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Design Innovation

Pneumatic Osteoarthritis Knee Brace

[+] Author and Article Information
Dimitrije Stamenović1

Department of Biomedical Engineering, Boston University, 44 Cummington Street, Boston, MA 02215dimitrij@bu.edu

Miloš Kojić

Department of Environmental Health, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115; Center for Scientific Research of the Serbian Academy of Sciences and Arts, University of Kragujevac, Jovana Cvijića bb, 34000 Kragujevac, Serbia

Boban Stojanović

Center for Scientific Research of the Serbian Academy of Sciences and Arts, University of Kragujevac, Jovana Cvijića bb, 34000 Kragujevac, Serbia; Faculty of Science, University of Kragujevac, Radoja Domanovića 12, 34000 Kragujevac, Serbia

David Hunter

Division of Research, New England Baptist Hospital, 125 Parker Hill Avenue, Boston, MA 02120; Boston University School of Medicine, 715 Albany Street, Suite 501, Boston, MA 02118

1

Corresponding author.

J Biomech Eng 131(4), 045001 (Jan 30, 2009) (6 pages) doi:10.1115/1.3072890 History: Received April 07, 2008; Revised October 21, 2008; Published January 30, 2009

Knee osteoarthritis is a chronic disease that necessitates long term therapeutic intervention. Biomechanical studies have demonstrated an improvement in the external adduction moment with application of a valgus knee brace. Despite being both efficacious and safe, due to their rigid frame and bulkiness, current designs of knee braces create discomfort and difficulties to patients during prolonged periods of application. Here we propose a novel design of a light osteoarthritis knee brace, which is made of soft conforming materials. Our design relies on a pneumatic leverage system, which, when pressurized, reduces the excessive loads predominantly affecting the medial compartment of the knee and eventually reverses the malalignment. Using a finite-element analysis, we show that with a moderate level of applied pressure, this pneumatic brace can, in theory, counterbalance a greater fraction of external adduction moment than the currently existing braces.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

A schematic depiction of the front view of the leg with a three-point-bending system of forces (arrows) applied by a brace to the knee. One of the forces acts at the lateral side and two at the medial side of the knee.

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Figure 2

The basic design of the pneumatic knee brace, which is comprised of a sock (light gray), a strap (medium gray), and three bladders (dark gray) attached to the strap. By inflating the bladders a three-point-bending system of forces is generated.

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Figure 3

Lateral-anterior view (left) and medial-anterior view (right) of the finite-element model of a leg-brace assemblage totally constrained at top and bottom. Lateral and medial bladders are loaded by pressure (P). Heavy black lines indicate contours of the strap and the bladders.

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Figure 4

Left: inflating pressure (P) produces abduction moment (M) around the x-axis. Right: The moment is calculated as a crossproduct between the radius vectors (rPK and rCJ) and corresponding forces acting on the leg (Eq. 6), including the proximal medial bladder nodal force FPK, calculated as the sum of the surface integrals of pressure P over the bladder area (Eq. 5), and the brace-leg contact forces FCJ, calculated at all contact nodes as forces in fictive trusses.

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Figure 5

Unloading abduction moment (M) versus bladder pressure (P) relationships predicted by the finite-element model for different sets of parameter values; numbers 1–8 correspond to the cases 1–8 given in Table 1.

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Figure 6

Unloading moment of the brace (M) as a fraction of the excessive adduction moment (ΔM) for human female and male patients, for different levels of inflating bladder pressure (P). M corresponds to the curve No. 8 from Fig. 5. ΔM is calculated from the anatomical data from the literature: for females ΔM=11.65 N m, and for males ΔM=14.61 N m. In the case of female patients, the M can completely counterbalance ΔM within the given range of P.

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