FOOT & ANKLE INTERNATIONAL
Copyright © 2003 by the American Orthopaedic Foot & Ankle Society, Inc.
Transverse Plane Motion at the Ankle Joint
Christopher J. Nester, BSc (Hon), Ph.D.; Andrew F. Findlow, BSc (Hons);
Peter Bowker BSc (Hon) Ph.D.; Peter D. Bowden, MSc
Salford, England
concept that the ankle joint is incapable of transverse
plane motion. The purpose of this paper is to present
further evidence for the capacity for transverse plane
motion at the ankle joint.
In one of the first studies to quantify the transverse
plane motion at the ankle joint, McCullough and Burge9
described approximately 17.5° of motion in eight cadavers (estimated from graph). Siegler et al.14 described a
mean of 26.5° of transverse plane motion at the ankles
of 15 unloaded cadavers. The discrepancy between
these figures is perhaps an indication of the importance
of loading on the range of transverse plane motion at
the ankle. In their invasive in vivo study of eight subjects, Lundberg et al.8 found an average of 8.4° of transverse plane ankle motion during 30° of external leg rotation. These data demonstrate that the ankle is clearly
capable of transverse plane motion. Furthermore, it is
probable that the role of the ankle joint in the mechanism that allows proximal transverse plane motions to
take place while the foot is fixed on the floor is not solely the ‘transfer’ of the transverse plane moment to the
subtalar joint, but is accommodating some of the motion
itself. The ankle is potentially as important to this mechanism as the subtalar joint.
We undertook studies to measure in vivo the kinematics of the combined ankle/subtalar complex under
static and dynamic conditions using a noninvasive
approach. By using the literature describing previous
work in this area, we intended to extrapolate from our
results conclusions regarding the transverse plane
motion at the ankle joint.
ABSTRACT
The ankle is often considered to have little or no capacity to move in the transverse plane. This is clear in the persistent concept that it is the role of the subtalar joint to
accommodate the transverse plane motion of the leg
while the foot remains in a fixed transverse plane position
on the floor. We present data from noninvasive in vivo
study of the ankle subtalar complex during standing
internal and external rotation of the leg and study of the
ankle subtalar complex during walking. These data reinforce the results of cadaver study and invasive in vivo
study of the ankle/subtalar complex. We suggest that the
ankle is capable of considerable movement in the transverse plane (generally greater than 15°) and that its role in
the mechanism that allows the foot to remain in a fixed
transverse plane position on the floor while the leg
rotates in the transverse plane, is not simply the transfer
of the transverse plane moment to the subtalar joint, but
is accommodation of some of the necessary movement.
INTRODUCTION
The combined ankle and subtalar complex are frequently attributed the role of allowing transverse plane
rotations to take place proximally while the foot is in a
fixed transverse plane position on the floor. An important element in this mechanism is the supposed lack of
transverse plane motion at the ankle joint. This allows
transverse plane tibial rotation to force the subtalar joint
to move and accommodate the tibial rotation via its
complex triplanar motion while still allowing the foot to
remain fixed on the floor. Increasingly, however, evidence is suggesting that this simplistic breakdown of
roles is not accurate. The primary inaccuracy lies in the
METHOD
Static Study
Twenty five subjects participated in this study (12 male
and 13 female), ranging from 21 to 44 years of age.
None had a history of lower limb injury or disease and all
gave consent to participate. Data describing the kinematics of the heel and leg were collected for both feet of
each subject during transverse plane rotation of the leg
in a custom built rig (Fig. 1). To assess for repeatability,
data for four subjects were collected twice, seven days
Corresponding Author:
Dr. C. Nester, Research Fellow
Centre for Rehabilitation and Human Performance Research
Brian Blatchford Building
University of Salford
Salford M6 6PU England
E-mail: C.J.Nester@salford.ac.uk
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TRANSVERSE PLACE ANKLE MOTION
165
To reduce the volume of data, the angular data from
the rotation of the leg from an externally rotated position
to an internally rotated position, and the angular data
from the rotation of the leg from an internally rotated
position to an externally rotated position were averaged.
The characteristics of rearfoot motion are the same during these two rotations, though the directions of motion
are reversed.1,5
The characteristics of the ankle/subtalar complex
were described using the range of motion in each cardinal body plane and the orientation of the axis of rotation. This latter quantity was calculated using a vector
summation method previously used by Downing et al.4
Fig. 1: Shows experimental rig used during static assessment. Rig
was based on design used by Van Langelaan.15 Reflective markers
can be seen on the leg, heel and forefoot (forefoot markers were
part of separate study). Black lines indicate motion of leg and foot
during internal leg rotation, white line the motion of the leg and foot
during external leg rotation.
Fig. 2: Marker set used for dynamic study on four subjects. Four
markers were mounted onto a plate attached to the leg, and three
markers were attached to the heel cup. Also visible are an additional
heel marker and markers on four anatomical landmarks on the leg.
These were used to define anatomically relevant local coordinate
systems for the leg and heel.
apart. Kinematic data for each segment were derived by
tracking the position of three reflective markers attached
to the heel and the leg, from which local coordinate systems were subsequently defined. Using these local coordinate systems, the transverse, sagittal and frontal plane
motions of the heel relative to the leg were calculated in
the planes of the global reference system.
Each subject moved through the following movement
sequence. The leg was in external rotation and the foot
supinated to the extent that the first metatarsal was
non-weightbearing (Fig. 1). The subject then internally
rotated their leg to the point of maximum internal leg
rotation (black lines in Fig. 1) and the subject then externally rotated the leg to return to the original start position (white lines in Fig. 1). Ten consecutive recordings of
this motion sequence were taken.
Dynamic Study
In this preliminary study, conducted by the second
author (AF), the three dimensional motion of the heel
relative to the leg during barefoot walking was measured using reflective markers attached to each segment. The data collection protocol was similar to that of
the static study in terms of marker locations, but followed the guidelines of the calibration method detailed
by Cappozzo et al.2,3 so that skin movement artefacts
were reduced. The leg was defined using reflective
markers mounted on a plastic platform moulded and
attached to the front of the leg and using the tibial
tuberosity, fibular head, medial and lateral malleoli as
calibration (anatomical) landmarks. The heel was
defined using three markers attached to a heel cup
(Fig. 2). Four male subjects were tested to provide preliminary data. Twenty gait cycles were recorded for
each limb of each subject and all the data combined to
produce average data representing the eight limbs.
RESULTS
The mean range of ankle/subtalar complex motion
during internal and external rotation of the leg (mean of
48 limbs) was 27.2° (SD 4.3°, range 19.6° to 35.4°) in
the transverse plane, 7.6° (SD 5.2°, range -0.7° to 24.3°)
in the frontal plane and -0.7° in the sagittal plane (SD
2.3°, range -7.5° to 6.3°). This indicates that during internal leg rotation the heel everted and abducted relative to
the leg, and during external rotation the heel inverted
and adducted relative to the leg. The direction of motion
in the sagittal plane was highly variable and was
dependent on the motion of the leg, rather than motion
of the heel. The range of frontal and transverse plane
motion at the ankle/subtalar complex of each of 48 limbs
is detailed in Figure 3. The difference between days in
the transverse and frontal plane ranges of motion measured for four subjects were on average 1.2° and 1.0° for
the transverse and frontal planes respectively. The mean
axis of rotation (calculated from the mean range of
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Foot & Ankle International/Vol. 24, No. 2/February 2003
motion) for the ankle/subtalar complex was angled 74.3° relative to the
transverse plane and -5.4° to the
sagittal plane, and is illustrated in
Figure 4.
The mean data for the motion at
the ankle/subtalar complex (motion
of the heel relative to the leg)
during walking are presented in
Figure 5. These data are the average of the eight limbs from the four
subjects.
DISCUSSION
The clear predominance of transverse plane motion at the ankle/
subtalar complex during the static
assessments is consistent with an
in vivo study of the maximum range
of motion at the ankle/subtalar comFig. 3: Illustrates the range of motion in the transverse and frontal planes at the ankle/subtalar
plex (actively produced by free rotacomplex during our static assessment. Data is detailed for each limb of each subject except
tion of the foot by the subjects). Nigg two limbs for which data was lost.
et al.11 described a mean total of
35.5° of frontal plane motion and
72.4° of transverse plane motion at an equivalent of the
ankle/subtalar complex in subjects aged 20 to 39. The
difference in the ratio of transverse to frontal plane
motion in the latter study compared to this current study
Mean ankle/subtalar complex
is most likely due to the fact that foot motion was proaxis (74.3°) from static study.
duced by muscle contraction in the Nigg et al. study. The
musculature around the ankle/subtalar complex is better
orientated for producing frontal plane motion than transMean subtalar joint axis
(33.5°) taken from comparable
verse plane motion. Thus, it is unlikely that these indidata from Lundberg et al.
viduals were able to exploit the full range of transverse
plane motion. In this study, where body weight and proximal transverse plane rotations were used to produce
ankle/subtalar motions, it is more likely that the full range
of transverse plane ankle/subtalar complex motion was
exploited.
The angulation of the ankle/subtalar axis to the transverse plane calculated from the data from the static
study was consistently high, ranging from 53.2° to 88.9°
and this reflects the predominance of transverse plane
Fig. 4: Axes of rotation for the ankle/subtalar complex as calculated
motion at the complex. This angulation of the axis is
in our static study, and the axis of rotation for the subtalar joint
generally greater than that of the subtalar joint, which
described by Lundberg et al. The difference in angulation to the
has been reported to range between 20° and 68°.6,7 This
transverse plane of the axes reflects the increased transverse plane
motion at the combined ankle/subtalar joints compared to the subtareflects the greater range of transverse plane motion
lar joint in isolation, and thus the transverse plane motion taking
available at the combined ankle and subtalar joints and
place at the ankle joint.
suggests that the ankle joint is moving a considerable
degree in the transverse plane. However, these results
for the combined ankle/subtalar complex must be furThe literature describes a variety of functional characther interpreted to elicit any characteristics of solely the
teristics for the subtalar joint, including subtalar joints
ankle joint.
that display more transverse than frontal plane motion
7
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Foot & Ankle International/Vol. 24, No. 2/February 2003
Fig. 5: Illustrates the transverse, frontal plane and sagittal motion at
the ankle/subtalar complex during our dynamic study (Figs in
degrees for 100% of stance). FF = Forefoot contact, HO = Heel off,
see text for explanation of . Positive values indicate internal leg
rotation, heel eversion and dorsiflexion.
and those that display more frontal than transverse
plane motion.1,8,15 These variations in the predominant
motion at the subtalar joint have been evident in all studies of the subtalar joint characteristics, and samples
have generally been much smaller than in this investigation. It is reasonable to assume, therefore, that the group
investigated in this study will also possess such variations in characteristics of the subtalar joint. Assuming
this is the case, then some deductions can be made
about the transverse plane motion at the ankle joint.
Some subjects in the static study, displayed more
than half as much frontal plane ankle/subtalar complex
motion as there was transverse plane motion during the
composite phase (the ratio value of transverse to frontal
plane motion was less than 2) (Fig. 3). Since it is known
that the principal source of frontal plane motion at the
ankle/subtalar complex is the subtalar joint,13 and within
our sample these subjects display the largest range of
frontal plane motion, then these individuals probably
possess a subtalar joint that displays more frontal than
transverse plane motion. If this is the case, then the
ankle joint must typically be moving approximately 15°
in the transverse plane. In contrast, some subjects in
the static study displayed very little frontal plane motion
at their ankle/subtalar complex (Fig. 3).
As we reported earlier, McCullough and Burge9 and
Siegler et al.14 have described transverse plane rotations
of similar to these hypothetical figures. More recently,
Michelson et al.10 have reported transverse plane motion
in excess of 8° at the ankle joint during simple plantar
and dorsiflexion of the leg relative to the foot. This is a
considerable degree of motion given that their experimental set up probably produced little or no external
transverse plane moment at the ankle. Clearly then, the
range of transverse plane motion through which the
TRANSVERSE PLACE ANKLE MOTION
167
ankle might move, as suggested by the results of our
static study and in the context of other evidence regarding the ankle joint, are quite feasible. If the range of
transverse plane ankle joint motion suggested here is
correct, then in general the ankle and subtalar joints contribute approximately equal amounts of transverse plane
motion to the overall function of the ankle/subtalar complex. This would be consistent with other literature that
has assessed the ankle and subtalar joint separately.
Siegler et al.14 reported 26.5° of transverse plane ankle
motion and 25.9° of transverse plane subtalar joint
motion during transverse plane rotation of the foot relative to the leg. Rosenbaum et al.13 described a mean
total of 11.1° of transverse plane motion at the ankle joint
and 12.3° at the subtalar joint during transverse plane
rotation of the foot relative to the leg.
The principal difficulty with the discussion so far is
that all the results are from studies of the ankle/subtalar
complex under static conditions. However, the data
from our dynamic study provides further weight to the
evidence that the transverse plane motion at the ankle
joint should be considered in how we conceptually
model the ankle joint. The data presented demonstrate
that transverse plane ankle motion is utilised during
walking, and is not simply a characteristic evident in
static studies. During the period from forefoot contact to
point indicated on the graph (Fig. 5), the leg is externally rotating with respect to the heel, and this occurs
independent of inversion of the heel relative to the leg,
which remains comparatively constant. This is similar to
data reported by Rattanaprasert et al.12 If the external
rotation of the leg during this period were occurring
solely at the subtalar joint then the coupled inversion
motion would have to occur at the same time, which it
does not. The most likely mechanism by which this
external rotation can take place without concurrent
inversion of the heel is by external rotation of the leg relative to the talus. This is in agreement with Van
Langelaan15 who observed that during initial external
rotation of the tibia, the talus did not follow the tibia
immediately. This “talar delay” was attributed to the
need to develop tension in the ankle ligaments before
the talus would follow the leg into external rotation.
SUMMARY
The ability of the ankle joint to move in the transverse
plane is clearly an important part of the kinematic chain
which allows the leg and proximal structures to rotate in
the transverse plane while the foot remains in a relatively fixed transverse plane position on the floor. Our
static and dynamic studies using a noninvasive in vivo
method have confirmed the findings of other studies
that have concluded that both the ankle joint and the
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NESTER, FINDLOW, BOWKER AND BOWDEN
subtalar joint are necessary parts of this mechanism
and it is not solely a function of the subtalar joint.
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