Radiographic discernable sensors and orthopedic applications for same
Implantable sensors for determining bone health are described that can be utilized in conjunction with orthopedic implants. The sensors can include passive strain gauges or passive chemical sensors that can be read by radiographic imaging techniques. Sensors can be affixed to implantable support devices so as to non-invasively monitor the effect of load on the implant for instance to provide a quantitative assessment of when a fracture is sufficiently healed to allow safe weight-bearing upon the limb. Alternatively, sensors can monitor the health of a local implant area, for instance to monitor the implant area of early stage infection or healing of a fusion procedure.
1. An implantable strain sensor comprising an indicator, the indicator including a first end and a second end, the first end being configured for direct or indirect fixation to an orthopedic implant, the second end comprising a first radiographically opaque material, the sensor further comprising a scale comprising a second radiographically opaque material, the scale being located in conjunction with the second end, wherein the strain sensor is a passive sensor such that a location of the second end with respect to the scale is discernible via X-ray imaging with no active interrogation of the first or second radiographically opaque materials.
2. The implantable strain sensor of claim 1 , further comprising a housing, the housing containing the indicator and the scale.
3. The implantable strain sensor of claim 1 , wherein the indicator comprises an elongated rod or an extendable material.
4. The implantable strain sensor of claim 1 , the scale comprising multiple features, each feature having a cross sectional dimension of from about 0.1 millimeters to about 1 millimeter.
5. The implantable strain sensor of claim 1 , the second end having a width of from about 0.1 millimeters to about 1 millimeter.
6. An orthopedic implant comprising the implantable strain sensor of claim 1 attached thereto.
7. The orthopedic implant of claim 6 , wherein the strain sensor is attached to an exterior surface of the orthopedic implant or is within a cannula of the orthopedic implant.
8. The implantable strain sensor of claim 1 , wherein the radiographically opaque material comprises tungsten, stainless steel, tantalum, mercury, gallium, galistan, a rare earth nitrate, gold, bismuth, gadolinium oxysulfide, polydimethyl siloxane, or an acrylic elastomer.
9. A method for determining health of orthopedic tissue comprising:
placing orthopedic tissue under a load, the orthopedic tissue having affixed thereto an orthopedic implant and a strain sensor, the strain sensor comprising an indicator, the indicator including a first end and a second end, the first end being directly or indirectly attached to the orthopedic implant, the second end comprising a first radiographically opaque material, the sensor further comprising a scale, the scale comprising a second radiographically opaque material;
examining the orthopedic tissue via an X-ray imaging process while the orthopedic tissue is under the load, the examination comprising no active interrogation of the first or second radiographically opaque materials, the X-ray imaging providing one or more images of the scale and the second end of the indicator.
10. The method of claim 9 , further comprising examining the orthopedic tissue via the X-ray imaging process while the orthopedic tissue is under no load, and comparing the examination results.
11. An implantable chemical sensor comprising an indicator, the indicator including an analyte-sensitive material and a radiographically opaque component configured for movement in response to a dimensional change in the analyte-sensitive material, wherein the chemical sensor is a passive sensor such that the radiographically opaque component is discernible via X-ray imaging with no active interrogation of the radiographically opaque component.
12. The implantable chemical sensor of claim 11 , wherein the analyte-sensitive material comprises an analyte-sensitive hydrogel or comprises a pH sensitive hydrogel.
13. The implantable chemical sensor of claim 11 , wherein the radiographically opaque component is an end of the analyte-sensitive material.
14. The implantable chemical sensor of claim 11 , wherein the radiographically opaque component is confined within a track.
15. The implantable chemical sensor of claim 11 , the indicator further comprising an indicator component in mechanical communication with the analyte-sensitive material, the indicator component including the radiographically opaque component.
16. The implantable chemical sensor of claim 11 , the analyte-sensitive material comprising a binding molecule or an analogue molecule for the analyte.
17. The implantable chemical sensor of claim 11 , further comprising a scale, the scale being located in conjunction with the radiographically opaque component such that the location of the radiographically opaque component with respect to the scale is discernable via X-ray imaging with no active interrogation of the radiographically opaque component.
18. The implantable chemical sensor of claim 11 , further comprising a semi-permeable membrane.
19. The implantable chemical sensor of claim 11 , comprising multiple analyte-sensitive materials each sensitive to at least one analyte.
20. The implantable chemical sensor of claim 11 , wherein the analyte-sensitive material is sensitive to glucose.
21. An orthopedic implant comprising the implantable chemical sensor of claim 11 .