Excessive Weight Bearing Compromises Foot Structure and Function Across the Lifespan - The Mechanobiology of Obesity and Related Diseases - page 158

4.3.1 Effects of Obesity in Adults on Foot Structure
Unlike the growing literature on the structure of children's feet, there is less
information explaining how obesity affects the structure of adult feet. Of the few
studies that have examined the feet of adults, most have confirmed that obese
adults typically display the broader, wider and flatter foot structure typical of obese
children [ 85 , 93 , 94 ]. For example, Gravante et al. [ 93 ] compared the contact area
of the feet of 38 obese young adults (23 women: age = 23.4 ± 3.6 years, BMI
38.0 ± 6.8 kg/m 2 ; 15 men: age = 23.9 ± 4.6 years, BMI 36.0 ± 7.4 kg/m 2 ) and
34 healthy controls (18 women: age = 23.3 ± 2.3 years, BMI 21.9 ± 1.4 kg/m 2 ;
16 men: age = 22.4 ± 1.9 years, BMI 22.6 ± 1.6 kg/m 2 ). Contact area was
quantified while the participants stood on a pressure platform over a 5 sec interval.
The total area of both feet was significantly increased in the obese participants
compared to the control groups (women +12.2 %; men +9.9 %), with significant
increases in both forefoot and rear foot areas.
Although the long-term effects of flat feet in children have not been fully
established, flat footedness in adults has been linked to excessive pronation during
both static stance and dynamic gait [ 8 , 95 , 96 ]. Flat feet have also been found to
predispose army personnel to stress fractures and other foot traumas [ 97 ]. A lower
limb pathology may be exacerbated in obese or overweight individuals due to
increased mechanical loading of the lower limbs caused by their additional mass.
Furthermore, if an individual wears ill-fitting shoes, such as high heels, there is a
tendency for the alignment of ligaments in the longitudinal arch to be disrupted.
This can alter the ligament's force absorption capacity, which may intensify any
foot dysfunction. Previous research has shown individuals with flat feet displayed
an increased loading under the midfoot region and an increased peak loading
measured on the lateral aspect of the forefoot [ 98 ]. The pathological flat foot
typically has a valgus calcaneus, imposing a pronatory gait pattern on the lower
limb. This pattern results in a medial shift in body weight, with an accompanying
poor propulsive lever compared to normal gait, and may increase the potential risk
of developing foot pathologies [ 99 ].
At present, there is no universally accepted definition of what constitutes
normal arch height in the adult foot, complicating the definition of flat feet and
associated pathological foot problems. Lowered arch height in adults, however,
has been related to the occurrence of tibial, femoral and metatarsal stress fractures
and plantar fasciitis, heel spur syndrome and hallux abductor valgus [ 100 , 101 ].
There is also the tendency for individuals with flat feet to have tight Achilles
tendons, which can alter forefoot plantar distributions and limit dorsiflexion [ 102 ].
Therefore, flat feet can have pathological consequences and, in turn, affect quality
of life of those individuals who display lowered arches.
Although flat feet associated with obesity have been implicated as causing
increased stress within soft tissue structures of the lower limb and increasing the
propensity for injury [ 96 ], whether the flatter footprints typical of obese adults
indicate a lowering of osseous structures of the feet or increased adiposity, is still
contentious. Sonographic examinations have revealed that increases in body