Northwestern University Feinberg School of Medicine

Northwestern University Prosthetics-Orthotics Center

Examinations of Balance and Balance Efficiency in Persons with Transfemoral Amputation

Principal Investigator: Steven A. Gard, PhD

Co-Investigators: Brian L. Ruhe, MS, and Rebecca L. Stine, MS

Funded by: National Institute on Disability and Rehabilitation Research (NIDRR)

Status: Completed

Introduction

The purpose of this investigation is to determine the underlying biomechanical factors contributing to static balance efficiency in persons with lower limb amputations. Unlike able-bodied persons who maintain an upright posture through foot, ankle, and sometimes knee kinematics, persons with lower limb amputation rely on the mechanical properties of their prosthesis, prosthetic alignment, and their intact hip and lumbar spine to remain balanced on all types of surfaces. As a result, the mechanical properties and alignment of prosthetic feet/ankles have a large impact on the ability of persons with lower limb amputation to efficiently balance on sloped surfaces. Passively compliant prosthetic foot/ankle devices improve the ability of persons with lower limb amputation to negotiate surface slopes by conforming to the surface through joint articulations. As these articulations occur under load, more of the prosthetic foot's surface area is in contact with the ground. This increases the base of support (BoS), however, articulations of these passive compliant feet create forces to return the foot/ankle to its neutral position. These forces must be managed by the prosthesis user, which affects overall standing balance efficiency. Prosthetic alignment is the positioning of the prosthetic foot/ankle and knee in three dimensional space under a prosthetic socket. It is believed that optimal prosthetic alignment decreases loads on the residual limb and improves functional performance of the human/mechanical system. Typically, alignment of a prosthesis is performed in a clinic on a level surface. A dynamic iterative process results in a prosthetic alignment that is a compromise between standing and walking on level surfaces, but there is a lack of data to understand how this alignment procedure affects the overall standing balance efficiency of persons with lower limb amputation on sloped surfaces. This goals of this study are to examine how compliant and non-compliant prosthetic feet/ankles and prosthetic foot/ankle alignment affect balance efficiency on level and sloped surfaces in persons with transfemoral amputations.

Specific Objectives

The specific aims of this project are: (1) to determine how sloped surfaces affect the kinematics, kinetics, electromyography (EMG), and metabolic energy expenditures of able-bodied persons; (2) to determine how sloped surfaces and prosthetic foot compliance affect the kinematics, kinetics, EMG, and metabolic energy expenditures of persons with unilateral transfemoral amputation where the prosthetic foot/ankle is 'neutrally' aligned in the clinic for everyday use; (3) to determine how sloped surfaces and prosthetic foot compliance affect the kinematics, kinetics, EMG, and metabolic energy expenditures of persons with unilateral transfemoral amputation where the prosthetic foot/ankle is aligned specifically for each sloped surface.

Preliminary ResultsModel of different body postures standing on slopes

Data were collected on a person with bilateral amputations where prosthetic foot/ankle alignment changes of a stiff prosthetic foot/ankle were implemented for different slope surfaces. Large angular changes in the hip (~25° increase in hip flexion) and trunk (~40° increase in trunk flexion) were employed to maintain balance on a +7.5° sloped surface with standard clinical alignment. When the foot/ankle was dorsiflexed approximately 7.5°, the hip and trunk flexion angles returned to values similar to standing on a level surface with standard clinical alignment (SCA). EMG data showed increases in the medial hamstrings and erector spinae when standing on inclined sloped surfaces with standard clinical alignment. With the baseline value set as standing on a level surface with SCA, the metabolic energy data shows increases of 54% when standing on the +7.5° surface with SCA, but only increased 6.1% with adapted alignment. (See Model of different body postures standing on slopes)

Clinical Implications

Preliminary data suggest that adaptable alignment can have positive affects on standing balance efficiency. Through simple changes in sagittal plane angular prosthetic foot/ankle position, more erect postures, decreases in muscular demands and metabolic energy consumption can be realized. The results of this study will provide a foundation for the design and development of prosthetic foot/ankle devices that can adapt to various terrains. The adaptable prosthetic foot/ankle has the potential to reduce kinematic compensations, ultimately reducing energy consumption. The reduction of energy consumption will allow users to increase functional activities to improve their daily lives.

Publications

Ruhe, B.L. Examinations of Balance and Balance Efficiency in Persons with TransFemoral Amputation: Preliminary Data. Midwest Chapter Meeting of the American Academy of Orthotists and Prosthetists, Joliet, IL, June 27-28, 2008.

Ruhe, B.L. and Gard, S.A. Effect of prosthetic foot/ankle alignment on balance efficiency while standing on sloped surfaces in persons with transfemoral amputations. Annual Meeting and Scientific Symposium of the American Academy of Orthotists and Prosthetists, Atlanta, GA, March 4-7, 2009. 

Ruhe, Brian L. (2009). “Investigations of Standing Balance Efficiency on Sloped Surfaces in Persons with Transfemoral Amputation", Doctoral Dissertation, Biomedical Engineering, Northwestern University.

Ruhe B, Hansen A, Gard S. Investigation of the Effect of Prosthetic Foot/Ankle Properties on Balance Efficiency while Standing on Inclined, Declined, and Level Surfaces. Paper presented at: 13th ISPO World Congress; May 10-15, 2010; Leipzig, Germany.