A comparison of cortical strain after cemented and press-fit proximal and distal femoral replacement

Proximal and distal femoral replacements with intramedullary stems are usually cemented in place but frequently show severe bone remodeling changes in the long term, which can contribute to a loosening process. The remodeling is likely to be associated with stress and strain distribution. This study compared the strain patterns, particularly the maximum principal strains, between cemented and press-fit components in five cadaveric femurs by using a photoelastic coating technique. The specimens were loaded with 2,000 N in the sequences of intact femur and press-fit and cemented stems. On the medial side of the bone for proximal femoral replacements, the strain values for the press-fit stems on the proximal, middle, and distal regions were 73 +/- 11%, 78 +/- 15%, and 80 +/- 15% of normal, respectively, but for the cemented stems they were 53 +/- 15%, 57 +/- 19%, and 60 +/- 20%. The differences were statistically significant (p less than 0.05). On the lateral side, the overall strain values for the press-fit stem were higher than those for the cemented stem, but the differences were not statistically significant (p greater than 0.05). On the medial side of the distal femoral replacement, the strain values for the press-fit stems in the proximal and middle regions were significantly closer to normal than for the cemented stems. Because the press-fit femoral stems (both the proximal and distal replacement) transferred closer to normal strains than the cemented stems, less adverse bone remodeling may be expected, which could be reflected in increased longevity.