The Journal of Bone and Joint Surgery, Vol 74, Issue 2 233-238, Copyright © 1992 by Journal of Bone and Joint Surgery, Inc
Consequences of an interference fit on the fixation of porous-coated tibial components in total knee replacement
JM Dawson and DL Bartel
Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, New York 14853.
A linearly elastic, axisymmetrical finite-element model was developed in an
attempt to explain observed long-term patterns of growth of bone into
tibial components. This model, which represents a portion of the tibial
tray, one peg, and the surrounding cancellous bone, was used to examine two
conditions of fixation in the immediate postoperative period. The first was
characterized by the use of an interference fit for initial fixation of the
component and the second, by the use of an interference fit with the hole
in the bone deeper than the length of the peg. Two conditions of long-term
fixation were also examined. In one, the bone was assumed to have grown
into all of the porous coating. In the other, the bone was assumed to have
grown only into the peg, and a layer of fibrous tissue was assumed to have
developed between the tray and the bone. An interference fit between the
peg and the cancellous bone produced considerable residual radial stresses
in the bone. These stresses provide conditions that are favorable for
ingrowth of bone into the pegs because the bone at the interface is
stressed, and these stresses inhibit relative motion at the bone-peg
interface. However, the interference fit of the peg relieved the stresses
in the cancellous bone under the tray of the implant. Lack of stress at
this interface is consistent with relative motion and subsequent formation
of a layer of fibrous tissue. Deepening of the hole for the peg in the
cancellous bone did not diminish the effects of the interference fit.
Stresses in the bone under the metal tray were relieved when a layer of
fibrous tissue under the tibial tray was represented in the model.