Anatomical landmarks for tibial nerve block
383
Table II. Correlation between anatomical landmarks of the tibial nerve motor branches and other ultrasound (US) and clinical features
(Spearman’s r)
Parameter
Tibialis posterior motor
GM motor branch
coordinates GL motor branch
coordinates Soleus motor branch
coordinates Vertical Horizontal Deep Vertical Horizontal Deep Vertical Horizontal Deep Vertical –0.327
0.404*
–0.161 –0.190
0.036
–0.024 0.123
0.289
0.186 0.141
0.072
–0.227 0.204
0.382
0.177 0.068
0.240
–0.010 0.142
0.143
–0.007 0.279
0.210
0.055 0.107
0.147
–0.210
–0.054
0.127
–0.082 0.250
0.284
0.077 0.459* –0.111
–0.140 –0.292
0.056
0.046 –0.207
–0.344
–0.281 0.162
–0.207
–0.223 0.113
–0.213
–0.075 0.080
0.019
–0.278
–0.033 0.253 –0.065 –0.255 –0.027
Time since onset
–0.388
Affected lower limb length
0.486*
Affected ankle PROM
0.046
Calf muscles spasticity
Modified Ashworth scale
0.401*
Tardieu scale grade
0.145
Tardieu scale angle
0.097
Spastic muscle echo intensity
GM
–0.020
GL
Soleus
Tibialis posterior
–0.141
0.112
0.132
–0.018
–0.168
–0.149
0.110
–0.062
–0.073
0.014
0.488* 0.298
0.534* 0.212
0.342 –0.033
branch coordinates
Horizontal Deep
0.701*
–0.039
–0.170
–0.049*
0.020
*Significant correlation (p < 0.05).
GM: gastrocnemius medialis; GL: gastrocnemius lateralis; PROM: passive range of motion.
sensorimotor nerve block) is used to differentiate spas-
tic muscle overactivity from contracture by inducing
a non-selective decrease in spastic overactivity of the
calf muscles (6). On the other hand, to determine the
respective role of different calf muscles (e.g. the soleus,
gastrocnemii and tibialis posterior muscles) in spastic
equinovarus pattern, a selective DNB of the tibial motor
nerve branches is needed (6, 8). From a therapeutic per-
spective, selective nerve blocks of the tibial nerve motor
branches may be performed with neurolytic agents (i.e.
phenol or alcohol) in order to provide a prolonged (but
not permanent) reduction in calf muscle tone in patients
with spastic equinovarus foot (6, 7).
Consistent with US evaluation of the affected leg per-
formed on a sample of 25 adult chronic stroke patients
with spastic equinovarus foot, this study located in space
(vertical, horizontal and deep) the anatomical landmarks
of tibial motor nerve branches to the gastrocnemii,
soleus and tibialis posterior muscles according to the
fibular head (upper end) position (proximal/distal) and
a virtual line from the middle of popliteal fossa to the
Achilles tendon insertion (medial/lateral). The location
of the soleus and tibialis posterior motor nerve branches
has been determined previously by Deltombe et al. in 12
stroke patients with spastic equinovarus, using computed
tomography scanning (8). Although the findings of the
current study are based on the same references and are
in line with those of Deltombe, the current study has 2
further strengths. First, patients were evaluated by means
of US, an imaging technique commonly used in daily
practice, which allows nerve blocks to be performed not
only by targeting the location of the motor nerve bran-
ches, but also by guiding the injection of anaesthetics or
chemical denervating agents (7). On this basis, the use of
US may solve some difficulties related to the (possible)
discrepancies between anatomical landmarks and the
“actual” nerve location due to the specific anatomy of
each patient (e.g. femoral and tibial bone rotation) (8).
Furthermore, US allows to (simultaneously) view the
target nerve, needle and spreading of injection agent.
US-guided nerve blocks have been reported to enable re-
duction of the injected volume by delivering the medica-
tion (e.g. local anaesthetic or neurolytic agent) precisely
to the target nerve, as well as reducing the risk of injury
to important adjacent structures, such as blood vessels
(20). This should be taken into account, in particular for
patients on anti-coagulant therapy. Secondly, the tibial
motor nerve branches to the gastrocnemius medialis and
lateralis were located, which are predominantly involved
in 12.5% of patients with spastic equinovarus foot (21).
The location of motor nerve branches to the soleus and
gastrocnemii muscles have also been defined previously
with the aim of facilitating neural blockade procedures
by Sook Kim et al. in 22 adult cadavers using anatomical
dissection (22). However, the findings of the current stu-
dy are not comparable with those of Sook Kim because
of the different population (chronic stroke patients with
spastic equinovarus vs adult cadavers) and anatomical
references considered (Sook Kim’s results are based on
femur epicondyles and malleoli position) (22).
Spastic muscle overactivity may affect limb anatomy,
causing the disruption of normal muscle architecture (13,
18). In particular, muscle fibrosis may lead to atrophy
and reduction in muscle volume (13). On this basis, one
might assume that the development of changes in sur-
rounding muscles due to spastic paresis would relate to
anatomical location of the nerve branches. Interestingly,
the findings of the current study do not appear to be in
line with this hypothesis. Indeed, this study failed to ob-
serve a clear association between anatomical landmarks
of the tibial nerve motor branches and the US/clinical
features recorded during evaluation (see Table II). This
was probably because patients showed few changes in
anatomy of the spastic calf muscles, as quantified using
the Heckmatt scale (see Table I).
This study has some limitations. First, the sample
size was small. Secondly, the study did not compare the
J Rehabil Med 51, 2019