Study of Changes in the Feet With Pregnancy

Musculoskeletal impairments are a significant cause of functional limitations and disability
in women. Women are at higher risk for osteoarthritis in comparison with men [1] and
functional limitations due to arthritis are also more common in women. [2, 3] In addition,
women are disproportionately affected (risk compared with men) by knee osteoarthritis
(1.8x),[4] greater trochanteric pain syndrome (3.3x),[5] incident hip osteoarthritis[6] and
chronic joint pain (1.3x),[7] including foot pain[8] knee pain[9] hip pain[9-12] and low
back pain (1.2x).[7, 13] Preventing even a portion of these could avoid functional
limitations and disability, enhance quality of life and result in considerable savings.[2]
However, the etiology for the increased risk for these musculoskeletal diseases and
impairments has not been elucidated.[1] Acute Changes in Foot Structure Are Reported with
Pregnancy The disproportionate risk for these musculoskeletal problems may, in part, relate
to biochemical and biomechanical changes that occur in a woman's body during pregnancy. For
example, hallux valgus deformity, lateral deviation of the great toe often in conjunction
with a bunion deformity, occurs in women at nine times the rate of men.[14] Both of these
have been linked to reduction in arch height.[15] Body mass increases by an average of 9-13
kg during pregnancy.[16] There is also a seven to ten-fold increase in the relaxin level
during pregnancy,[17-19] a peptide hormone produced by the corpus luteum which increases the
flexibility and remodeling of collagen in central and peripheral joints in pregnant
women.[17, 18, 20-26] Bearing increased weight on joints with increased laxity during
pregnancy could potentially lead to permanent changes in the feet.[19, 26-28] Increases in
foot length, width, and volume have been reported during pregnancy.[29, 30, 31] In addition
to the anatomic changes in the foot, there are also changes in gait pattern during
pregnancy.[32-35] Nyska found that the center of pressure on the foot during pregnancy
shifts posteriorly to compensate for the increased anterior abdominal mass.[36] The
combination of ligamentous laxity in the arch, increased body mass with pregnancy and the
shift in the center of pressure towards the posterior part of the foot may potentially
contribute to stretching of the ligaments supporting the arch, leading to loss of arch
height.

More important than the foot changes that have been reported during pregnancy is the issue
that these changes persist following completion of pregnancy. In a self-report study, we
found a dose-response relationship between the number of pregnancies and the frequency of a
report of a permanent change in foot size in women age 18-45.[37] We then conducted a
longitudinal study to determine whether arch height loss both occurs and persists
postpartum. Sixty women in their first trimester of pregnancy were enrolled and arch height
and function were measured at baseline and approximately 19 weeks postpartum. There was a
significant decrease in arch height and arch rigidity index at follow-up, with concomitant
increases in foot length and arch drop. This study revealed that, not only was pregnancy
associated with a permanent loss of arch height, but also the first pregnancy appeared to be
the most significant with a reduction in arch rigidity (p<0.0001) and increases in foot
length (p<0.0001), arch drop (p=0.0019) and center of pressure excursion during gait
(p=0.0019). These changes in the feet could contribute to the increased risk for subsequent
musculoskeletal disorders.

Arch Height Loss Leads to Adverse Biomechanical Changes at Other Joints Consideration of the
effect of foot structure on forces and torques at other joints in the lower limb and spine
as well as the need for energy generation and absorption by associated soft-tissue
structures illustrates the importance of these potential changes. With each step, a series
of events occurs that elicits biomechanical effects and compensations throughout the lower
limb kinetic chain, in which movement at each joint influences movement at other joints in
the chain.[38] Disruption of the complex interactions between skeletal, musculotendinous and
ligamentous structures through loss of arch height may predispose to painful musculoskeletal
conditions.[39-43] As the initial link in body loading during stance and movement, the feet
are "where the rubber hits the road." The arch dynamically deforms to distribute the force,
thereby absorbing the rapid impulse of loading. Changes in foot biomechanics that occur with
changes in the foot structure alter the normal control of forces propagating from the foot
to more proximal lower limb joints and the spine,[44] and contribute to pain in the feet,
knees, hips,[41-43] and low back.

Possibly the most common cause of such changes in biomechanics is the loss of arch height.
Excessive pronation strains the supporting structures of the foot and tendons that cross the
ankle, leads to impaired balance,[45] can strain passive stabilizers such as the Achilles
tendon, iliotibial band,[46] and anterior cruciate ligament,[47] and can contribute to
permanent impairments in the soft tissue structures in the lower limbs.[47, 48] Thus,
excessive pronation has been implicated in numerous musculoskeletal complaints, through
pathologically re-distributing the ground reaction force over the foot,[49] changing
patellar tracking in the femoral trochlea,[50] changing the angle of pull of muscular
stabilizers in the lower limbs, and inducing a functional leg length inequality that alters
hip and spine loading.[1] Therefore, there is a need to address this gap in knowledge to
inform preventive interventions if there are musculoskeletal sequellae.

Biomechanical Changes Contribute to Musculoskeletal Disease Risk As mentioned previously,
the permanent loss of arch height that occurs in about 40% of women with pregnancy leads to
excessive pronation of the foot. This foot posture causes increased rotation of the
tibia[51] and is communicated across the knee. These torques, in turn, may increase
compressive and shear stress on the medial tibiofemoral and lateral patellofemoral
compartments of the knee. This is important in light of previous work demonstrating that
elevated contact stress is predictive of development of incident symptomatic knee
osteoarthritis,[52] and the relative risk for knee replacement surgery increases with the
number of pregnancies carried.[53] Closing Knowledge Gaps May Attenuate Musculoskeletal
Disease Risk in Women In consideration of the evidence to date that pregnancy leads to a
drop in the arch and that loss of the arch may contribute to musculoskeletal disease and
disablement, there is a compelling rationale to characterize whether use of arch supports
during pregnancy can prevent these adverse changes in foot structure during pregnancy. The
proposed study will randomize women to either an arch-supportive insole or a control
group(that does not wear insoles) and will measure static and dynamic arch structure in the
early part of the first trimester and then again 8 weeks postpartum. Successful completion
will inform the extent to which loss of arch height with pregnancy can be ameliorated using
a conservative physical medicine intervention. This line of research holds great potential
to inform preventive interventions to reduce the disproportionate risk for musculoskeletal
disease and disability borne by women.

Inclusion Criteria:

- Women in their first trimester of pregnancy

- Ages 18 and 40

Exclusion Criteria:

- lower limb joint or spinal surgery

- inflammatory joint or muscle problems such as rheumatoid or psoriatic arthritis

- diabetes

- collagen disorder such as Marfan Syndrome, Ehlers-Danlos Syndrome, Mixed Connective
Tissue Disease, or Osteogenesis Imperfecta

- cannot walk without any assistance

- surgeries or have another medical condition that may affect their walking ability

- flat feet (absence of a longitudinal arch)

- inability to return for the follow-up visit 2 months after delivery