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.
In making the skin incision care should be taken to carry it back sufficiently far to allow of division of the lateral ligaments; in so doing, however, one should not divide the long saphenous vein and nerve at the posterior edge of the internal condyle. It is essential to recognize the joint-line; it is just below the lower edge of the patella and thence extends laterally about a finger-breadth above the head of the fibula. It is customary to carry the incision from near the posterior edge of the femur on the inner side to the posterior edge on the outer side at the joint-line, passing over the middle of the tendo patellae so as to allow this latter to be readily sutured later if desired.
Care is to be taken to avoid wounding the popliteal artery. This lies close to the posterior part of the capsule; hence the latter is not to be divided transversely but is to be separated by keeping the knife close to the bone. Finally, inasmuch as the bulk of the growth of the lower extremity occurs in the upper end of the tibia and lower end of the femur, it is essential to avoid removing the entire epiphyseal cartilages. For this reason formal resections have been abandoned in young children, and in adolescents as little tissue as possible is removed. The epiphyseal line in the femur runs transversely on a line with the adductor tubercle and passes close to the upper edge of the articular surface. The epiphyseal line in the tibia lies rather close to the articular surface, being 1.5 cm. (5/8 in.) below in adults and less in children; it slopes down in front to embrace the tibial tubercle (see Fig. 554). When the disease encroaches on the epiphyseal line, rather than remove it the affected parts are to be curetted away and the remainder left. In those cases where the knee is much contracted, either enough of the bone must be removed to allow of straightening or the hamstring tendons must be cut; if this latter is done the external popliteal nerve which runs on the inner posterior surface of the biceps tendon must not be wounded.
Fig. 554. - Antero-external view of the bones of the knee, showing the lines of the epiphyses.
The disease begins usually in the epiphyses adjacent to the joint and involves the joint secondarily. The tibia is more frequently the seat than the femur. The swelling and hypertrophy of the synovial membrane and involvement of the adjacent soft parts obliterate the hollows on each side of the patella and cause a bulging below the patella. The knee looks round and swollen, and the condition was formerly called white swelling from the surface being white in color. If liquid accumulates in the joint it becomes distended and flexed, assuming an angle of 120 degrees. The patella is raised from the condyles; it " floats" and if depressed by the finger can be felt striking on the femur beneath, thus demonstrating the presence of liquid in the joint. The swelling extends above the patella to an extent depending on whether or not the subfemoral bursa is involved and whether or not it communicates with the joint.
If pus forms it tends to find an exit beneath the lower edge of the posterior ligament or on either side of the patella at the upper end of the tibia. As the disease progresses the ligaments become weakened. The joint, being already flexed at approximately 120 degrees, is flexed still more by the hamstring muscles, and the head of the tibia in old cases becomes drawn backward in a position of subluxation (see Fig. 553, page 541). The pull of the biceps tendon while the leg is flexed rotates the leg outward and this position may persist: a condition of knock-knee is also some-' times marked.
The disease is treated conservatively by apparatus, but in exceptional cases the lesser operation of erasion or the greater of resection (see above) is done.