## 4 Discussion  
This prosthetic device was designed to address three main needs in the medical recovery and assistance process for patients with unilateral transtibial amputation: (1) early detection of limb length discrepancy (LLD) without the need for frequent visits to the clinician, for preventive purposes; (2) automatic correction of LLD without the assistance of a medical specialist, following an initial calibration; (3) automation of the limb alignment process using a device produced at low cost, suitable for patients in developing countries. Figure 12: Displacement performed by the prosthesis for a 10 mm LLD. Figure 13: Displacement performed by the prosthesis for a series of simulated LLDs (1–10 mm). A home-based LLD monitoring and control device, such as the one proposed in this study, can be useful given that patients do not perceive an LLD smaller than 20 mm--a value that is still clinically tolerable [2,11]. This discrepancy cannot be effectively managed, as it relies on the presence of a clinician to equalize limb lengths. All prosthetic length adjustments are manually performed by specialists using passive mechanisms [18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28], typically occurring only once or twice a year [17]. During daily use of a standard or bionic prosthesis, without regular adjustment of the prosthetic shaft length, an LLD exceeding the 20 mm threshold becomes harmful. This discrepancy can lead to fatigue and cause significant imbalances in gait biomechanics [12], potentially resulting in hip or knee osteoarthritis and other mechanical pathologies due to improper load distribution on the shorter limb, specifically the amputated and prosthetic one [3,14, 15, 16]. Furthermore, an LLD exceeding 20 mm is perceptible to prosthetic users [13]. Given that the clinically accepted threshold for LLD is a maximum of 20 mm between a prosthetic limb and an intact limb, and our tests demonstrated that the self-adjusting transtibial prosthesis automatically compensates for LLD with a relative error of 9.8%, the obtained results indicate promising clinical performance. Such an error is considerably low in the context of a 20 mm discrepancy, suggesting that the prosthesis could provide effective correction. The developed prosthesis achieves a performance level sufficient to compensate for most limb length discrepancies within the limits accepted by clinicians. In terms of accessibility, the self-adjusting prosthesis cannot be directly compared to a traditional prosthesis but rather to a set of classic prostheses of different sizes that need to be replaced approximately twice a year. Thus, the prosthesis proposed here can eliminate the additional costs of frequent replacements and, through its self-adjustability, reduce the need to purchase new prostheses. Furthermore, the prosthesis reduces the frequency of visits to the prostheticist and long-distance travel, which are costly and difficult for amputees to manage, especially in impoverished regions with a lack of trained prosthetists. Consequently, the self-adjusting prosthesis is more cost-effective in the long term, potentially eliminating the need for prostheticist intervention and providing an economical and accessible solution, even in conditions of limited resources. The authors estimate that such a prosthesis can reduce the cost of adequately fitting a patient with a prosthesis by about 30-40% compared to conventional prostheses. In our estimates, we did not include software development costs. We also do not exclude that the hardware element controlling the prosthesis could be used by multiple patients. For example, a whole group of prosthetized patients from a village in a poor country can benefit from the Master-Slave system of the self-adaptive transtibial prosthesis. This can also reduce costs by eliminating the need for a prostheticist to periodically adjust all these patients.