Post Market Clinical Protocol - Xtremity Polymer Prosthetic Socket System

Inclusion Criteria: * Male or female ≥ 19 years old * Unilateral or bilateral transtibial amputation * Subject has been informed of the nature of the study, agrees to participate and comply with all follow-up visits and has signed the consent form. * Currently using a standard carbon fiber or high temperature thermoplastic prosthetic socket. * Residual limb is between 26-34 cm circumference with a liner (when measured 4cm proximal to distal end) * Subject is eligible for standard carbon fiber or high temperature thermoplastic prosthetic socket if necessary. * Must be able to ambulate at least 100 yards with or without an assistive device. * Must be able to don and doff a prosthesis independently. * Estimated life expectancy \> 1 year Exclusion Criteria: * Amputation \< 6 months prior to enrollment * Residual limb less than (\<) 26cm and greater than (\>) 34cm circumference at the distal end. * Body weight greater than (\>) 275lbs. * Syme's amputations or total limb length over 30cm * Some bulbous or irregular limb shapes * Build height and circumference limitations * Wounds or skin issues that preclude normal fit * Unusual alignment of the socket or foot * Alignment outside the capability of the Xtremity System. * Planned for any major surgery within 6 months of enrollment. * Subject is pregnant or breastfeeding * Subject is incarcerated. * Subject anticipates that the socket will frequently be subject to temperatures greater than 110 degrees F while in their possession. * Subject anticipates that the socket will frequently be subject to direct sunlight * Limb circumference at the mid-patella tendon exceeds the maximum circumference (see sizing chart in the instructions for use) * Subject is participating in another research study of a device, medication, which could, in the opinion of the investigator, affect the results of this study. * Subject has other medical, social or psychological problems that in the opinion of the investigator would preclude them from receiving this treatment and the procedures and or participating in evaluations pre and post-treatment.