This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
A band of the capsule to which the name internal lateral ligament has been applied runs from beneath the adductor tubercle to the tibia below the internal tuberosity; it is strengthened by fibres from the tendon of the semimembranosus and has the internal articular vessels and nerves passing between it and the tibia. It will be noted that it lies toward the posterior portion of the joint, hence it limits extension (Fig. 546).
Externally the capsule has likewise the fibrous expansion of the quadriceps from the side of the patella and the fascia lata. This latter is the strong iliotibial band and goes downward to insert into the outer tuberosity of the tibia (Fig. 547).
There are likewise two band-like ligaments on the outer side, the long and short external lateral ligaments. The long external lateral ligament arises from a tubercle just below and in front of the outer head of the gastrocnemius muscle. It is about 5 cm. (2 in.) long and is attached below to the fibula, anterior to its styloid process. It is embraced on each side by the split tendon of the biceps. Beneath it pass the popliteus tendon in its sheath and the inferior external articular vessels and nerve. Note that this is likewise at the posterior portion of the joint and therefore it too limits extension.
The short or posterior of the two external lateral ligaments is often not to be recognized as a distinct structure, it passes from the styloid process of the fibula over the popliteus tendon to blend with the posterior capsular ligament on the external condyle. The lateral ligaments check extension and outward rotation of the tibia.
These pass from the tibia, the anterior being attached in front of and the posterior behind the spine, upward to the intercondylar notch of the femur. The anterior or external passes upward, outward, and backward. The posterior or internal passes upward, inward, and forward (Fig. 548). They are never very lax in any position of the joint, but the anterior is most tense in extension and the posterior in flexion. The anterior tends to prevent displacement of the tibia forward and the posterior ligament displacement of the tibia backward. The posterior crucial ligament blends with the posterior capsule and in resecting the knee care should be taken in dividing this ligament that the popliteal artery is not wounded. A ligamentous band runs from the posterior crucial ligament to the external semilunar cartilage; it is called the ligament of Wrisberg. The knee-joint in some of the lower animals is composed of two separate joints, one for each condyle, and the crucial ligaments of man are simply the remains of lateral ligaments when separate joints exist. They check inward rotation.
Fig. 548. - The crucial ligaments exposed by sawing off the inner surfaces of the femur and tibia.