p2.ch3.4.3
2. Planovalgus (Equinovalgus) Deformity
Planovalgus is another common deformity of the foot,
which disturbs wearing of shoes and inhibits stable weight bearing.
In this deformity, the calcaneus and the lateral column of the foot
are fixed in dorsiflexion, whereas the talus and the medial column
are fixed in plantar flexion. Weight bearing is concentrated on the
medial aspect of the forefoot. Adduction and internal rotation of the
hip is exaggerated in this foot deformity because of difficulty in
supporting the body weight on the lateral side of the sole, resulting
in decreased weight bearing ability.
Anatomical consideration
In equinus, supporting area is quite small, and inversion and
eversion forces of the tibialis posterior and peroneus longus do not
act. Skeletally, both the medial and lateral columns are
plantar-flexed. The body is mostly supported on the toes by toe
flexors, such as interossei, adductor hallucis, flexor hallucis and
flexor digitorum brevis. Therefore, stability is decreased very much.
In equinovalgus deformity, the lateral column is somewhat
dorsiflexed, while the medial column remains in plantar flexion.
However, fore part of the medial column is dorsiflexed at the
Chopart and Lisfranc joints, with the body weight being borne by
the sole of this medial column. This is skeletally and
developmentally a transitional position between equinus and
normal plantigrade foot. Weight is mostly borne on the inner side
of the medial column, and therefore base of the weight bearing in
valgus is broader than that of equinus deformity. However, since
body-supporting mechanism of the lateral column does not work
well, ability to prevent a lateral fall is reduced and hence patients
usually have to keep their feet in a wide based position while
walking to prevent a
lateral fall. So the mechanism of weight bearing is immature and
ineffective. In order to increase stability in patients with valgus
foot, facilitation of plantar flexion activity of the lateral column is
needed.
In normal plantigrade foot, both the medial and lateral
columns are well dorsiflexed. In this condition both the plantar
evertors and invertors are able to act alternately to prevent fall of
the body to the lateral and medial sides and provide sufficient
stability.
Historical Reviews
Subtalar Arthrodesis and Osteotomy:
Originally, attention was focussed on correction of this
deformity, by the use of bony surgery, such as subtalar arthrodesis
and calcaneus osteotomy, intending to provide the plantigrade foot,
for easy wearing of shoes.
Triple arthrodesis has been advocated by several authors, for
fixed and badly deformed feet.227, 228 However in 1993, Jenuta
documented that correction is not good and result is poor in the
feet with planovalgus deformity causing much residual problems
notably callosities, pseudoarthrosis and degenerative changes in the
ankle joints.229
Extra-articular arthrodesis has been the most popular and
ecommended procedure for correction of pes valgus deformity in
children. Originally, Grice reported this operation for paralytic
valgus foot.230 After this report, many surgeons started to practice
this procedure which has now been recommended as a useful
procedure in young children, for correcting the deformity, without
affecting subsequent growth of the tarsals.231-236
However, Ross and Lyne reported that 72 of 113 procedures
were rated as unsatisfactory, and many patients were made worse.
They also mentioned that Grice procedure has limited success in
those mildly afflicted children with hemiplegia. They also pointed
out the difficulty of the union due to slipped grafts, occurrence of
ankle valgus, subsequent instability of the ankle, and exostosis at
the ankle and midtarsal joints.237 McCall and associates reported
46% of failure rate, including 14 feet which were due to graft
failure, while the remaining were due to incomplete correction.238
Scott and associates also reported a retrospective review of 45
patients (62 feet) who had undergone Grice arthrodesis and
described that there were failures in 32% and poor results in 61%
of the cases. They mentioned that unrecognized ankle valgus,
overcorrection of the hind foot into varus, uncorrected calcaneus
deformity and anterior graft placement largely contributed to the
poor results.239 Bleck also stated that failure was 83% with the
Grice procedure using only the tibial graft.67
There are also many modifications of extra-articular subtalar
arthrodesis. Baker and Hill reported a horizontal osteotomy, below
the base of posterior articular process of the calcaneus, combined
with Grice procedure, with excellent and good results.232 Bleck
also stated that only 25% of the feet failed with the combined Grice
and Baker procedure.67 Jeray and associates presented a
modification of subtalar arthrodesis in which local bone graft from
the calcaneus and talus is used with internal fixation to obtain
fusion.240 The general concept is almost the same as with the
ordinary arthrodesis. They mentioned that 88% of the
feet had radiological union and 96% had a stable talocalcaneal
angle. Brown241, Seymour and associates242 in 1968, reported a
procedure devised by Bachelor, in which the fibular shaft bone
graft was driven, through a hole from neck of the talus into the
calcaneus. They mentioned that the results of the operation
appeared to be satisfactory.
This procedure seems reasonable as far as fixation of the
talus and calcaneus in neutral position is concerned. However, loss
of power of the peroneal muscles after resection of fibular bone can
be unpredictable. It also seems uncertain if muscular balance
between evertors and invertors can be maintained in adequate
neutral tension, since the extent of loss of everting power of the
peroneus muscles is not predictable. Rang also stated that the tibia
and fibula should never be used as grafts, because of possibility of
a fracture at the neck of the talus and progressive deformity, due to
surgery's effect on bone growth.
In 1976, Dennyson and Fulford described a new approach in
stabilization by mean of metallic internal fixation and autogenous
cancellous bone grafting. In their report, 45 gained union and 43
had satisfactory correction of the deformity with mobile pes planus
in 48 feet of 29 children. Most of them were children with cerebral
palsy.243 Barraso and associates also reported 95% of good or
excellent results with this procedure.244 In 1986, Rang and
associates described another approach in which internal metallic
fixation is used, driving the screw upwards from the calcaneus into
the talus. They also used Guttman's technique of a dowel from the
os calcis and a screw to hold it.66
Another approach of an extraarticular subtalar arthrodesis is
with the use of an absorbable screw described by Partio and
associates. They compared the postoperative results between
arthrodesis obtained by a self-reinforced poly-L-lactid (SR-PLLA)
screw on one side and ones obtained by standard AO screw on the
other side and mentioned that the functional status was improved
and radiographic union of the arthrodesis occurred in all 14 feet in
7 patients.245
Thus, technical problems of extraarticular arthrodesis have
gradually been overcome, and excellent results in bony fusion have
been reported. However, it is controversial if all these bony
rocedure can guarantee satisfactory function in CP children. In all
these literatures, attention has been focused only on acquisition of
the plantigrade foot. However, can these postoperative plantigrade
feet promise sufficient weight bearing, as seen in the
non-paralyzed human foot? Can the plantigrade foot treated with a
bony procedure work well to supinate the forefoot to prevent a
lateral fall?
I have a pessimistic opinion, regarding the usefulness of
bony surgery for improving stability in pes valgus, and hesitate to
use the bony procedure for improving antigravity stability of the
foot. I have observed so many pseudoarthrosis and stiff feet with
unsatisfactory weight bearing and less antigravity stability.
My opinion is as follows:
Even if the talocalcaneal joint is neutralized by the use of
bony procedure, antigravity inversion activities of the soleus and
tibialis posterior will not act well. Excessive eversion activities of
the evertors such as the peroneus muscles remain unreleased and
overwhelm the activities of the invertors, at the midtarsal and ankle
joints. The most important point in stable weight bearing is that
inverting force needs to be concentrated on the lateral column of
the foot, in order to prevent lateral shift of the gravity of the body
and to prevent a lateral fall, at the moment when the body is forced
to tilt laterally. I wonder, whether subtalar arthrodesis can preserve
such a fine and elaborate mechanism of antigravity activities on the
foot, in which alternate inversion and eversion movements are
brought about, by the combined activities of antigravity muscles.
Even if sufficient correction is obtained at talocalcaneal joint,
strong everting force of the evertors will be transmitted to the
ankle and midtarsal joints, causing excessive eversion. Thus, on
the whole, everted foot will remain uncorrected. In such situations,
degenerative changes will be caused at the ankle and midtarsal
joints. So we concluded that extraarticular subtalar fusion is not
our choice of surgery.
Loss of everting power with occurrence of equinovarus can
be another problem after resection of the fibular bone when it is
used as a bone graft. It seems logical to consider that not only can
the eversion deformity be decreased but also the everting force can
be reduced by resection of the fibular bone, since evertors arise
from the fibula. However, amount of loss of everting force cannot
be measured. We have a patient with bilateral marked equinovarus
deformity after Grice extraarticular arthrodesis, carried out by a
senior orthopaedic surgeon. Occurrence of equinovarus deformity
due to loss of everting force is not acceptable and occasionally
miserable (Fig. 116).
Fig 116: Equinus drop feet
after Grice Green subtalar arthrodesis
Basically, the subtalar arthrodesis destroys the most
elaborate antigravity mechanism brought about by the voluntary
eversion-inversion movements of the subtalar joint. For stability of
the human body, alternate concentration of antigravity forces to the
lateral and medial soles by the alternate inversion and eversion of
the foot would be most important. Aim of treatment of the pes
valgus should be directed at facilitating alternate antigravity
eversion and inversion movements, while rebalancing the activities
of invertors and evertor, and achieving flexible plantigrade foot.
Soft Tissue Surgery:
It is most reasonable in the treatment of pes valgus
deformity to restore the foot to a well-balanced and well-corrected
position by rebalancing activities of the evertors and invertors. For
this purpose, various attempts have been made. Bennet in 1982,
with the use of electromyographic study, pointed out that there is
diminished function in the tibialis posterior in valgus foot in
cerebral palsy, and treated pes valgus deformity by the means of
transfer of tendon of the peroneus brevis to tendon of the tibialis
posterior. However, he said that it is too early to report the results
of his surgery, and also noted that the main theoretical drawback
would be the risk of late varus deformity.246 Regarding release of
the peroneus brevis, Bleck in his own experience in 5 of 7 feet
expressed his critical opinion that lengthening of the peroneus
brevis at the time of extra-articular subtalar arthrodesis caused a
reversal to varus foot.67 I agree with Bleck's opinion, on the basis
of our own clinical observation in which the peroneus brevis is
found to be an important dorsiflexor and evertor. Pollock and
Carrell also used simultaneous transfer or section of the peroneus
brevis and peroneus longus tendons, on 108 of 112 procedures, and
reported 31 unsatisfactory results caused by late varus deformity.247
Thus, it seems that transfer or section of the peronei tendons
presents serious disaster of reverse equinovarus deformity
postoperatively.
In 1984, Nather and associates presented 30 feet of 20
cerebral palsy patients treated with intramuscular lengthening of
the peroneus brevis tendon, and reported that hind valgus
deformity could be reduced effectively only in 14 feet.248 Fulford
also opined the effect of this approach in his paper.234 However,
Evans in 1966 reported his experience with the peroneal tenotomy
and concluded that this procedure is among the most hazardous,
because of the risk of causing the opposite varus deformity.249
Thus, the release of the peroneal tendons has been considered
seriously by various surgeons for correction of valgus deformity.
However, there are serious and hazardous problems as described
by Evans. Hence a careful approach would be necessary.
We in 1980 presented our experience of the lateral release
surgery performed on 22 feet, including lengthening of the
peroneus brevis, peroneus longus and flexor hallucis longus, for
correction of valgus deformity.250 However, many hazardous
problems were disclosed, at follow-up. One of the serious
problems was occurrence of varus deformity, combined with
excessive dorsiflexion of the first metatarsal bone, after sliding
lengthening of the peroneus longus. Varus deformity in calcaneal
position was commonly induced after sliding lengthening of the
peroneus longus.
Another problem was occurrence of equinovarus deformity,
after division or lengthening of the peroneus brevis. In our series,
marked equinovarus was caused, after division of the peroneus
brevis.
In 1984, we again reported complete results of lateral
release operation performed on 48 feet with pes valgus deformity
in cerebral palsy, in which the peroneus longus tendon and the
peroneus brevis tendon were lengthened or sectioned
concomitantly or independently.251 Of 17 feet treated with
lengthening of the peroneus longus, 11 feet developed to adduction
and varus deformity. In 5 of the 11 feet with varus deformity,
marked dorsiflexion deformity (dorsal bunion) and weakness in
antigravity plantar flexor of the first metatarsal bone were noted.
On the basis of these miserable results, we confirmed that the
peroneus longus plays an important role, in supporting the medial
side of the sole, and therefore, concluded that Z lengthening alone,
or division of tendon of the peroneus longus should never be done.
We abandoned single sliding or Z lengthening of the peroneus
longus after this observation.
On the other hand, of 17 feet treated with division of the
peroneus brevis tendon, 10 had marked equinovarus and 3 had hind
foot varus with forefoot adduction. In the remaining 4 feet, late
equinus deformity presented problems. Even in 29 feet treated with
lengthening of the peroneus brevis tendon, we observed late
equinus or equinovarus in 18 feet and results have been
disappointing, and none of the patients were satisfied. The results
were miserable, since late equinovarus deformity worsened by the
year. All these clinical results clearly demonstrated that the
peroneus brevis is an important antigravity dorsiflexor with
eversion activities to clear the foot away from the ground against
gravity, and that division or lengthening of this muscle can cause
iatrogenic equinovarus deformity. We concluded that release of the
peroneus brevis should never be done, except for severe fixed
vertical talus. Thus, long term follow-up results of the lateral
release were miserable, and could be concluded as a failure. This
disastrous failure showed us that treatment of pes valgus foot by
balancing the muscle function is not so easy as that of pes varus
which can be treated appropriately by Z or sliding lengthening of
the tibialis posterior. On the basis of these serious failures, we are
now reestablishing a new approach for correction of equinovalgus
deformity, and also formulating selective release surgery
specifically for valgus deformity (Fig. 117AB).
A. Before osscs
B. After OSSCS
Fig. 117AB: Correction of valgus deformity by OSSCS
Now, at this point, it is most important for achieving
effective and promising result to identify the muscular factors,
which cause the valgus deformity, and to reconstruct a
well-balanced foot, by selective release of involved hypertonic
evertors, and by facilitating the antigravity activities of invertors
and plantar flexors.
Surgical Approaches
Fig. 118. Function of the flexor hallucis longus and
flexor digitorum longus
Under construction
Considerations:
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Surgical Techniques:
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