Porous composite prosthetic pylon for integration with skin and bone

Abstract

This article presents results of the further development and testing of the "skin and bone integrated pylon" (SBIP-1) for percutaneous (through skin) connection of the residual bone with an external limb prosthesis. We investigated a composite structure (called the SBIP-2) made of titanium particles and fine wires using mathematical modeling and mechanical testing. Results showed that the strength of the pylon was comparable with that of anatomical bone. In vitro and in vivo animal studies on 30 rats showed that the reinforcement of the composite pylon did not compromise its previously shown capacity for inviting skin and bone cell ingrowth through the device. These findings provide evidence for the safe and reliable long-term percutaneous transfer of vital and therapeutic substances, signals, and necessary forces and moments from a prosthetic device to the body.

Figure 1

Minimal force needed for detachment of skin cell from pylon. F₁ = “cell-to-wall” detachment (prior design), F₂ = “cell-to-wall-to-inner cell” detachment (current design).

Figure 2

Cross section of porous pylon with enforcing wires. Pitkin M, Raykhtsaum G, inventors. Skin integrated device. United States patent US 20070071788. 2005 (in process).

Figure 3

Estimate of moment M(α) relative to skin-pylon zone, where α is angle of dorsiflexion. D = lever arm of force F relative to point of skin-pylon connection, L = length of exposed part of pylon.

Figure 4

Bend test setup. Instron tensile machine (Model 1123; Instron, Norwood, Massachusetts).

Figure 5

Geometry used to model mechanical behavior of composite rods. r = radius, w = width, z = height.

Figure 6

Calculated variation of stiffness with porosity for three-wire geometry. Pitkin M, Raykhtsaum G, inventors. Skin integrated device. United States patent US 20070071788. 2005 (in process).

Figure 7

Calculated strength of three-wire composite structure compared with bone strength. Pitkin M, Raykhtsaum G, inventors. Skin integrated device. United States patent US 20070071788. 2005 (in process). f = fraction of wire.

Figure 8

Implanted composite porous titanium pylon (skin and bone integrated pylon 2) on day 28 after operation.

Figure 9

(a) Typical load-displacement curves for composite samples without enforcing wires and with 2 and 3 wires sintered at different temperatures. (b) Bend strength of samples with no reinforcing wires and with 2 and 3 wires sintered at 2,400 °F, 2,500 °F, and 2,600 °F. Pitkin M, Raykhtsaum G, inventors. Skin integrated device. United States patent US 20070071788. 2005 (in process).

Figure 10

Day 14 after pylon implantation. Skin on outside border with pylon in (a) experimental group (Hematoxylin-eosin staining ×100): 1 = hair follicle, 2 = oil gland, 3 = epidermis on border with pylon, 4 = neutrophils; (b) control group (Hematoxylin-eosin staining ×100): 1 = epidermis, 2 = derma, 3 = capillaries, 4 = neutrophil infiltration; and (c) experimental group (Van Gizon staining ×200): 1 = lymphocytes, 2 = hair. (d) Muscular tissue in experimental group (Van Gizon staining ×200): 1 = muscular tissue, 2 = blood vessel, 3 = neutrophil infiltration.

Figure 11

Day 28 after pylon implantation. (a) Muscular and connective tissues in experimental group (Van Gizon staining ×100): 1 = capillaries, 2 = neutrophils, 3 = connective tissue on border with pylon, 4 = muscular tissue. (b) Connective tissue capsule around implant in control group (Hematoxylin-eosin staining ×100): 1 = capillaries, 2 = neutrophils.

Figure 12

Day 42 after pylon implantation. (a) Muscular tissue in experimental group (Van Gizon staining ×100): 1 = muscular tissue, 2 = connective tissue between muscular fibrils, 3 = blood vessels. (b) Connective tissue capsule around implant in control group (Hematoxylin-eosin staining ×100): 1 = capillaries, 2 = neutrophils. (c) Electron scan of cross section of implant in experimental group (×200): 1 = fine wire of implant, 2 = pores of implant, 3 = tissue elements in pores.

Figure 13

Neutrophil and capillary count in experimental and control groups. SD = standard deviation.

Figure 14

Migration of human fibroblasts within (a) untreated sample of porous composite pylon (skin and bone integrated pylon 2 [SBIP-2]), ×1,000; (b) sample of porous composite pylon SBIP-2 pretreated with type I collagen, ×1,000; and (c) sample of porous composite pylon SBIP-2 pretreated with human fibrin, ×1,000. c = human fibroblasts.