Abstract:
Background
Radiolucent lines and sclerotic margins are often seen on knee radiographs taken a year or longer after
knee replacement surgery. Histology has shown that the radiolucent zone is predominantly
fibrocartilage and the sclerotic margin is lamellar bone. The reasons for their existence are not clearly
understood.
Methods
A three‐dimensional finite element model of the medial half of the proximal 75 mm of a tibia implanted
with a knee replacement was created and run over 365 iterations simulating 1 year of in vivo post
implant remodelling. After each iteration, new material properties were calculated for all elements of
the model using established bone remodelling and tissue differentiation rules. For comparison with
patient anteroposterior radiographs, “synthetic anteroposterior radiographs” were generated by
reverse calculating radiographic densities from material properties of the model after 365 iterations.
Von Mises stress of elements in the bone where the sclerotic line is usually seen were calculated after
365 iterations. These values were compared with the same entities assuming no remodelling.
Findings
The mean von Mises stress in the sclerotic region was higher when remodelling was assumed than when
not, suggesting that the presence of the soft tissue (radiolucent line) increased the stress in the
underlying bone.
Interpretation
The sclerotic line is caused by the stiffening of bone due to the relatively larger loads seen by the bone
just beneath the soft tissue (radiolucent line) adjoining knee replacements.
