hlear surface of the femur, passing
slightly higher on the medial aspect of the joint than on the lateral
(Fig. 80). The large bursa between the quadriceps muscle and the femur
(_sub-crural bursa_) generally communicates with the cavity of the
joint. The synovial cavity of the superior tibio-fibular articulation
is usually distinct from that of the knee-joint, but may communicate
with it through the popliteal bursa.

[Illustration: FIG. 80.--Section of Knee-joint showing extent of
Synovial Cavity.

_a_, Pre-patellar bursa.
_b_, Infra-patellar bursa.
_c_, Ligamentum mucosum.
_d_, Ligamentum patellae.
_e_, Posterior cruciate ligament.
_f_, Medial semilunar meniscus.

(After Braune.)]

A large bursa (_pre-patellar_) lies over the lower part of the patella
and upper part of the ligamentum patellae; and a smaller one separates
the ligamentum patellae from the tuberosity of the tibia. Several
important bursae are found in the popliteal space, one of which--the
semi-membranosus bursa--sometimes communicates with the knee-joint.

FRACTURE OF THE LOWER END OF THE FEMUR

Fractures involving the lower end of the femur, especially the
supra-condylar and T-shaped fractures, are to be looked upon as
serious injuries, on account of the difficulties attending their
treatment, and the risk of damage to the popliteal vessels and of
impairment of the usefulness of the knee-joint.

#Supra-condylar# fracture is usually the result of a fall on the feet
or knees, or of direct violence, and is most common in adult males.
The line of fracture is generally irregularly transverse, or it may be
slightly oblique from above downwards and forwards, so that the
proximal fragment passes forward towards the patella, while the distal
is rotated backward on its transverse axis by the gastrocnemius
muscle.

_Clinical features._--Soon after the accident a copious effusion of
blood and synovia takes place into the cavity of the knee-joint,
adding to the swelling caused by the displaced bones, and rendering it
difficult to recognise the precise nature of the lesion. As it is
important to make an accurate diagnosis, the X-rays should be employed
if possible, and a general anaesthetic should be given when necessary.

The proximal end of the distal fragment is usually palpable in the
popliteal space, while the proximal fragment is unduly prominent in
front. By flexing the knee the fragments may be brought into
apposition