# Damage-Based Assessment of the Risk of Cut-Out in
## 4 Discussion  
Assuming the femoral head and neck region, identified here as SP, as the most critical region for cut-out [11], this study found contradicting results for the male and female fema in the superior-inferior direction: the inferior positioning of the blade was less prone to cut-out for the female model, whereas for the male model it was the central positioning. Regarding the insertion depth, the results were consistent for both models, showing that the closer the tip of the blade to the femoral head surface, the lower the risk of cut-out. The best position of the PFNA blade in the superior-inferior direction is not consensual in the literature. [PERSON] et al. [5; 16], [PERSON] et al. [6] and [PERSON] and [PERSON] [17] defended that the blade should be placed centrally, while [PERSON] et al. [13], [PERSON] et al. [15] and [PERSON] et al. [12] recommended an inferior position. Interestingly, this study also found contradicting results between its male and female models, which may be explained by differences in their bone density distributions. For the female model, the blade was always positioned in regions of low bone density (average density of 0.22 g cm\({}^{-3}\) at the tip for central positions and of 0.18 g cm\({}^{-3}\) for inferior positions), whereas for the male model, the central positioning of the blade placed it in a region of higher bone density than when placed inferiorly (average density of 0.35 g cm\({}^{-3}\) at the tip for central positions and of 0.23 g cm\({}^{-3}\) for the inferior positions). If the superior-inferior placement of the blade is density-dependent, its positioning should be adapted according to each patient's density distribution. However, further investigation is necessary to assess the influence of bone density on the risk of cut-out. The depth of the blade placement was found to greatly influence the decrease of the risk of cut-out. For both male and female models, the results showed that the higher the distance from the tip of the blade to the external surface of the femoral head, the higher the  
Figure 4: Damage distribution (\(D\)) for the F-Inf-5 and F-Cent-20 models considering (**a**) the gait loading case and (**b**) the two-fold gait loading case. damage at the tip of the blade, the blade transition region, and the fracture region, which is consistent with the regions identified by [PERSON] et al. [11] and [PERSON] et al. [15] as critical for the risk of cut-out. The influence of the blade insertion depth was observed regardless of the positioning in the superior-inferior direction, as also observed by [PERSON] et al. [15]. Despite this result, the insertion depth of the PFNA blade must be considered with caution as other complications, such as medial perforations of the proximal femur [32], may arise if the PFNA blade is too close to the femoral head surface. In this study, the minimum distance considered between the tip of the PFNA blade and the femoral head surface was 5 mm based on the recommendations from the manufacturer [33]. Nevertheless, further investigation is necessary to identify the best balance between the risk of cut-out and the risk of proximal femoral perforation to help clinical decision-making. The difference in the risk of cut-out for different insertion depths was higher than that for different superior-inferior positions--for instance, for the female model, a deep central position was less prone to cut-out than a less deep inferior position. This suggests that the insertion depth of the blade is a more relevant indicator for the risk of cut-out than the superior-inferior position of the blade. Unlike previous biomechanical studies that assessed the risk of cut-out through the evaluation of minimum principal strains or stresses obtained from static analyses (e.g., [11; 15]), this study considered the progressive propagation of bone damage through the application of a damage model, which enabled an enhanced assessment of the risk of cut-out [18].