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J Dvorak

Publications and source records attributed to J Dvorak.

At least 109 records · Page 6Linked to original sources
PubMed1994

On the understanding of clinical instability.

STUDY DESIGN: Three-dimensional flexibility changes due to the application of an external fixator at C4-C5 were studied in cervical spine specimens. OBJECTIVES: To evaluate the biomechanical effects of applying a cervical external fixator to a patient using an in vitro model. SUMMARY OF BACKGROUND DATA: There is controversy regarding the relationship between the changes in spinal motion and clinical instability. METHODS: Using fresh cadaveric C4-C7 specimens, multidirectional flexibility was measured at all vertebral levels, before and after the fixator application at C4-C5, C5-C6, and C4-C6. RESULTS: The average ranges of motion for flexion, extension, lateral bending, and axial rotation were 8.3 degrees, 7.2 degrees, 5.3 degrees, and 5.6 degrees, which decreased by 40%, 27%, 32%, and 58%, respectively, because of the fixator application. The corresponding neutral zones were 3.4 degrees, 3.4 degrees, 3.0 degrees, and 2.0 degrees, which decreased by 76%, 76%, 54% and 69%, respectively. The decreases with the fixation at C4-C5 were similar to those for fixation at C5-C6. CONCLUSIONS: This in vitro study documented that the application of an external fixator to the cervical spine decreases the intervertebral motion in general, and decreases flexion, extension and torsional neutral zones in particular. The findings help explain the clinical instability of the spine and support the hypothesis that the neutral zone is more closely associated with the clinical instability than is the range of motion.

Adult↗
PubMed1994

The role of plate and screw fixation in occipitocervical fusion in rheumatoid arthritis.

STUDY DESIGN: In a clinical retrospective study, the results of occipitocervical fusion in patients with rheumatoid arthritis were studied and analyzed. OBJECTIVES: The results of two different operative techniques were compared. The advantages of screw fixation compared with wiring techniques in this population of patients were investigated. SUMMARY OF BACKGROUND DATA: Numerous different implants have been presented in the literature for occipitocervical fusion in patients with rheumatoid arthritis. The use of wires being the standard fixation technique. METHODS: Occipitocervical fusion was performed in patients with rheumatoid arthritis: 26 patients with the wiring technique and 33 patients with a new Y-plate fixation. The results were compared at a follow-up period of 24 months and 50 months, respectively. Clinical and radiologic results were investigated. RESULTS: The atlantodental distance could be significantly better reduced in the group with the Y-plate fixation and the neurologic improvement in the wiring group was 40%, whereas in the Y-plate fixation 86% of neurologic improvement was observed. Pseudarthrosis was seen in 27% of the wiring technique and in 6% in the plate and screw fixation technique. CONCLUSIONS: In occipitocervical fusion for patients with rheumatoid arthritis, the screw and plate fixation technique provides superior results than other techniques using wire fixations.

Arthritis, Rheumatoid↗
PubMed1994

Wilhelm Schulthess.

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History, 19th Century↗
PubMed1994

Jean-André Venel.

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History, 18th Century↗
PubMed1994

[Determining the status of the cervical spine after whiplash injury].

The results of medical investigations following acceleration mechanism to the cervical spine (so called "soft tissue neck injury") are to be described in common diagnostic terms. Biomechanical and legal considerations are beyond medical competence. In certain cases, the clinical examination must be completed in cooperation with specialists. Within the entire medical context, the neuropsychological and neuropsychiatric assessment may contribute to a comprehensive understanding of the consequences. In cases of litigation, the full array of facts, like the patients' previous history, and differential diagnoses, have to be drawn to attention. At present, compensation takes place only exceptionally and in a limited range, if an impairment by an accompanying brain injury is excluded.

Accidents, Traffic↗
PubMed1994

[The unstable spine--an "in vitro" and "in vivo study" on better understanding of clinical instability].

In cases of suspected painful instability of a cervical segment, temporary external fixation by means of external fixator was applied. The segmental immobilization caused immediate relief of pain. The pain reoccurred after removal of the immobilization. The effect of immobilization by external fixation was investigated in biomechanical tests using fresh cadaveric C4-7 specimens. Multidirectional flexibility was measured before and after application of the fixator at C4/C5, C5/C6 and C4-6. We measured the reduction in motion between the different segments. In every situation the neutral zone decreased more than the range of motion. The findings are helpful to understand the clinical instability of the spine and support the hypothesis that the neutral zone is more closely associated with clinical instability than range of motion. The combination of clinical application and biomechanical investigation allowed us to establish a direct correlation between instability and pain.

Accidents, Traffic↗
PubMed1993

Posture affects motion coupling patterns of the upper cervical spine.

Measurements of motions of the cervical spine are used to help diagnose the problems of clinical instability due to degenerative changes and trauma. For a better interpretation of the three-dimensional motions of the upper cervical spine, knowledge of the effects of posture on these motions is necessary. Seven fresh human cadaveric C0-C3 spinal specimens were utilized. Each specimen was put in three distinct sagittal plane postures: full flexion, neutral, and full extension. At each posture, two load types were applied: left and right axial torques, and left and right lateral bending moments up to 1.5 Nm. The resulting three-dimensional relative motions of C0-C1 and C1-C2 were measured, with use of nonconstraining stereophotogrammetry, in the form of load-displacement curves. We found that the curves were nonlinear. The most dramatic change due to modification in posture was found in coupled sagittal plane rotation, which changed from extension at extended posture to flexion at flexed posture at both levels and in response to both load types. For the axial torque, the main axial rotation and coupled lateral bending changed little with posture. For the lateral bending moment, the main lateral bending rotation and coupled axial rotation decreased; the latter changed direction at C1-C2 as the spine was put into flexed posture. The motions for the right and left load applications generally were mirror images, except for the coupled sagittal plane rotations, which did not change with the direction of the load.

Adult↗
PubMed1993

Genetic control of sex determination in birds and the potential for its manipulation.

The sex determination systems of Drosophila, birds, marsupial mammals, and eutherian mammals are briefly reviewed. Evidence from poultry polyploids, aneuploids, and gynandromorphs suggests that avian sex is determined by Z to autosome ratio and also that avian sex-limited traits may be under both cell-autonomous and hormonal controls. To identify aneuploids in avian populations, a cDNA clone linked to both the Z and W chromosomes of many avian groups was used to screen large numbers of psittacine birds and identified five birds with atypical patterns of restriction fragments. Two of these birds were examined by laparoscopy and found to be intersexes. These preliminary observations indicate that structural changes in the Z and W chromosomes result in alterations of sex determination.

Animal Husbandry↗
PubMed1993

[Neurological causes for wrist pain].

The most common cause of wrist pain, due to neurological disorder is carpal tunnel syndrome. In aging patients with atrophy of the hand muscles it is to be differentiated from s.c. myelopathic hand, caused by denervation of anterior horn cells in conditions such as cervical spondylosis. The referred pain affiliated with palpable bands and trigger points in the muscles has to be also considered as origin of pain.

Carpal Tunnel Syndrome↗
PubMed1993

[Significance of simultaneous fusion and surgical decompression in lumbar spinal stenosis].

In a prospective study 45 patients with clinically relevant spinal stenosis of the lumbar spine were randomized in three groups. Group 1 underwent isolated decompression without fusion, group 2 had decompression and selected fusion, and group 3 underwent fusion of all decompressed segments. Patients with previous surgery of the lumbar spine or obvious instability, such as spondylolisthesis, were excluded from the study. The results were dominated by the relevant clinical improvement in the symptoms of spinal stenosis in all three groups. There were no statistical significant differences in the clinical results between the patients with and without fusion. We conclude that in the absence of obvious segmental instability, no fusion is required for decompressive surgery in degenerative lumbar spinal stenosis.

Aged↗
PubMed1992

Translaminar screw fixation of the lumbar spine.

Lower lumbar spinal fusion was carried out in 72 patients by a technique which involved screw fixation of the facet joints. Stability was achieved and mobilisation was allowed immediately. Radiographs after operation showed bony fusion in 94.5%. Pain was diminished and 76% of the patients would undergo the same treatment again. There were no neurological complications. The technique is useful and safe for the fusion of short segments of the lumbar spine.

Adolescent↗
PubMed1992

Biomechanical evaluation of four different posterior atlantoaxial fixation techniques.

Four different techniques for posterior atlantoaxial fusion were tested in vitro: 1) wire fixation with one median graft (Gallie type); 2) wire fixation with two bilateral grafts (Brooks type); 3) transarticular screw fixation (Magerl); and, 4) two bilateral posterior clamps (Halifax). The experiment was designed to determine the immediate three-dimensional stability of the spinal construct. Ten fresh human cadaveric specimens were tested intact, injured, and instrumented with each of the fixation techniques. The injury consisted of a severe soft tissue injury model, in which the alar, transverse, and capsular ligaments were transected. The three-dimensional motions of C1 relative to C2 were measured as the specimens were subjected to loads of pure moments in flexion-extension, axial rotation, and lateral bending. Each fixation technique significantly decreased motion in all directions, as compared to the intact and injured spines. We found that the Gallie system generally allowed significantly more rotation in flexion, extension, axial rotation, and lateral bending than the other three fixation techniques. There was generally no significant difference between the amount of rotation with the other three fixation techniques. However, the Magerl technique tended to allow the least rotation. The anteroposterior translation of two points on C1 were about equal for all fixation techniques.

Atlanto-Axial Joint↗
PubMed1992

Age and gender related normal motion of the cervical spine.

The purpose of this study was to develop a clinical method for measuring three-dimensional motion of the cervical spine using the CA 6000 Spine Motion Analyzer (Orthopaedic Systems Inc., Hayward CA). Normal values for passive examinations of flexion-extension, lateral bending, rotation, rotation out of maximum flexion, and rotation out of maximum extension were obtained and analyzed for each gender in a group of 150 normal subjects. Gender classifications were further subdivided into age groups, with each decade containing asymptomatic volunteers. Values for each group were compared for differences with respect to age and gender differences. A detailed error analysis was also performed on the interobserver and intraobserver repeatability, differences between passive and active testing, and the use of different fixation devices. Significantly decreased motion differences were found between age groups within gender, and between gender groups in corresponding decades. Results of rotation out of maximum flexion suggest and support earlier conclusions that the rotation of the C1-C2 segment does not decrease with age, but rather increases slightly to perhaps compensate for the overall decreased motion in the lower segments.

Adult↗
PubMed1991

Chloroplast DNA evidence for a North American origin of the Hawaiian silversword alliance (Asteraceae).

Chloroplast DNA restriction-site comparisons were made among 24 species of the Hawaiian silversword alliance (Argyroxiphium, Dubautia, and Wilkesia) and 7 species of North American perennial tarweeds in Adenothamnus, Madia, Raillardella, and Raillardiopsis (Asteraceae-Madiinae). These data and results from intergeneric hybridization indicated surprisingly close genetic affinity of the monophyletic Hawaiian group to two diploid species of montane perennial herbs in California, Madia bolanderi and Raillardiopsis muirii. Of 117 restriction-site mutations shared among a subset of two or more accessions, more than one-fifth (25 mutations) separated the silversword alliance, M. bolanderi, and Raillardiopsis from Adenothamnus and Raillardella. An additional 10 mutations distinguished the silversword alliance, M. bolanderi, and R. muirii from Adenothamnus, Raillardella, and Raillardiopsis scabrida. Phylogenetic analyses of these data and production of vigorous hybrids of the combinations Dubautia laevigata x R. muirii and (Dubautia knudsenii x Dubautia laxa) x M. bolanderi reinforce and refine Carlquist's hypothesis [Carlquist, S. (1959) Aliso 4, 171-236] that the Hawaiian silversword alliance arose from American tarweeds. Ultimate origin of silversword alliance chloroplast DNA from within the Californian-endemic paraphyletic genus Raillardiopsis was supported with high bootstrap confidence. Geologic considerations and the distribution of sporophytic self-incompatibility among these species demonstrate that the tarweed ancestor of the silverswords overcame (i) a dispersal barrier of at least 3900 km of open ocean and (ii) the breeding barrier of self-incompatibility.

Journal Article↗
PubMed1991

Panfibrinonecrotic colitis in a dog treated by subtotal colectomy.

A dog with signs of small intestinal disease developed signs of severe large intestinal disease after being treated with multiple agents. Endoscopy and biopsy revealed total destruction of the colonic mucosa, which necessitated total parenteral nutrition plus subtotal colectomy. It was hypothesized that the multiple prior treatments led to an overgrowth of toxigenic or cytotoxic bacteria, which caused this colonic mucosal destruction.

Animals↗
PubMed1991

Effects of alar ligament transection on upper cervical spine rotation.

Fresh human cadaveric specimens of occiput (C0) to C3 were subjected to axial torque. The resulting physiological motions were studied in an unconstrained three-dimensional manner. Effects of sequential transections of the left and right alar ligaments on the relative motions of C0-C1 and C1-C2 were studied. After transection of the left alar ligament, ranges of motion--due to 1.5 Nm torque--increased at both the C0-C1 and C1-C2 joints. Increases were small, on average 1.9 degrees to each side and at each level. Increases due to subsequent cutting of the right alar ligament were, on average, only 0.5 degrees and statistically not significant. In general, neutral zones showed greater increases, e.g., 3.9 degrees to each side at the C1-C2 joint. Comparing right and left axial rotations, after transection of the left alar ligament, showed greater percentage increases for the right, as compared to the left, axial rotation, at both C0-C1 and C1-C2 joints. Functional loss of the alar ligaments indicates a potential for rotatory instability, which, however, must be determined in conjunction with other clinical findings, such as neurological dysfunction, pain, and deformity.

Adult↗