June 28, 2009 -- Brian L. Ruhe successfully defended his doctoral dissertation in Biomedical Engineering from Northwestern University.  His dissertation was entitled “Investigations of Standing Balance Efficiency on Sloped Surfaces in Persons with Transfemoral Amputation,” and investigated the effects of stiffness and alignment properties of prosthetic foot/ankle devices during quiet standing on sloped surfaces.  The prosthetic foot/ankle stiffness and alignment are normally set by a prosthetist in a clinic on a level surface.  Most prosthetic foot/ankle devices cannot dynamically change these properties; therefore, persons with amputation use proximal joint compensations to maintain balance.  It was hypothesized that: (1) able-bodied persons adapt to sloped surfaces using their foot/ankle systems with no increase in oxygen consumption; (2) decreasing prosthetic foot/ankle stiffness (without changing alignment) will decrease proximal joint compensations and reduce oxygen consumption of prostheses users; and (3) using adapted prosthetic foot/ankle alignment on sloped surfaces produce oxygen consumption, joint kinematics, and kinetic data that are similar to standing on level surfaces.
 
Ten able-bodied persons quietly standing on sloped surfaces were studied to quantify their energy consumption, kinematic, and kinetic adaptations.  Oxygen consumption was not significantly altered (p=0.098).  Able-boded persons’ proximal body segment kinematics (p=0.334) and anterior/posterior center of pressure location (p=0.164) did not change significantly while standing on sloped surfaces.  These results suggest that the able-bodied foot/ankle realigns its sagittal plane orientation to match the surface slope.

Ten persons with unilateral transfemoral amputation were studied to quantify their energy consumption, kinematic, and kinetic compensations.  These persons quietly stood on sloped surfaces with three prosthetic foot/ankle stiffness values and two prosthetic foot/ankle alignments.  Prosthetic foot/ankle stiffness did not have a significant effect on oxygen consumption (p=0.220); however, oxygen consumption was significantly increased for non-level standing trials (p=0.044).  The adaptable alignment prosthetic foot/ankle condition decreased oxygen consumption on inclined surfaces compared to standard alignment (p=0.034).  Realignment of the prosthetic foot/ankle device reduced sagittal plane hip compensations (p=0.005) and improved posture.
 
The results from these studies suggest current approaches using a single stiffness and alignment for prosthetic foot/ankle devices were not energy efficient for quiet standing on non-level surfaces.  It is believed that prosthetic foot/ankle devices that can change stiffness and alignment dynamically for the task performed would have a positive impact on persons with lower limb amputation.

May 6, 2009 -- Charles C. Wang has successfully defended his Master’s thesis in Biomedical Engineering from Northwestern University. His thesis, entitled “Effective Rocker Shapes and Ankle Kinematics of Able-Bodied Persons During Walking, Swaying, and Standing,” investigated the response of the able-bodied ankle-foot system while walking, swaying, and standing on rocker shoes of different radii. The roll-over shape (ROS) is the effective rocker shape that the lower limb system conforms to during stance phase, between heel contact and opposite heel contact. Recent studies have found that the ROS remains an invariant circular shape despite changes in walking speed, weight carriage, and shoe heel height. However, it is unclear what the shapes look like for swaying and standing, other important activities of daily living. A better understanding of these effective shapes could be used to develop improved prostheses for these tasks, perhaps improving balance and balance confidence in lower limb prosthesis users and potentially reducing the occurrence of falling in this population. We measured the effective rocker shapes and ankle kinematics of eleven able-bodied subjects during walking, swaying, and standing on regular and rocker shoes. We hypothesized that the swaying and standing effective shapes would be flatter than that of walking, contributing to inherent stability during these actions. We also hypothesized that the ankle would adapt to preserve an invariant ROS radius while walking on different rocker shoes. Our results strongly supported these hypotheses. We also hypothesized that the ankle would help to maintain a flatter effective shape during swaying and standing, regardless of rocker shoes. We found that, although ankle kinematics changed, the effective shape curvature during swaying also was significantly changed by the different rocker shoes. Future work is needed to discover whether able-bodied persons target other features for balance on rocker shoes.

May 5, 2009 -- Erin Boutwell successfully defended her Master’s thesis in Biomedical Engineering from Northwestern University. Her thesis was entitled “Study of Residual Limb-Prosthetic Socket Compliance in Transtibial Amputees,” and investigated the effect of gel liner thickness on peak pressure and relative motion between the residual limb and the prosthetic socket. Previous studies have identified both pressure and motion as sources of discomfort in transtibial amputees, but the effect of gel liner thickness on these variables has yet to be quantified. Two different thicknesses of gel liners were tested in unilateral transtibial amputee subjects. During a side-to-side loading experiment, the displacement of the socket with respect to the thigh was measured and used to estimate the compliance of each of the two liners. Subjects were also asked to walk at varying speeds; ground reaction forces, joint motion, and walking speed were analyzed during gait. It was hypothesized that the thicker gel liner would introduce more compliance into the limb-socket interface compared to the thinner liner, and that the added compliance would contribute to a more uniform distribution of peak pressures within the socket and a faster self-selected walking speed. The results of this study showed that the thicker gel liner provided slightly more compliance at the limb-socket interface when the prosthetic limb was loaded, and that this compliance contributed to a decrease in peak pressure over the fibular head. However, most gait variables were unchanged with the introduction of the thicker liner. Also, many subjects indicated that the thicker liner was more comfortable, particularly subjects with less soft tissue on their residual limbs. Therefore, although many gait parameters remained unchanged between liners, prescribing a thicker gel liner may yield improvements in comfort to some users with a transtibial amputation – particularly those with less anatomical soft tissue to redistribute impact forces.

December 4, 2008 -- Elizabeth Klodd has successfully defended her Master's thesis in Biomedical Engineering from Northwestern University. The thesis was entitled "The Effects of Prosthetic Foot Roll-over Shape Radius on Gait of Unilateral Transtibial Prosthesis Users," and investigated whether prosthetic foot roll-over shape radius affected motion or energy expenditure in persons ambulating with a unilateral transtibial prosthesis.  A brief summary of this research is posted below:

The Shape&Roll Prosthetic Foot was used to determine the effects of different roll-over shape radii on gait and oxygen cost of unilateral transtibial prosthesis users.  Ten persons with unilateral transtibial amputation walked overground with each of five experimental prosthetic feet having roll-over shape radii designed to be approximately 15%, 25%, 35%, 45% and 55% of their leg length. In general, subjects had increasing ankle flexion moments as roll-over shape radius increased. This increase was likely due to the greater moment arm about the ankle joint when subjects walked with feet having larger roll-over shape radii.  Greater first peaks of the vertical ground reaction force on the sound side were found when subjects used the foot with the smallest roll-over shape radius.  In all of the subjects, there was an increase in peak prosthetic ankle dorsiflexion with decreasing roll-over shape radius, and an increase in the effective foot length ratio with increasing radius.  No differences were found in cadence, step length, or vertical displacement of the body center of mass.  For nine subjects walking on a treadmill for seven minutes, no significant difference was found in oxygen cost between the different feet.  While some parameters of gait were changed by roll-over shape radius, these changes were not significant enough to change the prosthesis user's oxygen cost.  Further research is needed to determine the effects of roll-over shape radius on oxygen cost during overground walking.

April 1, 2008 -- William Brett Johnson has successfully defended his Master's thesis in Biomedical Engineering from Northwestern University. His thesis was entitled “Preliminary Quantitative Gait Analysis of Reciprocating Gait Orthosis (RGO) Users,” and sought to identify potential mechanical causes for the high energy requirements of ambulating with a RGO. This study found that during ambulation with a RGO, a large portion of weight was borne through the arms, which could lead to high energy expenditure. It was hypothesized that the motion and orientation of the trunk encouraged weight bearing through the arms. The results of this study also showed hip extension at the beginning of swing. This motion was counterproductive to the forward advancement of the swing leg and could have been caused in part by the orientation of the subjects’ trunks and compliance within the reciprocal link. Furthermore, small net flexion torques calculated at the hip during swing suggested that the reciprocal link contributed little to the forward advancement of the swing leg. Poor conservation of mechanical energy at the trunk was also observed, which could also contribute to increased energy expenditure. Deceleration of the body center of mass during the later half of swing was suggested as a possible cause for poor energy conservation.

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Master of Science | Doctor of Philosophy