Hazard Analysis — Kneeling & Squatting

Osteoarthritis of the Knee

Prepatellar Bursitis

Osteoarthritis of the Knee (OA)

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.

• 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.

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.

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.

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.

Prepatellar Bursitis

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.

• 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.

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.

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.

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.