margins may form a projecting collar which overhangs the
neck of the femur, or grasps it, so that even in the macerated
condition the head is imprisoned in the socket and the joint locked.
There is eburnation of the articular surfaces in those areas most
exposed to friction and pressure.

[Illustration: FIG. 120.--Upper End of Femur in advanced Arthritis
Deformans of Hip. The shaft is curved and the head of the bone is at a
lower level than the great trochanter.]

[Illustration: FIG. 121.--Femur in advanced Arthritis Deformans of Hip
and Knee Joints. The upper end of the bone shows the condition of coxa
vara; the lower end shows enlargement of the medial condyle and
alteration in the axis of the articular surface.]

These changes are necessarily associated with restriction of movement,
and in advanced cases with striking deformity, which consists in
shortening of the limb, usually with eversion and displacement of the
trochanter upwards and backwards in relation to Nelaton's line.

The _clinical features_ are usually so characteristic that there is
little difficulty in diagnosis. Restriction of the movements of
abduction and adduction, the presence of cracking and of grating of
the articular surfaces, and the aggravation of the pain and stiffness
after resting the limb, are characteristic of arthritis deformans. The
prominence of sciatic pain may lead to the disease being regarded as
sciatica.

The greatest difficulty is met with in cases in which the disease
occurs as mon-articular affection in adolescents, for the resemblance
to tuberculous disease of the hip and to coxa vara may be close.
Skiagrams do not always enable one to differentiate between them.

_Treatment_ is conducted on the same lines as in other joints. The
normal movements are maintained by suitable exercises, and an effort
is made to diminish the pressure on the articular surfaces in walking
by the use of sticks or crutches.

Shortening of the limb may be compensated by raising the sole of the
boot. When the X-rays show that the disability is mainly due to new
bone locking the head of the femur, such new bone may be removed by
operation, _cheilotomy_ (Sampson Handley). Excision of the joint has
in some cases yielded satisfactory results; it is indicated in young
patients who are otherwise healthy, and who are unable to walk on
account of pain and deformity.

#Osteo-chondritis Deformans Juvenilis.#--Under this term Perthes
describes an affect