Effects of Standing on Non-Ambulatory Children With Spinal Muscular Atrophy

Background: Non-ambulatory children with a neuromuscular disability such as spinal muscular
atrophy (SMA) are at significant risk for poor bone health as defined by low bone mineral
density (BMD) and increased propensity to fracture. Poor bone health is thought to be
related, at least in part, to abnormally low levels of load experienced by the skeleton. A
common physical approach for increasing bone density is to stimulate the musculoskeletal
system by increasing the amount and duration of weight-bearing in the lower extremities. For
non-ambulatory individuals, this takes the form of using an assisted standing device to
enable the child to spend time in a standing position with some degree of weight placed on
the lower limbs. Some of these physical interventions demonstrate variable improvement in BMD
in children with neuromuscular conditions, and some do not. A serious limitation in the
previous work in this area is a failure to objectively measure the magnitude and duration of
the loading experienced by the lower extremities. Thus, a lack of change in BMD may be due to
the extremities experiencing only a fraction of the body weight (due to load-sharing with the
assistive device) for an inadequate duration of standing time.

Methods: In order to investigate the efficacy of standing treatment for increasing BMD, we
will develop a simple, portable and inexpensive transducer that will measure the magnitude
and time course of the load experienced by the lower extremities of individuals with SMA who
use a stationary assisted standing device. This transducer will consist of an array of
sensors embedded within a mat that will be placed under an individual's feet while they are
in assisted standing. A prototype will be validated by comparing the output of this
load-sensing mat against known loads that will be applied to the surface of the mat
statically. The specific characteristics of the loading in the lower extremities of subjects
can then be correlated with changes in their BMD to obtain a true outcome assessment. As a
demonstration of this approach, we will recruit 3 children with SMA from Gillette Children's
Specialty Healthcare who are currently participating in a standing program. Once enrolled and
informed consent is obtained, the participants will use the mat provided to them to collect
load and duration data during a baseline period where they will continue their standing
program, and during a subsequent intervention period where they will increase the duration of
their standing. The specific goal of this proposed project will be to develop, validate and
establish the initial feasibility of such a measurement device.

Implications: Successful completion of this proposed project will provide the necessary
groundwork to move forward with a multicenter clinical trial on a large number of subjects
with a variety of neuromuscular conditions. The measurement device will allow us to correlate
change in BMD with the specific load history for each participant, thereby allowing us to
determine whether physical interventions can lead to increased BMD in individuals with
neuromuscular disabilities. Analysis of the data will help define a dose-dependent
relationship between load, duration and changes in BMD, thereby guiding providers and
therapists in prescribing standing interventions.

Inclusion Criteria:

1. Age 3-14 years old

2. Diagnosed with Spinal Muscular Atrophy (SMA)

3. Participating in a standing program using a stationary assisted standing device.

4. Gross Motor Function Classification System (GMFCS) Level IV or V

5. Parent must be able to provide consent.

Exclusion Criteria:

1. Currently on bisphosphonates