C-Leg 3 and C-Leg 4 Study in Transfemoral Amputees

Inclusion Criteria: * Person is \>18 years old. * Person is a unilateral transfemoral or knee-disarticulation amputee with stabilized residual limb. * Person is a K2, K3 or K4 ambulator based on Medicare Functional Classification Level (MFCL). * Person is currently fitted with a prosthesis using a non-microprocessor controlled prosthetic knee for at least 6 months. * Person was never fitted with microprocessor controlled prosthetic knee joint. * Person is willing and able to independently provide informed consent. * Person is willing to comply with study procedures. * Person wears prosthesis daily and ≥ 8 hours/day. * Person is walking on average 1km/day. * Person is walking not slower than 3km/h (\~0.8m/s) (based on 10m walk test conducted during recruiting). * Person is walking on level ground in a step over step manner. Exclusion Criteria: * Person is under 18 years of age. * Person who weighs more than 136kg. * Person who weighs less than 50kg. * Person who is pregnant. * Person has a history of chronic skin breakdown on the residual limb. * Person has conditions that would prevent participation and pose increased risk (e.g. unstable cardiovascular conditions that preclude physical activity such as walking). * Person falls ≥ once a week due to the reasons that could not be corrected by the new prosthesis (for ex. problems with vestibular system). * Person is using under arm axillary crutches or walker. * Person in an emergency, life threatening situation. * Person is u…