Application of Ergonomics to the Legs - Fundamentals and Assessment Tools for Occupational Ergonomics - page 585

injury (Kohatsu and Schurman, 1990; Holmberg et al., 2004). Sahlstrom and Montgomery (1997) report
that knee OAwas weakly associated with weight-bearing knee bending, which increases the dynamic load
on the knee when bending. In fact, when corrected for confounders, weight-bearing knee bending was no
longer significant. Being overweight was a significant risk factor, however. Likewise, Coggon et al. (2000)
found that obesity, defined as a BMI greater than or equal to 30 kg m 2 , and prolonged kneeling or squat-

ting on the job combined to substantially increase the risk of knee OA. Kohatsu and Schurman (1990)
found no relationship between leisure time activities and knee OA. Baker et al. (2003) report that while
occupational activities contribute to the hospital referrals for knee symptoms, participation in soccer
substantially increases the risk of knee cartilage injury.
Torner et al. (1990) reported that chronic prepatellar bursitis was the predominant knee disorder in
120 fishermen who underwent an orthopedic physical examination. Forty-eight percent of the men
examined showed this disorder. Interestingly, the finding was as common among the younger men as
in the older men. The authors believe that this disorder is a secondary effect of the boat's motion.
The knees are used to stabilize the body by pressing against gunwales or machinery as tasks are performed
with the upper extremities. Furthermore, just standing in mild sea conditions (maximum roll angles
of 8

/

) has been shown to considerably elevate the moments at the knees as the motion in the lower extre-
mities and the trunk are the primary means for counteracting a ship's motions (Torner et al., 1991).
Kivimaki (1992a) reported an increased thickness in the prepatellar or infrapatellar bursa was much
more common in carpet and floor layers than in a reference group of house painters. Carpet and
floor layers also experienced greater laxity in the knee joint (Kivimaki et al., 1994a), had more osteo-
phytes of the patella (Kivimaki et al., 1992b), and more frequently reported prior knee conditions
than house painters (Kivimaki, 1994b).
Several musculoskeletal colloquialisms have been used to describe occupationally related knee con-
ditions including “beat knee,” “carpet-layer knee,” “preacher knee,” and “housemaid knee” (Lee et al.,
2004). Housemaid knee is an inflammation of the prepatellar bursa whereas preacher knee is an infra-
patellar bursitis that is associated with excessive kneeling (Lee et al., 2004). The etiology of “beat
knee” was described by Sharrard (1963), who reported on the examination of 579 coal miners. Forty
percent of those examined were symptomatic or had previously experienced symptoms. Most of the inju-
ries could be characterized as acute simple bursitis or chronic simple bursitis. The majority of the affected
miners were colliers whose job requires constant kneeling at the mine face. There was a strong relation-
ship between the coal seam height (directly related to roof height in a mine) and the incidence of beat
knee. The incidence rates were much higher in mines with a roof height under 4 ft as compared with
those with greater roof heights. Obviously, this factor greatly affects the work posture of the miners.
With higher roof heights miners can alternate between stooped and kneeling postures but when
seams are 1 m or less, the stooped posture is no longer an alternative. Gallagher and Unger (1990),
for example, present recommendations for weight limits of handled materials in underground mines.
Below 1.02 m these are based on miners in kneeling postures. Sharrard (1963) also speculated on the
individual factors attributable to the disorder and found a higher incidence among younger men.
However, this may be due to the “healthy worker effect” (Andersson, 1991) in which older miners
with severe “beat knee” have left the mining occupation.
Tanaka et al. (1982) reported that the occupational morbidity ratios for workers' compensation claims
of knee-joint inflammation among carpet installers was twice that found in tile setters and floor layers,
and was over 13 times greater than that of carpenters, sheet metal workers, and tinsmiths. Others have
shown the knees of those involved with carpet and flooring installation were more likely to have fluid
collections in the superficial infrapatellar bursa, have a subcutaneous thickening in the anterior wall
of the superficial infrapatellar bursa, and have an increased thickness in the subcutaneous prepatellar
region (Myllymaki et al., 1993).
Thun et al. (1987) determined the incidence of repetitive knee trauma in the flooring installation pro-
fessions. While all flooring installers spend a large amount of time kneeling, the authors divided the 154
survey respondents into two groups, “tilesetters” and “floor layers,” based on their use of a “knee kicker.”
This device is used to stretch the carpet during the installation process. These respondents were

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