If it is no longer possible to preserve a short residual portion of the lower leg, the knee disarticulation amputation (through-the-knee-amputation) is executed. Only modular prostheses are used in the fitting of knee disarticulations because of the structural, practical, and cosmetic specifications.The residual limb may be fully filled after knee disarticulation, unlike a transfemoral amputation. Since femoral condyles move body weight to the prosthesis socket, there is no need for a tuberous seat. A rotational-stable connexion to the prosthetic socket is provided by the bulky form of the condylar residual limb. Within, a soft socket of thermoplastic PE foam is anatomically shaped and creates a conical appearance outside by compensating for the undercuts. This makes for easy donning of the prosthesis during sitting.

Since the adductors have not been transected, the residual limb musculature remains balanced, while the long laver arm allows for strong prosthesis control. There are benefits for both geriatric and athletic patients as opposed to the features of a transfemoral amputation. Only special knee joint construction may be employed because of the length of the residual limb. The rotation centre of these polycentric joints is located close to the anatomical rotation axis.