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.
The knee is rarely luxated and then only by such extreme trauma as sometimes to rupture the popliteal vessels and require amputation. It is frequently compound. The tibia may be luxated anteriorly (the most frequent), posteriorly, to either side, or it may be rotated on the femur. These displacements are usually due to hyperextension and rotation. The laceration of the surrounding tissues is so extensive that replacement is usually easy by direct traction and manipulation. As a result of weakening of the ligaments by disease the hamstring tendons frequently pull the tibia backward, producing a subluxation often difficult to replace (Fig. 553).
The semilunar cartilages do not become displaced in their entirety, but a portion of one of them is torn partly or completely loose and in moving about gets caught between the bones and produces the characteristic symptoms. The joint becomes useless at once and the patient may fall. The detachment of the cartilage, which is usually the internal one, is caused by either a direct blow on the part or by a twisting of the partly flexed limb. Use of the limb cannot be resumed until the caught cartilage is released. This is most readily achieved by extending the leg and then sharply flexing it. Sometimes the loosened cartilage instead of remaining attached at one end is free in the joint and may make its appearance alongside of the patella. In one of my cases one end of the semilunar cartilage was attached to the crucial ligament while the other was attached to the capsular ligament, thus allowing the part between to stretch across the surface of the condyle and be compressed in walking. These floating cartilages form the "gelenkmaus" of the Germans. These two conditions were first described by Hey under the name of internal derangements of the knee-joint. Synovial disease may also produce symptoms closely resembling those of detached cartilage.
The epiphyseal line marking the lower epiphysis of the femur starts at the adductor tubercle, at the upper edge of the internal condyle, and passes across transversely just above the edge of the articular surface. It joins with the shaft between the twentieth and the twenty-second year, sometimes as late as the twenty-fourth. The epiphysis of the tibia runs transversely across the tibia about 1.5 cm. (5/8 in.) below the articular surface and anteriorly passes down to embrace the tubercle (Fig. 554).
Fig. 552. - Dislocation of patella outward.
Fig. 553. - Subluxation of the knee from tuberculous disease showing the relation of the bones. (From an original sketch by the author).
These epiphyseal separations are produced either by direct violence, by force applied laterally, or by twisting - a common way is for the leg to be twisted by being caught between the spokes of a revolving wheel. They never occur later than the age of twenty years and usually occur several years before that age has been reached.
Often the displacement is not serious and is corrected before the patient is seen by the surgeon. Occasionally, especially when the lower epiphysis of the femur is affected, displacement is marked, and the fractured surface of the fragment may lie on the anterior surface of the shaft of the femur. Sometimes the injury is compound and the vessels so injured that amputation is required.
In spite of the fact that the greater part of the growth of the lower extremity occurs from the bones adjacent to the knee-joint epiphyseal separations almost never interfere with it. This is so true that epiphysiolysis or the deliberate separation of the lower epiphysis of the femur by bending the knee laterally over the hard edge of a table is the preferred operation with some surgeons for the correction of lateral deformities of the knee, especially knock-knee. The injury is usually treated as a simple fracture and heals without incident.