hta_ knee intro.qxp - Ministero della Salute

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Prostheses for TKR can be classified taking into account several variables:
• the method of fixation of the components (cemented, uncemented or hybrid);
• the retention of posterior cruciate ligaments (cruciate retaining or CR design) or their
sacrifice (posterior stabilised or PS design);
• the bearing mobility (fixed or mobile bearing);
• the profile of the femoral component (multiradius design, single-radius design, medial
pivot design or others).
Evidence and trends related to the use of a particular design instead of others are in Appendix 1.
2.2 The procedure
TKR is a bone resecting and resurfacing procedure. Specific sets of instrumentations and tools
are used to create exact surfaces to accommodate the implant. The knee joint can be approached
anteriorly (through a medial parapatellar approach), or by mid-subvastus approach. Osteophytes
and intra-articular soft tissues are then cleared. Bone cuts in the distal femur are made perpendicular
to the mechanical axis, usually using intermedullar alignment systems. The proximal tibia is
cut perpendicular to the mechanical axis of the tibia using either intermedullar or extramedullar
alignment rods. Restoration of mechanical alignment is important to allow optimum load sharing
and prevent eccentric loading through the prosthesis.
Sufficient bone is removed so that the prosthesis re-creates the level of the joint line. This
allows the ligaments around the knee to be balanced accurately and prevents alteration in patella
height, which can have a deleterious effect on patellofemoral mechanics. Patellofemoral tracking
is assessed with trial components in situ. If the patellofemoral joint is significantly diseased,
it can be resurfaced with a polyethylene “button”. If a cemented system is chosen, the definitive
components that have been selected are cemented into place by bone cement (polymethylmethacrylate,
PMMA). Uncemented systems are fixed with a press-fit fixation process 19,20 .
2.3 The alternatives
Most commonly, TKR is performed for OA of the knee. Initial management of most patients
with OA can be non-operative and may include nonsteroidal anti-inflammatory medications, intraarticular
viscosupplementation, analgesics, bracing, orthoses, shoe modifications, weight loss, and
ambulatory aids. Activity modification and home health care-assistive devices may also be necessary.
Joint aspiration and intra-articular steroid injection may be used to improve synovitis.
Because of the progressive nature of OA, many patients receive operative treatment after an initial
medical management 19 ; however TKR should not be undertaken unless a patient has received
full conservative management and that management is no longer controlling the patient's discomfort.
As the focus of this report is on TKR, non-surgical alternatives to TKA will not be considered
as well as other types of arthroplasty (unicompartmental and patello-femoral knee arthroplasty).