e in one of
the adjacent bones, or lesions of the nerves.

_Ankylosis_ is the term applied when impaired mobility results from
changes involving the articular surfaces. It is frequently combined with
contracture. Three anatomical varieties of ankylosis are
recognised--(a) The _fibrous_, in which there are adhesions between
the opposing surfaces, which may be in the form of loose isolated bands
of fibrous tissue, or may bind the bones so closely together as to
obliterate the cavity of the joint. The resulting stiffness, therefore,
varies from a mere restriction of the normal range of movement, up to a
close union of the bones which prevents movement. Fibrous ankylosis may
follow upon injury, especially dislocation or fracture implicating a
joint, or it may result from any form of arthritis. (b) _Cartilaginous
ankylosis_ implies the fusion of two apposed cartilaginous surfaces. It
is often found between the patella and the trochlear surface of the
femur in tuberculous disease of the knee. The fusion of the
cartilaginous surfaces is preceded by the spreading of a vascular
connective tissue, derived from the synovial membrane, over the
articular cartilage. Clinically, it is associated with absolute
immobility, (c) _Bony ankylosis_ or _synostosis_ is an osseous union
between articulating surfaces (Figs. 154 and 155). It may follow upon
fibrous or cartilaginous ankylosis, or may result from the fusion of two
articular surfaces which have lost their cartilage and become covered
with granulations. In the majority of cases it is to be regarded as a
reparative process, presenting analogies with the union of fracture.

[Illustration: FIG. 154.--Osseous Ankylosis of Femur and Tibia in
position of flexion.]

The term _arthritis ossificans_ has been applied by Joseph Griffiths to
a condition in which the articular surfaces become fused without evident
cause.

The occurrence of ankylosis in a joint before the skeleton has attained
maturity does not appear to impair the growth in length of the bones
affected; ankylosis of the temporo-maxillary joints, however, greatly
impairs the growth of the mandible. When there is arrest of growth
accompanying ankylosis, it usually depends on changes in the ossifying
junctions caused by the original disease.

To differentiate by manipulation between muscular fixation and
ankylosis, it may be necessary to anaesthetise the patient. The nature
and extent of ankylosis may be learned by skiagraphy;