Device to facilitate controlled rotation of the cervical spine

A device for controlled orientation of a person's cervical spine that is compatible with medical imaging machines. The device is capable of rotation about the axis of a patient's spinal column independent of, or in addition to, flexion/extension of a patient's spinal column. The device may incorporate locking mechanisms to secure rotational orientation and may include quantitative indicators of the degree of rotation.

BACKGROUND OF THE INVENTION

The present invention relates generally to a medical-imaging compliant apparatus for adjusting a patient's head position to facilitate controlled orientation of the cervical spine during medical imaging.

Medical imaging has become an indispensable tool for the diagnosis and treatment of conditions affecting a person's cervical spine. Images of the cervical spine provide doctors with insight into such conditions as cerebral spinal fluid flow patterns, nerve compression, spinal instability and intervertebral disk damage. Diagnosis of these, and other conditions, often requires that images of the patient's spine be taken while the spine is rotated about its axis or while undergoing flexion/extension. These specific configurations may need to be accurately recreated during subsequent imaging to facilitate diagnosis and treatment.

Medical imaging technologies, such as those used in magnetic resonance (“MR”) imaging and computed tomography (“CT”) imaging, are extremely sensitive to the amount and type of material, as well as its location in relation to the area to be imaged, of any equipment present during imaging. MR imaging uses a strong magnetic field to polarize nuclei whose position is then detected by special coils. The presence of conductive or magnetic material disrupts the detection and thus spatial encoding of the signals—ultimately degrading the clarity of the image and the information the doctor is able to learn from the MR scan.

CT imaging uses X-ray attenuation to reconstruct a three-dimensional image. Given that different materials and tissues cause varying attenuation of the X-rays used in a CT, it is critical that any support structure introduced into the scan be radiolucent, meaning the material does not substantially scatter or block the X-rays causing artifacts in the images.

Conventional wisdom has lead inventors to design cervical rotation devices that remove supporting structure from the area to be imaged to reduce image artifacts. When the material is unable to be removed from the imaging area, plastics are commonly used because of their low interaction with both MR and CT imaging machines. The removal of structure from the imaging area along with the use of imaging compliant materials is advantageous as it reduces the amount of interference caused by the fixture, therefore providing a more informative image.

One previous design consists of a head cradle shaped as a half-cylinder with one open end and one closed end. A pin mounted to the closed end supports the head cradle. The other end of the pin is rotatably mounted to the back of a frame having support legs extending on the left, back, and right of the head cradle minimizing the portion of the support structure within the imaging area of the head cradle. The design is effective at removing the majority of the structure from the imaging area; however, a single pin supports the entire weight of the patient's head. This cantilevered design places a tremendous amount of stress on the pin making it less suited for construction from CT and MR imaging compliant materials such as plastic. Additionally, orientating a patient's head is difficult given the high load placed upon the pin at the axis of rotation.

Another design incorporates an outer ring with radial slots around a portion of the circumference. A head cradle shaped as an open-ended half-cylinder has two collinear pegs extending radially outward from the head cradle. The head cradle is suspended within the large outer ring by placing the two pegs through the radial slots in the outer ring and independently clamping each peg in place. This design eliminates the high stresses placed on the single pin in the previous design, but the head cradle may be difficult to rotate because the weight of the patient's head acts to wedge the pegs downward in the radial slots.

It is critical that the portion of the spine being imaged remains immobile in the desired orientation throughout imaging. Common techniques to reduce head movement during imaging involve combinations of strategically located straps, clamps, and blocks. These techniques are time consuming and cumbersome because a health care professional must configure the individual pads and straps. The sight of clamps and straps may add to patient anxiety.

BRIEF SUMMARY OF THE INVENTION

The present inventors have determined that placing a bearing surface substantially beneath the patient's head allows a sturdy and relatively rigid support to be constructed of lightweight, non-metallic materials that do not substantially interfere with the CT or MRI imaging process. Furthermore, the present inventors have recognized that a head support pad having a sufficient configuration and compliance can comfortably and unobtrusively maintain a patient's head position during rotation of the fixture during imaging.

Specifically, the invention provides a fixture for adjusting a patient's head position in a medical imaging machine having a base supporting a head cradle defining a volume receiving and supporting a patient's head. The fixture also has a bearing, having first and second bearing surfaces moving with respect to each other about a first axis aligned with the patient's neck, the bearing is located between the base and the head cradle along a vertical line passing substantially through a center of mass of the patient's head when the head is at a predetermined position in the head cradle. The bearing is constructed of a material that is substantially transparent to the imaging machine.

It is thus one object of at least one embodiment of the invention to provide a support for rotation of a patient's cervical spine that is both sturdy and compliant with medical imaging technologies. The bearing surface beneath the head allows use of radiolucent and nonferrous material to provide sturdy support and smooth rotation.

The base may include a cradle support mounted to rotate about a second axis perpendicular to the first axis.

Thus, it is another object of at least one embodiment of the invention to adjust the flexion and extension of a patient's cervical spine before axial rotation.

The fixture may further include a first handle communicating with the head cradle to selectively rotate the head cradle about the first axis.

It is thus another object of at least one embodiment of the invention to provide a convenient means of rotating the patient's head.

The first handle may also selectively rotate the cradle support about the second axis.

Thus, it is another object of at least one embodiment of the invention to provide a single means of controlling the rotation and flexion/extension of a patient's cervical spine.

The first handle may include a first lock actuated by the first handle that selectively prevents rotation of the head cradle about the first axis.

It is thus another object of at least one embodiment of the invention to provide a single control that facilitates rotation about the axis of a patient's cervical spine and locks the fixture in the desired position.

The first lock may be a threaded member that is rotated to clamp the cradle support and the head cradle.

Thus, it is another object of at least one embodiment of the invention to provide a simple and reliable lock mechanism that provides both mechanical advantage and allows for secure positioning about the axis of a patient's cervical spine over a range of orientations.

The fixture may further include a second lock that selectively prevents rotation of the cradle support about the second axis.

It is thus another object of at least one embodiment of the invention to separate the rotational locks to allow rotation about one axis independent of rotation about the other axis.

The second lock may be a threaded member that is rotated to clamp the base to the cradle support.

Thus, it is another object of at least one embodiment of the invention to provide a lock mechanism that provides a mechanical advantage and allows for secure flexion/extension positioning of a patient's cervical spine in an infinite number of orientations.

The fixture may have a base configured to engage a medical imaging table.

It is thus another object of at least one embodiment of the invention to provide a fixture that may be installed on a variety of machines.

The fixture may include a first scale indicating rotation about the first axis from a predetermined position.

Thus, it is another object of at least one embodiment of the invention to provide for quantitative measurement of the amount of rotation of the device about the axis of a patient's cervical spine.

The fixture may include a second scale indicating rotation about the second axis from a predetermined position.

It is thus another object of at least one embodiment of the invention to provide for quantitative measurement of the amount of flexion/extension of a patient's cervical spine.

The fixture may further include a first marker mounted to the cradle support wherein the first marker is configured to be detected by a medical imaging device.

Thus, it is another object of at least one embodiment of the invention to provide an indication of the position of the cradle support that will be preserved in the final image to aid in diagnostics.

The fixture may further include a second marker mounted to the head cradle wherein the second marker is configured to be detected by a medical imaging device.

It is thus another object of at least one embodiment of the invention to provide an indication of the position of the head cradle that will be preserved in the final image to aid in diagnostics.

The bearing may also present a portion of a surface of a cylinder, the cylinder being coaxial about the first axis.

Thus, it is another object of at least one embodiment of the invention to have a bearing surface that provides isocentric rotation and approximates the general shape of the back of a patient's head to decrease the height of the head cradle while providing a broad area of contact.

The fixture may further include a mat sized and arranged to align the first axis and the axis of a patient's spine.

It is another object of at least one embodiment of the invention to provide a simple method for aligning the axis of a patient's spine to allow for pure rotation of the patient's cervical spine while allowing the bearing to be placed below the head surface.

The mat may be independent of the base.

Thus, it is another object of at least one embodiment of the invention to have a mat that can be manipulated independently of the fixture to allow for interchangeability of the mat to accommodate different patients.

Additionally, the invention provides a fixture for adjusting a patient's head position in a medical imaging machine having a base, a cradle support mounted to the base, and a head cradle communicating with the cradle support. The fixture also has a head support pad attached to the head cradle or the cradle support. The head support pad has a concave cross-section with a compliance that applies sufficient lateral pressure upon the temporal region of a patient's head, under the weight of an average patient's head, to substantially maintain the patient's head placement relative to the head cradle throughout movement of the head cradle and cradle support.

It is thus another object of at least one embodiment of the invention to provide a convenient device to stabilize a patient's head position during medical imaging.

Furthermore, the invention provides a fixture for adjusting a patient's head position in a medical imaging machine comprising a base, a first support and a second support attached to the base and extending upwardly from the base, an outer ring rotatably mounted between the first and the second supports having a first central axis and an inner surface sized to encompass a patient's head. Furthermore, the fixture has an inner ring having a second central axis and an outer surface sized to fit rotationally within the outer ring, wherein the first and second central axes are aligned.

Thus, it is another object of at least one embodiment of the invention to provide a device easily manufactured from rotatably engaged concentric rings rotatably mounted between side supports.

The fixture described above may further include a rollable bearing element and a first race sized to engage the bearing formed in the inner surface of the outer ring, the outer surface of the inner ring, or both.

It is thus another object of at least one embodiment of the invention to have a device with smooth and continuous rotation to promote patient comfort and ease of use.

The rollable bearing element may be a ball.

Thus, it is another object of at least one embodiment of the invention to be readily manufactured from commonly available plastic ball elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference toFIG. 1, the cervical spine rotation fixture9constructed according to the present invention has a generally rectangular base10with a planar upper surface and a convex lower surface configured to engage a variety of medical imaging machine tables11, including a magnetic resonance (“MR”) imaging machine or a computed tomography (“CT”) imaging machine.

A left pillar12and a right pillar14are attached in opposition at left and right sides of the base10and extend upwardly from the base10parallel to each other and perpendicular to the base10. As used herein, directions, such as “left” and “right”, will be with respect to a patient86lying supine on the patient table11with the patient's head above the base10.

An outer ring16, having a central axis18, fits between the left and right pillars12and14to be supported thereby on a shafts46(shown also inFIG. 5) passing through the left and right pillars12and14so that the outer ring16may rotate about a generally horizontal, flexion/extension axis20extending between the left and right pillars12and14. Ends of the shafts46are attached to plates45passing downward along the outer surfaces of the left and right pillars12and14to rotate with the shafts46.

An inner ring30fits within the outer ring16to rotate therein such that the central axis32of the inner ring30is coaxial with the first central axis18of the outer ring16. The inner ring30thus rotates, with respect to the outer ring16, about the first and second central axes18and32.

The outer ring16has a height measured along the central axis18of approximately one-half the height of an average human head measured in the superior/inferior direction and diameter slightly greater than the diameter of the average person's head. As shown also inFIG. 3, the inner ring30includes a lower shelf portion33extending in a superior direction approximately the height of the outer ring16beyond the outer ring16. The remainder of the inner ring is of the same height as the outer ring16.

The outer ring16has a first slot22extending approximately45degrees circumferentially clockwise and counterclockwise from a vertical axis24. A handle58, to be described below, attaches to the inner ring30and extends through the slot22. As shown also inFIG. 4, first scale26is affixed to the outer ring16to show the degree of axial rotation (angle beta) of the inner ring30about the first central axis18as indicated by position of the handle58.

The plates45likewise have arcuate slots47at a constant radius about axis20and of angular extent of approximately30degrees. Second handles62and66, also to be described below, attach to the left and right outer surfaces of the left and right pillars12and14, and extend through the slots47. As shown also inFIG. 3, second scales28are affixed to the plates45showing the degree of rotation (angle alpha) of the outer ring16and inner ring30in flexion/extension about axis20as revealed by the position of the handles62and66with respect to the scales28.

Referring now toFIG. 2, the interface between the outer ring16and inner ring30provides a first and second race formed of opposed hemicylindrical grooves34,36in each of the outer ring16and inner ring30, the grooves following a path coaxial with axes18and32. Each race has a hemicircular cross section approximately equal to the radius of a number of ball bearings42that may be placed in opposed grooves34,36to provide a slight gap44between the inner ring30and the outer ring16.

As shown inFIG. 3, the outer ring16may have fiducial markers52mounted in several locations around the circumference of the outer ring16to allow the location and flexion/extension orientation of the outer ring16to be captured by an imaging machine. The first markers52may have a circular cross-section and be constructed of radio opaque material for an x-ray CT or of an NMR contrast material, for example, a mixture of gadolinium and water, for MRI. Referring toFIG. 4, second fiducial markers56are mounted parallel to the second central axis32on the inner ring30to allow the axial orientation of the inner ring30to be captured by an imaging machine. The second markers56may also have a circular cross-section and be constructed of similar material to the first fiducial markers. The first markers52and second markers56are generally elongated such that the plane of a cross-sectional image will intersect a portion of the markers52,56.

Referring now toFIG. 5, relative rotation of the inner ring30about the central axes18,32with respect to the outer ring16may be locked by rotating handle58. Handle58includes internal threads engaging a threaded stud60that extends radially outward from the inner ring30through the first slot22in the circumference of the outer ring16. Upon rotating the first handle58, the inner ring30and the outer ring16are clamped together.

Likewise, rotation of the outer ring16and inner ring30about the flexion/extension axis20with respect to the left and right pillars12and14may be locked by turning the second handles62and66. Each of second handles62and66have internal threads receiving threaded studs64and68, respectively, extending horizontally outward from the left pillar12and right pillar14through an arcuate slots47in the respective plates45. Rotating these handles62and64, clamps the plates45to the respective pillar12or14.

For use in MR imaging, all elements of the fixture can be made from non-ferromagnetic and non-conductive materials such as polycarbonate, acrylic, polypropylene, nylon, and polyvinyl chloride, for example. Additionally, when compliance with CT imaging is desired, the use of radiolucent materials with low mass attenuation coefficients is preferred (e.g., carbon composites).

Returning briefly toFIG. 1, a rectangular mat72, sized and contoured to comfortably accommodate the body of an average person, has a central longitudinal axis74that is oriented parallel to the central axes18,32. The mat72can be configured to be attached to the base10or separate from the base10. The mat72has an appropriate thickness76necessary to align the axis of a patient's spinal column78with the second central axis32of the inner ring30. In one embodiment, the mat72has a thickness76of approximately4inches. The mat72can be made from a variety of materials that provide sufficient comfort and support including, for example, foam, rubber, and plastic. Different mats72of different thicknesses can be used for different purposes and patients.

As shown inFIG. 1, the head support pad80is sized to substantially encompass the posterior portion of a human head and is attached to the inner ring30approximately along the bottom half of the inner ring30and the shelf portion33of the inner ring30that extends beyond the outer ring16.

Turning toFIG. 4, the head support pad80has a substantially concave cross-section and is constructed from a material with a compliance that deforms under the weight of an average patient's head82. The head support pad80supplies a counteracting force84around the temporal and posterior regions of the patient's head82that stabilizes the patient's head82and helps maintain the orientation of the patient's head82with respect to the inner ring30under rotation about the central axes18,32and with respect to the outer ring16under rotation about the flexion/extension axis20. The head support pad80can be made from a material such as polyurethane foam or any other material having a sufficient compliance.

Returning toFIG. 1, during use of the device, the patient is positioned in a supine position on the mat72with the patient's spinal column78coaxial with the central axis18,32of the inner ring30and outer ring16. The patient's head82is placed within the inner ring30and secured by the head support pad80.

Once the patient86is secured, a health care professional can easily adjust the patient's head82about the flexion/extension axis20with one hand on handle58. Referring again toFIG. 5, to lock the position about the flexion/extension axis20, the health care professional may use a second hand to tighten one of the second handle62and third handle66. The second scale28or third scale70provide the health care professional with an indication of the amount of rotation about the flexion/extension axis20.

Once in the desired position, the health care professional may tighten the second handle62and/or third handle66to secure the outer ring16in place.

To rotate about the patient's spinal column78, the health care professional may continue to move the first handle58while observing the first scale26. Once the desired axial rotation is reached, the health care professional may tighten the first handle58to secure the inner ring30in place.FIG. 4shows the device after rotation about the patient's spinal column78.

It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but that modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments also be included as coming within the scope of the following claims.