An immediate fit adjustable prosthetic system is being investigated for children. The age range being recruited is from 3 years up to 18 years old. Phase I of this study will involve developing a final prototype by conducting in-lab testing on children with limb loss. Phase II will involve a two month home trial to further evaluate the comfort and usability of the socket. Outcome measures include a PEQ-based questionnaire, socket pressure measures and gait analysis.

Design Phase I is a testing session to obtain feedback on initial prototype designs for the immediate fit prostheses. This research will focus on PI observations and participant feedback through survey and comments during the in-person testing. There may be multiple appointments for participants during this time the device design is refined. In-lab testing only will occur. This information will influence the overall design of the final prosthesis.

PHASE I: For Phase I children with lower limb limb loss (below the knee or above the knee) age 3-12 are being recruited. Subjects should be able to ambulate with or without assistive devices. They will supply measurements and limb images prior to the appointment.

During the initial appointment, each participant will be consented and completed roughly 2-3 hours of device testing. The participant will be fit with an adjustable prosthetic by the PI. After ambulating in the lab, they will give feedback on the comfort, stability and ease of use of the prosthesis. Participants may be asked to return several times for future testing sessions once changes or alterations are made to the prosthesis design to see if these have been effective. The child and their parent will fill out a PEQ based questionnaire on their conventional prosthesis and the investigational device after fitting.

Phase II: We will be recruiting children ages 3-18 with lower limb loss to be with an adjustable prosthesis and wear it for a 2 month home trial. Children may be recruited at other locations such as the Children's Hospital of Philadelphia and Ai./duPont Nemours in Delaware. The child and their parent will fill out questionnaires on their current prosthesis as well as have pressure data and a gait analysis completed. Once they have worn the prosthesis for 2 months they will return and complete these same outcome measures.

Gait biomechanical analysis: This analysis will be conducted by having several reflective markers placed on the participant's lower body. The subject will then walk a minimum of 6 times along a 10meter walkway while being recorded by the motion analysis system. This will be conducted in both the adjustable and conventional prosthesis.

Internal pressure measurements of the socket using Fujifilm pressure paper will also be obtained. Five spots will be assessed by placing the paper on the participant's liner and then they will put on their socket and walk for 1 minute. This will be completed on both the test and conventional socket.

Inclusion Criteria:

• Four months post-amputation
• Subjects who have lost a limb due to any cause: trauma, congenital limb loss, dysvascular causes (peripheral vascular disease and diabetes), or malignancy will all be eligible for inclusion.
• Intact, protective sensation in their residual limbs.

Exclusion Criteria:

• open skin lesions
• excessive pain in the residual limb (phantom pain, residual limb pain, or neuroma)
• neurological disorders (e.g., stroke, severe polyneuropathy) causing weakness in the contralateral leg or marked gait impairment
• inability to follow instructions for trial