union.#--_Hallux valgus_ is that deformity in
which the great toe deviates towards the middle line of the foot and
comes to lie on the top of, or beneath, the second toe (Figs. 155,
157). The head of the first metatarsal projects on the medial border
of the foot, and, as a result of the pressure of the boot, an
adventitious bursa is formed, which, when thickened by chronic
inflammation, constitutes a prominent swelling or _bunion_. It is a
common affection in civilised and especially in urban communities, and
reaches its acme of development in adult women. It may occur on one or
on both sides, and is sometimes associated with flat-foot.

[Illustration: FIG. 157.--Radiogram of Hallux Valgus. The sesamoid
bone is seen displaced towards middle line of the foot.]

The deformity develops slowly, and is usually attributed to the
wearing of stockings which are unduly tight at the toes, and of
improperly made boots. The boot that favours the occurrence of hallux
valgus is one which is too short and has pointed toes, with the apex
in the middle line of the foot instead of being in line with the great
toe. The pressure of the boot displaces the great toe into the valgus
position, especially if a high heel is worn, as the toes are then
driven forward into the apex of the boot. Once the great toe is
abducted by the pressure of the boot, the deformity is increased by
bearing unduly on the medial side of the ball of the great toe, and by
pointing the foot outwards in walking.

Arthritis deformans is rarely the cause of hallux valgus, but the
changes characteristic of that affection are commonly present in the
joint of the great toe. In pronounced cases, the base of the first
phalanx is displaced on to the lateral aspect of the head of the first
metatarsal, the exposed head of which frequently shows fibrillation
and wearing away of the cartilage, and is often surrounded by new
bone, sometimes amounting to an exostosis. There are also fringes from
the synovial membrane that may be caught between the articular
surfaces. The distal end of the first metatarsal is displaced
medially, broadening the tread of the foot, and in severe cases its
shaft is rotated on its long axis, so that its dorsal surface looks
medially; the great toe is then similarly rotated (Fig. 157). The
flexor and extensor tendons and the sesamoid bones are displaced
laterally. The ligaments and other soft parts on the medial side are
elongated, while those on the lat