscopic view did not occur.

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Tobias Pitzen, Chris Lane, Darrell Goertzen, Marcel Dvorak, Charles Fisher, Dragos Barbier, Wolf-Ingo Steudel and Thomas Oxland

Object

The primary goal of this study was to determine if the stabilization provided to the spine by anterior cervical fixation with plating (ACFP) was dependent on the degree of posterior element injury. The secondary goal was to evaluate the effectiveness of additional posterior screw/rod stabilization in these injuries.

Methods

Following ACFP with interbody bone graft and stepwise transection of the posterior ligaments and facets at C5–6, eight fresh-frozen human C4–7 spine segments were loaded using pure moments of ± 1.5 Nm in flexion—extension, axial rotation, and lateral bending in the intact state. Posterior screw/rod fixation was performed after complete ligamentous destruction and complete removal of the facets. Repeated-measures analysis of variance and pairwise Student-Newman-Keuls tests were used to detect changes in the range of motion (ROM) and neutral zone (NZ). Statistical significance was assumed at a 95% level.

Significant increases in ROM occurred in each loading direction after transection of the capsular ligaments (p < 0.001) and again following facetectomy (p < 0.001) compared with the ACFP condition. Additional posterior fixation resulted in a significant decrease in ROM in all loading directions (p < 0.001). There was a significant increase in NZ for complete ligamentous destruction compared with ACFP (p < 0.05) and facetectomy compared with ACFP (p < 0.05) for flexion—extension. In lateral bending, a significant increase in NZ was found for facetectomy compared with ACFP (p < 0.05).

Conclusions

Capsular ligaments and articular facets are important structures in limiting three-dimensional vertebral motion in the presence of an anterior plate. Supplementary posterior fixation does reduce motion for all injury conditions.

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Ralf Ketter, Wolfram Henn, Isolde Niedermayer, Heike Steilen-Gimbel, Jochem König, Klaus D. Zang and Wolf-Ingo Steudel

Object. The goal of this study was to determine whether in meningiomas cytogenetic findings are suitable as a predictive parameter relevant to prognosis.

Methods. Between 1992 and 1998 at the Department of Neurosurgery, Saarland University, 198 patients underwent surgery to resect meningiomas. The meningiomas were investigated cytogenetically and the patients were followed up for a mean period of 33 months.

On the basis of the cytogenetic findings, the meningiomas were subdivided into four groups: Group 0 meningiomas displayed a normal diploid chromosome set; Group 1 tumors were found to have monosomy 22 as the sole cytogenetic aberration; Group 2 tumors were markedly hypodiploid meningiomas with loss of additional autosomes in addition to monosomy 22; and Group 3 meningiomas had deletions of the short arm of a chromosome 1, as well as additional chromosomal aberrations including loss of one chromosome 22.

One hundred ninety-eight patients in whom tumor resections were determined to be Simpson Grade I or II could be followed up after complete tumor extirpation. In 20 patients, one or several recurrences were documented during the period of observation. The tumors were classified according to their different, but mostly uniform chromosomal aberrations. Recurrences were found in six (4.3%) of 139 tumors in Groups 0 and 1 and in two (10.5%) of 19 tumors in Group 2; the highest rate of recurrence was found in 12 (30%) of 40 tumors in Group 3. This supports the notion that the deletion of the short arm of one chromosome 1 is an important prognostic factor in meningiomas. The results of this study document a significant correlation between histological grade (p < 0.0001), location (p < 0.0001), and recurrences of meningiomas (p < 0.0001) (significance determined using chi-square tests).

Conclusions. The cytogenetic classification of meningiomas provides a significant contribution to the predictability of tumor recurrence and is, therefore, a valuable criterion for the neurosurgeon's postoperative management protocol.