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PubMed1998

Normative data for strength and flexibility of women throughout life.

Previously established normative data for muscular strength, endurance and the flexibility of women have recently been criticized as being unreliable. Furthermore, no normative data for the muscular fitness of women over 70 years of age are established. The purpose of this study was to derive normative data for muscular fitness in women 20-70+ years old, and to compare these data to the most recently published norms of the American College of Sports Medicine (ACSM). A total of 304 independent-living women were evaluated for maximal performance of bench press, leg press, modified push-ups, grip strength, and sit-and-reach. Tables of normative values for each measurement were generated along with percentile rankings. Large discrepancies were found between these new data and those of the ACSM norms. Bench press norms from ACSM are comparatively high so that the average woman in this current sample scored below the 10th percentile of the ACSM rankings. Similarly, the average woman in our sample ranked in either the poor or fair category of the ACSM norms for modified push-ups, and in the poor ACSM category for sit-and-reach. In contrast, leg press scores for the average woman in this study fell within the good or excellent category of the ACSM norms, suggesting that the ACSM norms are too low. Grip strength for the middle-aged women in this study was higher than that in previous norms. These newly established norms are better suited for interpreting women's fitness test results than previously published norms.

Adult↗
PubMed2004

Emergence of adaptability to time delay in bipedal locomotion.

Based on neurophysiological evidence, theoretical studies have shown that locomotion is generated by mutual entrainment between the oscillatory activities of central pattern generators (CPGs) and body motion. However, it has also been shown that the time delay in the sensorimotor loop can destabilize mutual entrainment and result in the failure to walk. In this study, a new mechanism called flexible-phase locking is proposed to overcome the time delay. It is realized by employing the Bonhoeffer-Van der Pol formalism - well known as a physiologically faithful neuronal model - for neurons in the CPG. The formalism states that neurons modulate their phase according to the delay so that mutual entrainment is stabilized. Flexible-phase locking derives from the phase dynamics related to an asymptotically stable limit cycle of the neuron. The effectiveness of the mechanism is verified by computer simulations of a bipedal locomotion model.

Adaptation, Physiological↗
PubMed2005

'Initial state' coordinations reproduce the instant flexibility for human walking.

An important feature of human locomotor control is the instant adaptability to unpredictable changes of conditions surrounding the locomotion. Humans, for example, can seamlessly adapt their walking gait following a sudden ankle impairment (e.g., as a result of an injury). In this paper, we propose a theoretical study of the mechanisms underlying flexible locomotor control. We hypothesize that flexibility is achieved by modulating the posture at the beginning of the stance phase-the initial state. Using a walking model, we validate our hypothesis through computer simulations.

Adaptation, Physiological↗
PubMed2003

Active and passive behaviour in the regulation of stiffness of the lateral wall in outer hair cells of the guinea-pig.

The stiffness of the outer hair cell (OHC) lateral wall, measured by the micropipette aspiration technique, is non-linear, decreasing from the ciliary pole (stiffness parameter Sp 1.83+/-0.13 nN/microm n=10) towards the cell base (Sp 1.14+/-0.16 nN/microm, n=10) irrespective of the cochleoapical or cochleobasal origin of the cells. The length of the aspirated lateral wall segment was related exponentially to the duration of the applied negative pressure (6 cm H2O) in the synaptic region of the OHCs whereas an active, sigmoid component was observed between 30 and 60 s in the supranuclear regions. A significant increase of the midlateral wall stiffness (to 1.91+/-0.23 nN/microm; n=10) was observed in calcium-free medium and the sigmoid component of the response of the lateral wall was abolished. Salicylate (5 mM) had no significant effect on the active sigmoid behaviour of the lateral wall (n=10). Gadolinium (5 mM), a non-specific cation channel blocker, increased the stiffness of the lateral wall and attenuated the active component (n=10). The motor protein prestin thus does not seem to be involved in the active stiffness regulation seen in this study. A role for the cortical cytoskeleton in the regulation of stiffness seems reasonable according to our model. The mechanism may involve calcium-dependent metabolic modification of cytoskeletal or membrane proteins.

Animals↗
PubMed2005

Fine mapping of inherent flexibility variation along DNA molecules: validation by atomic force microscopy (AFM) in buffer.

Curvature and flexibility are structural properties of central importance to genome function. However, due to the difficulties in finding suitable experimental conditions, methods for studying one without the interference of the other have proven to be difficult. We propose a new approach that provides a measure of inherent flexibility of DNA by taking advantage of two powerful techniques, X-ray crystallography and nuclear magnetic resonance. Both techniques are able to detect local curvature on DNA fragments but, while the first analyzes DNA in the solid state, the second works on DNA in solution. Comparison of the two data sets allowed us to calculate the relative contribution to flexibility of the three rotations and three translations, which relate successive base pair planes for the ten different dinucleotide steps. These values were then used to compute the variation of flexibility along a given nucleotide sequence. This allowed us to validate the method experimentally through comparisons with maps of local fluctuations in DNA molecule trajectory constructed from atomic force microscopy imaging in solution. We conclude that the six dinucleotide-step parameters defined here provide a powerful tool for the exploration of DNA structure and, consequently will make an important contribution to our understanding of DNA-sequence-dependent biological processes.

Base Sequence↗
PubMed2003

Needlescopic appendectomy.

BACKGROUND: In this paper, we compare our experience with the techniques of needlescopic appendectomy (NA) (2-mm instruments) for the treatment of acute appendicitis with the more conventional approach of a laparoscopic appendectomy (LA). METHODS: We did a retrospective review of patients who underwent NA for the diagnosis of acute appendicitis between August 1996 and January 2002. Variables including operative time, blood loss, postoperative time to discharge, intra- and postoperative complications were analyzed and compared to data from control patients who had undergone an LA for acute appendicitis. RESULTS: The NA group had a longer average operating time (54.5 +/- l3 vs. 42.5 +/- 12.6 min, p = 0.0001) and a longer postoperative hospital stay (2.1 +/- 1.4 vs. 1.3 +/- 1.1 days, p = 0.01). Blood loss was similar for the two groups. CONCLUSIONS: With the exception of superior cosmesis, NA appears to have little advantage over the better-established LA; moreover, it has some disadvantages. A clearer benefit of this procedure over LA, as well as improvements in instrumentation, needs to be shown before it can be widely accepted.

Adolescent↗
PubMed1997

Deflectable endoscopic instrument system DENIS.

BACKGROUND: The degrees of intraoperative movement with rigid standard instruments during laparo-endoscopic surgery are limited to translation, rotation, and pivoting within the insertion point. Additional distal angulation and rotation of the instrument jaws are a potential improvement. METHODS: Different types of articulated instruments have been developed and tested in phantom and animal experiments. The final prototype was used on 30 patients during laparoscopic surgery following a standardized test protocol. RESULTS: The final design incorporates elastically linked tubular segments, 0-120 degrees variable curvature, and +/- 360 degrees rotation of the jaws element. All functions can be operated with one hand. Testing on phantom and in laparoscopic surgery showed improved handling of organs and tissue with no complications. CONCLUSION: We were able to demonstrate the feasibility of the technical design and the clinical applicability of a deflectable endoscopic instrument system. Although our initial results indicate an improvement in laparoscopic tissue manipulation, the current deflection and jaw rotation require further technical refinement.

Animals↗
PubMed2002

Single and incremental trauma models: a biomechanical assessment of spinal instability.

Biomechanical analysis of spinal injury in the laboratory requires the development of trauma models that simulate spinal instability. Current experimental trauma protocols consist of two types: single or incremental impacts. The incremental protocol has several advantages. However, the equivalence of the spinal instabilities produced by the two trauma protocols is currently unproven. The purpose of this study was to investigate whether the single and incremental trauma models produce equivalent soft tissue instabilities in the lumbar spine. Ten freshly frozen porcine lumbar spines were divided into two functional spinal units (FSUs), L2-L3 and L4-L5. FSUs were then randomized to either the single trauma (ST) or incremental trauma (IT) protocol. The IT protocol consisted of four sequentially increasing high-speed axial compression traumas, while the ST protocol was a single impact of the same magnitude as the final trauma of the IT. Before and after the final trauma, each FSU underwent flexibility testing under flexion/extension, lateral bending, and axial torsion pure moments. No significant differences were found in neutral zone or range of motion between IT and ST specimens in any of the three axes of motion, either before or after the trauma. In addition, no differences were found between the normalized motions of the IT and ST groups. The FSUs subjected to incremental trauma do not suffer greater injury than those subjected to a single impact. The data support the equivalency of the subfailure soft tissue injuries of the spine caused by the incremental and single trauma protocols respectively. This finding is important, because only with the incremental trauma protocol is one able to obtain injury threshold, study injury progression in the same specimen, produce a defined injury more accurately, and efficiently utilize scarce human cadaveric specimens.

Animals↗
PubMed2003

Three-dimensional stabilization provided by the external spinal fixator compared to two internal fixation devices: a biomechanical in vitro flexibility study.

We performed an in vitro study to investigate the stabilization (i.e. motion reduction) provided by the external spinal fixator (ESF), and to compare the three configurations of the ESF with two internal fixation techniques. Six human cadaveric lumbar spine specimens (L3-S1) were subjected to multidirectional flexibility testing in six configurations: (1) intact, (2) ESF in neutral, (3) ESF in distraction, (4) ESF in compression, (5) translaminar facet screw fixation, and (6) internal transpedicular fixation. Both the ESF and the internal fixation systems stabilized the specimens from L4 to S1. In each testing configuration, pure bending moments of flexion-extension, bilateral axial rotation, and bilateral lateral bending were applied to the uppermost vertebra stepwise to a maximum of 10 Nm. The rigid body motion between the vertebrae was measured using an optoelectronic camera system, and custom software was used to calculate the intervertebral rotations. For each applied motion in all testing configurations, the total range of motion (ROM) of L4-S1 is reported. All three ESF configurations stabilized the spine significantly when compared to the intact specimen. The ESF in compression provided significantly more stabilization in flexion-extension than the two other ESF configurations, but no other significant differences were found between the three ESF modes. In flexion-extension the ESF stabilized the spine significantly when compared with the two internal fixation devices. Only in bilateral lateral bending was the ESF inferior to internal transpedicular fixation in providing stabilization. The results of the present study suggest that the ESF provides a high degree of stabilization for preoperative assessment of selected low back pain patients. Whether other non-mechanical factors affect the pain relief experienced by the patients remains unknown.

Adult↗
PubMed2004

In vitro low-speed side collisions cause injury to the lower cervical spine but do not damage alar ligaments.

Whether injuries to the alar ligaments could be responsible for complaints of patients having whiplash injury in the upper cervical spine is still controversially discussed. It is known that these ligaments protect the upper cervical spine against excessive lateral bending and axial rotation movements. The objective of the present in vitro study was therefore to examine whether the alar ligaments or any other structures of the cervical spine are damaged in side collisions. In a specially designed acceleration apparatus, six human osteoligamentous cervical spine specimens were subjected to incremental 90 degrees side collisions from the right (1 g, 2 g, 3 g, etc.) until structural failure occurred. A damped pivot table accounted for the passive movements of the trunk during collision, and a dummy head (4.5 kg) ensured almost physiological loading of the specimens. For quantification of functional injuries, the three-dimensional flexibility of the specimens was tested in a spine tester before and after each acceleration. In all six specimens, structural failure always occurred in the lower cervical spine and always affected the facet joint capsules and the intervertebral discs. In four specimens, this damage occurred during the 2 g collision, while in the other two it occurred during the 3 g and 4 g collision, respectively. The flexibility mainly increased in the lower cervical spine (especially in lateral bending to both sides) and, to a minor extent, in axial rotation. In vitro low-speed side collisions caused functional and structural injury to discoligamentous structures of the lower cervical spine, but did not damage the alar ligaments. Since the effects of muscle forces were not taken into account, the present in vitro study reflects a worst-case scenario. Injury thresholds should therefore not be transferred to reality.

Acceleration↗
PubMed2005

Anterior C2-C3 fixation with screws: proposal of a new technique and comparative mechanical assays.

The technical difficulties involved in the anterior fixation of the C2-C3 vertebral segment by means of plates and screws, related to retraction of the structures around the vertebral segment, appropriate exposure of the site and positioning of the screws and plate, motivated the development of a new modality of fixation of this segment using only screws. Fixation of the C2-C3 vertebral segment according to the technique proposed requires less exposure of the vertebral segment and does not involve the technical difficulties of standard fixation with plates and screws. In order to study the mechanical properties of this new modality of vertebral fixation, mechanical tests were performed comparing the proposed technique (fixation solely with screws positioned in the craniocaudal direction) and routinely used fixation (H plate and screws). The tests were performed using 80 cervical spine segments from Landrace pigs aged 5 months. The vertebral segments fixed by the two techniques were divided into experimental groups of ten specimens each and submitted to mechanical tests of flexion, extension, lateral bending and rotation in a universal testing machine. The mechanical properties used to compare the results were the load necessary to produce a pre-established deformation and stiffness. No significant differences were observed between the values obtained for the production of the pre-established deformation in the flexion and rotation tests. In the extension and lateral bending tests, the mean values obtained for vertebral segments fixed only with screws were significantly higher. Analysis of stiffness showed no significant difference in the flexion, rotation and lateral bending tests, whereas in the extension tests, the mean values for the group fixed only with screws were significantly higher. The results of the mechanical tests performed showed that fixation of the C2-C3 segment only with screws was not inferior from a mechanical point of view when compared to fixation with H plates of the Orozco type.

Animals↗
PubMed2005

In-vivo demonstration of the effectiveness of thoracoscopic anterior release using the fulcrum-bending radiograph: a report of five cases.

Thoracoscopic anterior release of stiff scoliotic curves is favored because of its minimally invasive nature. Animal and human cadaveric studies have shown that it can effectively improve spinal flexibility in non-scoliotic spines; however it has not been demonstrated to be effective in actual patients with scoliosis. The fulcrum-bending radiograph has been shown to accurately reflect the post-operative correction. To demonstrate that the flexibility was increased after the anterior release; five patients with idiopathic thoracic scoliosis who underwent staged anterior thoracoscopic release and posterior spinal fusion were assessed using the fulcrum-bending radiograph. The average number of discs excised was four. Spinal flexibility as revealed by the fulcrum-bending technique, was compared before and after the anterior release. The patients were followed for an average of 4 years (range 2.2-4.9 years). Fulcrum-bending flexibility was increased from 39% before the thoracoscopic anterior spinal release to 54% after the release (P<0.05). The average Cobb angle before the anterior release was 71 degrees on the standing radiograph and 43 degrees with the fulcrum-bending radiograph. This reduced to 33 degrees on the fulcrum-bending radiograph after the release, and highly corresponded to the 30 degrees measured at the post-operative standing radiograph and at the latest follow-up. Previous animal and cadaveric studies demonstrating the effectiveness of thoracoscopic anterior release did not have scoliosis. We are able to demonstrate in patients with adolescent idiopathic scoliosis, that thoracoscopic anterior spinal release effectively improves the spinal flexibility.

Adolescent↗
PubMed2000

Biomechanical evaluation of the New Zealand white rabbit lumbar spine: a physiologic characterization.

Physiologic motions of the human, sheep, and calf lumbar spines have been well characterized. The size, cost, and ease of care all make the rabbit an attractive alternative choice for an animal lumbar spine model. However, comparisons of normal biomechanical characteristics of the rabbit lumbar spine have not been made to the spines of larger species. The purpose of this study was to establish baseline physiologic kinematic data for the rabbit lumbar spine. Ten skeletally mature New Zealand white rabbit osteoligamentous spines were obtained. L4-L7 spine segments were harvested and mounted. Multi-directional flexibility testing was performed by applying pure moments up to 0.27 Nm. Resulting rotations were measured using an Optotrak system. Data were analyzed for each intervertebral level in the three planes of rotation. The three levels tested had roughly similar range of motion (ROM). The mean (SD) angular ROMs in flexion for L4-L5, L5-L6, L6-L7 were 12.10 degrees (2.59 degrees), 12.38 degrees (2.70 degrees), and 15.17 degrees (3.22 degrees), respectively. The ROMs in extension were 5.86 degrees (1.21 degrees), 5.58 degrees (1.48 degrees), and 6.13 degrees (2.03 degrees). Lateral bending and axial rotation were roughly symmetric due to the symmetric nature of the spine. For right lateral bending, the ROMs were 8.25 degrees (2.44 degrees), 4.96 degrees (1.70 degrees ), and 4.25 degrees (1.20 degrees). For left axial rotation, the ROMs were 1.23 degrees (1.16 degrees), 0.35 degrees (0.61 degrees), 0.87 degrees (0.64 degrees ). Neutral zone (NZ) was on average 60% (29%) of ROM for the motions studied. The physiologic ROM of the New Zealand white rabbit lumbar spine was found to be similar between the rabbit and human. This relatively conserved physiologic flexibility supports the use of the rabbit as a model of the lumbar spine for kinematic studies. However, the overall NZ was found to be a greater percentage of ROM in the rabbit than the corresponding percentage in the human (60% as compared to 25%). This suggested that the rabbit lumbar spine has a greater laxity than that of the human.

Animals↗
PubMed1998

The role of supplemental translaminar screws in anterior lumbar interbody fixation: a biomechanical study.

The immediate stabilization provided by anterior interbody cage fixation is often questioned. Therefore, the role of supplementary posterior fixation, particularly minimally invasive techniques such as translaminar screws, is relevant. The purpose of this biomechanical study was to determine the immediate three-dimensional flexibility of the lumbar spine, using six human cadaveric functional spinal units, in four different conditions: (1) intact, (2) fixed with translaminar screws (TLS), (3) instrumented with anterior interbody cage insertion with the BAK system and (4) instrumented with BAK cage with additional TLS fixation. Flexibility was determined in each testing condition by measuring the vertebral motions under applied pure moments (i.e. flexion-extension, bilateral axial rotation, bilateral lateral bending) in an unconstrained manner. Anterior fixation with the BAK alone provided significant stability in flexion and lateral bending. Additional posterior TLS significantly reduced the motion in extension and axial rotation. TLS fixation alone resulted in smaller rotations than BAK fixation in all loading directions. Based on these results, it seems that interbody cage fixation with the BAK system stabilizes the spine in some, but not all, loading directions. The problematic loading directions of extension and axial rotation can be substantially stabilized by using translaminar screw fixation. However, one should emphasize that the degree of stability needed to achieve solid fusion is not known.

Biomechanical Phenomena↗
PubMed2001

Lumbar lateral interbody cage with plate augmentation: in vitro biomechanical analysis.

Many studies have concluded that stand alone cages provide limited stabilization to the spine, and this primary stabilization decreases postoperatively due to various factors. A supplemental fixation may, therefore, be needed to improve the stability. Extensive biomechanical analysis was performed in the present study to further evaluate the stabilization achieved by a laterally inserted cage and the role of an anterior lateral supplemental fixation. Eight human cadaver functional spinal units were subjected sequentially to four different test conditions: (1) intact, (2) instrumented laterally with a long cylindrical threaded cage, (3) the same cage supplemented with a lateral fixation plate, the plate being firmly connected to the cage, and (4) removal of the connection between the plate and the cage. Pure moments were applied to each specimen in a quasi static manner, ranging from -7 Nm to 7 Nm in flexion/extension, lateral bending and axial rotation. Three-dimensional segmental motions were simultaneously recorded under each loading condition. Statistical analysis was carried out on the motion parameters, including the range of motion (ROM) and the neutral zone (NZ). Inter-group comparisons were made using the Friedman test and the Wilcoxon test. The results showed that the stand alone lateral cage provided stabilization by increasing segmental stiffness above that of the intact spine. The stiffness increase ratios were: 1.6 in flexion/extension ( P=0.07), 1.3 in lateral bending ( P=0.4) and 1.0 in axial rotation ( P=0.67). A supplemental plate provided significant reinforcement of the stabilization. The stiffness increase ratios relative to the intact spine were: 3.1 in flexion/extension ( P=0.012), 5.0 in lateral bending ( P=0.012) and 2.3 in axial rotation ( P=0.012). After removal of the connection between the cage and the plate, the stiffness ratios were: 2.7 in flexion/extension ( P=0.027), 4.6 in lateral bending ( P=0.027) and 2.1 in axial rotation ( P=0.027). Globally, the cage alone increased the segmental stiffness above that of the intact spine by a factor of 1.1 ( P=0.39), with the supplemental plate, segmental stiffness increased by a factor of 3.1 ( P<0.01), and the unconnected cage/plate increased stiffness by a factor of 3.0 ( P=0.02). Supplementation of the lateral cage with an anterolateral plate was thus shown to provide significant additional stabilization in all directions, which may potentially compensate for the postoperative decrease in segmental stability.

Adult↗
PubMed2003

Effect of extracorporeal shock waves on callus formation during bone lengthening.

The effects of extracorporeal shock waves (ESWs) on callus formation during bone lengthening were studied in 25 female Japanese white rabbits. Bone lengthening of 9.8 mm was obtained over 2 weeks using the Orthofix M-100 bone fixator. ESWs were applied 3 weeks after surgery. Pins were removed 7 weeks after surgery, and specimens were prepared after the animals were killed at 9 and 24 weeks. The shock wave setting used was 0.42 mJ/mm(2) with a pulse interval of 2 Hz; 3000 shots each were applied to the central and peripheral areas. The specimens were evaluated using radiography, bone mineral density (BMD) measured by dual energy absorptiometry (DXA), and a three-point bending test to evaluate mechanical strength. Histological examination was performed on the lengthened portion. Radiographs and histological observations revealed no apparent fractures in nonlengthening tibias at the shock wave energy densities used. Radiographic observations revealed no apparent differences between the control group and the ESW group. BMD measurements by DXA revealed significantly increased bone mass in the ESW group 9 weeks after surgery. At 24 weeks after surgery the mean BMD had decreased to 25% and 15% of the values at 9 weeks in the control and ESW groups, respectively. The three-point bending test revealed no significant differences between the groups. Histological observations revealed significant capillary formation and osteoblasts and chondrocytes in the bone marrow as well as bridging of newly formed trabeculae 2 weeks after the bone was lengthened. At 4 weeks after treatment, observations included parts of the lengthened portion with no cortex or immature bone. At 9 weeks after surgery, cortex formation and a normal medullary cavity were clearly observed in the control group, whereas observations in the treated group included areas of the lengthened portion with no cortex and formation of immature trabecular structures and increased cancellous bone in the center of the lengthened portion. At 24 weeks after surgery, more prominent cortex formation and fatty marrow were observed in the ESW group than in the control group.

Animals↗