Application of Ergonomics to the Legs - Fundamentals and Assessment Tools for Occupational Ergonomics - page 586

compared with a group of millwrights and brick layers whose jobs did not require extended kneeling or
the use of a knee kicker. Of the 112 floor layers (those who used the knee kicker), the prevalence rate of
bursitis was approximately twice that found in the 42 tilesetters, and over three times that found in the
243 millwrights and brick layers. However, the prevalence in both groups of flooring workers of having
required needle aspiration of the knee was almost five times that of millwrights and bricklayers. These
results suggest that long durations of occupational kneeling is related to fluid accumulation, yet the
bursitis is due to the repetitive trauma endured by the floor layers using the knee kicker. Similar findings
were obtained by Jensen et al. (2000), who reported that the percentage of time performing “knee strain-
ing work” for floor layers, carpenters, and compositors (56, 26, and 0%, respectively) was positively
correlated with knee complaints. It is also important to note that these authors found age, seniority,
weight, BMI, smoking, and knee-straining sports were not significant covariates in the their analyses.
Village et al. (1991, 1993) found that the peak impulse forces generated in the knees of carpetlayers
when using the “knee kicker” were on the order of 3000 N. The opposite knee that was supporting
the body during this action had an average peak force of 893 N. Bhattacharya et al. (1985) reported
knee impact forces of 2469 N (about three times body weight) for a light kick and 3019 N (or about
four times body weight) for a hard kick. These light and hard kicks resulted in impact decelerations
of 12.3 and 20 g, respectively. The authors observed that the knee kicking action during flooring instal-
lation occurred at a rate of 141 kicks per hour. However, putting the knee injuries in perspective, pain was
reported by 22% of questionnaire respondents in the tufting job in a carpet manufacturer. However,
knees were only listed in 2.4% of the accident records. Thus, the knee is frequently the site of discomfort,
although there may be few lost days associated with knee pain (Tellier and Montreuil, 1991).
29.2.3 Stress Fractures
Cumulative trauma injuries can take the form of stress or fatigue fractures. While there have been many
studies investigating stress fractures in the lower extremity, the occupational concerns have primarily
been focused on military recruits (see the review by Jones et al., 2002). Linenger and Shwayhat (1992)
reported training-related injuries to the foot occurred in military personnel undergoing basic training
at a rate of three new injuries per 1000 recruit days. These authors found that stress fractures to the
foot, ankle sprains, and Achilles tendonitis accounted for the bulk of the injuries. Anderson (1990)
found the stress fractures to be most common in the distal second and third metatarsal bones but
could occur in any of the bones in the foot. Greaney et al. (1983) reported that 73% of the stress fractures
occurred in the tibia, with the most common site being the calcaneal tuberosity. Similarly, Giladi et al.'s
(1985) findings indicated that 71% of the stress fractures in their sample of military recruits occurred in
the tibia and 25% in the femoral shaft. Moreover, they found the fractures to occur later in the training
process than reported by others. Jordaan and Schwellnus (1994) reported that overuse injuries, when
normalized according to training hours per week, decreased from week 1 to week 4, showed a resurgence
in week 5, and a large peak in the final week of training. The injury rates corresponded to the weeks in
which there was increased marching and less field training. In a sample of 21 elite military recruits, Kiuru
et al. (2005) reported 75 bone stress injuries were detectable using magnetic resonance imaging; however,
only 40% of the injuries were symptomatic. These findings suggest that stress factures, many of which are
resolved without symptoms, may be much more common than originally thought when there is intense
increase in physical activity.
In an attempt to predict overuse injuries found during training of military recruits, some investigators
have looked into aspects of lower limb morphology as indicators of individual susceptibility. Giladi et al.
(1991) reported the influence of individual factors on the incidence of fatigue fractures; specifically, they
found that individuals with narrow tibia or a greater external rotation of the hip were more likely to
experience fatigue fractures. Cowan et al. (1996) reported the relative risk of “overuse” injuries was
significantly higher in military recruits with the most valgus knees. In addition, these authors showed
that the “Q” angle, which defines the degree of deviation in the patellar tendon from the line of pull
on the patella by the quadriceps muscles, was predictive of stress fractures.