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A Case for Porous/Hybrid Total Knee Arthroplasty Carolyn R. Hutchison, BSc,
M.D., MEd, F.R.C.S.(C) Assistant
Professor Division
of Orthopaedic Surgery University
of Toronto Mount
Sinai Hospital Toronto,
Ontario Over the years many different cemented and uncemented TKAs failed
because of poor design features. The
remaining designs on the market are those that performed well. Early uncemented designs did not take into
account the lessons learned from cemented TKA. However, more recent designs for uncemented TKA have highly
satisfactory results. The Patella It is clear that a metal-backed porous coated patellar component was
not a solution for the patella. In
fact this led to further problems.
Wear through the polyethylene to the metal backing created metal and
polyethylene debris. This likely
contributed to increased wear of the tibial polyethylene, massive osteolysis
and loss of bone stock. Although this
problem was unrelated to the method of fixation of the femoral and tibial
components, it gave uncemented TKA a bad name. The use of metal backing on a thin polyethylene patellar
component was a poor design. The Femur When we look at the femoral component, a case can be made for
uncemented fixation. The femoral
component is intrinsically stable.
The uncemented femoral component can reliably achieve fixation. The Tibia The greatest source of problems in both cemented and uncemented TKA
has been the tibial component. A
number of studies have focused solely on the tibial component in discussing
results of TKA. Both fixation methods
do not do really well with shearing forces and toggling or lift-off. Adding a stem to the tibial component has
improved the results of uncemented and cemented components. As Hugh Cameron pointed out, adding the
tibial stem to the uncemented tibial component has largely resolved the
medial-lateral motion but does not completely prevent anteroposterior motion. Gerard Engh reported on the treatment of 25 cases of tibial osteolysis
in cementless TKA. These were treated
with 3 options: 1) exchange of the tibial poly with screw removal 2) revision
of the tibial component with curettage and grafting of the osteolysis and 3)
revision of all components. At 2-6
years the clinical and radiographic results of those treated with full
revision were excellent. The 2
clinical failures were one with a poly exchange only and one with a tibial
revision only. They found that tibial
defects did not progress and new ones did not develop with curettage of the
defect and removal of sources of particulate debris. In
1994, Leo Whiteside reported on the 9-11 year results of cementless TKA. Of 163 knees, one loosened, 5 patella and
tibial components were revised for wear and 5 were revised for
infection. The 10 year survivorship
was 94%. He also found that the knees
requiring revision had excellent bone stock.
Revision of an uncemented femoral component can be achieved with
minimal bone stock loss using a gigli saw. In 1996, Schroder and colleagues reported on cementless TKA in rheumatoid arthritis. The success rate at 4-5 years was 97%. One tibial component was revised for aseptic loosening. At
Mount Sinai Hospital we generally cement all of our patellas and most tibial
components. On the femoral side we
will go to an uncemented component in the young active male. The
option of an uncemented femoral component and a cemented or uncemented tibial
component with a cemented patellar component has good long term results.  |
