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At least 19 recordsLinked to original sources
PubMed1997

Clinical outcome after spinal fusion with a rigid versus a semi-rigid pedicle screw system.

Several biomechanical studies have evaluated the quality of fusion obtained with a rigid versus a semi-rigid pedicle screw implant. Some studies indicate that increased rigidity of the implant system results in an increased strength of the fusion mass. Other reports have underlined the risk of stress shielding due to rigid implant systems. Based on these findings some authors have recommended the use of a semi-rigid system. There are, however, few studies focusing on any possible difference in clinical outcome between the two different types of implant systems. Questionnaires were sent to 89 patients who had undergone primary spinal fusion with either a rigid or a semi-rigid pedicle-screw-based implant system. In every case the diagnosis was spondylolisthesis or degenerative lumbar disease. The questionnaires were analysed using forward stepwise logistic regression analysis. Eighty (90%) of the questionnaires were returned. There was a mean follow-up of 4 years (range 2-8 years). It was not possible to demonstrate any difference in clinical outcome between patients undergoing lumbar fusion with a rigid implant system and those given a semi-rigid system. The overall patient satisfaction rate was 69%, with no difference between the two types of implant. No difference in clinical outcome between the two types of implant was found. Considering the fact that the primary goal of spinal fusion procedure is to obtain a solid fusion mass, biomechanical tests favour the used of a rigid pedicle screw system. This fact combined with the fact that early mobilisation is possible with rigid implants justifies the use of rigid implant systems, although no difference in clinical outcome could be demonstrated in this study.

Adolescent↗
PubMed2003

Semi-rigid vs rigid glass fibre casting: a biomechanical assessment.

OBJECTIVES: To determine if semi-rigid synthetic casts provide any measurable advantages compared to rigid synthetic casts. BACKGROUND: Glass fibre bandages are now commonly applied immediately post-injury to provide rigid immobilisation of the limb, for both weight bearing and non-weight bearing casts. However, composite casts that have inherent flexibility are also available and it is claimed they provide some functionality. METHODS: Five members of the orthopaedic department each applied a rigid and a semi-rigid below elbow (Colles) and a below knee walking cast to a single volunteer subject. Joint immobilisation and functional movement was assessed using electrogoniometry and limb support using pressure transducers. RESULTS: Semi-rigid Colles casts provided slightly greater immobilisation at the wrist while allowing full finger function and greater support to the forearm during hand movements. Similarly, semi-rigid below knee walking casts produced greater immobilisation at the ankle while allowing more forefoot movement and were less of an impediment to walking. CONCLUSIONS: Semi-rigid casting techniques have measurable advantages compared to rigid synthetic casts and represent a further development in the conservative management of fractures and soft tissue injuries. RELEVANCE: Semi-rigid casting is a relatively new technique that can reduce some of the problems of rigid cast immobilisation and could potentially shorten the rehabilitation phase following injury. Information about the performance of these casts to assess their value in specific applications is very limited.

Ankle Injuries↗
PubMed2005

Expandable and rigid endorectal coils for prostate MRI: impact on prostate distortion and rigid image registration.

Endorectal coils (ERCs) are used for acquiring high spatial resolution magnetic resonance (MR) images of the human prostate. The goal of this study is to determine the impact of an expandable versus a rigid ERC on changes in the location and deformation of the prostate gland and subsequently on registering prostate images acquired with and without an ERC. Sagittal and axial T2 weighted MR images were acquired from 25 patients receiving a combined MR imaging/MR spectroscopic imaging staging exam for prostate cancer. Within the same exam, images were acquired using an external pelvic phased array coil both alone and in combination with either an expandable ERC (MedRad, Pittsburgh, PA) or a rigid ERC (USA Instruments, Aurora, OH). Rotations, translations and deformations caused by the ERC were measured and compared. The ability to register images acquired with and without the ERC using a manual rigid-body registration was assessed using a similarity index (SI). Both ERCs caused the prostate to tilt anteriorly with an average tilt of 18.5 degrees (17.4 +/- 9.9 and 19.5 +/- 11.3 degrees, mean +/- standard deviation, for expandable and rigid ERC, respectively). However, the expandable coil caused a significantly larger distortion of the prostate as compared to the rigid coil; compressing the prostate in the anterior/posterior direction by 4.1 +/- 3.0 mm vs 1.2 +/- 2.2 mm (14.5% vs 4.8%) (p < 0.0001), and widening the prostate in the right/left direction by 3.8 +/- 3.7 mm vs 1.5 +/- 3.1 mm (8.3% vs 3.4%) (p = 0.004). Additionally, the ability to manually align prostate images acquired with and without ERC was significantly (p < 0.0001) better for the rigid coil (SI = 0.941 +/- 0.008 vs 0.899 +/- 0.033, for the rigid and expandable coils, respectively). In conclusion, the manual rigid-body alignment of prostate MR images acquired with and without the ERC can be improved through the use of a rigid ERC.

Biophysical Phenomena↗
PubMed1990

Striatal and nigral neuron subpopulations in rigid Huntington's disease: implications for the functional anatomy of chorea and rigidity-akinesia.

Neuropeptide immunohistochemistry was used to test several hypotheses of the anatomical bases of chorea and rigidity-akinesia. To test the hypothesis that elevated concentration of striatal somatostatin causes chorea, we visually compared the density of striatal neurons containing somatostatin and neuropeptide Y in brains affected by choreic or rigid-akinetic Huntington's disease (HD). The density of these neurons was elevated in both rigid-akinetic and choreic HD specimens with an apparently normal total number of these neurons, indicating that elevated somatostatin concentration, by itself, does not lead to chorea. We tested the hypothesis that rigid-akinetic HD results from deficient dopaminergic nigrostriatal neurotransmission by examining tyrosine hydroxylase-immunoreactive (TH-IR) neurons in the substantia nigra. In rigid-akinetic HD brains, there was no obvious reduction of nigral TH-IR neurons, indicating that rigid-akinetic HD is probably not due to loss of nigral dopaminergic neurons. Finally, we also examined the status of striatal projection neurons and found near total loss of all striatal neurons projecting to the lateral globus pallidus, medial globus pallidus, and substantia nigra in brains affected by rigid-akinetic HD in contrast to the preservation of neurons projecting to the medial globus pallidus in choreic HD. These results are consistent with the hypothesis that chorea results from preferential loss of striatal neurons projecting to the lateral globus pallidus and that rigid-akinetic HD is a consequence of the additional loss of striatal neurons projecting to the medial segment of the pallidum.

Adult↗
PubMed1993

Rigid and non-rigid kinetic depth effect with rotating discrete helices.

To examine the conditions in which human observers fail to recover the rigid structure of a three-dimensional object in motion we used simulations of discrete helices with various pitches undergoing either pure rotation in depth (rigid stimuli) or rotation plus stretching (non-rigid stimuli). Subjects had either to rate stimuli on a rigidity scale (Experiments 1 and 2) or to judge the amount of rotation of the helices (Experiments 3 and 4). We found that perceived rigidity depended on the pitch of the helix rather than on objective non-rigidity. Furthermore, we found that helices with a large pitch/radius ratio were perceived as highly non-rigid and that their rotation was underestimated. Experiment 5 showed that the detection of a pair of dots rigidly related (located on the helix) against a background of randomly moving dots is easier at small phases in which the change of orientation across frames is also small. We suggest that this is because at small phases the grouping of dots in virtual lines does occur and that this may be an important factor in the perceived nonrigidity of the helices.

Adult↗
PubMed1996

Craniofacial growth in rabbits after rigid or semi-rigid fixation of the frontonasal suture.

Treatment of craniofacial dysostosis involves complex remodeling of the cranium and facial bones. Maintenance of the newly positioned segments may be achieved by rigid fixation using plates; however, there is concern that, over time, these plates may interfere with normal growth. The purpose of this study was to test a method of "semi-rigid" fixation of an osteotomy of the frontonasal suture in juvenile rabbits by comparing standardized parameters of craniofacial growth after conventional suture plating with the experimental plating method and with growth after sham operation. Forty-five, 6-week-old, weanling rabbits were divided into three groups of 15 each (12 for cephalometry, 3 for histological examination): (group 1) control, sham operated; (group 2) rigid fixation; (group 3) semi-rigid fixation. Rabbits were maintained for 14 weeks. Craniofacial growth was assessed using three-dimensional image analysis techniques. Measurements were subjected to statistical analysis (one-way analysis of variance) to compare the three treatment groups. Pairwise comparison of means between the treatment groups was done using Bonferroni's method at the 0.05 significance level. Semi-rigid fixation permitted significantly more normal growth of the developing rabbit head than rigid fixation in total snout length, total vault length, left and right midface height, and left orbital length. Both semi-rigid and rigid fixation significantly restricted growth compared with sham operated animals in left and right posterior midface height, right orbital length, right and left nasal bone length, and left parietal width. There were no significant differences in the growth of all other parameters measured.

Animals↗
PubMed2006

Mechanical interactions of an implant/tooth-supported system under different periodontal supports and number of splinted teeth with rigid and non-rigid connections.

OBJECTIVES: This study investigated the mechanical interactions of implant-teeth splinting systems under different periodontal supports and number of splinted teeth with rigid and non-rigid connectors using non-linear finite element (FE) approach. METHODS: Two FE models with normal and compromised periodontal supports containing a Frialit-2 implant splinted to the first and second premolars were constructed. Non-linear contact elements were used to simulate a realistic interface fixation within the implant system and the sliding function of the non-rigid connector. ANOVA was used to test for relative importance of the investigated factors and main effects for each level of the three investigated factors (periodontal supports, teeth splinting and connector designs) in terms of the stress values were performed. RESULTS: The simulated results indicated that the cross-interaction of the periodontal support and the splinting situation was a major factor affecting the stress value in alveolar bone. An additional splinting decreased the stress values of bone significantly for a compromised periodontal support. The individual factor of periodontal support also influenced the stress found in the alveolar bone (28%) and implant (72%), and the stress values increased when the periodontal support was reduced. Using different connectors affected the stresses found in bone (15%), implant (21%) and prosthesis (99%). The stress values of the implant and prosthesis increased, but were decreased in bone when the splinting system used non-rigid connectors. The mobility of natural teeth and the implant system between non-rigid and rigid connections showed only small differences. CONCLUSIONS: A non-rigid connector should be used with caution since it breaks the stress transfer and increases the unfavorable stress values in the implant system and prosthesis. The tooth/implant-supported system with an additional splinting is more efficient in compromised periodontal supports.

Alveolar Process↗
PubMed1989

Rigid spine syndrome and rigid spine sign in myopathies.

We studied eight patients with rigid spine syndrome aged 8 to 20 years at the time of first examination. Muscle weakness, rigid spine, and flexion contracture of elbows and ankles were noted in the first 6 years of age. Radiological study of the cervical spine revealed considerable reduction not only of flexion, but also of extension, of the neck. The "alligator sign" was demonstrated. Progression of scoliosis and of contractures reduced the functional capacity in six patients. A restrictive ventilatory syndrome was observed in all, while central apneas with oxygen desaturation were shown in two. Cardiac arrhythmias were observed in four. We suggest that a distinction should be made between myopathic rigid spine and rigid spine syndrome. Myopathic rigid spine is a clinical sign which is rarely sought but is present in several types of well-defined myopathies, meaning the myopathic involvement of the extensor muscles of the spine. Rigid spine syndrome is an axial myopathy with peculiar clinical and radiographic signs and a characteristic natural history.

Adolescent↗
PubMed1996

Transtracheal aspiration using rigid bronchoscopy and a rigid needle for investigating mediastinal masses.

BACKGROUND: Use of the flexible needle via the fibreoptic bronchoscope to aspirate mediastinal nodes or masses has largely superseded the use of the rigid needle via the rigid bronchoscope. However, the yield at fibreoptic bronchoscopy is relatively low, although this improves with the use of a wider gauge needle. In this study the sensitivity and the safety of rigid needle sampling of the mediastinum in the diagnosis of lung cancer is evaluated. METHODS: Transtracheal needle aspiration (TTNA) was performed with the rigid bronchoscope and a rigid aspiration needle under general anaesthesia using a previous computed tomographic (CT) scan as a guide to the sample site. A cytopathologist immediately examined the specimens for adequacy and preliminary diagnosis, thus determining the number of aspirations. RESULTS: Twenty four patients were evaluated. The diagnostic sensitivity of TTNA was 88%. This led to a management decision in 21 patients. There were no false positives and no complications. CONCLUSIONS: TTNA using the rigid bronchoscope with CT scanning and a cytopathologist present is a sensitive and safe way of diagnosing lung cancer in patients with a mediastinal mass or enlarged mediastinal nodes.

Adult↗
PubMed1984

Maximizing rigidity: the incremental recovery of 3-D structure from rigid and nonrigid motion.

The human visual system can extract 3-D shape information of unfamiliar moving objects from their projected transformations. Computational studies of this capacity have established that 3-D shape can be extracted correctly from a brief presentation, provided the moving objects are rigid. The human visual system requires a longer temporal extension, but it can cope with considerable deviations from rigidity. It is shown how the 3-D structure of rigid as well as nonrigid objects can be recovered by maintaining an internal model of the viewed object and modifying it at each instant by the minimal nonrigid change that is sufficient to account for the observed transformation. The results of applying this incremental rigidity scheme to rigid and nonrigid objects in motion are described and compared with human perception.

Computers↗
PubMed1996

A comparative biomechanical analysis of resorbable rigid fixation versus titanium rigid fixation of metacarpal fractures.

Linear (two-dimensional) and three-dimensional (3D) plating systems (Poly-Medics) composed of the resorbable copolymer of polyglycolic acid (PGA) and poly-l-lactic acid (PLLA) (Lactosorb) were studied in vitro. The plates were applied to osteotomized fresh frozen human cadaveric metacarpal bones that were then tested for torsional rigidity and three-point bending strength and rigidity. The results were compared to those from another study of two low-profile titanium plating systems (Leibinger and Synthes). Analysis of variance revealed that the linear-flat Lactosorb plate and screws had apex dorsal rigidity and force-to-displacement measurements equal to all but two of the titanium plates (3D). The 3D-flat Lactosorb plate had the highest torsional rigidity of the resorbable system, but it was only moderately rigid compared to the titanium plating systems. This in vitro biomechanical study of the copolymer PGA-PLLA plating system indicates that, in clinical applications, it may be better suited for metacarpal fractures rather than proximal phalangeal fractures due to the lower demands of torsional loading compared to apex bending.

Biomechanical Phenomena↗
PubMed1993

Rigidity, sensitivity and quality of attachment: the role of maternal rigidity in the early socio-emotional development of premature infants.

The associations between a mother's rigidity, her sensitivity in early (3 month) interaction and the quality of her premature infant's attachment at 13 months were investigated. Rigidity as a personality characteristic was not found to be significantly associated with sensitivity or quality of attachment. Rigid attitudes to child rearing were related to sensitivity and to the responsivity of the infant. Rigid attitudes were not related to security of attachment. Infants who were rated less responsive at 3 months, however, tended to be less securely attached, and high Attitude Rigidity in the mother increased their chances of an insecure attachment.

Adult↗
PubMed2006

The influence of sole wedges on frontal plane knee kinetics, in isolation and in combination with representative rigid and semi-rigid ankle-foot-orthoses.

BACKGROUND: In earlier stages of knee osteoarthritis orthotic treatments with knee orthoses or modified footwear are often considered. Although the load reducing effects of knee orthoses have been well established, wearing modified footwear would be more comfortable for the patient and less encumbering. The effect of modified footwear on the frontal load of the knee is controversial. This article describes the effect of medial or lateral shoe wedges alone or together with two different types of ankle-stabilizing orthoses. METHODS: The effect on frontal knee loading was measured during standing and walking with medially and laterally placed wedges under the sole of the shoe. The wedges were also combined with two types of orthotic devices - an Ankle-Foot-Orthosis that was rigid in the frontal plane but allowed unrestricted sagittal plane motion and an ankle support that was semi-rigid in the frontal plane. Joint loading of 10 healthy persons (mean (standard deviation): age 34 (9) years, height 178 (4)cm, mass 73 (9)kg) was investigated by means of a special measuring device that accurately determines static loads (Lasar Posture) and with instrumented gait analysis (Vicon/Kistler). FINDINGS: Using a lateral wedge under the sole of the shoe (without orthotic support) showed no significant reduction in the mean maximal knee moment in the frontal plane. Adding an Ankle-Foot-Orthosis that is rigid in the frontal plane resulted in significant reduction in the maximal frontal moment from 0.54 Nm/kg to 0.38Nm/kg (p0.01). Using a medial wedge, without and with Ankle-Foot-Orthosis, produced a significant increase in the maximal frontal moment to 0.59 Nm/kg (p0.05) or 0.67 Nm/kg (p0.01), respectively. INTERPRETATION: These results suggest that the application of a sole wedge significantly influences frontal knee loading when used in combination with an Ankle-Foot-Orthosis that is rigid in the frontal plane.

Adult↗
PubMed1988

Transport properties of rigid bent-rod macromolecules and of semiflexible broken rods in the rigid-body treatment. Analysis of the flexibility of myosin rod.

The translational diffusion coefficients, rotational relaxation times and intrinsic viscosities of rigid bent rods, composed by two rodlike arms joined rigidly at an angle alpha, have been evaluated for varying conformation using the latest advances in hydrodynamic theory. We have considered semiflexible rods in which the joint is an elastic hinge or swivel, with a potential V(alpha) = 1/2Q alpha 2 with constant Q. Accepting the rigid-body treatment, we calculate properties of broken rods by averaging alpha-dependent values for rigid rods. The results are finally used to interpret literature values of the properties of myosin rod. Q is regarded as an adjustable parameter, and the value fitted is such that the average bending angle of myosin rod is approximately 60 degrees.

Mathematics↗
PubMed1998

The perceived rigidity of rotating eight-vertex geometric forms: extracting nonrigid structure from rigid motion.

In four experiments, subjects examined four categories of rotating eight-vertex geometric forms in parallel projection. Some of the figures appeared to deform, even though rigid three-dimensional interpretations were possible mathematically. Our results from several deformation-rating tasks indicated that most of the configurations maintained a rigid appearance throughout their rotations, although one category of stimuli appeared to deform more frequently than the others. Configurations from the category that contained a high proportion of stimuli that appeared to deform were also shown to be more difficult to discriminate from stimuli that had no rigid three-dimensional interpretation (measured using a signal detection task). To account for these findings, a theory was formulated based on the use of monocular depth cues in the perception of shape. Static monocular depth cues we define as those which are present in non-moving stimuli and Dynamic monocular depth cues are those that are only present in moving stimuli. We conclude that static cues dominate the perception of shape when humans respond to parallel (and, most likely, polar) projections of rotating objects with rigid three-dimensional interpretations. Further, subjects cannot respond to the motion or acceleration profile of part of such a stimulus without responding to the figure as a whole.

Adult↗
PubMed2005

Comparison of hexaminolevulinate based flexible and rigid fluorescence cystoscopy with rigid white light cystoscopy in bladder cancer: results of a prospective Phase II study.

INTRODUCTION AND OBJECTIVE: Several studies have shown that rigid fluorescence cystoscopy (RFC) with hexaminolevulinate (HAL) is superior to standard rigid white light (RWLC) cystoscopy in diagnosing bladder tumours, with a clinically relevant impact on the patient's management. These studies, however, have been done with rigid cystoscopes. We carried out a study to evaluate whether the technique of fluorescence cystoscopy with HAL was also feasible with a specially designed flexible fluorescence cystoscope (FFC). METHODS: 20 patients with known or suspected bladder cancer were included in a comparative within patient controlled Phase II study. All patients signed informed consent. All patients received 50 ml of HAL (Hexvix) 8 mM 1h prior to transurethral resection. Using a D-light-C system (Storz, Germany), FFC and RFC were performed followed by RWLC. All lesions visible during these three cystoscopies were mapped, taped and resected. RESULTS: In these 20 patients (mean age 71 years (49-89), 3 females) mean HAL instillation time was 81 min. Overall 27 histologically confirmed lesions were found in 19 patients. Detection rates in these 19 patients were 14 with FFC, 17 with RFC and 15 with RWLC. Of the 27 lesions 19 were detected with FFC, 23 with RFC and 20 with RWLC. Overall fluorescence intensity using the flexible system was 76% (30-147%) as compared to RFC using a visual analogue score. No side effects were noted which were attributable to HAL. CONCLUSION: The use of FFC is feasible and seems to be comparable to RWLC and slightly inferior to RFC. Larger studies should determine the role of flexible fluorescence cystoscopy.

Aged↗
PubMed1998

Comparison of the results of short-term rigid and semi-rigid cast immobilization for the treatment of grade 3 inversion injuries of the ankle.

In this prospective, randomized study, short-term immobilization with semi-rigid (Soft Cast) and rigid (Scotchcast Plus) synthetic cast materials were compared for the functional treatment of acute grade 3 lateral ligament injuries of the ankle. Degree of ligament injury was assessed by clinical criteria. Duration of immobilization was 2 weeks for both groups and home physiotherapy was started thereafter. Fifty-seven patients completed the study and both materials were found to be equally effective in providing a stable ankle at the end of 6 weeks follow-up. Soft Cast group had better range of motion and could walk better at 2 weeks, but these differences diminished at 6 weeks. With the Soft Cast, patient satisfaction was higher, need for a support for walking was less and return to work was earlier. When combined with the reduced cost of application, Soft Cast is the material of choice for the initial short-term immobilization for the functional treatment of acute ankle ligament injuries.

Adolescent↗