Spinal Compression Forces Research Articles

Biomechanical Evaluation of a Bed Feature to Assist in Turning and Laterally Repositioning Patients

This study investigated the effects of hospital bed features on the biomechanical stresses experienced by nurses when turning and laterally repositioning patients. Turn Assist, a common feature in ICU beds that helps to rotate patients, and side rail orientation were evaluated. Manual patient handling is a risk factor for musculoskeletal injury, and turning patients is one of the most common patient handling activities. No known studies have evaluated bed attributes such as the Turn Assist feature and side rail orientation that may affect the stresses experienced by the nurse. Nine female nurses laterally repositioned and turned a 63-kg and 123-kg subject on an ICU bed while motion capture, ground reaction forces, and hand force data were recorded. Loading of the spine and shoulder was modeled using 3D Static Strength Prediction Program (3DSSPP). Spine compression and shear forces did not exceed recommended limits when turning or laterally repositioning. However, the mean pull forces required to manually laterally reposition even the 63-kg subject was 340 Newtons, more than 50% greater than limits established in psychophysical testing. Turn Assist considerably reduced spine loading and pull forces for both turning and laterally repositioning. Lowering side rails reduced spinal compression by 11% when turning patients. Laterally repositioning patients as part of turning may pose an injury risk to caregivers. Turn Assist reduces physical loading on nurses when turning and repositioning patients. Caregivers should consider using Turn Assist and other aids such as mechanical lifts or sliding sheets especially when turning patients requires lateral repositioning.

Trunk Muscle Activation and Estimating Spinal Compressive Force in Rope and Harness Vertical Dance.

Rope and harness vertical dance takes place off the floor with the dancer suspended from his or her center of mass in a harness attached to a rope from a point overhead. Vertical dance represents a novel environment for training and performing in which expected stresses on the dancer's body are different from those that take place during dance on the floor. Two male and eleven female dancers with training in vertical dance performed six typical vertical dance movements with electromyography (EMG) electrodes placed bilaterally on rectus abdominus, external oblique, erector spinae, and latissimus dorsi. EMG data were expressed as a percentage of maximum voluntary isometric contraction (MVIC). A simplified musculoskeletal model based on muscle activation for these four muscle groups was used to estimate the compressive force on the spine. The greatest muscle activation for erector spinae and latissimus dorsi and the greatest trunk compressive forces were seen in vertical axis positions where the dancer was moving the trunk into a hyper-extended position. The greatest muscle activation for rectus abdominus and external oblique and the second highest compressive force were seen in a supine position with the arms and legs extended away from the center of mass (COM). The least muscle activation occurred in positions where the limbs were hanging below the torso. These movements also showed relatively low muscle activation compression forces. Post-test survey results revealed that dancers felt comfortable in these positions; however, observation of some positions indicated insufficient muscular control. Computing the relative contribution of muscles, expressed as muscle activation and estimated spinal compression, provided a measure of how much the muscle groups were working to support the spine and the rest of the dancer's body in the different movements tested. Additionally, identifying typical muscle recruitment patterns in each movement will help identify key exercises for training that should promote injury prevention.

The effects of operator position, pallet orientation, and palletizing condition on low back loads in manual bag palletizing operations

Many mining commodities are packaged and shipped using bags. Small bags are typically loaded onto pallets for transport and require a significant amount of manual handling by workers. This specific task of manual bag handling has been associated with the development of musculoskeletal disorders (MSDs), especially low back disorders. This study evaluates the biomechanical demands of different work layouts when performing manual palletizing of small bags, and evaluates the biomechanical stresses associated with different stacking techniques. Results indicate that peak forward bending moments as well as spinal compression and shear forces are higher when the pallet is situated at the side of the conveyor as opposed to the end of the conveyor. At low levels of the pallet, controlled bag placement results in higher peak forward bending moments than stacking at higher levels and when dropping the bag to lower levels. The results of this study will be used to inform the development of an audit tool for bagging operations in the mining industry. Relevance to industryIn many cases for workers loading small bags, compression forces exceed the NIOSH criterion of 3400 N. Orientation of the pallet has a significant impact on spinal compression, and positioning the pallet at the end of the conveyor reduces the estimated compressive loading on the lumbar spine by approximately 800 N.

Odontoid fracture biomechanics.

In vitro biomechanical study. To investigate mechanisms of odontoid fracture. Odontoid fractures in younger adults occur most often due to high-energy trauma including motor vehicle crashes and in older adults due to fall from standing height. Horizontally aligned head impacts into a padded barrier were simulated using a human upper cervical spine specimen (occiput through C3) mounted to a surrogate torso mass on a sled and carrying a surrogate head. We divided 13 specimens into 3 groups on the basis of head impact location: upper forehead in the midline, upper lateral side of the forehead, and upper lateral side of the head. Post-impact fluoroscopy and anatomical dissection documented the injuries. Time-history biomechanical responses were determined. Four of the 5 specimens subjected to impact to the upper forehead in the midline sustained type II or high type III odontoid fractures due to abrupt deceleration of the head and continued forward torso momentum. Average peak force reached 1787.1 N at the neck at 50.3 milliseconds. Subsequently, the motion peaks occurred for the head relative to C3 reaching 15.2° for extension, 2.1 cm for upward translation, and 5.3 cm for horizontal compression, between 62 and 68 milliseconds. We identified impact to the upper forehead in the midline as a mechanism that produced odontoid fracture and associated atlas and ligamentous injuries similar to those observed in real-life trauma. We were not able to create odontoid fractures during impacts to the upper lateral side of the forehead or upper lateral side of the head. Dynamic odontoid fracture was caused by rapid deceleration of the head, which transferred load inferiorly combined with continued torso momentum, which caused spinal compression and anterior shear force and forward displacement of the axis relative to the atlas.

Influence of spinal cord compression and traumatic force on the severity of cervical spinal cord injury associated with ossification of the posterior longitudinal ligament.

Retrospective review. To evaluate the influence of static compression factors and dynamic factors based on the various degrees of traumatic force on the cervical spinal cord injury (SCI) in patients with ossification of the posterior longitudinal ligament. Spinal cord disorder occurs as a result of various factors, including static factors and traumatic force. Discussions about the severity of paralysis resulting from SCI must therefore focus on dynamic factors based on the traumatic force as well as on static compression factors. However, the past reports did not describe the influence of traumatic force in detail. Fifty patients presenting with cervical SCI associated with ossification of the posterior longitudinal ligament were included in this study. The American Spinal Injury Association motor score 3 days after injury, the degree of the traumatic force, and the spinal cord compression rate were investigated, and the relationships among these factors were investigated. Paralysis at the time of injury was not determined by static factors alone or by traumatic force alone. The severity of paralysis at the time of injury was determined on the basis of a combination of both the static factors and the degree of traumatic force. Both the degree of spinal cord compression and the degree of traumatic force were found to be important factors associated with the severity of cervical SCI in patients with ossification of the posterior longitudinal ligament. 4.

Is it possible to estimate the compressive force in the lumbar spine from intradiscal pressure measurements? A finite element evaluation

Knowledge about in vivo spinal compressive forces is a basic requirement for spinal biomechanics. Their direct measurement is not yet possible. Therefore, compressive forces are estimated from in vivo measured intradiscal pressure values. However, it is still not evident how precise these estimations are.A finite element model of the spine was employed to simulate elementary body positions and the compressive force at level L4-5 was calculated. This value was compared with different estimations calculated by multiplying the intradiscal pressure with the disc's cross-sectional area and with a correction factor. A model specific and different previously employed correction factors were used. Separately, in vivo forces were estimated from previously measured pressure values.A model specific correction factor leads for all body positions to a good estimation (error <4%) of the force except for extension (error >27%). Non-model specific correction factors lead to estimation errors of up to 44%. When accounting for these limitations, in vivo forces were estimated e.g. for standing between 430N and 600N.Compressive forces can be estimated for non-extended body positions when the individual correction factor is known. In vivo forces can be estimated from intradiscal pressure values within a certain range.

Chronic Spinal Compression Model in Minipigs: A Systematic Behavioral, Qualitative, and Quantitative Neuropathological Study

The goal of the present study was to develop a porcine spinal cord injury (SCI) model, and to describe the neurological outcome and characterize the corresponding quantitative and qualitative histological changes at 4-9 months after injury. Adult Gottingen-Minnesota minipigs were anesthetized and placed in a spine immobilization frame. The exposed T12 spinal segment was compressed in a dorso-ventral direction using a 5-mm-diameter circular bar with a progressively increasing peak force (1.5, 2.0, or 2.5 kg) at a velocity of 3 cm/sec. During recovery, motor and sensory function were periodically monitored. After survival, the animals were perfusion fixed and the extent of local SCI was analyzed by (1) post-mortem MRI analysis of dissected spinal cords, (2) qualitative and quantitative analysis of axonal survival at the epicenter of injury, and (3) defining the presence of local inflammatory changes, astrocytosis, and schwannosis. Following 2.5-kg spinal cord compression the animals demonstrated a near complete loss of motor and sensory function with no recovery over the next 4-9 months. Those that underwent spinal cord compression with 2 kg force developed an incomplete injury with progressive partial neurological recovery characterized by a restricted ability to stand and walk. Animals injured with a spinal compression force of 1.5 kg showed near normal ambulation 10 days after injury. In fully paralyzed animals (2.5 kg), MRI analysis demonstrated a loss of spinal white matter integrity and extensive septal cavitations. A significant correlation between the magnitude of loss of small and medium-sized myelinated axons in the ventral funiculus and neurological deficits was identified. These data, demonstrating stable neurological deficits in severely injured animals, similarities of spinal pathology to humans, and relatively good post-injury tolerance of this strain of minipigs to spinal trauma, suggest that this model can successfully be used to study therapeutic interventions targeting both acute and chronic stages of SCI.

A polynomial equation to predict low back compression force: accounting for the effects of load height on instability

The purpose of this study was to develop a regression equation that, incorporating the potential energy of the load in the hands, was capable of improved predictions of spinal compression forces. A stepwise polynomial equation was developed from EMG profiles of 15 muscles, and its spinal joint loading predictions at L4/L5 were compared to current methods of calculating spinal compression. Absolute muscle activation was shown to increase with increased loading height, indicating that the central nervous system responds to changes in spinal stability. The inclusion of potential energy into the calculation of spinal disc compression at L4/L5 improved estimates of the compressive forces acting on the spine. This is the first model to incorporate potential energy into a predictive model for lumbar spine compression without the use of electromyography. It was concluded that potential energy plays a vital role in dictating the recruitment patterns of the trunk.

Biomechanical Effects of Mobile Computer Location in a Vehicle Cab

The objective of this research is to determine the best location to place a conventional mobile computer supported by a commercially available mount in a light truck cab. U.S. and Canadian electric utility companies are in the process of integrating mobile computers into their fleet vehicle cabs. There are no publications on the effect of mobile computer location in a vehicle cab on biomechanical loading, performance, and subjective assessment. The authors tested four locations of mobile computers in a light truck cab in a laboratory study to determine how location affected muscle activity of the lower back and shoulders; joint angles of the shoulders, elbows, and wrist; user performance; and subjective assessment. A total of 22 participants were tested in this study. Placing the mobile computer closer to the steering wheel reduced low back and shoulder muscle activity. Joint angles of the shoulders, elbows, and wrists were also closer to neutral angle. Biomechanical modeling revealed substantially less spinal compression and trunk muscle force. In general, there were no practical differences in performance between the locations. Subjective assessment indicated that users preferred the mobile computer to be as close as possible to the steering wheel. Locating the mobile computer close to the steering wheel reduces risk of injuries, such as low back pain and shoulder tendonitis. Results from the study can guide electric utility companies in the installation of mobile computers into vehicle cabs. Results may also be generalized to other industries that use trucklike vehicles, such as construction.

Low back injury risks during construction with prefabricated (panelised) walls: effects of task and design factors

New technology designed to increase productivity in residential construction may exacerbate the risk of work-related musculoskeletal disorders (WMSDs) among residential construction workers. Of interest here are panelised (prefabricated) wall systems (or panels) and facilitating an ongoing effort to provide proactive control of ergonomic exposures and risks among workers using panels. This study, which included 24 participants, estimated WMSD risks using five methods during common panel erection tasks and the influences of panel mass (sheathed vs. unsheathed) and size (wall length). WMSD risks were fairly high overall; e.g. 34% and 77% of trials exceeded the ‘action limits’ for spinal compressive and shear forces, respectively. Heavier (sheathed) panels significantly increased risks, although the magnitude of this effect differed with panel size and between tasks. Higher levels of risk were found in tasks originating from ground vs. knuckle height. Several practical recommendations based on the results are discussed. Statement of Relevance:Panelised wall systems have the potential to increase productivity in residential construction, but may result in increased worker injury risks. Results from this study can be used to generate future panel design and construction processes that can proactively address WMSD risks.

Intra-abdominal pressure and abdominal wall muscular function: Spinal unloading mechanism

Background The roles of antagonistic activation of abdominal muscles and of intra-abdominal pressurization remain enigmatic, but are thought to be associated with both spinal unloading and spinal stabilization in activities such as lifting. Biomechanical analyses are needed to understand the function of intra-abdominal pressurization because of the anatomical and physiological complexity, but prior analyses have been over-simplified. Methods To test whether increased intra-abdominal pressure was associated with reduced spinal compression forces for efforts that generated moments about each of the principal axis directions, a previously published biomechanical model of the spine and its musculature was modified by the addition of anatomically realistic three-layers of curved abdominal musculature connected by fascia to the spine. Published values of muscle cross-sectional areas and the active and passive stiffness properties were assigned. The muscle activations were calculated assuming minimized muscle stress and stretch for the model loaded with flexion, extension, lateral bending and axial rotation moments of up to 60 Nm, along with intra-abdominal pressurization of 5 or 10 kPa (37.5 or 75 mm Hg) and partial bodyweight (340 N). Findings The analysis predicted a reduction in spinal compressive force with increase in intra-abdominal pressurization from 5 to 10 kPa. This reduction at 60 Nm external effort was 21% for extension effort, 18% for flexion effort, 29% for lateral bending and 31% for axial rotation. Interpretation This analysis predicts that intra-abdominal pressure produces spinal unloading, and shows likely muscle activation patterns that achieve this.

The effects of a three-week use of lumbosacral orthoses on trunk muscle activity and on the muscular response to trunk perturbations

BackgroundThe effects of lumbosacral orthoses (LSOs) on neuromuscular control of the trunk are not known. There is a concern that wearing LSOs for a long period may adversely alter muscle control, making individuals more susceptible to injury if they discontinue wearing the LSOs. The purpose of this study was to document neuromuscular changes in healthy subjects during a 3-week period while they regularly wore a LSO.MethodsFourteen subjects wore LSOs 3 hrs a day for 3 weeks. Trunk muscle activity prior to and following a quick force release (trunk perturbation) was measured with EMG in 3 sessions on days 0, 7, and 21. A longitudinal, repeated-measures, factorial design was used. Muscle reflex response to trunk perturbations, spine compression force, as well as effective trunk stiffness and damping were dependent variables. The LSO, direction of perturbation, and testing session were the independent variables.ResultsThe LSO significantly (P < 0.001) increased the effective trunk stiffness by 160 Nm/rad (27%) across all directions and testing sessions. The number of antagonist muscles that responded with an onset activity was significantly reduced after 7 days of wearing the LSO, but this difference disappeared on day 21 and is likely not clinically relevant. The average number of agonist muscles switching off following the quick force release was significantly greater with the LSO, compared to without the LSO (P = 0.003).ConclusionsThe LSO increased trunk stiffness and resulted in a greater number of agonist muscles shutting-off in response to a quick force release. However, these effects did not result in detrimental changes to the neuromuscular function of trunk muscles after 3 weeks of wearing a LSO 3 hours a day by healthy subjects.

Validity of estimates of spinal compression forces obtained from worksite measurements

Estimates of peak spinal compression in manual materials handling were compared between a state-of-the-art laboratory technique and a method applicable at the worksite. Nine experienced masons performed seven simulated tasks in a mock-up in the laboratory and nine matched masons were studied during actual performance of the same tasks at the worksite. From kinematic and kinetic data obtained in the laboratory, compression forces on the L5S1 joint were calculated. In addition, compression forces were estimated from the horizontal and vertical position of the blocks handled relative to the subject measured at the worksite. Comparison of group-averaged values showed that the worksite method underestimated peak compression by about 20%. Rank ordering of tasks for back load was, however, consistent between methods, supporting validity of the worksite method to compare different tasks or to determine the effects of ergonomic interventions with regard to mechanical back load. Statement of Relevance:This study validated a method that can be used by ergonomists to determine the effects of (characteristics of) manual materials handling tasks on back load at the worksite.

A novel approach to evaluate abdominal coactivities for optimal spinal stability and compression force in lifting

A novel optimisation algorithm is developed to predict coactivity of abdominal muscles while accounting for both trunk stability via the lowest buckling load (P cr) and tissue loading via the axial compression (F c). A nonlinear multi-joint kinematics-driven model of the spine along with the response surface methodology are used to establish empirical expressions for P cr and F c as functions of abdominal muscle coactivities and external load magnitude during lifting in upright standing posture. A two-component objective function involving F c and P cr is defined. Due to opposite demands, abdominal coactivities that simultaneously maximise P cr and minimise F c cannot exist. Optimal solutions are thus identified while striking a compromise between requirements on trunk stability and risk of injury. The oblique muscles are found most efficient as compared with the rectus abdominus. Results indicate that higher abdominal coactivities should be avoided during heavier lifting tasks as they reduce stability margin while increasing spinal loads.

Comparison of trunk muscle forces and spinal loads estimated by two biomechanical models

Background Comparative studies between single-joint electromyography (EMG)- and optimization-driven models of the human spine in estimating trunk muscle and spinal compression forces have not been conclusive. Due to associated implications in ergonomic applications as well as prevention and treatment managements of low-back disorders, there is a need to critically compare existing single- and multi-joint spine models. Methods A comprehensive comparison of muscle forces and spinal loads estimated by a single-joint (L5–S1 or L4–L5) EMG-driven model (EMGAO) and a multi-joint (T1–S1) Kinematics-driven finite element model (KD) of the spine under different static lifting activities in upright standing posture is carried out. Identical geometry for the spine and trunk musculature as well as passive properties are used in both models. Required model inputs including kinematics, force plate and surface EMG data are collected from one asymptomatic male subject. Findings Contrary to somewhat similar external moments (with differences <11 Nm) as well as comparable compression forces at the L4–S1 joints (<20% except in the heaviest task with 52% difference) and sum of all trunk muscle forces (<26% except in the heaviest task with 44% difference), both models recruited trunk global and local lumbar muscles in markedly different proportions (ratio of total global over total local muscle forces in cases with load in hands remained >2.4 in the KD model whereas <1.0 in the EMGAO model) which in turn led to significantly different shear force estimates. Results of the EMGAO model were level dependent. Estimated L4–L5 intradiscal pressures were comparable to the measured data except for the heaviest task in which case the EMGAO model overestimated the measured pressure by 67%. Interpretation Differences in predictions between these modeling approaches vary depending on the task simulated and the joint considered in the single-joint models of the spine. Such studies are essential to critically evaluate relative performance of existing models and to propose modifications to improve accuracy in estimations. Ergonomic and clinical applications of such model studies should, hence, be carried out with due attention to associated underlying assumptions and shortcomings.

Two-dimensional biomechanical model for estimating strength of youth and adolescents for manual material handling tasks

Youth and adolescents are routinely engaged in manual material handling (MMH) tasks that may exceed their strength capability to perform the task and may place them at excessive risk for musculoskeletal disorders. This paper reports on a two-dimensional biomechanical model that was developed to assess MMH tasks performed by youth 3–21 years of age. The model uses age, gender, posture of the youth performing the MMH activity, and weight of the load handled as input, and provides an estimate of the strength demands of the task and spinal disc compression and shear force resulting from the activity as output. The model can be used to assess whether a specific MMH task exceeds the strength demands for youth of certain ages or genders, which of the internal muscle strengths are most affected, and provides information about the estimated spinal disc compression and shear forces on the spine as a result of the specified MMH task. These results would be helpful in deciding whether a task is appropriate for a youth to perform or whether a certain task modification may be sufficient in reducing the physical demands to a level acceptable for a youth of certain age and gender.

Does the asymmetry multiplier in the 1991 NIOSH lifting equation adequately control the biomechanical loading of the spine?

The aim of this research was to evaluate whether the asymmetry multiplier incorporated in the 1991 National Institute for Occupational Safety and Health lifting equation adequately controls the biomechanical spine loads during asymmetric lifting. Sixteen male subjects lifted a box from four initial locations varying in terms of the angular deviation from the mid-sagittal plane (0, 30, 60 and 90°). From each location, boxes that weighed the recommended weight limit (RWL) and three times the RWL were lifted at two qualitatively defined lifting speeds. Ground reaction forces were combined with kinematic data in a linked-segment model to quantify the 3-D moments at the base of the spine (L5/S1) and the spine compression forces. The results show that the twisting and lateral bending moments increased with task asymmetry despite the lessening of the RWL (p < 0.01). The flexion moment and the spine compression decreased with asymmetry, although at a slower rate than the RWL. When the dynamics were removed from the linked segment spine model to approximate the assumption of slow and smooth lifting, the estimated compression remained approximately 3400 N across all asymmetry conditions. Thus, the reduction in the RWL due to asymmetry multiplier appears appropriate and should not be changed, as been suggested by recent psychophysical studies.

Trunk muscle response to various protocols of lumbar traction

The purpose of this study was to compare trunk muscle activity, spinal decompression force, and trunk flexibility resulting from various protocols of spinal traction. Four experiments explored the effects of (1) sinusoidal, triangular, square, and continuous distraction-force waveforms, (2) 0, 10, 20, and 30° of pull angle, (3) superimposed low, medium and high frequency force oscillations, and (4) sham traction. Nineteen healthy subjects volunteered for this study. Surface EMG was recorded during traction and later used in a biomechanical model to estimate spine decompression force. Trunk flexibility was measured before and after each treatment. There were no differences in muscle activity between any of the experimental conditions except the thoracic erector spinae muscle, which had lower EMG during continuous compared to sinusoidal distraction-force waveform ( p = 0.02). Thoracic and lumbar erector spinae muscles were significantly less active during sham than real traction ( p = 0.01 and p = 0.04, respectively). The estimated L4–L5 spine compression force was 25 N. Trunk flexibility decreased after each experimental session ( p = 0.01), and there were no differences between sessions. Our results suggest that the trunk muscle activity is minimal and point toward fluid exchange in the disc as one of the key biomechanical effects of spinal traction.

Effect of ship motion on spinal loading during manual lifting

This study investigated the effects of ship motion on peak spinal loading during lifting. All measurements were done on a ship at sea. In 1-min trials, which were repeated over a wide range of sailing conditions, subjects lifted an 18 kg box five times. Ship motion, whole body kinematics, ground reaction forces and electromyography were measured and the effect of ship motion on peak spinal moments and compression forces was investigated. To investigate whether people time their lifts in order to reduce the effect of ship motion on back loading, trials were performed at a free and at a constrained (lifting every 10s) work pace. With increase of the (local) vertical ship acceleration, increased moments and compression forces were found. Furthermore, lifting at a free work pace did not result in smaller effects of ship motion on spinal moments and compression forces than working at a constrained work pace.

Pathophysiology of Low Back Pain during Exposure to Microgravity

Astronauts exposed to microgravity frequently report low back pain. This pain is described as moderate to severe in intensity. This condition warrants investigation as low back pain may hinder an astronaut's ability to perform challenging tasks by virtue of disruption of sleep and, subsequently, mental concentration. It is reported by astronauts that a "fetal tuck position" described as knees to chest position relieves back pain. It is possible that the pathogenesis of back pain in microgravity is discogenic (or mechanical) and somatic, referred from the sinuvertebral nerves due to excessive expansion of the lumbar intervertebral discs associated with reduction of gravitational compressive loads in space. The fetal tuck position may increase lumbar intervertebral disc hydrostatic pressure by flexion and transfer of spinal compressive forces toward the anterior region of the lumbar discs, subsequently reducing disc volume. Moreover, this position may reduce Type IV mechanoreceptor facilitation and nerve impulse propagation from the sinuvertebral nerves of the annulus fibrosus, and thus diminish low back pain perception. Elongated posterior soft tissues (apophyseal joint capsules and ligaments) with spinal flexion may potentially stimulate Type I and II mechanoreceptors. This neutralizes substance P in the spinal cord dorsal horn by increasing naturally occurring opioids such as enkephalins. Separately, other investigators have reported a higher incidence of herniated discs (HNP) in astronauts postflight. Further studies of countermeasures are recommended to prevent excessive spinal elongation and disc expansion, reduce low back pain in microgravity, and simulate 1-G disc homeostasis, which may also help prevent HNPs postflight.