Osteoarthritis (OA) of the knee joint is becoming increasingly common. Not only due to the aging of the population in the developed world, but also secondary to labour and sporting injuries affecting a younger population group.
Once again conservative treatment should be tried first in almost all the cases, reserving the multiple surgical procedures at hand for severely impaired knees or when non-surgical treatment has failed.
If surgery is required, the following options are available:
Medial compartment disease: valgus osteotomy of the proximal tibia is indicated for medial OA changes, in young and active patients (60 years being normally the higher age limit) with less than 15º of varus deformity and a good knee flexion beyond 90-100º. Radiographically the lateral and patellofemoral compartments should be free from disease. When patients are carefully selected and surgery is carried out in good terms, one can expect 5 to 7 years of symptomatic relief. More common complications of proximal tibial osteotomies include: under-correction, over-correction, avascular necrosis (AVN) of the plateau, patella baja and peroneal nerve injuries.
Multiple studies have shown that a total knee replacement (TKR) can be safely performed, once benefits from the osteotomy have been lost, and results obtained are similar to those of a primary TKR.
Lateral compartment disease: varus osteotomy (closing wedge osteotomy of the distal femur in the supracondylar region) is rarely performed nowadays. It is a very aggressive type of osteotomy and requires plate fixation of the distal femur (thus interfering with arthroplasty surgery should it be required at a later stage). When indicated it should be reserved for valgus deformities of more than 12-15º, the range of motion of the knee should exceed 100º and adequate ligamentous stability of the knee must be present.
Unicompartimental arthroplasty: reserved for single compartment disease (OA or osteonecrosis) as an alternative to high tibial osteotomy or distal femoral osteotomy, in patients with mild or no patellofemoral involvement. An ideal candidate for this type of replacement should have a stable knee, good bone stock, a low degree of axial malalignment, an absence of severe inflammatory synovitis and should not be overweight. The surgical technique must be extremely accurate as it is important that the tibial implant must be placed at right angles to the mechanical axis of the tibia, over-correction should be avoided and sagittal tilting of the prosthesis must be kept to a minimum. The most common complication of this type of implant is loosening. The rate of revision of unicompartimental knee arthroplasty is around 10% at 6 to 8 years post implantation.
Total Knee Arthroplasty (TKA) - Total Knee Replacement (TKR): it remains the 'gold standard' treatment for advanced OA of the knee; over 70,000 TKR are performed in the UK every year, and numbers have been rising continuously since knee registers are available. It is indicated in cases of disabling knee pain and decreased function due to arthritis/arthropathy that involves one or more compartments when conservative treatment has failed. It is contraindicated with active sepsis, prior surgical fusion, severe neuromuscular dysfunction, neuropathic joint and non-functioning knee extensor mechanism.
Most common implants are 'conforming', designed to sacrifice the anterior cruciate ligament (ACL) +/- posterior cruciate ligament (PCL). Conforming implants have condylar metallic femoral components and metal-backed polyethylene tibial components, that can be fixed or mobile. Both femoral and tibial components are normally cemented for primary fixation. New cementless femoral components have similar outcomes but cementless tibial trays lack the survival of their cemented counterparts. Controversy continues on whether to replace or not the patella; in my practice only one in ten patellas are resurfaced (when the remaining articular cartilage is minimal or doesn't exist).
In cases of severe bone loss, gross ligamentous instability, complex revision surgeries, and tumour conditions, 'hinged' prosthesis, which are fully constrained, may be required. Hinged implants require extensive bone removal, have a limited range of motion compared to conventional conforming knees, and long-term survival is decreased as rates of loosening are significantly higher than standard constructs.
A successful TKR (over 90-95% of procedures) requires good stability, proper implant alignment, normal patellofemoral tracking, adequate extensor mechanism and optimal range of motion (in most cases from full extension to 120º flexion).
Complications of TKR include: prosthetic infection (should be kept to less than 1% of cases), DVT, patellar fracture or instability, arthrofibrosis (post-op knee stiffness), peroneal nerve palsy...
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