Evaluating the primary stability of standard vs lateralised cementless femoral stems - A finite element study using a diverse patient cohort

Background: Restoring the original femoral offset is desirable for total hip replacements as it preserves the original muscle lever arm and soft tissue tensions. This can be achieved through lateralised stems, however, the effect of variation in the hip centre offset on the primary stability remains unclear. Methods: Finite element analysis was used to compare the primary stability of lateralised and standard designs for a cementless femoral stem (Corail (R)) across a representative cohort of male and female femora (N = 31 femora; age from 50 to 80 years old). Each femur model was implanted with three designs of the Corail (R) stem, each designed to achieve a different degree of lateralisation. An automated algorithm was used to select the size and position that achieve maximum metaphyseal fit for each of the designs. Joint contact and muscle forces simulating the peak forces during level gait and stair climbing were scaled to the body mass of each subject. Findings: The study found that differences in restoring the native femoral offset introduce marginal differences in micromotion (differences in peak micromotion < 21 mu m), for most cases. Nonetheless, significant reduction in the interfacial strains ( > 3000 mu epsilon) was achieved for some subjects when lateralized stems were used. Interpretation: Findings of this study suggest that, with the appropriate size and alignment, the standard offset design is likely to be sufficient for primary stability, in most cases. Nonetheless, appropriate use of lateralised stems has the potential reduce the risk of peri-prosthetic bone damage. This highlights the importance of appropriate implant selection during the surgical planning stage.