se of in measuring the length of the tibia. The lateral
condyle (tuberosity) of the tibia can also be palpated, and must not
be mistaken for the head of the fibula, which lies farther back and at
a slightly lower level, and can readily be identified by tracing to it
the tendon of the biceps. The tuberosity of the tibia, into which the
quadriceps extensor tendon is inserted, lies on the same level as the
head of the fibula. In the extended position of the limb, the patella
is loose and movable on the front of the trochlear surface of the
femur, while in the flexed position it sinks between the condyles,
resting chiefly on the lateral one and becoming fixed.

The popliteal artery and vein and the tibial (internal popliteal)
nerve lie in close relation to the posterior aspect of the joint; and
the common peroneal (external popliteal) nerve passes behind and to
the medial side of the biceps tendon.

The knee is an example of a joint which depends for its strength
chiefly on its ligaments. Not only are the tibial and fibular
collateral (external and internal lateral) ligaments and the posterior
part of the capsular ligament particularly strong, but the cruciate
ligaments and the menisci (semilunar cartilages) inside the cavity of
the joint further add to its stability. The powerful tendon of the
quadriceps extensor muscle, in which the patella is developed as a
sesamoid bone, protects and strengthens the front of the joint and
functionates as the anterior ligament of the joint. In the attitude of
complete extension in which the joint is locked, no demand is made on
the quadriceps apparatus; with the commencement of flexion, the
stability of the joint, and the weight-bearing capacity of the limb as
a whole, depend largely on the controlling influence of the
quadriceps muscle; this becomes evident on going down an incline and
more markedly on going down stairs. Hence it is, that in recurrent
sprains of the knee, including under this term the various forms of
internal derangement of the joint, the wasting with loss of tone of
the quadriceps is an important factor in aggravating the disability of
the limb and in retarding and preventing recovery. In the treatment of
recurrent sprains of the knee, therefore, special attention must be
directed towards the wasting of the quadriceps by means of massage and
appropriate exercises.

The synovial cavity extends from the level of the head of the tibia to
an inch or more above the troc