The ability to absorb the forces generated by the foot striking the ground
and to maintain balance while walking on uneven surfaces are the two main
functions of the subtalar
joint1,2.
This absorption of forces occurs through a short pronation movement
immediately after heel strike. Decreased motion of the hindfoot following
surgical treatment of a clubfoot deformity is
common1,3,4.
It has been postulated that decreased mobility of the subtalar joint impairs
the long-term functional result; however, there is little available
information concerning the influence of decreased mobility of the subtalar
joint.
Clinical measurement of mobility of the subtalar joint is neither accurate
nor reproducible5.
Increased compensatory mobility in the adjacent joints can be mistaken as
motion of the subtalar joint. It is even more difficult to assess functional
mobility of the joint during
gait6. It is
generally accepted that it is impossible to achieve complete, anatomical
correction of a severe
clubfoot5,7.
Therefore, the pattern of contact between a treated clubfoot and the floor may
be abnormal. Previous investigators have analyzed the pressure distribution of
a treated clubfoot with use of a
pedobarograph6,8,
a Kistler force
plate3,9,10,
or a pressure-sensitive
mat11, but those
studies have not led to any clearly discriminating conclusions. Recent
technical improvements in pressure-sensitive mats and computerized pressure
recordings have enhanced measurement and analysis possibilities.
Our hypothesis was that decreased mobility of the subtalar joint modifies
the pressure distribution under the foot. The purposes of this study were
first to validate parameters of dynamic foot-pressure measurement enabling
detection of pronation movement of the subtalar joint and second to analyze
the long-term results of operative treatment of idiopathic clubfeet with use
of the same parameters.
Patient Population
Between 1955 and 1961, thirty-one children with a total of forty idiopathic
clubfeet were operated on at our institution. Twenty-four patients had
undergone manipulative treatment and serial applications of plaster casts
beginning shortly after birth, and seven patients had had the same treatment
initiated between the ages of two and four months. Complete correction was not
achieved in any of the feet, and all were treated with the same standard
operative posterior release consisting of lengthening of the Achilles tendon
and posterior ankle capsulotomy. At the time of surgery, the mean age was
twenty months (range, six to forty-four months). Because of a relapse, a
second procedure was performed on eight feet (20%) in seven patients. The
revision procedure consisted of a repeated lengthening of the Achilles tendon
in two feet, a transfer of the tibialis anterior tendon in three, a
posteromedial release in two, and an arthrodesis of the subtalar joint in one.
The two feet treated with the posteromedial release and the foot treated with
the arthrodesis of the subtalar joint were excluded from the study. Four
patients had moved abroad, two were lost to follow-up, two had died, and one
refused to be examined, leaving nineteen patients with a total of twenty-four
feet for evaluation.
A complete medical history and all radiographs made since birth were
available for all of the patients. The patients had been followed annually
until the age of sixteen years in our pediatric orthopaedic unit.
Outcome Measurements
The patients were interviewed in person regarding pain, function, level of
sports activities, problems with shoe wear, and satisfaction with the final
result. A complete physical examination of the feet was performed in a
standardized and controlled manner for all patients. The clinical outcome was
assessed with the ankle-hindfoot score developed by the American Orthopaedic
Foot and Ankle Society
(AOFAS)12. A score
of 90 to 100 points was considered to be an excellent result; 80 to 89 points,
good; 70 to 79 points, average; 60 to 69 points, fair; and <60 points,
poor.
Anteroposterior and lateral weight-bearing radiographs of both feet were
made for all patients. The anteroposterior and lateral talocalcaneal angles
were determined on these radiographs.
Dynamic foot-pressure measurements were performed with a pressure-sensitive
mat consisting of four polymer sensors per square centimeter. Measurements
were recorded with a sample frequency of 376 Hz (footscan plate; RSScan and
Intersoft Electronics, Olen, Belgium). The pressure-time curve of the foot and
the pressure-time curves of eight selected measurement points as well as the
center of pressure path were analyzed (Figs.
1-A,
1-B, and
1-C). The pressure-time curve
of the foot has two peaks: the first corresponds to heel contact and the
second, to propulsion of the forefoot. In the normal foot, the peak of heel
strike is always higher than the peak of propulsion and the depression between
the two peaks is clearly marked and harmonious. It indicates the change in
foot-floor pressure during the gait cycle of the entire foot
(Fig. 1-A). The pressure-time
curves recorded simultaneously at eight well-defined anatomical
points—one each under the lateral and medial sides of the heel, one
under each metatarsal head, and one at the point of maximal pressure of the
great toe—allowed us to measure the duration of contact and the height
of the peak pressure at these selected points and to visualize the changes in
pressure in relation to time throughout the gait cycle
(Fig. 1-B). The center of
pressure path is a virtual graphic line indicating the instantaneous point of
application of the resultant vertical foot-floor force during the gait cycle.
This line connects each of about 250 centers of maximal pressure recorded
during one gait cycle (over 600 to 700 msec)
(Fig. 1-C).
Comparison Study
For the purposes of comparison with the patients with clubfeet,
foot-pressure measurements were recorded in a group of patients with normal
feet and in another group of patients who had had a prior arthrodesis of the
subtalar joint. The first group consisted of twenty employees of our
institution (ten women and ten men) with a mean age of thirty-six years
(range, twenty-four to forty-six years). None had had prior foot problems or
lower-extremity symptoms, and all had an American Orthopaedic Foot and Ankle
Society score of 100 points. The second group consisted of five patients with
a mean age of thirty-two years (range, thirty to thirty-six years) with a
prior subtalar joint arthrodesis performed because of painful osteoarthritis
of the subtalar joint at a mean age of sixteen years (range, thirteen to
eighteen years). They were selected from a group of twenty-six patients with
clubfoot who initially had been operated on, between 1966 and 1972, with an
extensive posteromedial release. The mean American Orthopaedic Foot and Ankle
Society score for the five patients with a subtalar fusion was 71 points
(range, 60 to 76 points). Three feet were pain-free, and two feet were mildly
painful on occasion. All patients had some difficulty walking on uneven
terrain, and four patients had some gait abnormality.
The statistical analysis was performed with use of the nonparametric
Mann-Whitney U test at the p < 0.05 level of significance. The analysis of
correlation was performed with use of the t test for independent groups with a
level of significance of r < 0.05.
Comparison Study
In the patients with normal feet, the dynamic foot-pressure measurement
immediately after heel strike was always characterized by three graphic signs
representing the mechanism of shock absorption due to pronation movement at
the subtalar joint. These consisted, first, of a short interruption of the
rise of the first peak of the pressure curve of the foot, forming a notch
(Fig. 1-A); second, of an even
clearer interruption of the initial rise of the pressure-time curve recorded
under the lateral part of the heel with a peak that was less high than the one
recorded under the medial part (Fig.
1-B); and, third, of a short and slight deviation of the center of
pressure path toward the medial side (Fig.
1-C).
In the patients with a subtalar joint fusion, three graphic signs confirmed
the absence of shock absorption or pronation movement (Figs.
2-A,
2-B, and
2-C): the initial rise of the
pressure-time curve of the foot was steep and uninterrupted
(Fig. 2-A), the rise of both
pressure-time curves recorded under the heel was steep and without
interruption and their courses were completely parallel and of the same height
(Fig. 2-B), and the center of
pressure path was characterized by a straight course to the lateral side
without an initial medial deviation (Fig.
2-C).
Study of Patients with Clubfoot
Nineteen patients (seven women and twelve men) with a total of twenty-four
operatively treated clubfeet were evaluated at a mean of forty-one years
(range, thirty-nine to forty-six years) postoperatively. Eighteen patients
were either satisfied or very satisfied with the final result, and only one
patient was not satisfied with it. The American Orthopaedic Foot and Ankle
Society score was excellent for eight feet, good for seven, average for five,
fair for three, and poor for one.
Twelve feet were not painful, seven were mildly painful on occasion, four
were moderately painful after strenuous activities only, and one foot was
severely and almost constantly painful. In the twelve feet with pain, the pain
was located in the hindfoot and had begun at a mean age of thirty-five years
(range, thirty-two to forty years). Thirteen patients were able to participate
in unlimited activities and could walk any distance without discomfort, five
had no limitation of daily activities but had limitation of some recreational
activities, and one patient was limited to walking less than six blocks.
Twelve patients chose an occupation that placed heavy demands on their feet,
but four had to later change jobs because of foot pain. Three patients had to
wear custom-made shoes. All of the others could wear ready-made shoes, but
eight patients were limited in their shoe choice and had noticed rapid
wearingout and some deformation of their shoes.
Physical and Radiographic Examinations
Seventeen patients had a normal gait, and two patients limped. All patients
were able to toe-walk, but four were not able to heel-walk. Motion of the
ankle joint in the sagittal plane (dorsiflexion plus plantar flexion) was
normal or mildly restricted (=30° of total motion in the sagittal
plane) in fifteen cases, was moderately restricted (15° to 29° of
total motion) in five, and was severely restricted (<15° of total
motion) in four. Ankle dorsiflexion was between 1° and 10° in twelve
cases and was >10° in four; four feet could just reach the neutral
position, and four could not reach the neutral position. The four ankles
without dorsiflexion were associated with a shortened duration of heel
contact. The mean dorsiflexion of the ankle was 7° (range, —10°
to 20°), and the mean plantar flexion was 25° (range, 10° to
30°).
All feet had limited inversion-eversion mobility of the hindfoot; the
limitation was moderate (25% to 74% of normal) in fifteen feet and marked
(<25% of normal) in nine. The ankle-hindfoot alignment, measured with the
patient standing, was in neutral in twelve cases, in varus malalignment in ten
(=5° of varus in eight and between 6° and 10° in two), and in
=5° of valgus malalignment in two. Thirteen feet had the clinical
appearance of a cavus foot. The clinical assessment showed malalignment of the
knee joint (5° of valgus) in only one patient. The mean American
Orthopaedic Foot and Ankle Society score for all twenty-four feet was 81
points (range, 28 to 97 points). There was no correlation between the range of
hindfoot motion and the American Orthopaedic Foot and Ankle Society score (r =
0.34).
The mean anteroposterior talocalcaneal angle was 13° (range, 0° to
24°), and the mean lateral talocalcaneal angle was 20° (range, 10°
to 30°). The functional results did not correlate with these angles (r =
0.46 for the anteroposterior angle, and r = 0.14 for the lateral angle). In
the two overcorrected feet with hindfoot valgus, the anteroposterior
talocalcaneal angles were 15° and 20° and the lateral talocalcaneal
angles were 20° and 23°. None of the feet showed obvious signs of
degenerative arthritis in the subtalar joint, such as narrowing of the joint
space or osteophytes.
Foot-Pressure Measurements
The dynamic foot-pressure measurements showed a pronation movement in
nineteen feet. Twelve of these feet were asymptomatic, and seven were
occasionally mildly painful, mainly during strenuous activities. In two of the
asymptomatic feet, the rise of the pressure-time curve was flat and
interrupted and the medial deviation of the center of pressure path was
increased and prolonged. An excessive pronation movement, a sign of muscular
imbalance after transfer of the tibialis anterior tendon, had developed in
both feet.
No pronation movement was detectable in five feet (Figs.
3-A,
3-B, and
3-C). The rise of the
pressure-time curve of the foot was steep and uninterrupted, and there was
hardly any depression between the first and second peaks
(Fig. 3-A). The two
pressure-time curves recorded under the heel were nearly parallel and reached
the same height (Fig. 3-B). The
center of pressure path was characterized by a straight course without an
initial medial deviation (Fig.
3-C). All five feet were painful: two were occasionally painful
during strenuous activities, two were occasionally painful during routine
activities, and one was painful during walking.
The mean American Orthopaedic Foot and Ankle Society score was 87 points
(range, 76 to 97 points) for the nineteen feet with pronation movement and 57
points (range, 28 to 72 points) for the five feet without pronation movement
(p < 0.001). The components of the score related to physical examination of
hindfoot motion did not demonstrate any difference between the two groups (p =
0.97) (Table I).
The pressure distribution of the measurement points under the five
metatarsal heads showed that the most frequent point of initial contact was
under the fifth metatarsal head in the clubfeet and under the fourth
metatarsal head in the normal feet. The highest pressure point in the forefoot
was situated under the third metatarsal head in the clubfeet and under the
second metatarsal head in the normal feet.
It is generally accepted that the purpose of either nonoperative or
operative treatment of idiopathic clubfoot is to eliminate or reduce all
deformities and to obtain a plantigrade, painless foot with lifelong normal
function and good mobility that fits into ready-made
footwear4.
The best way to achieve good function remains controversial. Is it more
important to obtain the best possible anatomical correction, even if extensive
soft-tissue release or repeated surgical interventions are necessary, or is it
preferable not to go beyond manipulative treatment (except perhaps to lengthen
the Achilles tendon) and to accept some residual deformity? This question can
be answered only with long-term studies following patients into adult life
with use of a reliable, accurate, and reproducible method to assess the level
of function4. Only a
few investigators have followed patients beyond
adolescence6,13,14.
In our study group, all of the patients had pain-free feet at sixteen years of
age and felt pain for the first time at a mean of thirty-five years of age.
Stiffness of the hindfoot also clearly developed after the age of sixteen.
Unfortunately, long-term studies also have limitations. Forty years ago,
the knowledge of the pathoanatomy of congenital clubfoot was incomplete.
Consequently, preoperative manipulative treatments were not optimal and did
not always start immediately after birth. Furthermore, surgery was often
delayed until the patient was older. Also, often a large number of patients
are lost to follow-up in long-term studies, reducing the reliability of the
results. We were able to review the results in 61% (nineteen) of our
thirty-one patients, which compares favorably with the 36% rate (forty-five of
126 patients) in the most frequently quoted long-term follow-up study, by
Cooper and
Dietz6.
The major limitation of our study was its size, but our patient group was
homogeneous as far as the aim of the study is concerned, since none of the
feet had a soft-tissue release of the subtalar joint. Subtalar joint mobility
was not affected in the two feet with lengthening of the Achilles tendon or in
the three feet with transposition of the tibialis anterior tendon during a
second intervention.
In the past, many different radiographic angles were analyzed to assess the
quality of correction or to correlate the images with
function15. Each of
the angles describes only some aspects of the clubfoot, and the
reproducibility of most such angular measurements is
poor5. Deformation,
a delay in ossification, and eccentric ossification of the tarsal bones in
young children make measurements of radiographic angles
inexact13,16;
this is especially true for one of the most frequently measured angles, the
anteroposterior talocalcaneal angle (Kite angle). Ponseti did not find a
correlation between the angles measured on radiographs and the functional
results4, and we
found no correlation between radiographic angles and American Orthopaedic Foot
and Ankle Society scores.
Ankle and hindfoot motion is frequently decreased following treatment of a
clubfoot
deformity1,3,4.
Aronson and Puskarich observed a mean total arc of ankle motion of 40°
after treatment of clubfeet compared with 71° in individuals with normal
feet (a 44%
decrease)3. The
dorsiflexion arc was 9° in the treated clubfeet and 27° in the normal
feet (a 67%
decrease)3. In our
patients with clubfoot, stiffness of the hindfoot increased notably after the
age of sixteen years. However, physical examination of hindfoot motion does
not allow one to discriminate between good and poor results. Cooper and
Dietz6 measured
inversion and eversion of clubfeet with an electrogoniometer during gait, but
they found no correlation between reduced joint motion and functional outcome.
Because the pronation movement takes place in the subtalar joint, assessment
of that joint motion during gait is of primary interest.
Grundy et al.17
were among the first to investigate the center of pressure path in patients
with various foot problems and to suggest that this measurement might be
useful. Brand et
al.9 and Aronson and
Puskarich3 concluded
that the measurement was not accurate enough to differentiate clubfeet from
normal feet reliably. Widhe and
Berggren10 found
some relationship between the symptoms of patients with bilateral clubfoot and
lateralization of the center of pressure path, but the duration of follow-up
in their study was short (nine years) and they recorded at a rate of 25 Hz,
which we believe is insufficient. Hutchinson et
al.8 found some
difference in the distributions of pressure across relapsed clubfeet before
and after correction with the Ilizarov technique. Bowen et
al.11 pointed out
that dynamic foot-pressure measurement could be used to distinguish between
specific clinical deformities.
In the studies described above, the sensor platform had a local resolution
of two sensors per square centimeter and a recording frequency of between 25
and 70
Hz3,6,8-11.
However, the duration of the stance phase at walking velocity is only about
600 to 700 msec, and the pressure distribution of a normal foot has wide
variability. To detect slight changes such as a short interruption in the
initial rise of the pressure-time curve or an initial medial deviation of the
center of pressure path, it is crucial to use computerized systems of
foot-pressure measurement with higher sensitivity and capacity of recording,
as we did in this study. Another technical improvement in this study was the
capacity to record the pressure-time curve simultaneously at eight
well-defined anatomical points, allowing, for example, the analysis of two
pressure-time curves under the heel. Thus, for the first time it has been
possible to correlate objective criteria with long-term functional
outcome.
The purpose of treatment must be to achieve the best possible correction of
the clubfoot deformity. However, in order to obtain good long-term functional
results, mobility of the subtalar joint should be preserved. The pronation
movement of the subtalar joint immediately after heel strike is an important
mechanism to absorb and dissipate the forces generated by the foot striking
the ground. It is a passive mechanism, and the amount of motion appears to
depend entirely on the configuration of the articulating surfaces, their
capsular attachments, and their ligamentous
supports2,18.
This study leads to the conclusion that preservation of functional mobility
of the subtalar joint is an important factor for good, lifelong results of the
treatment of clubfeet, even when the feet are only partially corrected. The
presence of a pronation movement of the subtalar joint immediately after heel
strike enabled us to discriminate between good and poor long-term functional
results in our patients with clubfoot.