# Footnote 1
## 5 Conclusions  
The number of results per database does not reflect the effectiveness of each search engine. For this research, priority was given to search engines that provided useful data such as direct links to patents, the inventor's name, and IPC codes. Nevertheless, there are some difficulties with some of them, such as the lack of options for filtering results or IPC categories, among others. Besides, some applicants may be included in the name of their companies (for example, [PERSON] in Massachusetts Institute of Technology); this is because some search engines only show the applicant/owner's name instead of the inventor. In some cases, there is a lack of consistency between the author's names in different patents (for example, [PERSON] and [PERSON], [PERSON], [PERSON]); these kinds of inconsistencies were clustered, but still, results could not be entirely precise. The United States has 56% of patent applications and 34% of scientific documents registered. These results do not necessarily display that they produce most of the knowledge on this topic, but because of the language, most of the search engines are capable of accessing the data, unlike languages such as Spanish, Chinese, or languages spoken in India. Therefore, some designs could remain undiscovered for this investigation. Based on the obtained results, it can be established that for this study, the effectiveness per search engine is as follows: Derwent 8.4%, Google patents 0.34%, Patentscope 3.2%, The Lens 19.9%, and Espacenet 13.95%. Figure 16: Comparative static analysis of ESAR prosthesis. Figure 17: Results of deformations on uneven terrain. The classification of the 208 prosthesis patents related to prostheses designs was obtained according to the main technology used; results show that the ESAR mechanical prosthesis is the main patent object by 44%, although claims are different for each one. All of them can be classified based on the five ESAR categories presented in this document. Outcomes also show a tendency for the use of ESAR regardless of the technology used. For 151 removable foot/ankle patent prostheses analyzed, 53% use only ESAR-type prosthesis, and 90% use ESAR in its components. From these, the more commonly used were selected and compared using Ansys, with no major differences between A and C, but for B, results show a more elastic foot thanks to its mass-centered design. The significant trend in the use of ESAR prostheses may be because of their lower cost and greater energy efficiency. Different designs are used according to the user's lifestyle. The minimum amount of components found for designing an active prosthesis is a DC motor, housing, a power transmission unit, a composite foot or equivalent, an energy storage device (springs, locking systems), a linkage system, an energy power supply, and a prosthesis/socket connector. From these components, most prostheses use a Maxon(r) Brushless motor between 12 and 200 W. Power variations are mostly due to the gear ratio used (the more power, the lower the gear ratio), springs with stiffness between 60-445 kNm, and a Li-ion battery between 12-24 V. From these components it is especially important to consider when designing a BKA prosthesis the linkage system that needs to support most of the necessary loads, and it must be capable of tolerating at least 2 kN (for an 80 kg patient) without any failure. Materials also play a vital role in supporting loads with 4000/5000 duty cycles per day; that is why aluminum, carbon fiber, and other composites are used in fabrication, and sometimes load reduction along the system is necessary and archived using a parallel spring arrangement. The current development of batteries allows active prostheses to obtain enough power and charge duration without adding extra mass and weight, but for hydraulic and pneumatic prostheses, power supply currently is a problem because most of these systems are connected externally and the mass could reach up to 15 kg. Nevertheless, these systems are more efficient in mimicking human ankle movements.