EXCISION OF KNEE-JOINT.--_Removal of Bone._--In every case the excision of the joint ought to be complete. Some attempts have been made to save one or other of the articular surfaces, but they have proved failures. The patella has frequently been left when it was not diseased, as is often the case, but the results have not been such as to recommend such a practice. _Direction of Section of the Bones._--The bones should be cut transversely, and, as far as possible, be in accurate and complete apposition. A slight bevelling at the expense of the posterior margin will produce an anchylosis of the limb in a very slightly flexed position, which is found to aid the patient in walking. It has been proposed by some[64] to cut both bones obliquely, so as to obviate the difficulty of making the transverse surfaces parallel. This involves a still greater practical difficulty in keeping these oblique surfaces in position during the after-treatment. This plan might possibly be valuable in cases where the disease was limited to one or other edge of the bone. Among the various incisions recommended, the best seems to be the _Semilunar Incision_. _Operation._--The limb being held in an extended position, a single semilunar incision (Plate I. fig. B.) is made, entering the joint at once, and dividing the ligamentum patellæ. It should extend from the inner side of the inner condyle of the femur to a corresponding point over the outer one, passing in front of the joint midway between the lower edge of the patella and tuberosity of the tibia. The flap is then dissected back, the ligaments divided, when by extreme flexion of the limb the articular surface of the tibia and femur are thoroughly exposed. The crucial ligaments must then be divided cautiously, and the articular portion of the femur cleaned anteriorly by the knife, posteriorly by the operator's finger, so far as possible to avoid injury of the artery. The whole articular surface of the femur must then be removed by a transverse cut with the saw as exactly as possible at a right angle with the axis of the bone. The amount of the femur which will require removal will in the adult vary from an inch to an inch and a half or even more. It _must_ involve all the bone normally covered by cartilage; and this being removed, if the section shows evidence of disease, slice after slice may require removal till a healthy surface is obtained. Occasionally, if the diseased portion appears limited, though deep, the application of a gouge may succeed in removing disease without involving too great shortening of the limb. Specially in children, it is of great importance to avoid removing the whole epiphysis. The tibia must then be exposed in a similar manner, and a thin slice removed; if the bone be tolerably healthy, even less than half an inch will prove quite sufficient.