Orthotic Dose Response Study

The aim with this proposal is to better understand how in-shoe foot orthoses achieve
improvements in foot and ankle function for people with ankle osteoarthritis (OA) and/or
adult acquired flatfoot resulting from posterior tibial tendon dysfunction (PTTD). The
investigators also aim to be able to predict what the optimal, personalized orthotic device
is for each patient is. These are common, painful, and often highly debilitating conditions,
with ankle OA estimated to affect around 6% of the adult population and adult acquired flat
foot around 3.3% percent of females. It has been shown that foot orthoses can be an effective
conservative intervention for these conditions, and can help to postpone or negate surgery.
However, for a significant proportion of patients foot orthoses are unsuccessful, and there
is evidence that this may be a result of significant inter-individual variability in joint
movement and loading response to the intervention. This may be due to a number of factors,
including foot bone shape, muscle strength, and/or joint range of motion. In addition, the
design of foot orthoses is often inconsistent between suppliers, largely because of the
manual approach that is used to design and manufacture them. A further complicating factor is
that prescriptions for foot orthoses are often vaguely written. Improving the investigators'
understanding of different foot and ankle responses to variation in foot orthotic design is
essential if the investigators are to improve how these devices function at the level of the
individual patient. To measure how the individual bones of the foot move using traditional
techniques is, however, very difficult. Such methods rely on skin-mounted markers that are
tracked in space to determine foot and ankle kinematics. However the size and position of the
foot and ankle bones means that it is not possible to measure them all of them individually.
Moreover, the movement between the skin and the underlying bones, known as soft tissue
artifact, introduces significant errors into the measurements. This is further complicated by
the need to wear shoes for orthoses to function properly. The group has developed a biplane
fluoroscopy system that is tailored to address the unique issues of measuring foot
kinematics. This system has the additional advantage of being able to measure the effects of
foot orthotics in unmodified shoes. To achieve the objective of understanding and being able
to predict the effects of orthoses, the specific aims are:

- [1]: To collect, via biplane fluoroscopy, kinematic data describing the effect of
varying the angle of hindfoot posting in foot orthotics. These data will be obtained
from 90 participants: 30 with ankle OA; 30 with symptomatic PTTD; and 30 healthy
controls.

- [2]: Using the data from SA1, carry out a regression analysis to identify factors
obtained from biplane fluoroscopy and clinical exam that significantly influence an
individual's response (i.e., hindfoot kinematics) to the orthotic intervention. These
factors include: foot type, bone geometry, static foot posture, joint axis location,
range of motion, and muscle strength.

- [3]: Using the data from SA1, generate a musculoskeletal model of the foot that allows
detailed analysis of the muscles and ligaments controlling ankle movement. This will be
developed in the OpenSim modeling platform and made freely available upon project
completion.

- [4]: To compare the kinematic responses to orthotic devices prescribed using standard
methods and those prescribed using algorithms and insight from SA2 and SA3 in a separate
group of participants. Biplane fluoroscopy will be used to collect kinematic data from
10 patients with ankle OA and 10 with PTTD to compare the performance of the three pairs
(one traditional, one from SA2 and one from SA3) of orthotics. This data will also be
used to validate the predictions resulting from SA2 and SA3. This proposed research
project will improve the investigators' understanding of how foot orthotics work and
will help us to prescribe more effective devices to patients. This will benefit the
large number of people in the population with ankle osteoarthritis and adult acquired
flat foot.

Inclusion Criteria:

- diagnosis of ankle OA or PTTD [non-control subjects only]

- undergoing conservative care (i.e., prescribed a foot orthosis) and deemed not to be a
surgical candidate

- between 18 and 80 years of age

- ambulatory (able to walk at least 15 m) with the primary impediment to pain-free
ambulation being ankle OA or PTTD

Exclusion Criteria:

Exclusion criteria for all subjects include:

- recent (<1 year) surgical, neurological, metabolic or lower limb musculoskeletal
problem that might impair the ambulation measures in the study, such as severe knee or
hip osteoarthritis

- rheumatoid arthritis or other inflammatory disease

- foot ulceration or partial foot amputation

- inadequate cognitive or language function to consent or to participate

- lack of a telephone number or stable mailing address