436
B. J. H. van Lith et al.
Table II. Distribution of botulinum toxin per leg
Units/ml
Gracilis
Adductor magnus
Adductor longus
Percentage thigh
length*, %
MAS 1 MAS ≥ 2
15
35
60
15
35
15
35 20/1.00
20/1.00
20/1.00
40/2.00
40/2.00
40/2.00
20/1.00
15/0.75
15/0.75
15/0.75
30/1.50
30/0.75
30/1.50
15/0.75
*Upper leg length was calculated from pubis bone to medial femoral condyle.
Thigh-length percentages were expressed from pubis.
The BTX-A was distributed over the gracilis, adductor magnus
and adductor longus muscles according to Table II. Muscle
selection was based on muscle volume and its moment arm
with respect to the hip joint. Thigh length was measured from
the pubic bone to the medial femoral condyle and thigh length
percentages were calculated from the pubic bone (see Fig. 1).
All BTX-A injections were placed under ultrasound guidance.
During the 16-week study period, participants were instructed
to perform stretching exercises of the hip adductors (with the
hips both flexed and extended) for approximately 10 min, 3
times per day, and to log their exercises in a diary. The exercises
were individually demonstrated and instructed by a physio
therapist at the day of the BTX-A injections until each partici-
pant was able to correctly perform the exercises independently.
Outcome measures
Instrumented gait assessments. For instrumented gait as-
sessment, the GAITRite system was used (CIR Systems, Inc.,
Sparta, NJ, USA), which is a 4.88-m long carpeted walkway
that contains pressure sensors that detect the position of each
footfall (12). Participants started at one end of the GAITRite
and were instructed to walk 3 times across the walkway with
(adapted) shoes and/or orthoses at their preferred speed. Sub-
sequently, they walked 3 times across the walkway at their
maximal speed without risking a fall. For each step, gait width
was determined by the GAITRite system (and stored as “stride
width”) and exported to Microsoft Excel. For each participant,
the median gait width of all steps was calculated to avoid a
Fig. 1. Schematic view of injection locations in percentages thigh length
from the pubic bone to the medial femoral condyle. At the indicated
thigh lengths, botulinum toxin (BTX) was injected into the adductor
longus (L), adductor magnus (M) and gracilis (G).
www.medicaljournals.se/jrm
disproportional influence of a single outlying step. Gait width
was determined for both the preferred (primary outcome) and
maximal gait speed. In addition, the mean preferred and mean
maximal gait speed of the 3 trials was calculated.
Instrumented dynamic balance assessments. For instrumented
dynamic balance assessments, the Radboud Falls Simulator was
used (RFS). The RFS is a moveable platform (240 × 174 cm;
BAAT, Enschede, The Netherlands (13)) that can translate in
multiple directions. In this way, perturbations can be imposed
that mimic natural situations. In this study, only sideways
perturbations were used, where a leftward platform translation
resulted in a rightward balance perturbation and vice versa. In
the remainder of this text, we consistently refer to the direction
of the balance perturbations.
At the start of each measurement, participants were instructed
to sustain all perturbations by making a single lateral step with
out grabbing the handrails, while the perturbation direction was
known to the participants. All participants wore a safety harness
attached to the ceiling that prevented them from falling. In addi-
tion, a railing system was present at both sides that participants
could grab in the case of a fall. At the first measurement (T0),
participants were exposed to increasing perturbation intensities
that started at 0.125 m/s 2 and were increased by at least 0.125
m/s 2 between trials. The maximum perturbation intensity that
each participant could successfully sustain with a single step at
least once out of 3 trials (without falling or grabbing the railing
system) defined the individual limit of stability. To familiarize
them with the test situation, during the subsequent measure-
ments (T1 and T2), participants were again exposed to at least
15 incremental perturbation intensities until their individual
limits of stability were reached.
During all measurements each participant was twice (ran-
domly) exposed to 5 leftward and 5 rightward perturbations at
their individual limits of stability. During the first 10 perturba-
tions, the perturbation direction was known to the participant,
whereas during the last 10 trials the perturbation direction was
unknown. These 20 trials were used for statistical analysis.
During all balance assessments, kinematic data were recor-
ded by an 8-camera 3D motion analysis system (Vicon Motion
Systems, Oxford, UK) at a sample rate of 100 Hz. Reflective
markers were placed at anatomical landmarks according to the
full-body PlugInGait configuration (14). For all trials in which
the participant succeeded to make a sidestep following the
perturbation, the leg angle (primary outcome) was calculated at
the instant of stepping-foot contact, as the body configuration at
step contact appears to critically determine the successfulness
of balance recovery responses (15). The leg angle was defined
as the angle between the absolute vertical and a line connecting
the mid-pelvis and the ankle marker of the stepping foot. The
medians of the 5 right and 5 left leg angles were calculated to av-
oid a disproportional influence of a single outlying value. These
medians were averaged for each person into a single leg angle
score for the perturbations with known and unknown directions
separately. Furthermore, the success rates of the lateral stepping
responses were calculated for the perturbations with known and
unknown directions separately. A trial was scored as successful
if the participant maintained balance with a single sidestep.
Physical tests. Muscle strength of the hip adductors and hip
abductors was assessed with the Medical Research Council
(MRC) scale (0–5), with lower scores indicating more muscle
weakness (16). Muscle tone of the hip adductors was assessed
using the MAS (0–5), with higher scores indicating more hy-
pertonia (17). Furthermore, passive range of motion (ROM) on