Development of clinical protocols for the evaluation of safety and performances of active lower limb prosthetic components

According to the most recent Hospital Discharge Records from the Italian Ministry of Health, in the decade from 2008 to 2018 there were about 135’000 new lower limb amputations (LLA), entailing that every year there are approximately more than 12’000 new LLA, of which 1100 transtibial and 3300 transfemoral. The evolution of lower limb prostheses began with passive devices (mechanical and microprocessor prosthesis), and then developed on powered devices, which fully provide for all motor functions of the lower limb, particularly during activities in which energy expenditure becomes prohibitive, such as walking uphill, climbing stairs, and getting up from a chair. The current powered prosthetic offer allows to reach a good level of autonomy, but there is some dissatisfaction with aspects such as comfort (weight), reliability (battery autonomy, safety), cost, and ease of use. These are the key features of the HyperLeg project, which was developed in collaboration between Centro Protesi INAIL and the Italian Institute of Technology (IIT). HyperLeg is a lower limb prosthesis composed of a powered knee joint (Hybrid) and a powered ankle joint (Smart Ankle). In order to assess the safety and performance of prosthetic prototypes, a detailed clinical protocol must be devised, describing the objective, rationale, design, methodology, and organization of the clinical investigation. Until now, no unified experimental methodology exists for addressing this issue, for this reason, the aim of the thesis was to develop a robust clinical protocol to evaluate a powered lower limb prosthesis. A systematic review of scientific publications was undertaken to determine which types of tests, outcome measures, and methodologies were previously explored. Following the findings, two experimental protocols for evaluating Hybrid and Smart Ankle were devised, and to assess the feasibility of the protocols, the timing and the order of all the activities were included in the analysis. The experimental set-up included a stereo-photogrammetry system, an instrumented treadmill, a magneto-inertial measurement unit, force plates, and a wearable metabolic system. The experimental trial lasted six days, and the activities included were so developed: -Baseline assessment (2-days): functional and biomechanical evaluation with the user's current prosthesis. The functional trial included: Six-Minute Walking Test, L-Test, stair and slope climbing while wearing the metabolic system, sit-to-stand trials while wearing a magneto-inertial measurement unit. The biomechanical trial included: treadmill walking, stair climbing, and sit-to-stand analysis using a stereo-photogrammetry system and force plates. -Training (2-days): rehabilitation with the new prototype, including gait training, sitting, slope and stair ascending and descending. -Post-training evaluation (2-days): repetition of the tests carried out during the baseline assessment with the new prototype. The outcomes analysed for the comparison between the actual prosthesis and the prototype were the number of stumbles and adverse events, biomechanical data, functional test scores, and the metabolic cost. In conclusion, a robust protocol was devised accounting for 5 different fields of analysis: walking tests, slope walking tests, stair climbing tests, sitting trials, and functional tests, lasting a total of 6 days. In perspective, the protocol could be adopted to test powered prototypes, standardizing the process of evaluating lower limb prostheses' performance and safety.