This investigation aims to compare the functional performance of a new passive microprocessor-controlled Prosthetic Knee to subjects usual microprocessor-controlled prosthetic knee.

The primary objective of this study is to evaluate the efficacy of the investigational device compared to other passive MPKs (Rheo Knee 4, C-leg 4, Genium, X3, Plié 3, Orion 3, Quattro, Allux) regarding satisfaction in descending activities for moderate to high active prosthesis users within the intended population for the investigational device.

Additionally, to evaluate the balance confidence, perception of safety and comfort in standing with the investigational device compared to other passive MPKs (Rheo Knee 4, C-leg 4, Genium, X3, Plié 3, Orion 3, Quattro, Allux).

In phase I the performance in descending activities will be compared to any other passive MPK and in phase II there will be a subgroup analysis comparing to hydraulic MPKs and Rheo Knee 3, specifically.

The test will be a non-randomized single group open label prospective repeated measures (ABA) design.

Amputees are a small proportion of the general population. The population group specified in the inclusion/exclusion criteria is a further subsample of amputees. For practical reasons, i.e. to achieve statistical power, it is therefore more feasible to use within-subject comparison rather than creating study arms to compare. Furthermore, as mobile amputees generally have and use a prosthetic device for their daily activities, within-comparison is feasible comparing to the subject's previous device.

All investigational activities will be conducted at prosthetic out-patient clinics.

As stated above the primary endpoint is Satisfaction on descending stairs, and the secondary endpoints are satisfaction on descending ramps, balance confidence and standing comfort in that respective order of significance. In addition, there are two exploratory endpoints on mobility and balance during ambulation.

Procedures:

i) Recruitment Potential subjects will be identified from the customer base of the Local Principal Investigator (LPI). LPI evaluates, based on previous experience of interaction with and servicing of patients, if a potential participant is cognitively capable. If a potential participant fits the inclusion and exclusion criteria the LPI will contact them via telephone. During the telephone call the LPI will verify if they are interested in participating in a study. If interest is expressed at this point they will answer some screening questions and if the eligibility criteria are met an appointment will be made for the clinical visit and signing of the ICF. Questions relating to the duration of the study, number of clinical visits required and the investigational device will be answered.

Potential risk of participating in the investigation will be explained to the subject at this point to the candidate for enrolment.

The LPI will communicate to the study monitor and sponsor co-investigator the number of users he has identified that meet the inclusion criteria and are willing to participate.

ii) Test procedure There are three scheduled study events. Three sites will be included in the study, 4-10 users will be recruited at each site. At the initial visit, the first study event, for each subject a researcher qualified to obtain informed consent will seat the subject and proceed as described.

Prior to fitting the subject will be asked to provide feedback on the current prosthesis, by filling in a set of questionnaires (Including background information) and perform functional tests. The users will be fitted within the standard methods of prosthetic fitting, alignment, introduction, training and walking on various terrain.

After initial fitting, subjects will receive standard training on the investigational device by a certified prosthetist (the LPI) with support from sponsor investigators. When training is complete, and subjects feel comfortable and safe they will leave the site on the investigational device to use as their primary prosthesis in their daily life for 3 weeks. During this 3 week period the LPI will be in weekly contact with subjects via telephone to check on any issues that may arise.

The second visit will be at three weeks after visit 1. During this visit subjects will complete the same functional tests and questionnaires as at visit 1 (excluding background information) on the investigational device, with the addition of a usability questionnaire. They will then be fitted back to their prescribed device.

The third visit will be three weeks later. During this visit subjects will complete the same functional tests and questionnaires as at visit 2 (excluding usability questionnaire) on their prescribed device, as well as completing a qualitative interview on their experiences with both microprocessor knee devices.

iii) Measurements and data collection The same questionnaires, consisting of three valid instruments (PEQ questions, PLUS-M and ABC), will be used and filled in at three separate points in time. Background information will be collected at baseline only, usability questionnaire at visit 2 only and qualitative interview at visit 3 only. An activity report will be generated from the investigational device at visit 2 and an activity report from subjects prescribed device at visit 3, if applicable.

Inclusion Criteria:

• 45Kg< body weight < 136Kg
• Cognitive ability to understand all instructions and questionnaires in the study;
• Unilateral TF/KD amputees that are regular prosthesis users for at least 3 months
• Current MPK users (passive MPKs only)
• Age ≥ 18 years
• Willing and able to participate in the study and follow the protocol
• Moderate to high active users (PLUS M T-score>4021)

Exclusion Criteria:

• Users with stump pain
• Users with socket problems
• Pregnant Users
• Users using Power Knee, Kenevo or mechanical knees as their prescribed prosthesis
• Alignment that cannot be matched with the Rheo Knee 4 setup, as described in Instructions for use.
• Osseointegration

adverse event data were collected over the time of participation starting with the first visit until the third visit (6 weeks for each participant)

Prosthetic use time was not monitored or controlled for during the adaptation time period, the actual time each subject used the investigational device is therefore unknown.

The sample of the trial represents only a small portion of the whole population with above knee amputation.