Page 246 - Clinical Anatomy

ECA4 7/18/06 6:47 PM Page 231

The bones and joints of the lower limb 231

The capsule is attached to the margins of these articular surfaces but
communicates above with the suprapatellar bursa (between the lower
femoral shaft and the quadriceps), posteriorly with the bursa under the
medial head of gastrocnemius and often, through it, with the bursa under
semimembranosus. It may also communicate with the bursa under the
lateral head of gastrocnemius. The capsule is also perforated posteriorly by
popliteus, which emerges from it in much the same way that the long head
of biceps bursts out of the shoulder joint.
The capsule of the knee joint is reinforced on each side by the medial and
lateral collateral ligaments, the latter passing to the head of the fibula and
lying free from the capsule.
Anteriorly, the capsule is considerably strengthened by the ligamentum
patellae, and, on each side of the patella, by the medial and lateral patellar reti-
nacula, which are expansions from vastus medialis and lateralis.
Posteriorly, the tough oblique ligament arises as an expansion from the
insertion of semimembranosus and blends with the joint capsule.

Internal structures (Figs. 169, 170)

Within the joint are a number of important structures.
The cruciate ligaments are extremely strong connections between the
tibia and femur. They arise from the anterior and posterior intercondylar
areas of the superior aspect of the tibia, taking their names from their tibial
origins, and pass obliquely upwards to attach to the intercondylar notch of
the femur.
The anterior ligament resists forward displacement of the tibia on the
femur and becomes taut in hyperextension of the knee, it also resists rota-
tion, the posterior resists backward displacement of the tibia and becomes
taut in hyperflexion.
The semilunar cartilages (menisci) are crescent-shaped and are triangular
in cross-section, the medial being larger and less curved than the lateral.
They are attached by their extremities to the tibial intercondylar area and by
their periphery to the capsule of the joint, although the lateral cartilage is
only loosely adherent and the popliteus tendon intervenes between it and
the lateral collateral ligament.
They deepen, although to only a negligible extent, the articulations
between the tibial and femoral condyles and probably act as shock
absorbers. If both menisci are removed, the knee can regain complete func-
tional efficiency, although it is interesting that, following surgery, a rim of
fibrocartilage regenerates from the connective tissue margin of the excised
menisci.
An infrapatellar pad of fat fills the space between the ligamentum patellae
and the femoral intercondylar notch. The synovium covering this pad pro-
jects into the joint as two folds termed the alar folds.

Movements of the knee

The principal knee movements are flexion and extension, but note on