Total Knee Arthroplasty (TKA) is an operation that restores knee function by relieving pain and stiffness. This ensures a good quality of life for about 20 years. In about 10% of patients, however, a second operation may be needed, namely a revision of total arthroplasty. The revision consists in replacing some or all of the implants with a new implant. It is a complex surgery that requires very good preoperative design, specialized materials and instruments, significant surgical experience, familiarity with complex and demanding techniques.

There are many causes that may lead to unsatisfactory functioning of total knee arthroplasty and the need for its replacement. The most important are:

• Natural deterioration of materials due to expiry of their life span

• Loosening of implants: proper functioning of arthroplasty requires a steady attachment of the prosthesis to the underlying bone. Over time, due to friction between the materials, particles of metal, plastic or cement are produced. These stimulate the defense system of the organism, causing an immune response, which, in an effort to entrap and isolate them, destroys the bone itself leading to osteolysis. As time passes, bone depletion increases and the implant, which was firmly attached to the bone, gets loosened. Deformity and instability occur, so that the patient feels pain and can not walk.

• Infection and inflammation: Contamination of arthroplasty is a very serious complication. It usually happens a few days or weeks after surgery, but its appearance many years later can not be ruled out. The presence of microbes in the blood after dental procedures, respiratory infections, skin or urinary tract infections can lead to colonization of the prosthesis, that is, to installation of microbes on the prosthesis. Contamination of arthroplasty is manifested by pain, edema and possibly fluid outflow from the incision. As antibiotic treatment is not effective, the implant has to be removed and replaced by a new one. In order to ensure the definitive eradication of microbes, the procedure is performed in two stages. In the first operation, the old prosthesis is removed and replaced by a temporary one of cement enriched with antibiotics (spacer). After a few months and when all tests show that the microbe has been eradicated, a second operation is performed, in order to remove the temporary prosthesis and replace it by the permanent one.

• Fractures around the prosthesis: Fractures around total arthroplasty are called periprosthetic. Depending on their extent, they may cause loss of implant support. In this case, a revision is required.

• Instability due to injuries to the ligaments that support the joint.

Regular postoperative follow-up is very important and can help prevent major problems. Pain, deformity, stiffness, edema, redness, and fluid discharge from the incision site are symptoms that need to be thoroughly investigated by clinical examination, radiology, blood tests, and bone scintigraphy. If non-functional or inflamed arthroplasty is detected then a revision is needed. Based on the results of the examinations, a plan will be made preoperatively, concerning the method, materials and instruments to be used to achieve the best result.

A revision is technically more complex and difficult than the first total arthroplasty surgery, as it is performed in two stages, each with special difficulties and peculiarities. As a first step, the old prosthesis is carefully removed, because despite loosening, the implant keeps a degree of adherence to the bone, so that there is a risk of fracture. If there is significant bone loss, grafts may be used to fill the gaps. Finally, the new prosthesis is placed, which can be of the same type as the original or of a special type with long stem. The choice of materials and their placement require a large surgical experience, as they must be adapted to the particularities of each case. The duration of surgery is about twice as long and there is usually a larger postoperative bleeding, which may require transfusion.

Postoperative treatment is similar to that for classic arthroplasty. It includes antibiotics, analgesics, antithrombotic prophylaxis and physiotherapy. In cases of advanced age or of severe bone loss, the recovery time is longer. These patients may at first walk with the aid of a walker, without applying their full weight on the leg until the soft tissues and the bone around the prosthesis have recovered. Ultimately, however, the result is again a stable, painless, functional joint.

Concluding, when a patient undergoes total knee arthroplasty, he should be examined by his doctor at regular intervals, usually once a year, to ensure early diagnosis of problems, before major bone loss and deformity occur. With a regular follow-up, revision may be limited to part of the implant. This will make operation and recovery much easier for both patient and surgeon.