Obesity, Osteoarthritis and Aging: The Biomechanical Links - The Mechanobiology of Obesity and Related Diseases - page 177

1.1 m/s) are sufficient to result in equivalent sagittal-plane knee-joint loads as a
normal weight adult walking at 1.4 m/s [ 21 ]. However, external knee adduction
moments, which are implicated in OA pathology [ 22 , 23 ], are sufficiently elevated
in obese adults compared to normal weight adults such that they remain elevated
even at slower walking speeds [ 21 ]. Varus-valgus knee alignment has been
implicated in OA risk [ 24 , 25 ], especially for progressive OA compared to incident
OA [ 26 , 27 ]. Varus malalignment in particular is associated with the greatest OA
risk in overweight and obese individuals [ 28 , 29 ]. Interestingly, though, valgus
malalignment appears to be more prevalent than varus malalignment in young and
old obese individuals without knee OA [ 29 , 30 ]. Whether or not valgus malalign-
ment protects against knee OA in obese individuals is not well understood. More
functional measurements of dynamic joint loading and in vivo tissue strain are
expected to improve our understanding of how alignment contributes to OA risk.
Dynamic gait patterns contribute to knee adduction moments independent of
limb alignment. One important factor that determines the knee adduction moment
is the size of the moment arm of the ground reaction force vector about the center
of rotation of the knee joint in the frontal plane. Changes in limb posture, including
step width and toe-out angle, as well as upper body medial-lateral sway are
potential mechanisms for altering the knee adduction moment arm through
dynamic gait changes. In a recent cross-sectional study, the peak adduction
moment of normal weight individuals remained unchanged across an age range
spanning from 20-59 years-of-age [ 30 ]. In contrast, the peak adduction moment
increased with age in obese individuals. The increased adduction moment was not
associated with age-dependent changes in limb alignment, toe-out angle, or step
width; rather, it was associated with a significant increase in the relative medial-
lateral distance between the knee and pelvis at the instance of peak adduction
moment [ 30 ]. These data suggest that factors associated with medial-lateral gait
dynamics, such as balance control [ 31 ], become impaired in aging obese indi-
viduals and contribute to elevated knee adduction moments [ 30 ]. An improved
understanding of how muscle forces contribute to knee adduction moments, and
how muscle force dynamics change with aging and obesity, are an important next
step in identifying the neuromechanical basis for the aging-dependent increase in
knee adduction moment that occurs with obesity.
In addition to changes in gait, obesity is associated with reductions in moderate-
to-vigorous physical activity and an increase in sedentary behavior [ 32 , 33 ],
including a significant reduction in time spent standing and walking [ 34 ]. More-
over, the reductions in physical activity and increased sedentary behavior are even
greater in obese adults with OA than those without [ 35 ]. Taken together, the
changes in joint biomechanical stimulation that occur with obesity involve
dynamic, age-dependent changes in intra-articular joint loading patterns as well as
overall reductions in the time spent in weight-bearing postures and the number of
daily bouts of joint loading.
The extent to which obesity-induced changes in static and dynamic knee joint
loading alter the local cartilage mechanical environment is not well understood.
One reason for this uncertainty is because cartilage is a mechanosensitive tissue,