Northwestern University Feinberg School of Medicine

Northwestern University Prosthetics-Orthotics Center

Optimization of Prosthetic Foot and Ankle Stiffness for Standing and Walking

Principal Investigator: Steven Gard, PhD

Co-Investigators: Matthew Major, PhD; Rebecca Stine, MS; Marc Applebaum, MD

Research Assistants/Graduate Students: Sarah Chang, PhD; Thomas Curran, MS

Clinical Faculty: Michael Cavanaugh, CPO

Funded by: Department of Veterans Affairs

Status: In Progress

Overview

College Park Venture prosthetic footPersons who walk with lower-limb prostheses are generally less efficient ambulators than able-bodied individuals (Waters et al., 1976) and their stability is compromised, attributable in part to deficiencies in the function of their prostheses (Gard & Fatone, 2004). Anatomical ankle joint stiffness in able-bodied persons adapts with walking speed (Hansen et al., 2004a) and for standing (Hansen & Wang, 2010). Fitting lower-limb amputees with prosthetic foot and ankle mechanisms that attempt to replicate corresponding anatomical functions is desirable (Hansen et al., 2004a,b, 2007, 2010). We previously demonstrated that prosthetic ankle joints improve walking performance in persons with transtibial (below-knee) amputation (Su et al., 2007, 2008, 2010). In that study, research subjects clearly preferred walking with the prosthetic ankle components, but several indicated that they felt unstable during standing (Su et al., 2010). Subsequent analyses of those data indicated that the addition of a compliant prosthetic ankle unit significantly reduced the radius of the ankle-foot roll-over shape (Gard et al., 2011), which can adversely affect standing stability and gait performance (Gard & Childress, 2001; Klodd et al., 2010a,b).

The purpose of this investigation is to determine how systematically varying the prosthetic foot keel stiffness and prosthetic ankle joint stiffness affects standing and walking in persons with unilateral, transtibial amputations. The specific aims for this study are:

  1. To determine how different combinations of prosthetic foot and ankle stiffness affect gait biomechanics of unilateral, transtibial prosthesis users. Kinematic, kinetic and energy expenditure data will be collected as subjects walk at different speeds and with different combinations of prosthetic foot and ankle stiffness.
  2. To determine how different combinations of prosthetic foot and ankle stiffness affect standing stability of unilateral, transtibial prosthesis users. Standing balance of subjects will be evaluated using a series of tests that measure balance and recovery stability as balance is perturbed.

Subjects will also be administered questionnaires to document their perceptions of comfort, exertion and stability while using the different prosthetic foot-ankle configurations.

Compliant foot-ankle mechanisms that allow for a normal range of ankle joint motion during walking are expected to increase gait performance, but decrease standing stability. Conversely, a rigid foot-ankle combination will likely maximize standing stability, but decrease gait performance. Determination of an optimal prosthetic foot and ankle stiffness combination will require a compromise between the apparent disparate objectives for these two activities.

Increased understanding about how different prosthetic foot-ankle stiffness combinations affect standing and walking abilities will facilitate appropriate component selection by prosthetists, encourage development of prosthetic foot-ankle mechanisms with adaptable stiffness, and ultimately improve quality of life for prosthesis users.

References

Gard, S.A. and Childress, D.S. (2001). What Determines the Vertical Displacement of the Body During Normal Walking? Journal of Prosthetics and Orthotics, 13(3), 64-67.

Gard, S.A. and Fatone, S. (2004) Biomechanics of Lower Limb Function and Gait. Report of a Consensus Conference on the Orthotic Management of Stroke Patients, ISPO (International Society for Prosthetics and Orthotics), Copenhagen, Denmark, 55-61.

Gard, S.A., Su, P.F., Lipschutz, R.D. and Hansen, A.H. (2011). Effect of Prosthetic Ankle Units on Roll-Over Shape Characteristics During Walking in Persons with Bilateral Transtibial Amputations. Journal of Rehabilitation Research & Development, 48(9), 1037-1047.

Hansen, A.H., Childress, D.S., Miff, S.C., Gard, S.A. and Mesplay, K.P. (2004a). The Human Ankle During Walking: Implications for Design of Biomimetic Ankle Prostheses and Orthoses. Journal of Biomechanics, 37(10), 1467-1474.

Hansen, A.H., Childress, D.S. and Knox, E.H. (2004b). Roll-over Shapes of Human Locomotor Systems: Effects of Walking Speed. Clinical Biomechanics, 19(4), 407-414.

Hansen, A.H., Gard, S.A. and Childress, D.S. (2007). Quasi-Stiffness of the Ankle During Able-Bodied Walking at Different Speeds: Implications for Design of Prostheses. Foot and Ankle Motion Analysis: Clinical Treatment and Technology, CRC Press, Boca Raton, FL, pp. 599-612.

Hansen, A.H., Miff, S.C., Childress, D.S., Gard, S.A., and Meier, M.R. (2010). Net External Energy of the Biologic and Prosthetic Ankle during Gait Initiation. Gait & Posture, 31, 13-17.

Hansen, AH & Wang, CC. (2010). Effective rocker shapes used by able-bodied persons for walking and fore-aft swaying: implications for design of ankle-foot prostheses. Gait & Posture. 32(2):181-4.

Klodd E, Hansen A, Fatone S, Edwards M. (2010a). Effects of prosthetic foot forefoot flexibility on oxygen cost and subjective preference rankings of unilateral transtibial prosthesis users Journal of Rehabilitation Research & Development, 47(6):543-52.

Klodd E, Hansen A, Fatone S, Edwards M. (2010b). Effects of prosthetic foot forefoot flexibility on gait of unilateral transtibial prosthesis users. Journal of Rehabilitation Research & Development, 47(9):899-910.

Su, P., Gard, S.A., Lipschutz, R.D. and Kuiken, T.A. (2007). Gait Characteristics of Persons with Bilateral Transtibial Amputations. Journal of Rehabilitation Research & Development, 44(4), 491-502.

Su, P., Gard, S.A., Lipschutz, R.D. and Kuiken, T.A. (2008). Differences in Gait Characteristics Between Persons with Bilateral Transtibial Amputations, Due to Peripheral Vascular Disease and Trauma, and Able-bodied Ambulators. Archives of Physical Medicine and Rehabilitation, 89(7), 1386-1394.

Su, P., Gard, S.A., Lipschutz, R.D. and Kuiken, T.A. (2010). The Effects of Increased Prosthetic Ankle Motions on the Gait of Persons with Bilateral Transtibial Amputations. American Journal of Physical Medicine and Rehabilitation, 89(1), 34–47.

Waters, R.L., Perry, J., Antonelli, D., and Hislop, H. (1976). Energy Cost of Walking of Amputees: The Influence of Level of Amputation. The Journal of Bone and Joint Surgery, 58-A(1), 42-46. 

Related Publications

Curran, Thomas (2016) The Effects of Foot-Ankle Components on the Mechanical Properties of Dynamic Response Prosthetic Feet. Master of Science Thesis, Biomedical Engineering, Northwestern University.