Abstract
Background: Originally introduced by Morton, the concept of
hypertrophy of the medial cortex and the entire shaft of the second metatarsal
as an objective sign of increased mobility of the first ray has not been
subjected to much scrutiny. The goal of the current study was to assess the
clinical relevance and reliability of radiographic measures of hypertrophy of
the second metatarsal in relation to mobility of the first ray, pes planus,
and tightness of the gastrocnemiussoleus in both control subjects and patients
with diagnosed disorders of the forefoot.
Methods: Four study groups of forty-three subjects each were
evaluated. The cohort included an asymptomatic control group as well as three
groups made up of patients with symptoms and a diagnosis of hallux valgus,
hallux rigidus, or interdigital neuroma. Mobility of the first ray (as
measured with a device and method described by Klaue et al.), arch height, and
ankle dorsiflexion were measured on physical examination. Plain weight-bearing
radiographs and previously established equations were used to determine
hypertrophy and the length of the second metatarsal, and the hallux valgus and
first-second intermetatarsal angles were measured on plain radiographs as
well.
Results: There was no significant difference between the control and
symptomatic groups with regard to the values for hypertrophy of the second
metatarsal. The patients with hallux valgus deformity had significantly
greater mobility of the first ray (p < 0.001) compared with the controls.
No correlation was found between values for hypertrophy of the second
metatarsal and mobility of the first ray, the length of the first metatarsal,
pes planus, or restricted ankle dorsiflexion. No correlation was found between
mobility of the first ray and either pes planus or restricted ankle
dorsiflexion. A weak correlation (r = 0.4) was noted between increased
mobility of the first ray and the hallux valgus angle.
Conclusions: Our findings do not support Morton's concept that
medial cortical hypertrophy and increased shaft width of the second metatarsal
are associated with increased mobility of the first ray or relative shortness
of the first metatarsal. In addition, hypertrophy of the second metatarsal was
not associated with either pes planus or restricted ankle dorsiflexion. We
found the practice of using hypertrophy of the second metatarsal as an
indicator of mobility of the first ray to be unreliable, and thus we consider
it to be an inappropriate indication for arthrodesis of the first
metatarsocuneiform joint in the treatment of hallux valgus deformity.
Level of Evidence: Diagnostic study, Level IV-1
(case-control study). See Instructions to Authors for a complete description
of levels of evidence.
The concept of hypermobility of the first ray was introduced by
Morton1, who
suggested that, as a result of either dorsal extension of the first metatarsal
or a short first
metatarsal2, the
first ray becomes ineffective and nonfunctional as a weight-bearing structure.
It was
Lapidus3-5,
however, who suggested that increased mobility of the metatarsocuneiform joint
was a cause of hallux valgus. Morton claimed that hypermobility was
characterized by increased motion of the first ray on clinical
examination1, but he
thought that the most notable structural feature associated with hypermobility
of the first ray was hypertrophy of the second metatarsal
bone6.
Morton2 also
suggested that the symptoms associated with interdigital neuromas were
probably caused by instability of the first metatarsal. Others have speculated
that hallux rigidus is associated with instability of the first ray as
well7-10.
Furthermore, Morton and others have linked pes planus to a short first
metatarsal1,6,11,12,
hypermobility of the first
ray1,6,11,12,
and a contracture of the gastrocnemius or Achilles
tendon1,2,12.
While other authors have questioned the association between hypermobility
of the first ray and cortical hypertrophy of the second metatarsal in normal
subjects13 and in
those with hallux
valgus14, the
concept of medial cortical hypertrophy of the second metatarsal as an
objective finding associated with a hypermobile hallux valgus deformity has
been accepted with few or no supporting objective data in a number of
reports11,12,15-19.
Our goal in the current study was to assess the clinical relevance and
reliability of radiographic measurements of the length, width, and cortical
thickness of the second metatarsal in relation to mobility of the first ray,
pes planus, and tightness of the gastrocnemius and soleus in both normal,
asymptomatic subjects and those with a diagnosis of hallux valgus, hallux
rigidus, or interdigital neuroma.
Approval
All subjects participating in this study received a thorough explanation of
the risks and benefits of inclusion and gave informed consent. Approval from
the institutional review board was obtained prior to the start of this
study.
Inclusion Criteria
Subjects were selected for inclusion in one of four different study groups.
Only one foot of each patient was included. The control group was composed
initially of ten patients who had been treated for a corn on the fifth toe of
the contralateral foot but had no symptoms or previous injury or surgery in
the normal foot. The study was then expanded to include an additional
thirty-three asymptomatic volunteers who also had never had any symptoms,
injury, or treatment of the foot. These subjects were recruited from hospital
staff employees on a random basis.
The three other study groups included subjects with a diagnosis of hallux
valgus, hallux rigidus, or interdigital neuroma who presented to the office of
the senior author (M.J.C.) for management. Each subject had only one of the
three forefoot diagnoses.
Subjects were enrolled consecutively if they met the criteria for inclusion
in one of the three study groups, but they were matched for gender. To be
included in the study, a subject with a diagnosis of hallux valgus had to have
a moderate or severe clinical deformity with a radiographic finding of hallux
valgus of
=25°20. All
subjects were candidates for operative treatment, but the evaluation was
completed prior to any surgical intervention.
A subject with a diagnosis of hallux rigidus was included in the study only
if the disorder was Grade 2 or 3 as determined on both clinical and
radiographic
examination21. All
patients were candidates for operative treatment, but the evaluation was
completed before any surgical intervention.
To be included in the study, subjects with a diagnosis of interdigital
neuroma had to have classic neuroma
symptoms22 and to
have undergone surgical treatment with intraoperative and pathologic
confirmation of the diagnosis. These patients were evaluated after the index
surgery, but all measurements pertaining to this study were made on their
preoperative radiographs.
Demographic Data (Table
I)
The average age of the entire cohort was fifty years (range, twenty to
seventy-eight years). The four groups were matched for gender; 88% of the
subjects in each were women.
Physical Examination
All physical examinations and radiographic measurements were performed by
the junior author (B.R.G.).
Tightness of the Achilles Tendon (Examination of Ankle
Dorsiflexion)
Each patient was examined in a seated position (with the knee flexed and
extended), with attention focused on tightness of the gastrocnemius-soleus
muscle (restricted ankle dorsiflexion). Care was taken to ensure that the foot
was held in a neutral position (with the talonavicular joint reduced to
eliminate transverse tarsal or subtalar
motion)23,24
with respect to the forefoot and hindfoot during assessment of the
gastrocnemius-soleus. Ankle joint motion was measured with a hinged goniometer
(with 5° increments) placed on the lateral aspect of the foot and ankle
and with the fibula and the plantar-lateral border of the foot used as
landmarks for each limb of the goniometer. A right angle was considered to be
the neutral position.
Harris Mat Studies
Harris mat pressure studies were performed for all patients in order to
assess arch height, not to specifically document individual pressure areas.
Patients were asked to stand 18 in (46 cm) from the Harris mat and to then
step forward, placing the foot onto the center of the prepared mat, and to
continue walking forward beyond the mat, leaving an imprint of the foot and
the
hallux24-26
(Fig. 1).
Mobility of the First Ray
Mobility of the first ray was measured in all patients with use of the
device and method described by Klaue et
al.27. A
measurement of =9 mm of excursion with use of the device is considered
normal for the first
ray27
(Fig. 2).
Radiographic Examination
Angular Measurements
Standardized anteroposterior weight-bearing radiographs were made and
reviewed for all subjects. The hallux valgus angle (normal, =15°) and
the first-second intermetatarsal angle (normal, =9°) were measured
according to the guidelines set forth by the American Orthopaedic Foot and
Ankle Society on Angular
Measurements20
(Fig. 3).
Measurement of the Length of the First Metatarsal
The length of the first metatarsal was measured and compared with that of
the second metatarsal (metatarsal protrusion distance) on the anteroposterior
radiograph. Length measurements within 1 mm of each other were considered to
be equal. Both Morton's
method2 and the
technique used by Hardy and
Clapham26 (arc
measurements) (Fig. 4) were
used, in order to compare the results in our studies with those in previous
studies. According to Hardy and Clapham, Morton's technique does not allow for
measurement changes in the length of the first metatarsal due to angular
malalignment (hallux valgus and metatarsus primus varus). The arc technique of
measurement allows for variation in the angle of the first metatarsal.
Measurement of Cortical Thickness
Electronic digital slide calipers (catalog #721 A-6/150; L.S. Starrett,
Athol, Massachusetts) were used to measure all cortical and metatarsal widths.
The calipers have a measuring error of 0.03 mm.
Morton's Ratio of Metatarsal
Width2
The width of the second metatarsal in comparison with that of the lateral
three lesser metatarsals was measured on the anteroposterior radiograph at
both (1) the junction of the proximal and middle thirds of each of the lateral
four metatarsals and (2) across the neck of each of these metatarsals. The
formula described by
Morton2 was used to
create a ratio with which to compare the relative widths of the second
metatarsals (Fig. 5).
Morton's Ratio of Cortical
Thickness2
At the midpart of the diaphysis of all four lateral metatarsals, the entire
width of the shaft and the width of the medullary canal were measured. The
individual cortical thickness was then calculated, as described by
Morton2, by
subtracting the medullary width from the shaft width. A ratio was calculated
from these values in an attempt to eliminate variability that might occur as a
result of the differences in the sizes or ages of the subjects
(Fig. 5).
Technique of Prieskorn et
al.13
At the midpart of the diaphysis of the second metatarsal, the entire width
of the shaft, the width of the medullary canal, and the medial cortical width
were measured. Ratios (medial cortical width to medullary canal width and
medial cortical width to shaft width) were then calculated in order to obtain
a standardized value regardless of foot size
(Fig. 6).
Statistical Analysis
Statistical analysis was performed with use of Instat software (Graphpad,
San Diego, California). Comparisons among the four groups were performed with
one-way analysis of variance. Significant differences identified with analysis
of variance were evaluated with the Dunn multiple-comparisons test.
Significance was determined by a p value of <0.05. The Pearson correlation
matrix was used to assess correlation between variables for all samples.
Coefficient values (r values) closer to one indicate strong correlation,
whereas values closer to zero indicate weak or no correlation.
Radiographic Measurements
(Table II)
Angular Measurements
The average hallux valgus angle was 34.6° (range, 25° to 55°)
and the average first-second intermetatarsal angle was 15.4° (range,
10° to 23°) in the hallux valgus group. The hallux valgus group
differed significantly from the other three groups with regard to both the
hallux valgus angle (p < 0.001) and the first-second intermetatarsal angle
(p < 0.001).
Length of First Metatarsal
With use of Morton's transverse line
technique2 to
measure the first metatarsal protrusion distance, 53% (twenty-three) of the
forty-three first metatarsals in the control group were found to be shorter
than the second metatarsal. With use of the arc method of
measurement26, 30%
(thirteen) of the first metatarsals were found to be shorter than the second
metatarsal.
When used in the other three groups, the Morton and arc techniques provided
distinctly different values, with a marked reduction in the prevalence of
short first metatarsals when the arc technique was employed. In the hallux
valgus group, 63% of the first metatarsals were determined to be short with
use of the Morton technique whereas only 5% were noted to be shorter when the
arc technique was used. In the entire cohort, 58% (ninety-nine) of the 172
feet were found to have a short first metatarsal when measured with Morton's
technique, whereas 22% (thirty-seven) were found to have a short first
metatarsal when measured with the arc technique.
Cortical Thickness
The average medial cortical thickness of the second metatarsal shaft was
3.0 mm in the control group, 3.1 mm in the hallux valgus group, 3.3 mm in the
hallux rigidus group, and 2.9 mm in the neuroma group. The differences between
the control and the other three groups were not significant. Also, there was
no significant difference among the four groups with regard to the midshaft
width of the second metatarsal, the ratios obtained from Morton's equations
for shaft and cortical thickness of the metatarsals, or the values obtained
with Prieskorn's equations for medial cortical thickness of the metatarsals
(Table III).
Physical Examination (Table
IV)
Mobility of the First Ray
Sagittal motion of the first ray averaged 6.9 mm in the hallux valgus
group, 6.3 mm in the hallux rigidus group, 4.9 mm in the neuroma group, and
4.9 mm in the control group. The mobility of the first ray in the hallux
valgus group was significantly greater than that in the control group (p <
0.001) and that in the neuroma group (p < 0.001), but it was not
significantly different from that in the hallux rigidus group (p > 0.05).
The mobility of the first ray in the hallux rigidus group was also
significantly increased compared with that in the control group (p < 0.01)
and that in the neuroma group (p < 0.001). There was no significant
difference between the control and neuroma groups with regard to mobility of
the first ray (p > 0.05).
Contracture of the Achilles Tendon
In the evaluation of tightness of the gastrocnemius and soleus, no group
was found to have <5° of dorsiflexion on average. Both the hallux
valgus and the hallux rigidus group had, on average, >10° of ankle
dorsiflexion. The hallux rigidus group had the greatest ankle dorsiflexion,
with an average of 11.9°, which was significantly greater than the values
in the control (p < 0.01) and neuroma groups (p < 0.01) but not
significantly greater than the value in the hallux valgus group (p > 0.05).
The control group had the lowest average ankle dorsiflexion (8.6°): 19%
(eight) of the forty-three subjects in that group had =5° of ankle
dorsiflexion; 81% (thirty-five), =10°; and 95% (forty-one),
<15°. Of the entire cohort of 172 subjects, 20% (thirty-four) exhibited
ankle dorsiflexion of =5°; 70% (120), =10°; and 76% (131),
<15°.
Pes Planus
The Harris mat studies demonstrated that a low arch (pes planus) was
significantly more common in the hallux valgus group than it was in the
control group (p = 0.04), hallux rigidus group (p = 0.01), or neuroma group (p
= 0.02). Of the subjects with hallux valgus, 23% (ten) had moderate or severe
pes planus deformity (a grade of +2 or greater for the Harris mat imprint).
There was no significant difference among the other three groups (p >
0.05).
We analyzed the relationship between pes planus and a short first ray as
measured with the arc technique, and we found that only five (23%) of the
twenty-two subjects with moderate or severe pes planus deformity had a short
first metatarsal. We also found that only six (27%) of the twenty-two feet
with moderate or severe pes planus demonstrated increased mobility of the
first ray (>9 mm of motion as measured with Klaue's device). Three (14%) of
the twenty-two patients with moderate or severe pes planus had both a short
first metatarsal and increased mobility of the first ray.
Correlations (Table
V)
Of all of the variables that were considered, only the hallux valgus angle
and the first-second intermetatarsal angle showed a strong correlation (r =
0.8). No other variables showed strong correlation across the entire sample.
Only a weak correlation was noted between pes planus and hallux valgus
deformity (r = 0.3) and between pes planus and the first-second
intermetatarsal angle (r = 0.2). There was also weak correlation between
mobility of the first ray and hallux valgus deformity (r = 0.4) and between
mobility of the first ray and the first-second intermetatarsal angle (r =
0.3).
Morton2 based his
conclusion that hypertrophy of the second metatarsal is a sign of
hypermobility of the first ray on an analysis of 150 subjects who presented
with forefoot pain. Of those patients, fifty-one were diagnosed as having
moderate or severe hypermobility of the first ray. In the current study, we
examined 172 subjects, and we assessed only one foot of each subject. There
were forty-three subjects in each of four study groups: asymptomatic controls,
patients with hallux valgus, patients with hallux rigidus, and patients with
interdigital neuroma. The asymptomatic control group was evaluated for
characteristics of the second metatarsal and was compared with the groups of
symptomatic patients. A group with interdigital neuroma was included to
evaluate Morton's
notion2 that
hypermobility of the first ray is associated with development of neuromas, and
a group with hallux valgus was examined to evaluate Lapidus's contention that
hypermobility is associated with hallux
valgus3-5.
Patients with hallux rigidus were selected as the fourth group because of the
implication that hypermobility is also associated with this
diagnosis7-10,12.
Morton1 stated
that the most notable feature associated with hypermobility of the first ray
was hypertrophy of the second metatarsal, which was manifested as either
widening of the shaft or thickening of the
cortex2,6,28.
He surmised that this hypertrophy was due to either a short first metatarsal
or hypermobility of the first metatarsal that made the first ray less
effective as a weight-bearing structure, increasing the weight-bearing burden
being shifted onto the lesser metatarsals. Morton hypothesized that the
majority of this burden was absorbed by the second metatarsal, resulting in
hypertrophy, although he offered no anatomic or statistical proof of his
hypothesis2.
Prieskorn et
al.13 found no
correlation between motion of the first metatarsocuneiform joint and the
medial cortical thickness of the second metatarsal in a study of 100 normal
feet. Later, Faber et
al.14 reported no
significant correlation between mobility of the first metatarsocuneiform joint
and the shaft width or medial cortical thickness of the second metatarsal in
ninety-four patients with hallux valgus. In both of those studies, the
investigators used radiographic techniques to assess mobility of the first
ray, which was measured in degrees, and those are the only reports on the
subject that we could find in the literature. Using Klaue's device, we
measured motion of the first ray in millimeters. The technique that
Morton2 used early
on as well as the technique used later by
others13,14,29
to measure metatarsal hypertrophy employed ratios rather than absolute values
to compensate for varying foot and metatarsal sizes. We chose to use both of
these techniques in order to be consistent for comparison purposes.
Our results with the use of Klaue's device to measure mobility of the first
ray confirm the findings in the radiographic studies of Prieskorn et
al.13 and Faber et
al.14, as we found
no correlation between mobility of the first ray and the length, shaft width,
or medial cortical width of the second metatarsal. Furthermore, we found no
correlation between mobility of the first ray and the results of Morton's two
equations for cortical hypertrophy and size. We also found no correlation
between mobility of the first ray and medial cortical thickness in patients
with hallux valgus, hallux rigidus, or interdigital neuroma, and there was no
significant difference between the values in any of the symptomatic groups and
those in the control group.
Morton1,28
observed unusual shortness of the first metatarsal bone when he compared it
with the second, and he suggested that this shortness led to increased
pressure beneath the lesser metatarsals and to excessive pronation. Harris and
Beath30, however,
disputed this notion in their study of 7167 feet of male military recruits;
they observed an equal frequency of disturbed weight-bearing in feet in which
the first metatarsal was equal to or longer than the second metatarsal and in
those with a short first metatarsal. Overall, they found that 32% of feet had
a short first metatarsal when they used the arc technique of measurement. The
vast majority of their subjects with a short first metatarsal had no symptoms
or evidence of disturbed weight-bearing. They concluded that shortness of the
first metatarsal relative to the second did not mean that the first metatarsal
could not readily reach the ground or that less weight was transmitted through
this bone. Using the same measurement technique, we found an overall 22%
prevalence of feet with a short first metatarsal, which was lower than the
prevalence reported by Harris and
Beath30.
The relative lengths of the first and second metatarsals can be measured
with different techniques. When metatarsal length is measured with use of arcs
intersecting the distal articular surfaces of the first and second
metatarsals26,28,
the relative lengths of the metatarsals are not influenced by variation in the
intermetatarsal angle or by metatarsus adductus; thus, we prefer this method
of measurement. When this technique was used in the current study, the
prevalence of a short first metatarsal was found to be 30% in the control
group and 5% in the group with hallux valgus.
Morton2 utilized
transverse lines to quantify metatarsal length and reported various degrees of
shortness of the first metatarsal in 51% (seventyseven) of his 150 patients
with metatarsalgia. In the current study, when metatarsal length was
determined with use of transverse lines, the prevalence of a short first
metatarsal increased dramatically, from 5% to 63%, in the group with hallux
valgus and it increased between two and twelvefold in all three study groups.
We believe that Morton's notion of a high prevalence of a short first
metatarsal in patients with metatarsalgia was largely due to a measurement
artifact with his novel technique. However, regardless of whether the
transverse line or the arc method was used, we found no correlation between a
short first metatarsal and the shaft width or cortical hypertrophy of the
second metatarsal.
The concept of hypermobility of the first ray was introduced by Morton in
19281. While Morton
claimed that hypermobility of the first ray led to a multitude of foot
disorders1,2,
he noted that he had been unable to devise a method with which to quantify the
degree of dorsal hypermobility of the first
ray2. Recently,
attempts have been made to quantify mobility of the first ray on the basis of
either
degrees13,31-33
or millimeters of either dorsal displacement or total
excursion27,34-37.
Our data are comparable with those in previous reports in which mobility
was measured in millimeters of displacement with Klaue's
device27,38.
Klaue et al.27
defined a first ray as hypermobile if there was >9 mm of measured motion.
We found Klaue's device to be reliable and to provide reproducible
measurements of excursion of the first ray when we repeated the measurements
on the same individuals. While the applied force is not standardized when this
device is used, it is similar in magnitude to that employed in a manual
examination12,18,39.
Voellmicke and
Deland39 proposed
that a similar level of mobility of the first ray (8 to 10 mm) found with a
manual examination is indicative of hypermobility.
While the group with hallux valgus in our study did demonstrate greater
mobility of the first ray than did the other three groups, mobility of the
first ray did not correlate with increased medial cortical width of the second
metatarsal, increased midshaft width of the second metatarsal, or any of the
results of the formulas suggested by either
Morton2 or Prieskorn
et al.13. On the
basis of our data, we cannot support Morton's
theory6 that the
most notable structural feature associated with hypermobility of the first ray
is hypertrophy of the second metatarsal bone.
Hardy and
Clapham40 reported
a correlation between an increased hallux valgus angle and the first-second
intermetatarsal angle, which we found as well.
Lapidus5 (in
1960) and
others12,15-18,27,41
believed that hallux valgus was associated with hypermobility of the first ray
and recommended a metatarsocuneiform arthrodesis. While Fritz and
Prieskorn29 and
Faber et al.31
reported no correlation between mobility of the first metatarsocuneiform joint
and the magnitude of the first-second intermetatarsal angle, we did observe a
correlation between mobility of the first ray and an increased hallux valgus
angle. Only a prospective study on the treatment of hallux valgus will enable
us to evaluate the importance of this finding.
Morton42 defined
normal ankle dorsiflexion as a minimum of 15°. In the control group in the
current study, 95% of the subjects had <15° of ankle dorsiflexion when
examined with the knee in full extension and the hindfoot in neutral. Using
=5° of ankle dorsiflexion as a guideline, DiGiovanni et
al.43 observed that
eight (24%) of thirty-four normal subjects had restricted dorsiflexion, and
when they used =10° as a guideline, they found that fifteen (44%) of
the normal subjects had restricted dorsiflexion. In the current study, eight
(19%) of the forty-three subjects in the control group had ankle dorsiflexion
of =5°, thirty-five (81%) had =10°, and forty-one (95%) had
<15°.
It has been suggested that a gastrocnemius contracture plays a vital
biomechanical role in chronic foot and ankle
problems43. While
lengthening of the gastrocnemius has been recommended for patients with a
limitation of dorsiflexion of =5° who are undergoing surgical treatment
for selected foot
disorders12, we
suggest that since 81% of the subjects in our control group demonstrated
=10° of ankle dorsiflexion, this finding may not be abnormal.
To be consistent with the evaluation techniques of
Morton2 and
others24,26,30,
we used a foot imprint to determine pes planus deformity and low arch height.
It has been suggested that pes planus is often the result of either an
anatomically short or a functionally short (hypermobile) first
ray6,11.
Morton1 concluded
that this shortening leads to ineffective weight-bearing by the medial column,
pronation of the foot, and a depression of the longitudinal arch as evidenced
by the foot imprints in his study.
Lapidus3 also
suggested that there was an association between pes planus and hypermobility
of the first ray but linked it to medial deviation of the first metatarsal and
hallux valgus deformity.
Others24,40,
however, have challenged the notion that pes planus is associated with an
ineffective first ray. Harris and
Beath24 found that
the prevalence of pronation and pes planus when the first metatarsal was short
was similar to that when it was long. Hardy and
Clapham40 concluded
that there was no correlation between mobility of the first metatarsocuneiform
joint and pes planus. Neither of these studies, however, included a
statistical analysis of the results, and Harris and
Beath24 evaluated
only male military recruits.
We found no correlation between pes planus and either mobility of the first
ray or the length of the first metatarsal. Only 23% of individuals with pes
planus had a short first metatarsal, only 27% of individuals with pes planus
demonstrated increased mobility of the first ray, and 14% of individuals with
pes planus demonstrated both a short first metatarsal and increased mobility
of the first ray. Our findings are in accord with those of Harris and
Beath24 and Hardy
and Clapham40;
thus, we cannot support Morton's theory that mobility or shortness of the
first ray leads to a pes planus deformity.
We are not aware of any report on the prevalence of pes planus and hallux
valgus in adult patients.
Coughlin25,
however, reported that 16% of forty-five adolescent patients with hallux
valgus demonstrated pes planus and that flat feet were no more common in his
patients than in the general population. Our finding of pes planus in 11% of
the individuals in our control group supports a previous finding that 10% to
20% of the population has an asymptomatic pes planus
deformity24. While
there was indeed a higher prevalence of pes planus in the group with hallux
valgus than in the control group in our study, when we examined the entire
cohort, we found only a weak correlation between the hallux valgus angle and
pes planus. This finding may be due to our sample size; a larger study group
may have demonstrated a stronger correlation.
Morton42
suggested that, in addition to being associated with mobility of the first
ray, pes planus deformity was associated with a tight Achilles tendon. In the
current study, we found no correlation between pes planus and limited ankle
dorsiflexion.
Morton2 thought that
pronation of the foot as a result of either a tight Achilles tendon or
dysfunction of the first ray shifted weight laterally onto the forefoot and
that these stresses were concentrated on the second metatarsal, which resulted
in widening of the shaft and thickening of the cortex. We found no association
between pes planus and the shaft width or cortical hypertrophy of the second
metatarsal.
In conclusion, Morton stressed that a majority of forefoot problems are
related to insufficiency of the first ray and associated pes planus and
Achilles tendon contracture. He considered the most notable evidence of
insufficiency of the first ray to be hypertrophy and medial cortical
thickening of the second metatarsal as seen on plain radiographs. The results
of our investigation demonstrated no significant difference between
asymptomatic controls and symptomatic subjects with hallux valgus, hallux
rigidus, or an interdigital neuroma with regard to hypertrophy or cortical
thickness of the second metatarsal. In addition, we found no correlation
between hypertrophy of the second metatarsal and pes planus, restricted ankle
dorsiflexion, mobility of the first ray, or length of the first ray.
As we found no evidence to support Morton's theory that mobility of the
first ray is characterized by hypertrophy of the second metatarsal, we cannot
support the practice of considering cortical hypertrophy of the second
metatarsal to be an indication for arthrodesis of the first metatarsocuneiform
joint in the treatment of a hallux valgus deformity.
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