llis is merely stretched, this
tendon may be shortened by splitting it longitudinally and making the
ends overlap, or its insertion may be displaced downwards. When the
ankle is flail-like, it may be necessary to perform arthrodesis.

Jones gets rid of the cavus deformity by resecting a wedge with its
base towards the dorsum from the middle of the tarsus; the foot is
then placed in a position of extreme calcaneus, the dorsum coming into
contact with the front of the leg. Four weeks later a wedge is taken
from the posterior part of the talus large enough to bring the foot
down to a right angle with the leg; the articular surfaces of the
tibia and fibula being denuded of cartilage, ankylosis takes place in
a good position.

#Pes Calcaneo-valgus.#--This deformity, which consists in a
combination of dorsiflexion at the ankle and eversion of the foot, is
as common as pure calcaneus (Figs. 148 and 149); the heel is
depressed, the sole looks laterally, and its medial border is convex.
Although it may be congenital, it is usually acquired as a result of
poliomyelitis. The calf muscles are paralysed while the peronei retain
their power, and, along with the tibialis anterior and the extensors
of the toes, become secondarily contracted. Treatment is conducted on
the same lines as in pes calcaneus, and the valgus may be controlled
by implanting the peroneus brevis into the navicular.

[Illustration: FIG. 148.--Pes Calcaneo-valgus with excessive arching
of foot.]

[Illustration: FIG. 149.--Pes Calcaneo-valgus, the result of
Poliomyelitis.]

#Pes Calcaneo-varus.#--In this rare deformity the heel is depressed
and the sole of the foot looks inwards.

#Pes Cavus.#--In this deformity, which is known also as _hollow
claw-foot_, _pes arcuatus_, or _pes excavatus_, the longitudinal arch
of the foot is exaggerated as a result of the approximation of the
balls of the toes to the heel (Fig. 150). It is most frequently met
with as an addition to pes equinus or pes calcaneus of paralytic
origin, and has already been described. There is a mild form which is
congenital, and which is quite independent of paralysis; another
variety occurs in diseases of the spinal cord, such as Friedreich's
ataxia.

The name hollow claw-foot appropriately indicates the clinical
appearances. The arch is exaggerated and the instep abnormally high;
there is hyper-extension of the toes at the metatarso-phalangeal
joints, and plantar-flexion at the inter-phalan