# Biomechanical Analysis of Two Types of Oseointegrated Transfemoral Prosthesis
## Materials and Methods  
### Experimental Evaluation of Loads  
To experimentally evaluate the loads on the prosthetic limb during different fall scenarios, one healthy subject (male, 90 kg, 1.80 m, 31 years old) has been recruited. The subject was equipped with appropriate protections on knees, elbows and hands. The experimental tests were carried out on a wooden walkway (Figure 1) containing one force plate (P-6000, BTS Bioengineering, BTS Bioengineering, Garbagnate Milanese, Italy).  
Reflective markers were placed on the subject following a custom and simplified marker protocol (Figure 2).  
The markers were placed on the external side of both lower limbs to track the positions of the femurs, the tibias and the feet (Figure 3).  
A 4-camera motion capture system (BTS Smart-DX, BTS Bioengineering, Garbagnate Milanese, Italy) was used to acquire marker trajectories during all tests. Marker trajectories and force data were collected at 400 Hz. Volume and static calibrations were performed according to the BTS Smart-DX guidelines before the experimental tests. Kinematic data of hip, knee and ankle along the sagittal plane were elaborated in the dedicated motion capture software (BTS Smart Tracker and BTS Smart Analyzer, BTS Bioengineering, Garbagnate Milanese, Italy) for all the falling scenarios. The position of the knee center during falls was interpolated through the BTS Smart Analyzer software, since it was not possible to place the markers on anatomical landmarks, such as epicondyles, due to knee protections. The following common fall scenarios have been investigated:  
* Fall Forward (FF): during walking, the subject falls forward and impacts both knees on the ground;
* Fall Forward with Balance Loss (FF BL): during walking, the subject loses balance and falls forward with his hands on the ground and leans on the prosthetic limb by bending the hip and the knee;
* Fall Backwards with Balance Loss (FB BL): from an orthostatic position, the subject goes back, impacts his healthy foot against an obstacle and loses balance. To restore it, the subject extends the hip and leans on his prosthetic limb;
* Fall Backwards \"By Push\" (FB BP): from an orthostatic position, the subject experiences a sudden push along the sagittal plane. The subject loses balance, and steps back with the contralateral limb lifted and the prosthetic limb on the ground.  
The analysed fall scenarios were previously identified as typical and frequently occurring in individuals with transfemoral amputation [40]. Each type of fall was repeated 10 times to verify the repeatability of the test and the accuracy of the data collected. The measured kinematic data (positions of femur, tibia, knee and foot) were correlated with the forces measured by the force-plate during falls.  
Figure 3: Subject equipped with protections and reflective markers for motion capture.  
In this way, after synchronizing kinematic data and measured loads, the forces and moments at the distal part of the residual femur have been evaluated through force-transfer calculations.  
The schemes and reference systems used for force-transfer calculations are shown in Figure 4, where:  
* The lower limb is schematically represented with three uniaxial and infinitely rigid elements (red in Figure 4);
* X-Y-Z is the reference system of the force plate;
* xB-yB-zB is the reference system of the bone (femur);
* \(t\) is the length of tibia;
* \(f\) is the distance between the knee and the implant position along the femur;
* \(c\) and \(g\) represent, respectively, the angle between foot and tibia and the angle between tibia and femur.  
Calculated forces and moments have been used as boundary conditions for subsequent FEM analyses.