Do Transfemoral Prostheses with Powered Prosthetic Knee Flexion and Extension Improve Mobility? A Biomechanical Evaluation of the Ossur Power Knee

The anatomical knee is a complex, polycentric joint characterized by a large range of motion in the sagittal plane and limited mobility in the coronal and transverse planes (1). The sagittal plane motion is used for progression in stance phase, and limb clearance and advancement in swing (2). Limb prostheses are intended to restore

function and cosmesis in persons with limb loss. The complexity and function of prosthetic components have advanced significantly as technology has improved, but a state-of-the-art artificial limb is still a relatively poor substitute for an anatomical one. Microprocessor-controlled knees (MPKs) do not typically utilize motors to power

joint rotation, but they automatically adjust resistance or damping in the joint to improve swing- and/or stance- phase control as appropriate for the user during gait. The Ossur Power Knee (6-9), which was first introduced in 2006, is the only MPK that uses a motor to provide active power generation during walking and other activities

involving knee flexion and extension. Last year, Ossur released the 3rd generation of its Power Knee and appears to have addressed many of the previous shortcomings in terms of reduced weight, less noise, lower cost and longer battery life. Therefore, we believe that the newest version of the Power Knee warrants a fresh

evaluation since it is, in essence, substantially different in design and function from previous models. The purpose of this proposed investigation is to perform biomechanical evaluations of the new Ossur Power Knee during walking and other activities by transfemoral prosthesis users. Using a cross-over experimental

design, approximately 20 unilateral, transfemoral amputee subjects (10 men and 10 women) will be evaluated in the Jesse Brown VAMC Motion Analysis Research Laboratory (MARL) while wearing the Ossur Power Knee and Ossur Rheo XC, which is a passive MPK device. Furthermore, we believe that the Ossur Power Knee may

offer distinct advantages to female prosthesis users, so we intend to compare mobility between men and women to determine if differences exist on the basis of sex. The specific aims and hypotheses of this project are: Aim 1: To compare the effects of the Ossur Power Knee and Ossur Rheo XC on the gait of unilateral,

transfemoral prosthesis users during level walking. Kinematic and kinetic data will be collected as subjects walk in the MARL. We hypothesize that the active knee flexion and extension provided by the Ossur Power Knee will (1) improve walking performance, and (2) reduce metabolic energy cost during ambulation.

Aim 2: To compare the effects of the Ossur Power Knee and Ossur Rheo XC on stairs, slopes and during sit-to-stand/stand-to-sit activities of unilateral, transfemoral prosthesis users. Kinematic data will be collected as subjects perform these activities. We hypothesize that subjects will have improved

performance when using the Ossur Power Knee. Aim 3: To analyze and compare gender specific data between subjects using the Ossur Power Knee and the Ossur Rheo XC. We hypothesize that male and female subjects will demonstrate substantially different abilities to use the two knee components, indicating that gender specific components should

be further investigated and developed. Research focusing on the unique prosthetic needs of women Veterans is currently a special emphasis area of the VA RR&D Service. Subjects will also be administered questionnaires and provided at-home diaries to document their perceptions of comfort, exertion and stability while using the different prosthetic knee units. Increased understanding about

how the Ossur Power Knee affects the abilities of transfemoral prosthesis users will facilitate appropriate component selection by prosthetists and ultimately improve quality of life for prosthesis users.