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Hazard Analysis — Kneeling & Squatting
Workers who install asphalt roofs may face hazards from kneeling & squatting.
Working in kneeling or squatting posture while installing asphalt roofs can increase forces in the knee. The cumulative effects of kneeling or squatting may lead to knee injuries such as bursitis or osteoarthritis and in some cases may contribute to low back pain.
Osteoarthritis (also called OA or degenerative joint disease) is the deterioration of the cartilage of the knee leading to the narrowing of the joint space. Cartilage acts as a cushion in joints. If cartilage is destroyed there is direct bone on bone contact, which causes OA.Work-Related Risk Factors
- Awkward knee postures
- Repetitive knee flexion (e.g. bending, kneeling, squatting, and climbing)
- Heavy lifting on a regular basis, especially from a squat position
- Work that combines both heavy lifting, and kneeling or squatting
Osteoarthritis can also be caused by injuries to the knee joint and obesity. There may be a genetic tendency to develop OA.Development and Progression
Frequently bending the knee while performing activities such as kneeling, squatting, climbing, and heavy manual material handling create pressure on structures in the knee (compressive forces). These compressive forces gradually wear down the cartilage, leaving no cushioning between the bones. With the loss of this protective cushioning, the synovial lining and bones thicken, which in turn causes a build up of fluid known as "water on the knee." Bone spurs develop in many cases.Common Symptoms
Individuals with OA often complain of stiffness and pain in the affected joint. Swelling and redness of the affected joint are also common. Until OA is severe, pain is often relieved with rest.Common Treatment
Exercise, weight loss, and bracing of the knee can be effective therapies for resolving pain due to OA. Nonsteroidal anti-inflammatory drugs (NSAIDs, e.g. ibuprofen or naproxen), acetaminophen and other medications are often helpful. Other treatments include rest, heat applications, and physical therapy. Injections of corticosteroids ("cortisone injections") may be beneficial in the short term. Injection of a synthetic lubrication fluid is sometimes used in severe OA.
Surgical treatment, including arthroscopy, osteotomy, and arthroplasty (joint replacement), are sometimes necessary to regain normal function in the knee joint.
Alternative treatments such as acupuncture, magnetic pulse therapy, vitamin regimes, and topical pain relievers have also been shown effective for some in the resolution of symptoms of OA.
The prepatellar bursa is a flat sac on the front of the kneecap (patella).Irritation of the bursa causes bursitis. Prepatellar bursitis, also called "housemaid's knee," is common among roofers, carpet layers, and other workers who kneel often. Repeated knee bending can also irritate other bursa in the knee.Work-Related Risk Factors
- Prolonged kneeling
- Prolonged and repeated squatting
Bursas act to reduce friction between bony structures, or between bones and other soft tissue. Normal bursas are a flat sac somewhat like a zip-lock bag. When the bursa is irritated, fluid enters the bursa and causes it to expand. This, in turn, leads to swelling and pain of the knee.Common Symptoms
Workers with prepatellar bursitis often notice rapid swelling on the front of kneecap. Pain occurs with activity, and the front of the kneecap may be tender and warm to the touch. The swelling leads to stiffness of the knee and pain with walking. Individuals may have a slight limp when first getting up from sitting.Common Treatment
Initial treatment includes rest, ice, and compression of the knee with an elastic bandage. Application of heat and nonsteroidal anti-inflammatory drugs (NSAIDs, e.g. ibuprofen or naproxen) are often helpful. The bursa may need to be drained (aspiration) by a physician. Physical therapy can help with stretching of muscles around the knee if these muscles are tight. Strengthening exercises are often needed in chronic knee bursitis. Correcting gait abnormalities, such as those caused by a difference in leg lengths, is also important.
Level of Risk:
Frequent squatting may cause musculoskeletal disorders of the knee, including osteoarthritis (degenerative joint disease). Biomechanical studies have shown that forces in the knee are highly increased when the knee is deeply bent beyond 120 degrees. Forces during deep squatting are approximately three to five times the body weight. These forces can lead to cartilage loss and eventually to osteoarthritis.
Several epidemiologic studies have examined the link between squatting/kneeling and musculoskeletal disorders of the knee. In a national survey of working adults (aged 33-41) the incidence of musculoskeletal disorders including knee injuries was found to be linked to the hazardous job activity of kneeling or crouching. Workers who kneel or squat frequently often experience higher rates of knee disorders. Other studies have shown that squatting increases the risk of moderate to severe knee osteoarthritis and knee pain while kneeling does not.
Time spent in a kneeling posture has also been linked to development of low back pain.
Dahlkvist, NJ, Mayo, P & Seedhom, BB. (1982). Force during squatting and rising from a deep flexion. New England Journal of Medicine, 11, 69-76.
Dembe, AE, Erickson, JB & Delbos, R. (2004). Predictors of work-related injuries and illnesses: National survey findings. Journal of Occupational and Environmental Hygiene, 1(8), 542-550.
Gallagher, S. (2005). Physical limitations and musculoskeletal complaints associated with work in unusual or restricted postures: A literature review. Journal of Safety Research, 36, 51-61.
Holmström, E, Moritz, U & Engholm, G. (1995). Musculoskeletal disorders in construction workers. Occupational Medicine-State of the Art Reviews, 10(2), 295-312.
Tangtrakulwanich, B, Chongsuvivatwong, V & Geater, A. (2006). Habitual floor activities increase the risk of knee osteoarthritis. Clinical Orthopaedics and Related Research, 10 (4), 217-220.
To assess exposure to kneeling and squatting postures, determine how many hours per day the worker spends with their knee(s) bent deeply >120°.Thomas Bernard's website contains practical ergonomic tools.
To assess the exposure to kneeling and squatting, it is necessary to observe a worker installing floor coverings, carpet and tile. Look for:
- time spent with the knee deeply bent (more than 120°)
- time spent directly on the knees
The risk of injury increases with more time spent in a kneeling or squatting posture and a greater degree of bending. Thomas Bernard's website has a host of practical ergonomics tools.
Regulations & Standards:
There is no Federal OSHA standard specifically for this hazard. However, hazardous work activities or exposures that are not covered by a specific standard are covered by the general duty clause, which requires each employer to provide a safe and healthful workplace.
Regulations adopted by a state must be at least as protective as the corresponding federal standard. Work may also be subject to rules of other federal, state and local agencies. Even where there is no hazard specific standard, OSHA provides a general duty for the employer to provide a work site free from recognized hazards.
The American National Standards Institute (ANSI) has a standard which applies to construction work where there may be risk factors for musculoskeletal disorders. ANSI standard A10.40 is not a regulation, but implementing this standard can help reduce the risk of MSDs. The standard is available for purchase from the American Society of Safety Engineers: http://www.asse.org/departments/standards/.
Federal OSHA Standards are enforced by the U.S. Department of Labor in 26 states. There are currently 22 states and jurisdictions operating complete State plans (covering both the private sector and state and local government employees) and 5 - Connecticut, Illinois, New Jersey, New York and the Virgin Islands - which cover public employees only. If you are working in one of those states or jurisdictions you should ensure that you are complying with their requirements.
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