Spinal implants including a sensor and methods of use

[0001] The present application is directed generally to spinal implants, such as interspinous implants, and more particularly to spinal implants having a sensor associated therewith and methods of using the sensor.

[0002] The spine includes a number of vertebral members that are typically vertically spaced apart by intervertebral discs. This arrangement permits the spine to undergo slight flexion, extension, lateral flexion, and rotation. In addition, the vertebrae typically include bony protrusions, called spinous processes, that extend posteriorly from the spinal axis.

[0003] Various medical procedures include spacing apart the vertebral members that extend along a section of the spine. These procedures may be required due to damage to one or more of the vertebral members and/or intervertebral discs caused by a specific traumatic event, a degenerative condition, a tumor, infection, or the like. These procedures typically involve decompressing the relevant vertebral members and installing some form of spinal implant. For example, a bone plate may be secured to adjacent-vertebral members to fix their relative positions. However, many procedures call for the vertebral members to remain moveable relative to each other, at least to some extent. For example, a spacer may be inserted between adjacent spinous processes, or other vertebral elements, to provide elastic resistance to relative compression between the elements. The mechanical properties of the-spacer (e.g., its size and stiffness) help determine how and to what extent the spacer stabilizes the spinal column. As such, it may be desirable to determine target mechanical properties for the spacer, which is not always possible to predict a priori with the desired level of accuracy.

[0004] In one illustrative embodiment, the present application provides a method of spacing spinal elements comprising: installing a first spinal implant having a sensor associated therewith; selecting a second spinal implant based on measurement data provided by the sensor; and replacing the first spinal implant with the second spinal implant. The first and second implants may be installed in separate surgical procedures, or during the same surgical procedure, and the implants may be positioned between a superior spinous process and an inferior spinous process and advantageously directly engage the same. The selection of the second implant may be based on the data provided by the sensor and a material property of the second spinal implant, such as its stiffness. The measurement data may correspond to strain or force data. The sensor may be, but is not required to be, embedded in the first spinal implant, such as in a removable module. A corresponding apparatus is described.

[0005] FIG. 1 shows a spinal implant in accordance with one embodiment.

[0006] FIG. 2 shows a portion of a spine with an installed sensor-equipped test spinal implant.

[0007] FIG. 3 shows a portion of a spine with an installed long-term spinal implant replacing the sensor-equipped test spinal implant.

[0008] FIG. 4 shows alternative embodiments of the spinal implants using a common receiver body and multiple modular inserts.

[0009] In one embodiment, the present application relates to an interspinous implant 20 that has an associated sensor 30. See FIG. 1. Such an implant 20 may be used to space a superior spinous process 12 from an inferior spinous process 14 in adjacent vertebrae 10. See FIG. 2. The implant 20 may be put in place temporarily in order to obtain measurement data, and may therefore be sometimes referred to herein as a test implant 20.

[0010] The implant 20, sometimes referred to as a spacer, typically includes a superior saddle 22, an inferior saddle 24, and a midsection 26 therebetween. The superior and inferior saddles 22,24 are formed by respective lugs 22a,24a extending from the midsection 26, and are configured to receive the superior and inferior spinous processes 12,14, respectively. The saddles 22,24 may be symmetric or asymmetric, as is desired. The midsection 26 is intended to substantially fill the space between the spinous processes 12,14, and is advantageously flexible and elastic. For additional information, attention is directed to U.S. Pat. No. 6,626,944 to Taylor, which is incorporated herein by reference.

[0011] A sensor 30 is associated with the implant 20. The sensor 30, in one embodiment, may take the form of a conventional strain gage. Such a strain gage 30 should be oriented to measure vertical strain on the implant 20 between the spinous processes 12,14; however, the sensor 30 may alternatively or additionally measure strains in other directions. In various alternative embodiments, the sensor 30 measures load, pressure, stress, strain, vibration frequency, and the like, either at a moment in time, or over time. The sensor 30 may advantageously be disposed in the midsection 26 of the implant 20, such as embedded therein, although this is not required.

[0012] It is intended that the sensor 30 will generate measurement data about the implant 20 and/or its mechanical environment. Typically, this measurement data is indicative of the forces acting on the implant 20 and/or the resulting strain of the implant 20. This measurement data may be transmitted from the implant using a suitable analog or digital transmitter, which may use radio frequency, thermodynamic, capacitance, or other means to convey the data signal. Alternatively, the measurement data may be supplied via suitable wires or other transmission media to a computer or other measurement data gathering station. The measurement data may be collected from the implant 20 while the implant is in the body, or after the implant 20 is removed from the body.

[0013] The sensor-equipped test implant 20 may be inserted between the superior and inferior spinous processes 12,14 of adjacent vertebrae 10 during a surgical procedure. The surgical procedure may be similar to that used for the product sold under the trade name DIAM Spinal Stabilization System, available from Medtronic Sofamor Danek, Inc. of Memphis, Tenn. Post-operatively, the implant's sensor 30 generates measurement data as discussed above. This data is reviewed and used to help select a second implant 40 which replaces the first implant 20 via a second surgical procedure. More particularly, a plurality of candidate implants, such as implants 40,50, may be provided with differing material properties. Like implant 20, the candidate implants 40,50 have respective superior saddles 42,52, inferior saddles 44,54, and midsections 46,56; but, unlike implant 20, the candidate implants 40,50 advantageously do not include associated sensors. Based on the measurement data from sensor 30, one of the candidate implants 40,50 is chosen so that its material properties will be appropriate for the situation. For example, based on the measurement data, a doctor may conclude that a spacer between the spinous processes 12,14 should have a certain overall stiffness. The candidate spacer implants 40,50 may have a variety of stiffness levels, indicated in the drawings as stiffness #1 and stiffness #2. One of the available stiffness levels should correspond with the desired stiffness identified by the doctor, and the corresponding candidate spacer implant (e.g., candidate implant 40) is chosen. Then, the first implant 20 is removed and replaced with the chosen implant 40 during a second surgical procedure. Thus, the chosen implant 40 is used to create a spinal stabilizer 60 between the spinous processes 12,14 that helps space the two spinous processes 12,14 apart. It is intended that the spinal stabilizer 60 formed thereby will be in place long-term; as such, the replacement implant may be conceptually thought of as a long-term implant 40. The long-term implant 40 may, in some embodiments, be secured in place using tethers, as disclosed in U.S. Pat. No. 6,626,944.

[0014] In another embodiment, various implants 20,40,50 may be formed of a common receiver body 61 in combination with various modular inserts 72,74a,74b. See FIG. 4. The receiver body 61 may include a superior saddle 62, and an inferior saddle 64. The various inserts 72,74a,74b may be joined to the receiver body 61 and be disposed between the saddles 62,64, such as in a corresponding bay 63 within midsection 66. Thus, a sensor-equipped test implant 20 may be formed by inserting sensor module 72, having sensor 30 disposed therein, into receiver body 61. The same receiver body 61 may then be used to form candidate implant 40 by removing the sensor module 72 and inserting a different module 74a, or form candidate implant 50 by inserting module 74b. Advantageously, the modules 74a,74bhave differing material properties, such as different stiffness levels.

[0015] The discussion above has assumed that the sensor-equipped test implant 20 is replaced by long-term implant 40 or 50 in a second surgical procedure. During the time period between the first and second surgical procedures, the sensor 30 may be used to collect relevant data with the patient in more “real world” circumstances. The interval between surgical procedures may be a few hours to a month or more. However, in some embodiments, the test implant 20 and the long-term implant 40 or 50 may be installed in the same surgical procedure. For example, the test implant 20 may be installed, the patient may be manipulated by the surgeon during the procedure to allow the sensor 30 to generate the relevant measurement data, long-term implant 40 selected based thereon, and test implant 20 replaced by long-term implant 40, all within the same surgical procedure.

[0016] It should be noted that the term “material property” as used herein refers to elastic modulus, flexural modulus, flexural strength, stress-strain curve, Young's modulus, hardness, compression strength, dampening or viscous properties, and the like, whether of a homogenous material or of a composite, and excludes physical dimensions.

[0017] Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc and are also not intended to be limiting. Like terms refer to like elements throughout the description.

[0018] As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an”and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.

[0019] The present embodiments may, of course, be carried out in other specific ways than those herein set forth without departing from the essential characteristics of the application. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.