Clinical Biomechanics

Editiorial Board

2010-02-01

Viscoelastic properties of the ovine posterior spinal ligaments are strain dependent

2009-11-23

Abstract: Background: The biomechanical role of the posterior spinal ligaments for spinal stability has been stated in previous studies. The investigation of the viscoelastic properties of human lumbar spinal ligaments is essential for the understanding of physiological differences between healthy and degenerated tissues. The stress-relaxation behavior of biological tissues is commonly described with the quasi-linear viscoelastic model of Fung, which assumes that the stress-relaxation response is independent of the applied strain. The goal of this study was to investigate the stress-relaxation response of ovine posterior spinal ligaments at different elongations to verify the above-mentioned hypothesis.Methods: Twenty-four ovine lumbar spinal segments, consisting of only the supraspinous and interspinous ligaments and adjoining spinous processes, were elongated uniaxially to different strain levels within the physiological elastic region (5–20%). The experimental data were described with a non-linear viscoelastic model: the modified superposition method of Findley.Findings: A linear dependency of the relaxation rate to the applied strains was observed on intact segments, when both ligaments were considered, as well as on each individual ligament. This result can be applied to the human spinal ligaments, due to similarities observed between the sheep and human spinal segment under physiological loading.Interpretation: The non-linear viscoelastic modified superposition method of Findley is an appropriate model for describing the viscoelastic properties of lumbar spinal ligaments in vitro due to its ability to address variation in applied strain during the force relaxation measurements.

Torso muscle EMG profile differences between patients of back pain and control

Shrawan Kumar, Narsimha Prasad — 2009-11-30

Abstract: Background: Electrophysiological criteria that identify and characterize low back pain can lead to better understanding of the afliction and possibly aid in its treatment.Method: Nineteen male and 22 female subjects with chronic back pain, without lumbar radiculopathy; and 30 male and 33 female control subjects with no history of low back pain in the last 12months, were recruited into the study. All subjects flexed, extended, laterally flexed, flexed anterolaterally and extended posterolaterally isometrically to 20% and 100% of their maximal voluntary contraction (MVC). Additionally, patients were asked to do these activities to their pain threshold levels and control subjects to 60% maximum voluntary contraction. Surface electromyograms (EMG) were recorded from lumbar erectores spinae, external obliques and rectus abdominis bilaterally. The electromyogram was subjected to magnitude, Fast Fourier Transform, and wavelet analyses. The median frequency and frequency bands were calculated with their power. The wavelet decomposition was done and a logistic discriminate analysis was carried out to classify patients and normal controls.Findings: The normalized peak electromyograms of patients were significantly greater than controls (P<0.01). The muscle conduction velocity was not disturbed by pain. Significant differences were found in total power between patients and controls (P<0.01). The analysis correctly classified patients and controls 65% and 98% of the time, respectively at 20% MVC, 95.1% (patients) and 86.8% (controls) at pain threshold/60% MVC, and 74.3% (patients) and 86.4% (controls) at pain tolerance/MVC (P<0.05).Interpretation: The surface electromyography can be used in discriminating chronic low back pain patients and controls. This would be an objective test over and above other subjective tests, such as pain provocation.

Comparison of trunk stiffness provided by different design characteristics of lumbosacral orthoses

Jacek Cholewicki, Angela S. Lee, N. Peter Reeves, David C. Morrisette — 2009-12-10

Abstract: Background: Lumbosacral orthoses (LSOs) are class I medical devices that are used in conservative and postoperative management of low back pain. The effectiveness of LSOs depends on their design aimed at enhancing trunk stiffness. Therefore, the purpose of this study was to compare two lumbar supports: extensible (made of neoprene and lycra) and non-extensible (made of polyester and nylon).Methods: Trunk stiffness and damping was estimated from trunk displacement data in response to a quick force release in trunk flexion, extension, and lateral bending. Fourteen male and 6 female subjects performed five trials at each experimental condition: (1) No LSO, (2) extensible LSO, (3) non-extensible LSO, (4) non-extensible LSO with a small rigid front panel, and (5) non-extensible LSO with a large rigid front panel. Testing order was randomized and the LSOs were cinched to a pressure of 70mmHg (9.4kPa) measured between posterior aspect of the iliac crest and the orthosis.Findings: The non-extensible LSO reduced trunk displacement by 14% and increased trunk stiffness by 14% (P<0.001). The extensible LSO did not result in any significant change in trunk displacement or stiffness. The addition of rigid front panels to the non-extensible LSO did not improve its effectiveness. The trunk damping did not differ between the LSO conditions.Interpretation: A non-extensible LSO is more effective in augmenting trunk stiffness and limiting trunk motion following a perturbation than an extensible LSO. The rigid front panels do not provide any additional trunk stiffness most likely due to incongruence created between the body and a brace.

A comparison of ultrasound and electromyography measures of force and activation to examine the mechanics of abdominal wall contraction

Stephen H.M. Brown, Stuart M. McGill — 2009-11-02

Abstract: Background: Ultrasound imaging is a valuable tool which, when applied appropriately, has the potential to provide information regarding the mechanics of abdominal muscle contraction. Typically, changes in muscle thickness are obtained and interpreted. However, the link between ultrasound measures of muscle thickening and EMG measures of activation is not clear.Methods: Five healthy males performed a series of abdominal muscle contractions while surface EMG and trunk posture were monitored and ultrasound images of the internal oblique and external oblique were captured both at relaxation and upon contraction. Ramped isometric flexor and extensor moment contractions were also assessed and compared between EMG and ultrasound.Findings: No definitive relationship between increases in muscle activation and corresponding measures of thickening was observed. Correlations between the two measures, across all contraction types, were 0.14 for internal oblique and −0.22 for external oblique.Interpretation: The lack of clear association between abdominal muscle activation and thickening may be due to the composite laminate-like structure of the abdominal wall, with force being transmitted between obliquely oriented muscle layers. Thus, ultrasound alone may not be a valid measure of muscle activation or force in the unique architecture of the abdominal wall.

The effects of a Pilates training program on arm–trunk posture and movement

Kim Emery, Sophie J. De Serres, Ann McMillan, Julie N. Côté — 2009-11-02

Abstract: Background: Shoulder biomechanics and spine alignment have been found to be related to occasional and/or chronic neck–shoulder pain. Pilates is a physical training approach that focuses on posture, flexibility, segmental alignment and core control, through posture and movement exercises. The objectives of this study were to determine the effect of a Pilates training program on arm–trunk posture, strength, flexibility and biomechanical patterns during a functional shoulder flexion task.Methods: Nineteen subjects (9 controls, 10 experimental) were assessed twice, 12weeks apart, during which the experimental group was submitted to a Pilates training program (two 1-h sessions per week). The assessment consisted of trials of seated posture, abdominal strength, shoulder range of motion, and maximal shoulder flexion, during which neck, shoulder and trunk kinematics and the activity of 16 muscles were recorded.Findings: After training, subjects showed smaller static thoracic kyphosis during quiet sitting and greater abdominal strength. The experimental group also showed reduced posterior and mediolateral scapular displacements, upper thoracic extension and lumbar lateral flexion, as well as higher activity of the ipsilateral cervical erector spinae, contralateral rhomboid muscles and lower activity of the ipsilateral lumbar erector spinae during the shoulder flexion task.Interpretation: The Pilates training program was effective in improving abdominal strength and upper spine posture as well as in stabilizing core posture as shoulder flexion movements were performed. Since deficits in these functional aspects have previously been associated with symptoms in the neck–shoulder region, our results support the use of Pilates in the prevention of neck–shoulder disorders.

The effect of obesity and gender on body segment parameters in older adults

April J. Chambers, Alison L. Sukits, Jean L. McCrory, Rakié Cham — 2009-12-11

Abstract: Background: Anthropometry is a necessary aspect of aging-related research, especially in biomechanics and injury prevention. Little information is available on inertial parameters in the geriatric population that account for gender and obesity effects. The goal of this study was to report body segment parameters in adults aged 65years and older, and to investigate the impact of aging, gender and obesity.Methods: Eighty-three healthy old (65–75years) and elderly (>75years) adults were recruited to represent a range of body types. Participants underwent a whole body dual energy X-ray absorptiometry scan. Analysis was limited to segment mass, length, longitudinal center of mass position, and frontal plane radius of gyration. A mixed-linear regression model was performed using gender, obesity, age group and two-way and three-way interactions (α=0.05).Findings: Mass distribution varied with obesity and gender. Males had greater trunk and upper extremity mass while females had a higher lower extremity mass. In general, obese elderly adults had significantly greater trunk segment mass with less thigh and shank segment mass than all others. Gender and obesity effects were found in center of mass and radius of gyration. Non-obese individuals possessed a more distal thigh and shank center of mass than obese. Interestingly, females had more distal trunk center of mass than males.Interpretation: Age, obesity and gender have a significant impact on segment mass, center of mass and radius of gyration in old and elderly adults. This study underlines the need to consider age, obesity and gender when utilizing anthropometric data sets.

In vivo three-dimensional evaluation of the functional length of glenohumeral ligaments

Chen Yang, Akira Goto, Wataru Sahara, Hideki Yoshikawa, Kazuomi Sugamoto — 2009-11-27

Abstract: Background: Glenohumeral ligaments play an important role in stabilizing the shoulder. However, it is impossible to know how they function in vivo during shoulder motion. To help elucidate this stabilizing role, we studied the in vivo three-dimensional kinematics of the normal shoulder joint using a markerless bone-registration technique.Methods: Our technique utilized image registration to determine corresponding relations between several image volumes represented at different coordinates. Magnetic resonance images of 14 shoulder joints of seven healthy volunteers were acquired for seven isometric abduction orientations between 0° and 180°. We then calculated three-dimensional shortest path between the origin and insertion of each ligament based on anatomical study in each abduction orientation.Findings: At 0° of abduction, the posterior band of the coracohumeral ligament displayed the maximum length. At 30° of abduction, the superior glenohumeral ligament displayed the maximum length. At 60° of abduction, the anterior band of the coracohumeral ligament and the middle glenohumeral ligament displayed the maximum length. At 120° of abduction, the anterior band of the inferior glenohumeral ligament displayed the maximum length.Interpretation: Based on progressive abduction of the arm, each ligament had different pattern in change of length. At different arm orientation of abduction, each ligament displayed the maximum length. We think that each ligament might play an important role in stabilizing the shoulder at different arm orientation.

Limited hip and knee flexion during landing is associated with increased frontal plane knee motion and moments

Christine D. Pollard, Susan M. Sigward, Christopher M. Powers — 2009-11-16

Abstract: Background: It has been proposed that female athletes who limit knee and hip flexion during athletic tasks rely more on the passive restraints in the frontal plane to deceleration their body center of mass. This biomechanical pattern is thought to increase the risk for anterior cruciate ligament injury. To date, the relationship between sagittal plane kinematics and frontal plane knee motion and moments has not been explored.Methods: Subjects consisted of 58 female club soccer players (age range: 11–20years) with no history of knee injury. Kinematics, ground reaction forces, and surface electromyography were collected while each subject performed a drop landing task. Subjects were divided into two groups based on combined sagittal plane knee and hip flexion angles during the deceleration phase of landing (high flexion and low flexion).Findings: Subjects in the low flexion group demonstrated increased knee valgus angles (P=0.02, effect size 0.27), increased knee adductor moments (P=0.03, effect size 0.24), decreased energy absorption at the knee and hip (P=0.02, effect size 0.25; and P<0.001, effect size 0.59), and increased vastus lateralis EMG when compared to subjects in the high flexion group (P=0.005, effect size 0.35).Interpretation: Female athletes with limited sagittal plane motion during landing exhibit a biomechanical profile that may put these individuals at greater risk for anterior cruciate ligament injury.

Age-differences in the free vertical moment during step descent

John G. Buckley, Steven F. Jones, Louise Johnson — 2009-11-18

Abstract: Background: This study utilises a rarely examined biomechanical parameter – the free vertical moment to determine age-related differences in rotational kinetics of the body about the vertical-axis when stepping down from a stationary position.Methods: Ten older and 10 young adults completed step-downs from three heights. Free vertical moment impulse and peak during step-initiation double-support and the subsequent step-execution phase, and vertical-axis pelvis angular displacement and velocity at instant of landing were compared.Findings: The free vertical moment during double-support was directed away from the intended lead-limb side, producing a change in vertical-axis rotational momentum that moved the lead-limb in a forwards-medial direction about the stationary support/trailing limb during the subsequent step-execution phase. The free vertical moment during step-execution was directed towards the lead-limb side and acted to slow/halt the body’s vertical-axis rotation away from lead-limb side. Free vertical moment impulse and peak during double-support were similar between groups (P>0.05), but during step-execution were significantly reduced in older adults (P=0.002). As a result older adults had greater vertical-axis pelvis angular displacement and velocity at instant of landing (directed away from lead-limb side), with significant (P<0.001) group-by-step height interactions indicating that differences between groups became more pronounced with increasing step-height.Interpretation: These findings highlight that older adults were unable to exert the same vertical-axis control during single-support as young subjects did. Findings also highlight that the analysis of free vertical moment data can be a useful biomechanical tool to highlight age-related differences in how steps/stairs are negotiated.

Joint-specific power absorption during eccentric cycling

Steven J. Elmer, Matthew L. Madigan, Paul C. LaStayo, James C. Martin — 2009-11-23

Abstract: Background: Previous investigators have reported that long term eccentric cycling increases muscle size and strength in a variety of populations. The joint-specific strategies used to absorb power during eccentric cycling, however, have not been identified. The purpose of this investigation was to determine the extent to which ankle, knee, and hip joint actions absorb power during eccentric cycling.Methods: Eight active males resisted the reverse moving pedals of an isokinetic eccentric ergometer (60rpm) while targeting 20% of their maximum concentric cycling power. Pedal reaction forces and joint kinematics were recorded with an instrumented pedal and instrumented spatial linkage system, respectively. Joint powers were calculated using inverse dynamics; averaged over complete crank revolutions and over extension and flexion phases; and differences were assessed with a one-way ANOVA.Findings: Ankle, knee, and hip joint actions absorbed 10 (SD 3)%, 58 (SD 8)%, and 29 (SD 9)% of the total power, respectively, with 3 (SD 1)% transferred across the hip. The main power absorbing actions were eccentric knee extension (−139 (SD 21) watts), eccentric hip extension (−51 (SD 31) watts), and eccentric hip flexion (−25 (SD 6) watts).Interpretation: Eccentric cycling was performed with a combination of knee and hip joint actions which is consistent with submaximal concentric cycling. These data support and extend previous work that eccentric cycling improves knee extensor function and hip extensor muscle cross sectional area. Such information may allow clinicians to take even greater advantage of eccentric cycling as a rehabilitation modality.

Biomechanical evaluation of proximal tibia behaviour with the use of femoral stems in revision TKA: An in vitro and finite element analysis

A. Completo, A. Rego, F. Fonseca, A. Ramos, C. Relvas, J.A. Simões — 2009-11-30

Abstract: Background: Recognized failure mechanisms after revision total knee arthroplasty include failure of fixation, instability and loosening. Thus, extended stems have been used to improve fixation and stability. In clinical cases where the stem is only applied in the femur, a question concerning the structural aspect of tibia may arise: Does a stemmed femur changes the structural behaviour of proximal tibia? It seems, that question has not yet been fully answered and the use of stems in the opposite bone structure requires further analysis.Methods: Proximal cortex strains were measured with tri-axial strain gauges in synthetic tibias for three different types of implanted femurs, with two constrained implants. To assess the strains at the cancellous bone under the tibial tray, it was considered a closest physiological load condition with the use of finite element models.Findings: No significant differences of the mean of the tibial cortex strains for the stemmed femur relatively to the stemless femur were observed. The R2 and slopes values of the linear regressions between experimental and finite element strains were close to one indicating good correlations. The strain behaviour of cancellous bone under the tibial tray is not completely immune to the use of femoral stem extensions. However, the level of this alteration is relatively small when compared with the strain magnitudes.Interpretation: The main insight given by the present study could probably lie in the fact that the use of femoral stems does not contribute to an increase of the risk of failure of the tibia.

The biomechanical effects of osteoporosis vertebral augmentation with cancellous bone granules or bone cement on treated and adjacent non-treated vertebral bodies: A finite element evaluation

Licheng Zhang, Guojing Yang, Lijun Wu, Binfeng Yu — 2009-11-18

Abstract: Background: In order to reduce the complications of bone cement, many efforts are underway to replace bone cement augmentation with cancellous bone granule augmentation for treating compression fractures of osteoporotic vertebral bodies. The goal of this study was to investigate the biomechanical effects of cancellous bone granule augmentation of Optimesh and polymethylmethacrylate augmentation of kyphoplasty on treated and adjacent non-treated vertebral bodies.Methods: Three-dimensional, anatomically detailed finite element models of the L1–L2 functional spinal unit were developed on the basis of cadaver computed tomography scans. The material properties and plug forms of the L2 centrum were adapted to simulate osteoporosis, cancellous bone granule and polymethylmethacrylate augmentation. The models assumed a three-column loading configuration as the following types: compression, flexion and extension.Findings: Compared with the osteoporotic model, changes in stress and strain at adjacent levels both of cancellous bone granule and polymethylmethacrylate augmentation models were minimal, but stresses/strains within the two reinforcement material plugs were modified distinctly and differently. In addition, osteoporosis and augmentation had little effect on either the axial compressive displacement of the three columns or the average disc internal pressure in all models.Interpretation: Both cancellous bone granule and polymethylmethacrylate augmentation restore the total strength and stiffness level of treated vertebral bodies and benefit the reconstruction of vertebral function. Regarding the material mechanical compatibility and the biocompatibility of the treated vertebral body and reinforcement material, however, the morcelized cancellous bone is better than polymethylmethacrylate augmentation.

Temporal changes in the tensile strength of ultra-high-molecular-weight polyethylene cable embedded in muscle tissue

2009-11-23

Abstract: Background: Wires and cables have been used extensively for spinal sublaminar wiring, but damages to the spinal cord due to compression by metal wires have been reported. We have used more flexible ultra-high-molecular-weight polyethylene cable (Tekmilon tape) instead of metal wires since 1999 and have obtained good clinical outcomes. Although the initial strength of Tekmilon tape is equivalent to metal wires, the temporal changes in the strength of Tekmilon tape in the body should be investigated to show that sufficient strength is maintained over time until bone union is complete.Methods: Tekmilon tape was embedded into the paravertebral muscle of 10-week-old male Japanese white rabbits. Samples were embedded for 0, 1, 3, 6 or 12months. At the end of each period, sequential straight tensile strength and sequential knot-pull tensile strength were measured.Findings: The initial strength of Tekmilon tape in muscle tissue was maintained over time, with 92% straight tensile strength and 104% knot-pull tensile strength at 6months, and values of 77% and 100% at 12months, respectively. Since single knot is clinically relevant, it is very important that the knot-pull tensile strength did not decrease over a 12-month period. This suggests that temporal changes in the tensile strength of Tekmilon tape are negligible at 1 year.Interpretation: Tekmilon tape maintains sufficient strength in vivo until bone union has occurred. It is useful for sublaminar wiring instead of metal materials due to its flexibility and strength and may reduce the risk of neurological damage.

Impact of freezing on bone graft incorporation biomechanical evaluations in rats

O. Reikerås — 2009-11-23

Abstract: Background: With an increasing clinical application of grafting for bone reconstruction, it is important to understand the physiological and biological events of graft incorporation. In this study, we have investigated the impact of deep freezing on the biopotency for incorporation of bone grafts.Methods: Fresh and deep-frozen autogenous bone grafts were implanted in an 8-mm segmental defect in the tibia. The construct was stabilized with intramedullary nailing. Incorporation of the graft was assessed with use of conventional radiography, biomechanical testing and measurements of bone mineral content and density after 2 and 4months, respectively.Findings: Frozen grafts were significantly less integrated after 2months as compared to fresh grafts. After 4months, however, the frozen grafts showed an overall reconstruction that was not significantly different from the fresh grafts. Both frozen and fresh grafted segments had only reached 70% strength of intact bone at 4months.Interpretation: This study indicates that in the long run there are no significant consequences, radiologically or biomechanically, of deep freezing as compared to fresh bone grafts.

Transmission of whole body vibration in children while standing

Eadric Bressel, Gerald Smith, Jaimie Branscomb — 2009-11-30

Abstract: Background: Whole body vibration has recently been used as a therapeutic intervention for the treatment of children with disabling conditions. Researchers of these studies observed encouraging results; however, children may not be capable of attenuating high vibration accelerations to the head because of low mass. The purpose of this study was to determine if children transmit vibration differently than adults while standing on a vibration platform.Methods: The experimental protocol required 11 children and 10 adults to stand on a commercially available vibration platform at progressively greater frequencies (28, 33, and 42Hz). Transmissibility of vibration to various skeletal landmarks was assessed with a high speed motion analysis system.Findings: Transmissibility in children was 42% and 62% greater than adults for the ankle and hip, respectively (P=0.03; effect size=0.84–1.29). The values at the head were not different between groups (P=0.92) and remained 86% and 50% lower than values at the ankle and knee, respectively (effect size=4.75–19.1).Interpretation: Transmissibility of whole body vibration while standing is not markedly different between children and adults. In fact, the only differences are the transmissibility to the ankle and hip which are greater in children when the vibration platform is set at 33Hz. More importantly, transmissibility to the head is not different between groups. These results do not suggest vibration therapy is safe as the biological response of children to acute or chronic acceleration impacts during whole body vibration is unknown.