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Editorial

Motion preservation following anterior cervical discectomy

Michael G. Fehlings and Doron Rabin

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Michael D. Staudt, Doron Rabin, Ali A. Baaj, Neil R. Crawford and Neil Duggal

OBJECTIVE

There are limited data regarding the implications of revision posterior surgery in the setting of previous cervical arthroplasty (CA). The purpose of this study was to analyze segmental biomechanics in human cadaveric specimens with and without CA, in the context of graded posterior resection.

METHODS

Fourteen human cadaveric cervical spines (C3–T1 or C2–7) were divided into arthroplasty (ProDisc-C, n = 7) and control (intact disc, n = 7) groups. Both groups underwent sequential posterior element resections: unilateral foraminotomy, laminoplasty, and finally laminectomy. Specimens were studied sequentially in two different loading apparatuses during the induction of flexion-extension, lateral bending, and axial rotation.

RESULTS

Range of motion (ROM) after artificial disc insertion was reduced relative to that in the control group during axial rotation and lateral bending (13% and 28%, respectively; p < 0.05) but was similar during flexion and extension. With sequential resections, ROM increased by a similar magnitude following foraminotomy and laminoplasty in both groups. Laminectomy had a much greater effect: mean (aggregate) ROM during flexion-extension, lateral bending, and axial rotation was increased by a magnitude of 52% following laminectomy in the setting of CA, compared to an 8% increase without arthroplasty. In particular, laminectomy in the setting of CA introduced significant instability in flexion-extension, characterized by a 90% increase in ROM from laminoplasty to laminectomy, compared to a 16% increase in ROM from laminoplasty to laminectomy without arthroplasty (p < 0.05).

CONCLUSIONS

Foraminotomy and laminoplasty did not result in significant instability in the setting of CA, compared to controls. Laminectomy alone, however, resulted in a significant change in biomechanics, allowing for significantly increased flexion and extension. Laminectomy alone should be used with caution in the setting of previous CA.

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Abhaya V. Kulkarni, Doron Rabin and James M. Drake

Object. In the measurement of clinical outcome in pediatric patients with hydrocephalus the condition's effects on a child's physical, emotional, cognitive, and social health are frequently ignored. The authors developed a quantitative health status measure, the Hydrocephalus Outcome Questionnaire (HOQ), designed specifically for children with hydrocephalus, which can be completed by the children's parents.

Methods. The standardized steps in the development of a health status measure were followed. Item generation required involvement of health professionals and focus groups with parents of children with hydrocephalus. A comprehensive list of 165 unique health status items was thus generated. To streamline the list, questionnaires were sent to 69 sets of parents to solicit their opinions regarding the most important of these health issues, and the 51 most significant items were then selected to represent the following health domains: physical, social-emotional, and cognitive. In another cohort of 90 sets of parents, the 51-item questionnaire was then tested for reliability and construct validity against the following independent measures of specific components of health: Health Utilities Index, Wide Range Achievement Reading Test, Strengths and Difficulties Questionnaires, and Functional Independence Measure for Children.

The HOQ took approximately 10 to 15 minutes for the parents to complete and demonstrated excellent test—retest reliability (0.93, 95% confidence interval [CI] 0.88–0.96), interrater reliability (0.88, 95% CI 0.79–0.93), and internal consistency (Cronbach alpha 0.94). Pearson correlation testing demonstrated very good construct validity between domain scores and their respective independent measures.

Conclusions. The HOQ for children with hydrocephalus demonstrated excellent reliability and validity properties. This tool will be valuable for a wide range of clinical research projects in pediatric hydrocephalus.

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Izabela Kowalczyk, Bruno C. R. Lazaro, Marie Fink, Doron Rabin and Neil Duggal

Object

Cervical arthroplasty has emerged as a means of preventing adjacent segment disease by preserving motion, restoring sagittal balance, and mimicking natural spinal kinematics. The purpose of this retrospective in vivo study was to characterize the impact of arthroplasty on sagittal balance and segmental kinematics of the cervical spine.

Methods

Sixty patients receiving the Bryan disc, ProDisc-C, or Prestige LP disc were retrospectively analyzed. Only single-level arthroplasty cases were included in this study. Lateral dynamic radiographs of the cervical spine were evaluated using quantitative measurement analysis software to determine the kinematics at the index level both preoperatively and 1 year postoperatively. Collected parameters included range of motion (ROM), disc angles, shell angles, anterior and posterior disc heights (ADHs/PDHs), translation, and center of rotation (COR). Preoperative and postoperative data were compared using the Student t-test, with p < 0.05 indicating significance.

Results

The Bryan and Prestige LP discs preserved motion, whereas the ProDisc-C increased segmental ROM from extension to flexion. Following surgery, the Bryan disc exhibited significant shell angle kyphosis, while ProDisc-C and Prestige LP retained lordosis. Both ADHs and PDHs decreased following insertion of the Bryan disc. In contrast, the ProDisc-C increased the ADHs and PDHs by 80% and 52%, respectively, and the Prestige LP disc increased the ADHs and PDHs by 20%. Only the ProDisc-C demonstrated significant translation of 0.7 mm. The ProDisc-C shifted the COR x by 0.9 mm anteriorly, while the Prestige LP disc demonstrated a significant superior shift of 2.2 mm in COR y.

Conclusions

All discs adequately maintained ROM at the surgical level. The greatest difference among the 3 devices was in the disc height and index angle measurements.

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Editorial

En bloc resection for metastatic spinal tumors: is it worth it?

Michael G. Fehlings and Doron Rabin

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Bruno C. R. Lazaro, Kemal Yucesoy, Kasim Z. Yuksel, Izabela Kowalczyk, Doron Rabin, Marie Fink and Neil Duggal

Object

Cervical total disc replacement has emerged as a surgical option to preserve motion and potentially avoid adjacent-segment disease after anterior cervical discectomy and fusion. Recently, much attention has been directed at the ability of a given device to maintain and/or restore normal segmental alignment. Nonphysiological disc and segmental angulation could result in increased stresses transmitted to the facet joints and posterior elements, conflicting with the essence of arthroplasty and potentially leading to adjacent-segment disease. The goal of this study was to contrast device alignment and segmental kinematics provided by 3 different cervical disc prostheses.

Methods

Sixty patients were retrospectively analyzed and divided into 3 groups receiving the Bryan, ProDisc-C, or Synergy disc. Only single-level arthroplasty cases were included in the study. Lateral dynamic radiographs of the cervical spine were analyzed using quantitative motion analysis software (Medical Metrics, Inc.) to analyze the kinematics at the index level both preoperatively and postoperatively. Several parameters were noted, including range of motion, disc angles, shell angles, anterior and posterior disc heights, translation, and center of rotation. Preoperative and postoperative data were compared using the Student t-test with a significance level of p < 0.05.

Results

Postoperatively, all 3 disc groups maintained adequate range of motion at the implanted level. With respect to the shell angles, the Synergy disc demonstrated the least variability, maintaining 6° lordotic configuration between the device endplates. In the Bryan disc group, significant shell kyphosis developed postoperatively (p < 0.0001). Both ProDisc-C and Synergy discs significantly increased anterior and posterior disc heights (p < 0.0001). The Bryan and Synergy discs maintained the natural center of rotation, whereas significant anterior shift occurred with ProDisc-C.

Conclusions

The goal for motion preservation at the implanted level was achieved using all 3 devices. The Synergy disc was unique in its ability to alter device angulation by 6°. The Bryan disc demonstrated device endplate kyphosis. Both the Synergy disc and ProDisc-C increased disc space height.

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Editorial

Surgical complications in adult spondylolisthesis

Michael G. Fehlings and Doron Rabin

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Abhaya V. Kulkarni, James M. Drake, Doron Rabin, Peter B. Dirks, Robin P. Humphreys and James T. Rutka

Object. In the preceding article, the authors described the Hydrocephalus Outcome Questionnaire (HOQ), a simple, reliable, and valid measure of health status in children with hydrocephalus. In the present study, they present their initial experience in using the HOQ to quantify the health status in a typical cohort of children with hydrocephalus.

Methods. The mothers of children with hydrocephalus completed the HOQ and, with the child's attending surgeon, provided a global rating of their children's health. An exploratory analysis was performed using a multivariate analysis of variance (ANOVA) to determine which variables might be associated with worse health status.

The mothers of 80 children, ranging in age from 5 to 17 years, participated in the study. The mean HOQ Overall Health score was 0.68, a value estimated to be equivalent to a mean health utility score of 0.77. The global health ratings provided by the mothers and the surgeons were moderately correlated with the HOQ scores (Pearson correlations 0.58 and 0.57, respectively). Results of the multivariate ANOVA indicated that the presence of epilepsy was strongly associated with a worse health status (p < 0.0001, F-test).

Conclusions. The health status of a typical sample of children with hydrocephalus was measured using the HOQ. The only consistently significant association with health status found was the presence of epilepsy.