Low back pain – manual material handling

1. Low back pain – manual material handling • Handling materials is among the most frequent and the most severe causes of injury all over the world, with strains in lower back predominating.

2. Introduction • Manual material handling (MMH) and low back pain are intricately connected. • The spine’s anatomy and mechanics will be reviewed with preventative low back pain measures, which will then be applied to MMH.

3. Low-back disorders • Low back pain occurs with a 60-90% lifetime prevalence. • 5-35% annual incidence in athletes and non-athletes. • Low back pain is the most frequent cause of industrial disability payments and the second most common medical cause of industrial work-loss. • The total cost of low back pain per year in the USA alone is about $90 billion • Pain may occur in any of the spinal structures (discs, facets, ligaments, vertebrae, and muscles).

4. Low back pain (LBP) • Despite the many medical advances, the number of people disabled with low back pain increased by 168% from 1971 to 1981. • However, 60% of patients return to work within one week. • Eighty percent return in less than six weeks and 90% of lower back patients recover within three months, regardless of the treatment.

5. LBP and return to work • An employee returning to work after low back pain has 50-60% chance of low back pain recurring one year after the initial problem. • Therefore, employees should be monitored and their condition medically managed. • Lifting tasks should only being resumed after a regimen of rehabilitative exercises have been performed.

6. Preventative measures for LBP • It has been recommended that the squatting posture (straight back and bent knees) is safer, instead of a stooped (flexed spine) posture when lifting a load from the floor . • Squat lifting is preferred over stoop lifting because the load is transferred to the legs which are stronger than the back, the load is closer to the lumbar spine, if the dimensions of the load are not excessive, resulting in a smaller moment arm, and the ligaments of the back are subjected to less maximal strain.

7. Intra-abdominal pressure (IAP) • Intra-abdominal pressure (IAP) is not a direct reducer of spinal compression but is used to stiffen the trunk and prevent tissue strain. • IAP increases just before lifting, and as IAP pressure increases so does intervertebral disk pressure. • Abdominal belts worn during MMH have been found to increase IAP, although this has not been thoroughly proven (McGill et al 1990).

8. Exercise and LBP • People in good physical condition have less risk of low back pain. • 87% of chronic low back pain patients returned to work after rehabilitation with trunk strengthening exercises.

9. Manual materials handling • Three approaches are mainly used in manual materials handling research. • Biomechanical approach. • Physiological approach. • Psychophysical approach.

10. The biomechanical approach • The biomechanical approach uses the human body as a model of mechanical links and joints corresponding to the human skeleton. • Both external and internal forces are modeled to estimate the mechanical stresses. • For MMH the focus is on the L5/S1 spine segment

11. External load estimation • For static models, the calculations require information on: • the orientation of the links in the model (subject’s posture) • the length of each segment • the mass of each segment, • the location of the centre-of-mass of each segment.

12. External load estimation • Dynamic models require a further: • angular joint accelerations • linear accelerations of each segment at the centre-of-mass • the moment of inertia of each link through the centre of mass.

13. Estimating internal muscle forces • The two muscles most researched are the erector spinae and the rectus abdominis in two dimensional studies. • In three dimensional studies the cross sectional area, the muscle line of action, and the muscle moment arm vector must be given for a larger number of muscles acting in the lumbar region (normally 10-22 muscles).

14. Physiological approach • The physiological approach is interested in the repetitive lifting within the limits of the physical strength of the worker.. • Therefore the physiological approach aims to predict the physiological cost of individuals engaged in repetitive MMH tasks.

15. Psychophysiological approach • The psychophysiological approach deals with the relationship between sensations and their physical stimuli. • The strength of the sensation is directly related to the intensity of the physical stimulus.

16. Recommendations for MMH • The following rules are recommended for MMH • Rule 1 Reduce the size, weights and forces involved. • Rule 2 Provide good handholds. • Rule 3 Keep the object close to the body – do not twist. • Rule 4 For lifting, keep the trunk up and the knees bent.

17. Recommendations for MMH • Rule 5 Minimise the distance through which the object must be moved. • Rule 6 Move horizontally, not vertically: convert lifting and lowering into pushing, pulling or carrying. Provide material at the proper work height. • Rule 7 Plan all the movements, and make them smooth. • Rule 8 Do not lift/lower anything that must be lowered/lifted later.

18. The future of MMH • At the present time typical MMH jobs have a variety of differing work components that make it difficult to apply any of the methods in the pure sense. • Workers are often required to lift, carry, hold and lower loads that vary in location and weight throughout the day. • Further research will concentrate on providing insight into the musculoskeletal risks of jobs and careers instead of tasks.

19. Laboratory • See handouts.