p2.ch3 4. Foot and Ankle
1. Functional anatomy and characteristics of the deformities
Muscle Functions
Muscles are divided into two groups: the dorsiflexors and
plantar flexors.
The plantar flexors are divided into three sub groups: Plantar
flexors of the ankle, plantar flexors of the midtarsal joint and
plantar flexors of the toes. Each of these three sub groups can be
divided into antigravity muscles and non-antigravity muscles
(Table 10).
Dorsal flexors are divided into three sub groups: dorsiflexors
of the foot and ankle, dorsiflexors of the midtarsals, and
dorsiflexors of the toes. Each of these three sub groups can be
divided into antigravity dorsiflexors and non-antigravity
dorsiflexors (Table 11).
Plantar Flexors
Plantar Flexors of the Foot and Ankle:
Non-antigravity Muscle
-Gastrocnemius (See Part 1. Chapter 2)
This muscle has two proximal origins: the lateral head and
medial head. .
These proximal portions of the gastrocnemius flex the knee
and cause flexion deformity, when they are hyperactive. These
gastrocnemius muscle fibers run distally and end in tendon fibers of
the aponeurosis. This aponeurosis is thickened as it descends
distally, and tendoachilles is formed by these thickened tendon
fibers. The gastrocnemius is an important plantar flexor and an
accelerator of the body, at the push-off stage of the gait. There are
less antigravity activities. In cerebral palsy and cerebro-vascular
accident, hypertonicity of this muscle causes equinus deformity.
Antigravity Muscle
-Soleus (See Part 1. Chapter 2).
The muscular fibers of the soleus run distally, end into a
broad aponeurosis, which forms the tendoachilles and attach to the
medial part of the posterior aspect of calcaneus. This muscle
plantarflexes the ankle and supports the body upright. White
discussed rotation of the tendonachilles and expressed the opinion
that a better lengthening procedure is to section the medial half of
the tendon at the proximal, and the anterior-half at the distal.
Midtarsal Plantar Flexors:
There are two midtarsal plantar flexors: the tibialis posterior
and peroneus longus. These muscles have opposite functions. The
tibialis posterior is an invertor, while the peroneus longus is an
evertor.42,61 Both these muscles also have their own antigravity
muscle fibers originating from the more distal part of the tibia and
fibula.
-Tibialis posterior
This muscle inverts and adducts the midtarsal joint. This
muscle acts against the peroneus longus, which is an antagonistic
evertor and abductor, in the horizontal plane. Clinically, the distal
fibers of this muscle act more as antigravity invertors, preventing
excessive lateral shift of the body weight on the sole, keeping
center of gravity of the body within the area of the sole of the foot,
and supporting the body in a standing posture. On the other hand,
proximal fibers of this muscle are less antigravity invertors, but
propel the body forwards.
In patients with cerebral palsy, this muscle, especially the
muscle fibers with long tendon fibers originated from proximal
portion is hyperactive, causes equino-varus deformity of the foot,
and decreases stability. In such situations, hypertonicity of this
muscle can be reduced by selective intramuscular release at the
musculotendinous junction,30 and sliding lengthening at the distal
tendon (Fig. 105, 110).
-Peroneus longus
This muscle everts the foot at the subtalar joint and abducts
the forefoot at the midtarsal joint, such as Chopart and Lisfranc
joints. Clinically, the distal fibers of this muscle act more as
antigravity evertors, preventing excessive medial shift of the body
weight on the sole, keeping center of gravity of the body within the
area of the sole, and supporting the body upright. On the other
hand, proximal fibers of this muscle are less antigravity evertors,
but propel the body forwards.
In severely deformed valgus feet, the whole muscle,
especially fibers of the proximal portion show hypertonicity, cause
valgus deformity, and decrease stability. In such situations,
hypertonicity of this muscle can be reduced by selective
intramuscular lengthening at the musculotendinous junction,30,61
and sliding lengthening at the distal tendon (Fig. 105, 110).
Fig. 105. Functions of
the tibialis posterior and peroneal longus
Under construction
Plantar flexors of the Toes:
Long Flexors (Non-antigravity Muscles)
-Flexor digitorum longus (Invertor)
These tendons receive the tendinous insertions of the
quadratus plantae muscle. This is a flexor of the four lateral toes
and ankle, and also an invertor and flexor of the midtarsal and
subtalar joints. Clinically, this muscle is the most hypertonic
invertor and flexor and causes flexion deformity of the toes and
equinovarus deformity of the foot in cerebral palsy (Fig. 118).30, 35.61
-Flexor hallucis longus (Evertor)
This is a flexor of the great toe and foot, and also an evertor
of the foot at the midtarsal and subtalar joint. Clinically, this is the
most hyperactive everting muscle, causing flexion deformity of the
great toe and equinovalgus deformity of the foot in cerebral palsy.
This is also a muscular factor, which causes the hallux valgus
deformity (Fig. 118).
30,35,61
Short Flexors (Antigravity muscles)
-Flexor digitorum brevis (Invertor)
This is the flexor of the proximal phalanx of the toes.
It also acts as a mild invertor of the foot. Clinically, the
muscle fibers with tendon fibers originated from the proximal
portion are less antigravity and more hyperactive in cerebral palsy,
and the ones without tendon fibers originated from the distal
portion are more antigravity and less hyperactive.48, 202 This
difference can be used for treatment of equinus and equinovarus
deformities.
-Adductor hallucis (Evertors)
This is a flexor, an adductor and evertor of the great toe.
This is a monoarticular muscle, and clinically can be considered as
an antigravity supporter of the body.61, 202 Clinically however,
the muscle fibers originated from the proximal portion are less
antigravity and more hyperactive in cerebral palsy, and the ones
originated from the distal portion are more antigravity and less
hyperactive.61, 202 This difference in activities can be used for
treatment of hallux valgus deformity.
-Flexor hallucis brevis (Evertor)
This is a flexor, adductor and evertor of the great toe, and
clinically can be considered as an antigravity supporter of the body.
Clinically, the muscle fibers originated from the proximal portion
are less antigravity and more hyperactive in cerebral palsy, and the
ones originated from the distal portion are more antigravity and
less hyperactive.202 This difference can be used for treatment of
hallux valgus deformity.
-Interossei and flexor digiti minimi brevis.
The interossei and flexor digiti minimi brevis are important
antigravity flexors of the MP joints, and support the body on the
proximal phalanges, by plantar flexing the MP joints against the
metatarsus when standing.
-Abductor hallucis
This muscle is an abductor of the proximal phalanx of the
great toe, and supports the body at the proximal phalanx, by
abducting the MP joint when standing.
-Abductor digiti minimi
This muscle is an abductor of the phalanx of the fifth toe,
and supports the body on the proximal phalanx of the fifth toe, by
abducting the MP joint when standing.
Dorsiflexors
Dorsiflexors of the Ankle and Foot:
-Tibialis anterior (Invertor)
Clinically, the distal fibers of this muscle arised from distal
part of the tibia and fibula dorsiflex the foot
and assist the foot to clear the ground at the swing phase of gait as
well as at the phase of loading response. This part is the most
important dorsiflexor, adductor and invertor of the foot, with
antigravity activities. On the other hand, fibers originated from
proximal part of the tibia anf fibula seem to swing the foot
forwards and act at the phase of loading response as the
decelerator of the body to control excessive forward movement of
the body though less antigravity activities.
-Peroneus tertius (Evertor)
This muscle dorsiflexes and everts the foot at the ankle joint,
and clears the foot from the ground during gait as an antigravity
evertor and dorsiflexor.
-Peroneus brevis (Evertor)
This muscle dorsiflexes and clears the foot away from the
ground at the swing phase of gait. This muscle is also an important
dorsiflexor, abductor and evertor of the foot, with antigravity
activities, and therefore should not be released or lengthened, for
correction of valgus deformity.
Dorsiflexors of the Toes: (Non antigravity muscles)
-Extensor hallucis longus (Invertor)
This muscle is an extensor of the big toe, and also a
supplemental invertor and dorsiflexor of the foot.
-Extensor digitorum longus (Evertor)
This muscle is an extensor of the four lateral toes, and a
supplemental dorsiflexor and pronator of the foot as well.
Dorsiflexors of the Middle and Proximal Phalanx
(Antigravity muscles):
-Extensor hallucis brevis (Invertor)
This muscle is an antigravity extensor and supinator of the
big toe.
-Extensor digitorum brevis (Evertor)
This muscle is an antigravity extensor of the proximal
interphalangeal joints of the second, third, and fourth toes and also a
dorsiflexor and pronator of the forefoot. Functionally, the extensor
digitorum brevis can also be considered to be an extensor of the
MP joints.
Interossei
The interossei are primarily antigravity plantar flexors of the
metatarso-phalangeal joint of the lateral toes. However, interossei
combined with extensor digitorum longus and brevis are also
antigravity extensors of the distal and proximal interphalangeal
joints of the lateral toes.able foot is the fundamental aim of
treatment of cerebral palsy. Hence all critical concerns should be
focused, on achieving a well-balanced antigravity stability on the
feet.
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