Northwestern University Feinberg School of Medicine

Northwestern University Prosthetics-Orthotics Center

Effect of Prosthesis Stiffness on Impact Forces During In Vivo Step Loads and Gait

Principal Investigator: Steven A. Gard, PhD

Student Investigator: Erin Boutwell, MS

Funded by: National Institute on Disability and Rehabilitation Research (NIDRR); Orthotic and Prosthetic Education and Research Foundation (OPERF); and the Jesse Brown VA Medical Center (Chicago, IL).

Status: Completed

Purpose

Shock absorption is an inherent function of the intact lower limbs during walking that is substantially reduced in people who have lost some or all of their lower limbs. These individuals are often acutely aware of the jarring impact forces that can occur when they step with their prosthesis. Prosthetic components with reduced stiffness are commonly prescribed to change the mechanical response of the prosthesis to an applied load, with the intent of providing shock absorption and reducing forces transmitted to the residual limb during gait. However, contrary to expectations, these components do not generally decrease ground reaction force (GRF) loading peaks, an indicator of shock absorption during walking. This finding may suggest that either these reduced-stiffness components do not work in the intended fashion, or else subjects are implementing compensatory strategies to exert some control over total limb stiffness.

Reduced stiffness component.To investigate these possibilities, this study will evaluate reduced-stiffness components in two different loading conditions: an impact "drop" test (similar to stepping off a curb) and a walking study. No change in the GRF peaks is expected during gait, as previous literature has indicated that prosthesis users adapt to analogous changes in prosthetic stiffness. In contrast, decreased force peaks are anticipated in the impact testing, as the controlled, rapid drop will minimize adaptation by the user and permit the reduced-stiffness component to function as intended. Additionally, the level of stiffness that provides optimal shock absorption is currently unknown. Therefore, the proposed study involves a systematic variation of the internal spring of a shock-absorbing pylon (i.e., the reduced-stiffness component) over a range of stiffness values. The results of these experiments will provide information on the effect of prosthesis stiffness on impact forces under varying loading and stiffness conditions, yielding information for the future design and prescription of reduced-stiffness components.

Related Publications

Boutwell E and Gard S. (2013) "Effect of Prosthetic Stiffness on Impact Forces during Walking and Sudden Limb Loading." (Poster). Annual Meeting of the Gait and Clinical Movement Analysis Society (GCMAS). May 14-17. Cincinnati, OH.

Boutwell E and Gard S. (2013) "Investigation of In Vivo Prosthesis/Residual Limb Stiffness Using a Novel Impact Test Apparatus." International Society for Prosthetics and Orthotics (ISPO) 14th World Congress. February 4-7. Hyderabad, India.

Boutwell E, Stine R, Gard S. (2014) “A Novel in vivo Impact Device for Evaluation of Sudden Limb Loading Response.” Medical Engineering & Physics:doi:10.1016/j.medengphy.2014.10.008.

Boutwell E. (2014) Effect of Prosthesis Stiffness on Impact Force during In Vivo Step Loads and Gait. Midwest Chapter of the American Academy of Orthotists and Prosthetists, One Day Fall Symposium, November 15, Hickory Hills, IL.

Boutwell E, Stine R, Gard S. (2015) Influence of longitudinal prosthetic stiffness modifications on ground reaction forces during transtibial gait. Annual meeting and Scientific Symposium of the American Academy of Orthotists and Prosthetists, February 18-21, New Orleans, Louisiana.

Boutwell E, Stine R, Gard S. (2015) Influence of longitudinal stiffness modification on impact forces within the transtibial prosthesis. Annual meeting and Scientific Symposium of the American Academy of Orthotists and Prosthetists, February 18-21, New Orleans, LA.

Boutwell E, Stine R, Gard S. (2015) The effect of prosthetic stiffness on shock absorption during transtibial gait. Annual meeting of the Gait and Clinical Movement Analysis Society, March 18-21, Portland, OR.

Boutwell E, Stine R, Gard S. (2015) Effect of longitudinal prosthesis stiffness on force transmission during transtibial amputee gait. 15th World Congress of the International Society of Prosthetics and Orthotics, June 22-25, Lyon, France.

Boutwell E, Stine R, Gard S. (2015) Effect of longitudinal prosthesis stiffness on force transmission during in vivo impact loading. 15th World Congress of the International Society of Prosthetics and Orthotics, June 22-25, Lyon, France.