Componentry for Lower Extremity Prostheses

Prosthetic components for both transtibial and transfemoral amputations are available for patients of every level of ambulation. Most current suspension systems, knees, foot/ankle assemblies, and shock absorbers use endoskeletal construction that emphasizes total contact and weight distribution between bony structures and soft tissues. Different components offer varying benefits to energy expenditure, activity level, balance, and proprioception. Less dynamic ambulators may use fixed-cadence knees and non–dynamic response feet; higher functioning walkers benefit from dynamic response feet and variable-cadence knees. In addition, specific considerations must be kept in mind when fitting a patient with peripheral vascular disease or diabetes. With the advent of new materials, designs, and technologic advances, the field of lower extremity prostheses has expanded dramatically. Prosthetic components have a significant impact on functional performance. The choice of components varies depending on a patient’s functional level; this is especially true regarding the specific needs of patients with amputation secondary to peripheral vascular disease or diabetes. These critical needs include protecting the sound limb, considering abnormal and excessive forces on the residual limb, and factoring in the metabolic costs of ambulation. Understanding lower extremity prosthetic componentry and how application varies is important. Application is based on the level of amputation in the context of the expected functional level of the user. A classification scale can assist in determining appropriate components corresponding to each functional level. Etiology and Incidence of Amputation In the United States, lower extremity amputation is not uncommon; approximately 110,000 people undergo some level of lower limb amputation surgery each year.1 Of those amputations, most are a result of disease (70%), followed by trauma (22%) and congenital etiology and tumor (4% each).1 Approximately 54,000 amputations secondary to diabetes are performed annually in the United States.2 Further, more than half of all lower limb amputations occur in individuals with diabetes; below-knee or distal amputations are more common in this population than transfemoral amputations. Between 9% and 20% of patients with diabetes who have had an amputation undergo a second amputation ipsilaterally or a new amputation contralaterally within 12 months of the first amputation.2 Thirty percent Karen Friel, PT, DHS Dr. Friel is Associate Professor and Chair, Department of Physical Therapy, New York Institute of Technology, Old