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Research Papers

Determination of Optimal Counter-Mass Location in Active Prostheses for Transfemoral Amputees to Replicate Sound Limb Swing

[+] Author and Article Information
M. Telwak

Department of Biomedical Engineering,
Marquette University,
1637 West Wisconsin Avenue,
Milwaukee, WI 53233
e-mail: MTelwak@gmail.com

P. Voglewede

Department of Mechanical Engineering,
Marquette University,
1637 West Wisconsin Avenue,
Milwaukee, WI 53233
e-mail: Philip.Voglewede@Marquette.edu

M. B. Silver-Thorn

Department of Biomedical
and Mechanical Engineering,
Marquette University,
1637 West Wisconsin Avenue,
Milwaukee, WI 53233
e-mail: Barbara.Silver-Thorn@Marquette.edu

Manuscript received August 22, 2013; final manuscript received March 8, 2014; published online August 19, 2014. Assoc. Editor: Rita M. Patterson.

J. Med. Devices 8(4), 041003 (Aug 19, 2014) (7 pages) Paper No: MED-13-1199; doi: 10.1115/1.4027231 History: Received August 22, 2013; Revised March 08, 2014

Recent advances in lower limb prostheses have involved the design of active, powered prosthetic knee and ankle-foot components capable of generating knee and ankle torques similar to that of normal gait. The associated componentry results in increased mass of the respective prosthesis, which affects the swing phase of gait. The goal of this study was to develop a computer model of the transfemoral residual limb and prosthesis, inclusive of an active ankle-foot, and investigate counter-mass magnitude(s) and location(s) via model optimization that might improve lower limb kinematic symmetry between the residual/prosthetic limb (approximated by the computer model) and the sound limb (approximated by able-bodied motion data) during swing phase. Single- (thigh only, shank only) and multisegment (both thigh and shank) optimization of counter-mass magnitudes and locations indicated that a 2.0 kg counter-mass added 8 cm distal and 10 cm posterior to the distal end of the knee unit within the shank segment approximated knee kinematics of the sound limb. This counter-mass location, however, reduced hip flexion during swing phase. While such a counter-mass location and magnitude demonstrated theoretical potential, the location is not clinically realistic; mass can only be practically added within the prosthesis, distal to the residual limb. Clinically, realistic counter-masses must also keep the total prosthetic mass to less than 5 kg; greater mass may require supplemental prosthetic suspension, may increase energy expenditure during ambulation and may increase the likelihood of fatigue, even with active prosthetic components. The ability to simulate the kinematic effects of active prosthetic components, inclusive of varying placement of battery and signal conditioning units, may advance the design of active prostheses that will minimize kinematic asymmetry and result in greater patient acceptance.

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References

Figures

Grahic Jump Location
Fig. 1

(a) Physical model of the TF amputee residual/prosthetic limb, respective marker locations (filled circles) for motion analysis and approximate locations of the thigh and shank segment COM (white diamond). (b) Close-up of the physical model suspension, pseudoresidual limb with uniaxial hip joint and prosthetic socket.

Grahic Jump Location
Fig. 2

Double pendulum model of the lower limb including hip, knee, and ankle joints. Thigh (ψT) and shank (ψS) angles were defined with respect to the horizontal; hip (θH) motion was defined relative to vertical. The knee (θK) angle was the relative angle between the thigh and shank segments. The ankle angle, between the shank and foot segments, was fixed at 90 deg.

Grahic Jump Location
Fig. 6

Locations of the optimized thigh only (white square), shank only (filled cross), and thigh/shank counter-masses (open circle) presented on the TF amputee physical model

Grahic Jump Location
Fig. 5

Sagittal plane hip (left) and knee (right) joint motion during swing phase for the TF amputee computer and physical models. Positive angles indicate flexion; negative angles indicate extension.

Grahic Jump Location
Fig. 4

Potential counter-mass locations at the distal thigh and proximal shank segments, defined relative to the hip joint and distal end of the knee unit. Location fields included both proximal/distal (± local Y, along the respective segment length) and anterior/posterior (± local X) manipulations within the solution space (gray regions, ±0.10 m).

Grahic Jump Location
Fig. 3

Piecewise linear approximation of normalized TF amputee residual limb hip torque [30]. The vertical line represents the transition from preswing (late stance) to initial swing.

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