Cementless curved endoprosthesis stem for distal femoral reconstruction in a Chinese population: a combined anatomical & biomechanical study

BACKGROUND: The endoprosthetic knee reconstruction using a current universal femoral stem might not be suitable for local population due to the anatomical difference between Chinese and Western populations. We measured the anatomical parameters of Chinese femurs as reference for stem design, and proposed a cementless, curved, short endoprosthesis stem for the reconstruction of distal femur. This study analyzed the biomechanical performance of the newly designed stem aimed at the identification of better operative strategy. METHODS: The CT–scanning data of femurs derived from 96 healthy Chinese volunteers were imported into the Mimics software, and a segmental measurement strategy was applied to evaluate the radius of curvature (ROC) of the femoral medullary cavity. Then, 4 kinds of endoprosthetic replacement models were created based on the measurement results. Model A: the distal tumor resected femora + straight stem A; Model B: the distal tumor resected femora + curved stem B; Model C: the distal tumor resected femora + curved stem C; Model D: the distal tumor resected femora + curved stem D. Finally, the mechanical difference among these models were compared by finite element analysis. RESULTS: The mean femoral ROC of Segment(1, 2, 3, 4, 5) measured in the present study was 724.5 mm, 747.5 mm, 1016.5 mm, 1286.5 mm, and 1128 mm, respectively. Based on the femoral ROC of Segment(2,) the stem ROC of the curved stem B, C, and D was designed as 475 mm, 700 mm, and 1300 mm, respectively. Generally, all endoprosthetic replacement models showed a normal–like stress distribution on the femurs. However, compared to the straight stem, the biomimetic curved stem showed better biomechanical performance both in terms of reducing the extent of the stress shielding of the femur and in terms of minimizing the stress distribution of the implant. CONCLUSIONS: The uncemented, curved, short stem with suitable ROC can perfectly match the Chinese femoral canal morphology which has better mechanical properties than the conventional femoral stem. Thus, this newly designed femoral stem might be an optimized method for treatment of malignant femoral tumours in the Chinese populations in the case that the numerical results are supported by future experimental studies.