In adults, the operation consists in excising the joint; in children the aim is to remove the diseased tissues without damaging the epiphysial cartilages.
Amputation is performed when the disease has relapsed after excision and there is persistent suppuration, and when life is threatened by the occurrence of tuberculosis in the lungs or elsewhere.
#Treatment of Deformities resulting from Antecedent Diseases of the Knee.#--Flexion is the commonest of these; when due to contracture of the soft parts, these are either stretched by degrees, the limb being encased in plaster after each sitting, or they are divided by open dissection in the popliteal space. If there is fibrous or osseous ankylosis, the choice lies between arthroplasty, the removal of a wedge of bone which includes the joint, or, in patients who are still growing, of a wedge from the femur above the level of the epiphysial cartilage. Backward displacement of the tibia, genu recurvatum, and genu valgum also require operative treatment.
#Pyogenic diseases# result from infection through the blood stream, from one of the adjacent bones, or from a penetrating wound of the joint. The commoner types include the _synovitis_ associated with disease in the adjacent bone, _acute arthritis of infants_, joint suppuration in _pyæmia_, _pyogenic arthritis_ following upon penetrating wounds, and the affections which result from _gonorrhœal_ or _pneumococcal_ infection.
_Treatment._--The limb is immobilised on a posterior splint so padded as to allow slight flexion at the knee, and extension applied with sufficient weight to relieve the pain; it is also of benefit to induce hyperæmia by one or other of the methods devised by Bier. To tap the joint, the needle is introduced obliquely into the supra-patellar pouch, and if it is necessary to open the joint, the incision is made on one or on both sides of the patella, and Murphy's plan of inserting formalin-glycerine may be employed. If the infection progresses and threatens the life of the patient, it may be necessary to lay the joint freely open from side to side, sawing across the patella, and, the limb being flexed, the whole wound is left open and packed with gauze. As the infection subsides, the limb is gradually straightened. If these methods fail, amputation through the thigh may be the only means of saving life.