Biomedical subjects

Karin Werner

Publications and source records attributed to Karin Werner.

4 recordsLinked to original sources

PubMed2006

Biomechanical evaluation of a new total posterior-element replacement system.

STUDY DESIGN: In vitro study to characterize the flexibility of a new total posterior-element system when instrumented to L4-L5 segments. OBJECTIVE: The goal of this in vitro study was to investigate whether an optimized version of the TOPS implant (Impliant Ltd., Ramat Poleg, Israel) is capable to restore the physiologic motion characteristic of a spinal segment after facetectomy. SUMMARY OF BACKGROUND DATA: The TOPS implant is designed to replace the posterior elements of a functional spinal unit, to provide flexible restabilization and spinal alignment, while maintaining the intervertebral disc. The implant is composed of bilateral pedicle screws, connected with 2 crossbars in the transversal plane. The crossbars are joined together by an elastic element capable of transmitting tensile and compressive loads, as well as shear forces. METHODS: Six human cadaver specimens (L3-S1) (median age 61 years: minimum 47 and maximum 74 years) were used for this in vitro experiment. The specimens were loaded with pure moments of +/-7.5 Nm in flexion/extension, lateral bending, and axial rotation. The following states were investigated: (1) intact; (2) after bilateral laminectomy, including facetectomy of the lower facet joints, of the upper vertebra L4; and (3) after device implantation. The range of motion (ROM), neutral zone, and intradiscal pressure were determined from a third cycle. In a second step, the ROM in axial rotation was determined as a function of different flexion/extension postures. RESULTS: In the neutral position, the laminectomy and facetectomy increased the median values of the ROM in flexion plus extension, lateral bending right plus left, and significantly in axial rotation left plus right from: 8.2 degrees, 7.6 degrees, 3.6 degrees to 12.1 degrees, 8.5 degrees, and 8.5 degrees (Wilcoxon signed rank test; P < 0.05). After fixation of the implant, the ROM was again reduced to 6.8 degrees, 7.8 degrees, and 3.8 degrees. In a flexed posture, the ROM in axial rotation was slightly increased compared to the neutral position. With increasing extension, the axial rotation decreased linearly from 3.7 degrees in neutral position to 2.3 degrees in 4 degrees extension in the segment L4-L5. The characteristic of the intradiscal pressure versus load with the implant was similar to that of the intact specimen. CONCLUSION: The TOPS implant almost ideally restored the ROM in lateral bending and axial rotation compared to that of the intact specimen. In the sagittal plane, 85% of the intact ROM could be obtained. The ROM in axial rotation as a function of flexion and extension angle also mimics the biomechanical behavior of the posterior complex of a lumbar spine. This relationship between ROM and posture emphasizes the importance of a proper implantation.

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PubMed2006

Validity and interobserver agreement of a new radiographic grading system for intervertebral disc degeneration: Part II. Cervical spine.

A new radiographic grading system for a more objective assessment of lumbar intervertebral disc degeneration has been described and tested in Part I of this study. The aim of the present Part II of the study was to adapt this system to the cervical spine, and to test it for validity and interobserver agreement. Some modifications of the grading system described in Part I were necessary to make it applicable to the cervical spine. Its basic structure, however, stayed untouched. The three variables "Height Loss", "Osteophyte Formation" and "Diffuse Sclerosis" first have to be graded individually. Then, the "Overall Degree of Degeneration" is assigned on a four-point scale from 0 (no degeneration) to 3 (severe degeneration). For validation, the radiographic degrees of degeneration of 28 cervical discs were compared to the respective macroscopic ones, which were defined as "real" degrees of degeneration. The interobserver agreement was determined between one experienced and one unexperienced observer using the radiographs of 57 cervical discs. Quadratic weighted Kappa coefficients (kappa) with 95% confidence limits (95% CL) were used for statistical evaluation. The validation of the new version of the radiographic grading system showed a moderate agreement with the "real", macroscopic overall degree of degeneration (kappa=0.599, 95% CL 0.421-0.786). In 64% of all discs the "real" overall degree of degeneration was underestimated but never overestimated. This underestimation, however, was much less pronounced and the Kappa coefficients were significantly higher for the three variables: Height Loss, Osteophyte Formation, and Diffuse Sclerosis separately. The agreement between the radiographic ratings of the experienced and the unexperienced observer was substantial for the overall degree of degeneration (kappa=0.688, 95% CL 0.580-0.796), almost perfect for the variable, Height Loss, moderate for Osteophyte Formation and fair for Diffuse Sclerosis. In conclusion, we believe that the new version of the radiographic grading system is a sufficiently valid and reliable tool to quantify the degree of degeneration of individual cervical intervertebral discs. In comparison to the version for the lumbar spine described in Part I, however, a slightly higher tendency to underestimate the "real" overall degree of degeneration and somewhat higher interobserver differences have to be expected.

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PubMed2005

Validity and interobserver agreement of a new radiographic grading system for intervertebral disc degeneration: Part I. Lumbar spine.

Many different radiographic grading systems for disc degeneration are described in literature. However, only a few of them are tested for interobserver agreement and none for validity. Furthermore, most of them are based on a subjective terminology. The aim of this study, therefore, is to combine these systems to a new one in which all subjective terms are replaced by more objective ones and to test this new system for validity and interobserver agreement. Since lumbar and cervical discs need to be graded differently, this study was divided into the present Part I for the lumbar and a Part II for the cervical spine. The new radiographic grading system covers the three variables "Height Loss", "Osteophyte Formation" and "Diffuse Sclerosis". On lateral and postero-anterior radiographs, each of these three variables first has to be graded individually. Then, the "Overall Degree of Degeneration" is assigned on a four-point scale from 0 (no degeneration) to 3 (severe degeneration). For validation, the radiographic degrees of degeneration of 44 lumbar discs were compared to the respective macroscopic ones, which were defined as "real" degrees of degeneration. The agreement between observers with different levels of experience was determined using the radiographs of 84 lumbar discs. Agreement was quantified using quadratic weighted Kappa coefficients (Kappa) with 95% confidence limits (95% CL). The validation of the new radiographic grading system revealed a substantial agreement between the radiographic and the "real" macroscopic overall degree of degeneration (Kappa=0.714, 95% CL: 0.587-0.841). The radiographic grades, however, tended to be slightly lower than the "real" ones. The interobserver agreement was substantial for all the three variables and for the overall degree of degeneration (Kappa=0.787, 95% CL: 0.702-0.872). However, the inexperienced observer tended to assign slightly lower degrees of degeneration than the experienced one. In conclusion, we believe that the new radiographic grading system is an almost objective, valid and reliable tool to quantify the degree of degeneration of individual lumbar intervertebral discs. However, the user should always remember that the "real" degree of degeneration tends to be underestimated and that slight differences between the ratings of observers with different levels of experience have to be expected.

Adult↗

PubMed2003

[Stem cell network North Rhine-Westphalia].

The Stem Cell Network NRW is an initiative of the North Rhine Westphalian Ministry of Science and Research. A statewide organization involving research facilities in Aachen, Bielefeld, Bochum, Bonn, Cologne, Düsseldorf, Essen and Münster, it covers virtually the whole spectrum of scientific issues in the field of adult and embryonic stem cell research. The Network consists of two working groups. One focuses on biomedical, the other on ethical, legal and sociological issues. In these groups, top scientists, doctors, philosophers, theologians, sociologists and legal experts combine their expertise with a view to making stem cell research responsible and transparent. The Stem Cell Network NRW is a model example of the North Rhine Westphalian government's strategy of identifying, promoting and creating a common platform for the research disciplines of the future--for the benefit of science, business and above all society at large.

Adult↗