[Biomechanical effect of mushroom shaped surface prosthesis on femoral neck after replacement]

To investigate whether the biomechanical effect of mushroom shaped surface prosthesis on femoral neck is in the scope of safety after the replacement.

Four donated fresh-adult specimens of upper femur under the age of 55 years old were used. The strains of detecting points A (lateral) and B (medial) on the narrow place of femoral neck in the standing position were simulated for three stages before or after the prosthesis replacement, namely the pre-replacement, the initial stage during which the interspace of the prosthesis was filled with cancellous bone, and later stage during which the interspace of the prosthesis was filled with bone cement. Then they were compared by using linear regression analysis in Excel and reliability analysis.

The regression analysis showed that the values of correlation coefficient r were all more than 99% at the different stages, indicating the strain of femoral neck' s cortical bone was proportional to the load and there was no occurrence of the plastic deformation of the femoral neck. For point A, the slope of the trend line of strain was 0.6719 at the pre-replacement stage. The value of the initial stage after replacement was 0.6192 and its change rate was -7.8%; while corresponding value was 0.6627 and -1.4% at the later stage after replacement. For point B, the slope of the trend line of strain was -1.0561 at the pre-replacement stage. The value of the initial stage after replacement was -1.1292 and its change rate was 6.9%; while corresponding value was -1.0851 and 2.7% at the later stage after replacement.

The mechanical strength of femoral neck is in the scope of safety after surface replacement of the femoral head. The change rate of strain at the later stage is smaller than the initial stage.