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The OSU Biodynamics Laboratory uses MSC Software to assess lumbar spine forces with different lift devices during patient handling.
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Introduction
An increased risk of low back pain (LBP) among health care workers has been recognized for quite some time1,6,7,10,17,18,35,36,38,42. Specifically, patient handling has been recognized as a high risk activity4,5,7,8,11,12,19,21,35,36,39,41,42. Patient lift devices are considered a potential intervention, however, few biomechanical analyses have investigated the spine loads associated with these devices. The objective of this study was to assess the spine loads occurring when operating ceiling-based and floor-based patient handling devices under typical patient handling conditions.

Methods
Study Participants
Ten subjects were recruited in the study. The average(SD) age of the subjects was 24.2 years (4.7 years), while height and weight of the subjects were 175.1 cm (12.0 cm) and 70.7 kg (16.1 kg) respectively.


Figure 1: Subject using ceiling-based lift device

Independent measures
The independent variables consisted of the patient handling system, patient weight, and control required to maneuver the course path. The two patient handling systems consisted of a ceiling-based (Likorail 243ES 230 kg capacity; Liko, Inc.™, Franklin, MA, USA) and a floor-based (Viking L 250 kg capacity; Liko™) patient transfer system. The floor-based system was tested using two different wheel configurations(large and small) and under two different floor conditions (hard floor surface and short pile carpet). Patients were represented by anthropometric 'dummies' of different mass, three patient weights were selected consisting of 125 lb(56.8 kg), 160 lb (72.7 kg) and 360 lb (163.6 kg). The path over which the patients were maneuvered was divided into four different sections that varied according to the degree of caregiver control required to operate the system. These sections consist of: 1) straight (no turn section); 2) a sharp (90°) turn section; 3) a gradual turn (as would be expected when turning with no constraints); 4) a sharp (90°)turn within a confined space.


Figure 2: Subject using floor-based lift device

Dependent Measures
The dependent measures consist of the compression, A/P shear and lateral shear forces occurring at the inferior and superior levels of each intervertebral disc between the first sacrum (S1) and the 12th thoracic level (T12).

Equipment
The lumbar motion monitor (LMM), a tri-axial electrogoniometer, was used to measure spine motion and has been previously validated23. An electromyography (EMG) system (Delsys, Boston MA) was used to measure muscle activity of the latissimus dorsi, erector spinae, rectus abdominus, external obliques, and internal oblique muscles. All surface EMGs were collected on both the right and left side. Nine magnetic/gravitational sensors (Xsens Technologies™, Enschede, The Netherlands) were placed on the torso, upper and lower legs, upper arm and pelvis in order to track body posture during the experimental conditions. Figures 1 and 2 show a fully instrumented subject performing the task.


Figure 3: EMG-assisted biomechanical model

Data analysis
The raw EMG signals were processed and then imported, along with the kinematic data, into a subject specific, biologically-assisted (EMG-assisted) model created in the MD ADAMS software (MSC.Software) environment with the LifeMOD (LifeModeler, Inc.) biomechanical plug-in (Figure 3). The model is unique to the individual subject and is calibrated to their specific anthropometry, muscle origins and insertions, as well as their specific EMG activities. While there is no practical way to directly measure spinal forces in vivo, using the ADAMS software to simulate dynamic loads on the body allows our EMG-assisted biomechanical model to estimate the spine forces resulting during the patient handling tasks2,3,13,14,15,16,20,22,23,24,25,26,27,28,29,30,31,32,33,34,40.

Discussion
Ceiling-based patient lift systems provide marked benefits compared to manual patient handling techniques. Floor-based patient handling systems also provide a benefit over manual lifting of patients. In general, they are associated with low levels of spine compression. However, under many of the floor-based system maneuvers observed in this study, A/P shear forces were found to be of a magnitude suffcient to lead to disc damage for the caregiver. These damaging forces occurred at the mid to upper levels of the lumbar spine and became particularly problematic as the caregiver attempted turning maneuvers and especially when turns were made in confined spaces, such as bathrooms. In addition, patient weight had no effect on the spine load of caregivers using ceiling-based lifts, whereas A/P spine shear forces became much greater when attempting to turn floor-based lift systems. Therefore, ceiling-based lifts are preferable to floor-based patient lift systems. If floor-based systems must be used, the floor surface and device wheel conditions must be considered in order to reduce LBP risk exposure.

References
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For further information, please refer to the following publication
Marras, W.S., Knapik, G.G. and S. Ferguson 2009. Lumbar Spine Forces during Manoeuvring of Ceiling-based and Floor-based Patient Transfer Devices. Ergonomics, 52(3), 384-397.