# Biomechanical Analysis of Two Types of Oseointegrated Transfemoral Prosthesis
## 4 Discussion  
Today, lower limb amputations can be treated by socket prostheses, which represent the standard of care for amputees but often are associated with significant socket-interface problems, or by osseointegrated prostheses, which involves direct attachment of the artificial limb to the skeletal residuum. Because osseointegrated limb prostheses are a fairly recent method, numerous studies have been carried out in recent years, mainly to investigate which parameters could reduce implant failures. Many studies have investigated osseointegrated implants during normal daily activities such as walking. Currently, in fact, most of the research activities have investigated the stresses' distribution  
Figure 11: Fall Backwards with Balance Loss (FB BL) scenario: von Mises stress distribution on femur using the OPRA (**top**) and the OPL (**bottom**) device. in the bone during static loading, but no relevant studies have investigated how the safety of the implantation is affected by the stresses generated during a fall. In the present study, different fall scenarios have been investigated to experimentally determine the loads on a limb in a critical event like a fall. Subsequently, the calculated loads have been used to compare, by FEM analyses, the behaviour of two different transfemoral osseointegrated prostheses during falls, to verify if failures of bone or implant could occur. A typical screw-type implant (OPRA) and a press fit one (OPL) have been analysed. As regards the measured loads on the limb in different fall scenarios, it was found that the most stressful configurations are the falls forward (both FF and FF BL) and the fall backwards with balance loss (FB BL), while the fall backwards \"by push\" has shown, on average, the lowest values of forces and moments. In particular, it was observed that:  
* Peak values of the longitudinal force occur during falls forward;
* Very high values of the anteroposterior flexion moment on the limb occur in the FB BL fall scenario. This last result could be justified by analysing the dynamics of this kind of fall scenario. In fact, a fall caused by loss of balance, especially if backwards, could be more unpredictable and unexpected than other types of fall (e.g., falls caused by push), during which the subject could forecast the impact. For this reason, the high bending moment calculated in the FB BL fall could be due to the unexpected loss of balance and the following extreme attempt to restore it. Moreover, this result agrees with those obtained by [PERSON] et al. (2017) and [PERSON] et al. (2011). In both studies, different fall scenarios (both forward and backward) were analysed through a musculoskeletal model to determine the influence of transfemoral amputation length on the loads of OI prosthetic implants. Both studies found that fall backward scenarios are the most dangerous and, above all, the ones with highest anteroposterior moment at the level of amputation. These findings are consistent with the loads obtained experimentally in our study by motion capture. However, in ([PERSON] et al., 2017; 2018) no FEM analyses were performed, so no comparison can be made in terms of stresses on bone, implant and their interface. Regarding the comparison between OPRA and OPL implants, for all analysed falls, it emerged that peak values of the equivalent stress on the femur are always quite similar. On the other hand, sometimes very different stress distributions over the bone have been found. In particular, it was found the distal part of the residual bone is, on average, more stressed using the OPL device. This is clear when observing plots of the von Mises stress on the bone, for example in Figures 11 and 12 that show the equivalent stress distributions for FB BL and FF BL scenarios. It can be noticed that the internal areas of the distal femur are much more stressed (larger red coloured zones) when using the OPL prosthesis than the OPRA one.