Lecture 7: Ergonomics and Musculoskeletal Disorders PDF

# Lecture 7 ## Risk Factors for Cumulative Trauma Disorders (CTD) 1. Deviated wrist postures from the neutral position: - reduce the volume of the carpal tunnel and, thus, increase tendon friction, compress the median nerve - reduce the grip strength dramatically due to the change in the l...

# Lecture 7 ## Risk Factors for Cumulative Trauma Disorders (CTD) 1. Deviated wrist postures from the neutral position: - reduce the volume of the carpal tunnel and, thus, increase tendon friction, compress the median nerve - reduce the grip strength dramatically due to the change in the length-strength relationship of the muscles (nonoptimal length) 2. Increasing the frequency or repetition of the work cycle, increase the friction within the tendons, thereby accelerating the cumulative trauma progression 3. In general, the greater the force by the hands and fingers during a work cycle as required by the work task demands will result in greater tension within the long tendons rather than the muscles 4. The median nerve becomes very superficial at the palm of the hand. Any direct impacts to the palm assault the median nerve and initiate compression symptoms (contact stress) ## Hand grips - **Power grip:** When an object needs to be held forcefully and then moved by more proximal muscles. - **Precision grip:** When an object is manipulated with fingers. ### Power grips 1. **Cylindrical grip:** Fingers flexed around an object. Thumb on one side and fingers on the other, like gripping a hammer or racquet. 2. **Spherical grip:** Fingers and thumb are together around an object; like grabbing or an apple, doorknob. 3. **Hook grip:** The second through fifth fingers flexed around an object in a hook-like manner. Thumb is extended and not involved. 4. **Lateral prehension:** When objects are held between fingers (rarely used). ### Precision Grips 1. **Pad to pad grip (pinch grip):** Either the thumb and one finger gripping, or thumb and many fingers gripping like holding a pencil. 2. **Tip to Tip grip (pincer grip):** Tip of thumb against tip of a finger, like to pick up a coin. Difficult with long fingernails. 3. **Lumbrical grip (plate grip):** MCP and PIP joint flexed and the DIP extended and the thumb opposes. This grip is used to hold something horizontal like a plate. Lumbricals are used to flex the MCP joint. ## Hand grip and CTDs - CTDs result from incorrect choice of the grip type which required by the task demands or - Improper design of the hand held tool that puts the wrist and hand in a deviated position. ## Matched anthropometry - A diagram of a hand holding a cylindrical object is shown. - This is demonstrating the proper measurements for hand grasps. ## Which worker is gripping the hammer from the correct part of the handle? - Two pictures of workers hammering are shown. - The image on the right demonstrates the correct grip of the hammer. ## Motorized hand held tools - An image of multiple different power tools are shown - Reduce to a great extent the physical body stresses, and the need for repetitions of work cycles ## The neck - Neck disorders may also be associated with sustained work postures. - Upright neck positions also have the advantage of reducing the extent of fatigue experienced in the neck. - When the head is tilted forward by 30° or more from the vertical position, significant neck fatigue happens rapidly. - From a biomechanical standpoint, as the head is flexed, the center of mass of the head moves forward relative to the spine; this increases the head weight moment arm and necessitates increased activation of the posterior neck musculature. ## How to measure the neck flexion angle? - The intersection between two lines; the first is the vertical line passing through C7, and the second connects C7 to the tragus of the ear. ## The burden of staring at a smartphone - A chart is shown with varying degrees of forward head tilt and how much of the force is put on the spine. ## Visual acuity to be checked in chronic neck problems - A picture of a woman working on a laptop is shown. ## The back - A labeled drawing of the spine is shown. - The image points out the following: Vertebral body, anterior portion, pedicle, posterior portion, transverse process, lamina, spinous process, facet joints, intervertebral disc. ## The anterior portion related traumas - It has been documented that loads on the lumbar spine are greater when a worker is seated compared to standing. - The posterior (bony) elements of the spine form an active load path when one is standing. - However, when seated these elements are disengaged and more of the load passes through the intervertebral disc. - The features of the chair design could influence disc loading. - **A diagram of the intervertebral discs and pressure they are under in various positions is shown.** ## How to decrease the disc loading? - **In standing workstations:** - Preserving the normal lordotic curve of the lumbar spine through erect posture. - Use of an anti-fatigue mat. - **In sitting workstations:** - Increase the backrest angle over 90°. - Use of lumbar support. - Small downward slope of the seat pan (10°). - So, the posterior elements play more of a role in providing an alternative load path. ## **A graphic representation that relates the angle of the backrest to the amount of force placed on the intervertebral discs is shown.** - The graph demonstrates that a higher backrest angle and use of lumbar support is better for limiting the force put on the lumbar discs. ## **Multiple pictures of varying different types of work environments (ex: lifting a child, working with a child sitting on a therapy ball, etc) are shown.** ## **Multiple pictures of varying different types of work environments (ex: Working with a therapy ball, etc) are shown.** - Two pictures are shown. - The first picture shows a woman sitting on a therapy ball with a child. The woman can see the child's back as the child faces away from the woman. The child is also holding onto a rope connected to the ceiling. Another woman is standing next to the ball making adjustments on the rope. - The second picture shows a woman sitting on the floor with a child facing away from her, and the woman is holding a rope connected to the ceiling that the child is holding. The child is sitting on a therapy ball. - Two pictures of a "LIFTMAX" black belt with a cushioned interior are shown. ## The posterior portion related traumas - Related to assuming hyper-extension of the trunk in the workplace. **Multiple pictures of workers in different work environments (ex: Auto assembly, food processing etc) are shown.** ## The back muscles - The trunk muscles may experience low-level static exertion conditions and may be subject to the static overload through the muscle static fatigue process. - Muscle fatigue can result in lowered muscle force generation capacity and can, thus, initiate the cumulative trauma sequence of events. - The fatigue and cumulative trauma sequence can be minimized through two actions. ## First action - **Foot rails (rest)** can provide a mechanism to allow relaxation of the large back muscles and thus increased blood flow to the muscle. This reduces the static load and subsequent fatigue in the muscle. - When a leg is rested on the foot rest, the large back muscles are relaxed on one side of the body and the muscle can be supplied with oxygen. - Alternating legs placed on the foot rest or on the ground provides a mechanism to minimize back muscle fatigue throughout the day. ## **A picture of an assembly line with workers standing on a platform with their feet on a footrest is shown.** ## Second action - Floor mats can decrease the fatigue in the back muscles provided that the mats have proper compression characteristics. - Floor mats are believed to facilitate body sway and decrease the magnitude of ground reaction force (GRF) which enhances the pumping of blood through back muscles, thereby minimizing fatigue. ## Pain tolerance (Biopsychosocial model) - An interdisciplinary model that looks at the interconnection between biology, psychology, and socio-environmental factors. ## This risk classification is the baseline for selecting safety actions to be implemented and when defining the timescale, i.e. the urgency of the implementation of the corrective safety measures. | Category of risk | Evaluation of tolerability | Guidance on necessary action and timescale | |---|---|---| | Very low | Acceptable | These risks are considered acceptable. No further action is necessary other than to ensure that the controls are maintained. | | Low | Acceptable | No additional controls are required unless they can be implemented at very low cost (in terms of time, money and effort). Actions to further reduce these risks are assigned low priority. Arrangements should be made to ensure that the controls are maintained. | | Medium | Risks that should be reduced so that they are tolerable or acceptable. | Consideration should be given as to whether the risks can be lowered, where applicable, to an acceptable level, but the costs of additional risk reduction measures should be taken into account. The risk reduction measures should be implemented within a defined time period. Arrangements should be made to ensure that the controls are maintained, particularly if the risk levels are associated with harmful consequences. | | High | Acceptable | Substantial efforts should be made to reduce the risk. Risk reduction measures should be implemented urgently within a defined time period and it might be necessary to consider suspending or restricting the activity, or to apply interim risk control measures, until this has been completed. Considerable resources might have to be allocated to additional control measures. Arrangements should be made to ensure that the controls are maintained, particularly if the risk levels are associated with extremely harmful consequences and very harmful consequences. | | Very high | Unacceptable | These risks are unacceptable. Substantial improvements in risk controls are necessary, so that the risk is reduced to a tolerable or acceptable level. The work activity should be halted until risk controls are implemented that reduces the risk so that it is no longer very high. If it is not possible to reduce risk the work should remain prohibited. | ## Phase (3):Risk control (designing and implementing of safety control measures, as well as training) - Risk control is the stage where the actions to identify and implement safety measures to control risks are performed having in mind the protection of workers' health and safety. - However, it is important not to forget that additional or different safety measures may be required to protect workers with special needs (such as pregnant women, young workers, aging workers and workers with disabilities). - It is very important to take account of the risk analysis, and the number of individuals exposed to the risk when setting priorities and timescales to the implementation of safety control measures. ## Design safety control measures - The first step of risk control is the design of the safety control measures to eliminate risks. The risks that cannot be avoided or eliminated should be reduced to an acceptable level. - The employers must perform a cost-benefit analysis to balance the cost (include money, time, trouble and effort) they could have to reduce a risk against the degree of risk presented. It should be demonstrated that the cost involved in reducing the risk further would be grossly proportionate to the benefit gained. ## Implement safety control measures - The safety control measures to be implemented should be based on up-dated technical and/or organizational knowledge, and good practices. Safety control measures implementation should be done using the following hierarchy order: - Prevention measures - Protection measures - Mitigation measures ## Prevention measures - The aim of implementation of prevention measures is to reduce the likelihood of work accident or occupational disease occurrence.   - **a) Using engineering or technical measures to act directly on the risk source, in order to:** - Remove it, i.e. ensure that during the workplace design phase risks are 'designed out' - Reduce levels of hazardous materials. For instance, provide effective ventilation through local or general exhaust ventilation systems. - Replace it, i.e. substitute the risk by a less risky material, equipment or substance (These measures are more efficient and economical when accomplished during the workplace design phase). - **b) Using organizational or administrative measures to force changing of behaviors and attitudes and promote a safety culture:** - Information and training (awareness) - Establish appropriate working procedures and supervision - Management and proactive monitoring - Routine maintenance and housekeeping procedures ## Protection measures - Implementation of Protection measures should consider, first, collective measures and then individual measures. - **a) Collective Protection measures:** - Isolate the risk through the use of guards, protection of machinery and parts, or remote handling techniques. - Physical barriers (railings, packaging, acoustic, thermal or electrical barriers). - Using organizational or administrative measures to diminish the exposure duration: job rotation of workers; timing the job so that fewer workers are exposed; Implementation of safety signs, for instance restricting entry to authorized persons. - **b) Individual Protection -** use of Personnel Protective Equipment (PPE) to protect workers from the residual risk. The worker should participate in the selection of PPE and should be trained in its use. ## Mitigation measures - When prevention and protective measures fail a work accident or an occupational disease could happen. The company needs to be prepared and to have mitigation measures implemented. The aim of mitigation measures is to reduce the severity of any damage to facilities and harm to employees and public. - Several examples of measures that can be used to achieve this aim are: emergency plan, evacuation planning, warning systems (alarms, flashing lights), test of emergency procedures, exercises and drills, fire-extinguishing system, or a return-to-work plan. ## Training and information - Managers must know the risk their workers are exposed to. Workers must know the risks they are exposed to. - Providing information and Training courses to workers is a legal requirement according to the federal Occupational Safety and Health Act of 1970 (OSH Act), workers have the “Right to Know” – about the hazards they are exposed to, the harm they might cause, and precautions that could prevent these harmful effects. ## Phase (4):Review and update - The risk management process should be reviewed and updated regularly, for instance **every year,** to ensure that the safety measures implemented are adequate and effective. - Additional measures might be necessary if the improvements do not show the expected results. This is also a highly recommendable procedure since workplaces are dynamic due to change in equipment, machines, substances or work procedures that could introduce new hazards in the workplace. - Another reason is that new knowledge regarding risks can emerge; either leading to the need of an intervention or offering new ways of controlling the risk. ## Document the process - The entire process has to be documented because of the legal responsibility. Documentation should provide an overview of the identified hazards, respective risks and subsequent safety control measures implemented. - Namely, it should include the following items: work activity/area under assessment; employees at risk; list of occupational risks and hazards, likelihood of harm; severity of harm; risk levels and their acceptability or controls in place. ## Thank You - A picture of a floral wreath with the words Thank You inside.