Functional effects of botulinum toxin in patients with HSP
significant effect of time (χ 2 ) = 15.800, p < 0.001), as the
MRC scores decreased from baseline to T1 (p = 0.005),
and increased from T1 to T2 (p = 0.003) to baseline
values (T0 vs T2, p = 0.480). Hip abductor muscle
strength did not significantly differ between the 3
measurements (χ 2 (2) = 4.957, p = 0.084). Furthermore,
there was a significant time effect on hip abduction
ROM (F(2,42) = 31.613, p < 0.001), which increased
from baseline to T1 (p < 0.001) and decreased from T1
to T2 (p = 0.001), although it was still above baseline
values at T2 (T0 vs T2, p < 0.001).
Functional tests
Because the 6MWT was too demanding for 5 parti-
cipants, the analysis was performed on the remaining
17 participants. This analysis showed no signifi-
cant effect of time on the 6MWT (F(2,32) = 2.498,
p = 0.098). Likewise, the BBS (χ 2 (2) = 4.031, p = 0.133),
TUG (F(2,42) = 0.198, p = 0.821), and ABC scale
(F(2,42) = 2.048, p = 0.142) also did not show signifi-
cant time effects.
DISCUSSION
The aim of this study was to evaluate the effects of
BTX-A treatment and subsequent stretching of the hip
adductors on gait and balance capacities in patients
with pure HSP. The results support our hypothesis
that bilateral BTX-A injections in, and subsequent
stretching of, the hip adductors improve both gait width
and lateral stepping responses in known perturbation
directions coinciding with reduced hip adductor tone 6
weeks after treatment compared with baseline. These
functional effects were retained, although some recur-
rence of hip adductor muscle tone was found 10 weeks
later. In addition, comfortable gait speed increased 6
weeks post-injections, which effect was even a little
stronger after 16 weeks. In contrast, maximal gait speed
and lateral stepping responses in unknown perturbation
directions did not respond to the treatment, nor did
other functional tests (BBS, TUG, 6MWT, ABC scale).
Besides a prolonged reduction in hip adductor
muscle tone lasting up to 16 weeks after treatment, we
observed a similar and substantial improvement in hip
abduction ROM (on average 13.3°) and a temporary
reduction of hip muscle strength (on average 1 point
on the MRC scale, 6 weeks after treatment). These
findings are in line with several previous studies (2, 3,
5, 6, 8, 9, 11). The mean improvement of muscle tone
at 6 weeks post-injections was 1.5 point on the MAS,
which can be considered substantial and clinically re-
levant (22). Interestingly, the observed temporary loss
of muscle strength did not seem to have a detrimental
439
effect on balance and gait capacities, since functional
tasks improved (or remained stable) 6 weeks after
treatment. This result is in agreement with a previous
study from our group (2) and suggests that loss of
muscle strength after BTX-A injections in spastic
muscles is probably of relatively short duration and
without noticeable functional disadvantage.
The observed improvement in gait width was, on
average, 1.1 and 1.5 cm for comfortable and maximal
walking speed, respectively, and was probably the
direct result of reduced hip adductor tone and impro-
ved hip abduction ROM. Remarkably, this effect was
found even though comfortable gait speed improved
in parallel. It is conceivable that a higher gait speed
might coincide with faster leg swing and, thus, ag-
gravate velocity-dependent hip adductor spasticity,
but this effect apparently did not occur. Instead, the
reason why comfortable gait speed improved may be
that reduced hip adductor tone allowed patients to make
larger and/or faster steps. In a prior study of patients
with spastic paraparesis of various origins, BTX-A
injections in the hip adductors also led to increased gait
velocity (23). In addition, previous studies of patients
with HSP in which hip adductors were injected with
BTX-A in combination with other muscle groups also
showed increased gait speed (6, 8, 9). These findings
have important clinical implications as reduced sponta-
neous gait speed is one of the most frequent problems
reported by patients with HSP (24). Notably, maximal
gait speed did not improve after treatment, which is in
agreement with the notion that the hip adductors are
not the key muscles for gait propulsion (25). Neverthe-
less, gait width during walking at maximal gait speed
improved even more strongly than during comfortable
walking, indicating the robustness of the treatment ef-
fects on widening the base of support while walking.
The observed effect size for gait width in this study
may seem small, but it constitutes a 10–15% increase
compared with baseline. Hence, the observed increase
in gait width of 1.1–1.5 cm may be clinically relevant
in terms of improved frontal-plane balance, but this
conclusion needs to be supported by future studies.
To our knowledge, the effects of bilateral BTX-A in-
jections on reactive lateral stepping responses have not
been investigated previously. In the present study, we
only observed beneficial effects on stepping responses
to perturbations in known directions. Interestingly, no
improvements in stepping leg angle or success rate were
observed upon perturbations in unknown directions. As
hip adductor spasticity decreases, less muscle activity of
the hip abductors is supposedly needed to make a lateral
step. One explanation for the observed discrepancy bet-
ween known and unknown perturbation direction may
be that the individual maximal perturbation intensity at
J Rehabil Med 51, 2019