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.
To provide for the support required to be given by the lower extremity, the ligaments and tendons binding the bones of the knee together are both numerous and strong. The bond of union is so strong that dislocations from traumatic causes are comparatively rare, and it is only when the ligaments have been weakened by disease that subluxations take place.
The knee possesses the usual capsular ligament but so hidden by strengthening bands and tendinous expansions that but little of it is seen. Anteriorly the capsule is strengthened by the tendon of the quadriceps, the patella, and the tendo patellae (Fig. 545). Viewing these structures as a whole we see that their lower end is firmly attached at the tibial tubercle, but above their attachments are far removed from the joint. They are so strong and thick that pus from within does not tend to go through but goes around them. Their upper attachment is muscular, so they do not act to restrain movements except when the muscle is contracted; hence flexion is limited by contact of the soft parts posteriorly rather than by tension of the ligaments anteriorly. In complete extension the bulk of the patella rises above the articular surface, and connecting its upper edge with the anterior surface of the femur is only the thin capsular ligament, hence effusions into the joint bulge upward at this point. Extending about 5 cm. (2 in.) above the patella is the subfemoral bursa; this in 8 out of 10 cases communicates with the joint, and effusions readily distend it. The patella normally lies in contact with the femur but when there is effusion in the joint it is pushed or raised up and is called a floating patella. Pressure on it causes it to strike on the femur beneath, which is readily felt and enables one to diagnose effusions within the joint. Posteriorly the capsule is thick, being strengthened by an expansion, called the posterior ligament or ligamentum Winslowii, which goes upward and outward from the tendon of the semimembranosus muscle at the upper edge of the tibia. It is pierced by the branches of the azygos articular artery. The capsular ligament is weak below at the margin of the tibia and here pus may find an exit. It is less liable to come out above, but the bursa under the inner head of the gastrocnemius frequently (17 per cent., Macalister) communicates with the joint and is usually the origin of the ganglion so often seen in the popliteal region. When the joint becomes subluxated by disease the tibia is drawn backward and this posterior capsular ligament may shorten and prevent reposition forward. So strong is it that forcible attempts are liable to cause fracture. Internally the capsular ligament is strengthened by the lateral expansion from the side of the patella and from the fascia lata over the vastus interims; these go to the inner tuberosity of the tibia and strengthen the lower part of the joint, but toward the upper edge of the internal condyle the capsule is again thin and effusions puff it out at that point.
Fig. 546. - View of the inner side of the knee-joint; the capsule has been cut away from the edge of the patella to the internal lateral ligament, exposing the interior of the joint.
Fig. 547. - View of the outer side of the knee-joint. The capsule has been cut away from the edge of the patella to the external lateral ligament.