- Progression of hallux valgus deformity causes
subluxation of the first metatarsophalangeal (MTP) joint
- Congruity of the first metatarsophalangeal joint is
an important factor for decision making of bunior
- surgery. Two studies which were described below would
be presented in this lecture. First, concerning the
anatornical cause of the malalignmertt, it is not knnown
whether lateral deviation of the first proximal phalange
or rnedial deviation of the first metatarsal head causes
the sùbluxation. To answer this question, a two
dimensional coordinate system was devised for evaluation
of a weight-bearing dorsoplantar radiograph (Study 1).
Next, recently, a distal metatarsal articular angle
(DMAA) gets into the news im the foot and ankle field.
Identification of a lateral edlge of distal joint surface
on the first metatarsal head is essential for evaluation
of the congruity, however that is sometimes difficult in
plane radiographs. Tble findings of the congruity in the
plain radiographs were verifiedl by those in 3D-CT (Study
2).
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- Precise Anatomic Configuration Changes in the
First Ray of the Hallux Valgus Foot (Study 1)
-
- Two hundred and twenty-nine feet of 144 female
patients (10-76 years, mean 42 years) with symptomatic
hallux valgus and 94 feet of 64 normal female subjects
(16-77 years, mean 41 years) were studied for precise
anatomical configration changes in the first ray. Each
accurate weightbearing radiograph was evaluated by two
dimensional coordinate system; the axis of the shaft of
the second metatarsal is the x axis, the intersection of
the x axis with the proximal end of the second metatarsal
is the point of origin, and perpendicular to the x axis
that passes through the point of origin is the y axis.
Using a digitizer, x, coordinates were measured at 4
points: the tip of the distal phalanx (DD1), the midpoint
of the proximal joint surface of the proximal phalanx
(PP1), and points of intersection between the axis of the
first metatarsal and the distal and proximal ends of the
metatarsal (MH1, MB 1). The values were expressed as
- percentage of the length of the second metatarsal.
Sixty-four percent of the feet in the hallux valgus group
and 4 % in the normal group had subluxation of the first
MTP joints. The mean values of the hallux valgus angle in
the hallux valgus group and the normal group were 29.4fl
and 9.7fl, and those of the distal metatarsal articular
angle were 8.0fl and 2.3fl. The mean values of the y
coordinates of DD1, PP1, MH1, and MB 1 in the hallux
valgus were 14.9, 36.1, 45.9, and 23.7% and those in the
normal group 27.6, 35.4, 38.8, and 23.9%, respectively.
Those of the y coordinates of DD1 and MH1 were
significantly different between the two groups
(p<0.001). There was no significant difference in the
mean x values of any 4 points and the
- values of PPI and MB 1. The present study showed that
the first metatarsal head of the hallux valgus foot was
located on the medial side of that of the normal foot and
the base of the proximal phalange of the hallux valgus
foot was located on the same point of that of the normal
foot. This means that subluxation of the MTP joint in
hallux valgus is caused by metatarsus primus varus. As a
principle of bunion surgery this study indicated that
first metatarsal osteotomies are theoretically correct
methods.
-
-
- Inspection of the Congruity of the First MTP Joint
in Hallux Valgus using 3D-CT Images (Study 2)
- Thirty feet in seventeen female patients with hallux
valgus were studied. The lateral edges of the distal
joint surface on the first metatarsal head in the plane
radiographs were identified by a bony protrusion, a
dimple and a trabecular shadow. Congruence was defined as
a proximal joint surface of the proximal phalanx
completely adapted to the metatarsal head, and
incongruence was defined as only a small part of proximal
joint surface was subluxated Six feet were in congruence,
21 feet in incongruence, and 3 feet in reservation of
judgement in plane radiographs, and 5 feet, 25 feet, and
O foot in 3D-CT, respectively. One foot that was judged
as congruence using the index of the dimple had been
misread. Three feet in which judgement was reserved were
subluxated in 3D-CT. The bony protrusion and the
tubercular shadow always represented the lateral edges,
but the dimple did not indicate the lateral edge. I
concluded that the accurate indices of the lateral edge
of distal joint surface were the bony protrusion and the
tubercular shadow.
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