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Rehabilitation of the Locomotor System -
UNICAMP. Instrumentation was designed at USP,
and pilot trials performed by healthy subjects were
carried out on both laboratories.
The instrumented Lofstrand crutch has four
strain gauges in Wheatstone bridge configuration,
compensating temperature variation. The voltage
across the centre of the bridge is applied to
instrumentation amplifier, assuring adequate range
of signal and isolation of measurement circuit.
Besides, the instrumentation amplifier presents rail-
to-rail output (range of 4.8V) and makes the
connection between the bridge and the biofeedback
module (Leite and Cliquet, 2002).
2.1 Biofeedback Module
The main components of the biofeedback module
are microcontroller, binary-coded decimal (BCD) to
7-segment decoder, 8-bit monolithic digital-to-
analog converter (DAC), comparator circuit and
non-retriggerable monostable multivibrator (Figure
1).
Figure 1: Block diagram of the biofeedback module,
including the instrumented Lofstrand crutch.
The microcontroller used was PIC16F84
(Microchip Technology Inc., Chandler, AZ, USA)
and it was programmed to determine the value
corresponding to 20% of body weight (N) from body
mass (kg) of the crutch user. Furthermore, through
the calibration equation of the crutch, this value is
converted into a digital electrical signal; and then,
applied to the DAC.
The comparator circuit, which used an
operational amplifier as active component, receives
electrical signals from the crutch instrumentation
amplifier and the DAC. It compares the desired load
exerted on the crutch with the actual load and, if the
load on the crutch is greater than the desired one for
longer than 1s, the multivibrator is activated.
Based on the 555 monolithic timing circuit, the
non-retriggerable monostable multivibrator was
configured to generate an audio signal with duration
of 1s.
The whole electronic circuit, including the
original circuit of the crutch, is powered by two
rechargeable batteries (9V, 150mAh).
2.2 Pilot Trials
Five healthy subjects were recruited to participate in
this study (Table 1). Inclusion criteria were body
mass above 50kg and normal gait pattern. Exclusion
criteria were based on the presence of any upper
extremity musculoskeletal disorders, and not being
able to understand the instructions for the trials.
Subject C had no experience with assistive devices
for ambulation, and others had previous experience
(less than 3 months of use). Informed consent and
Ethical Committee approvals were obtained.
Table 1: Subjects characteristics.
Subjects Gender Age (year) Body mass (kg)
A
M 23.9 80.1
B
M 22.7 76.7
C
F 22.0 68.6
D
M 23.7 73.9
E
M 26.1 82.4
For each subject, before initiating the trials, the
body mass was determined using a bathroom scale
equipped with high precision sensor (Accumed
Produtos Médico Hospitalares Ltda., Duque de
Caxias, RJ, Brazil). The crutch was fitted according
to the user height, such that the handle was
approximately at the level of the greater trochanter,
leaving the elbow flexed about 30
o
(Edelstein, 2013;
Moriana et al., 2013; Laufer, 2003). Thus, the use of
the crutch is not influenced by user height.
Pilot trials were based on two activities (static
and dynamic) acquiring force values on the crutch,
and a period of training using the biofeedback
module. Each activity was repeated 3 times. Left
lower limb injury was simulated by the subjects;
thus, they used the crutch on the right forearm
(contra lateral side) (Melis et al., 1999). For all
trials, subjects were instructed to exert 20% of body
weight on the crutch.
During static activity, the subjects remained
standing, with the feet aligned. The tip of the crutch
was 100mm lateral and 150mm anterior to the right
foot (Edelstein, 2013). This activity lasted 10s, and
marks were put on the floor to help the subject and
standardize the trials (Figure 2).
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