ANKLE DISTRACTOR AND METHOD OF USE
1
TECHNICAL FIELD This invention is in the field of devices used to position two bone structures in a desired position relative to one another to facilitate diagnosis or treatment of tissues in the vicinity of the bone structures.
BACKGROUND OF THE INVENTION In the treatment of tissues in the vicinity of a joint such as an ankle, it often becomes necessary to create a separation or displacement of one bone structure relative to another bone structure. This displacement can be required in order to give access, for example, for surgical instruments or for radiographic imaging. Depending upon the joint or other bone structure being examined or treated, and depending upon the treatment being undertaken, different degrees of displacement may be required. Further, the displacement may be required as an in-line separation of one bone from another, or it may be desirable to create or modify an angular displacement between the bones. Finally, it is desirable to hold or maintain the bone structures in the desired positional relationship once the displacement has been achieved.
When two such bone structures are displaced, the force required to achieve the displacement is resisted by the tissues surrounding the bones, including muscular and connective tissues. It is highly desirable to avoid overstressing these resistive tissues by limiting the displacement of one bone structure from the other. It is difficult to define a limit which should not be exceeded, in terms of measured displacement, or in terms of measured resistance. The limit may vary from one procedure to another, even when performed on a given joint, and it may vary according to the medical history of the patient or the history of the joint.
The most reliable gauge of a limit, beyond which displacement should not go, is the tactile feel of the resistance as sensed by an experienced physician. This is because the physician will have available to him a variety of information about the patient, about the joint being treated, about the quality of the bone, and about the specific procedure being performed, that will impact the desirable limit of the displacement or of the resistance. It would be difficult or impossible to quantify all of this information and include it in a formula which could define a displacement limit or a resistance limit. Known devices exist which are designed to displace one bone structure from another by the use of a mechanical advantage to assist in achieving the displacement and in maintaining the relative displacement once achieved. Such devices, for instance, typically use a screw mechanism or a lever mechanism to assist the manual force applied by the physician to achieve the desired displacement of the bone structures. These devices lessen the amount of force that the physician must exert, but they also necessarily reduce or eliminate the tactile feedback available to the physician. Therefore, these devices overlook the value of giving the physician the necessary tactile feedback to accurately gauge the displacement and resistance being generated. These devices also often create stress fractures due to the excessive pressure applied to distract the joint.
It is therefore an object of the present invention to provide a method and apparatus for selective displacement of one bone structure relative to another, by application of unassisted manual force. It is also an object of the present invention to provide a method and apparatus for providing tactile feedback to a physician during displacement of one bone structure from another. It is a still further object of the present invention to provide a method and apparatus for holding two bone structures in a desired relative displacement after the desired displacement has been achieved. Finally, it is an object of the present invention to provide a method and an apparatus, for achieving and maintaining a desired displacement between two bone structures, which are easy and cost effective to implement.
SUMMARY OF THE INVENTION
The ankle distractor of the present invention, by way of the example of a preferred embodiment, consists of two extendable frames, one locatable on either side of the bone structures to be distracted. While the device is described in terms of two frames, it is possible to use only one frame, located to one side of the bone structures, without departing from the spirit of the present invention, if sufficiently stiff materials of construction are selected. Each of the aforementioned frames is extendable by virtue of being constructed with an upper section and a lower section slidably attached together. Alternatively, other extendable structural variations could be utilized as desired, such as two sections pivotably attached together. A first handle is attached to the upper section of each frame, and a second handle is attached to the lower section of each frame. Alternatively, one handle could be attached, for instance, to the lower sections of the frames, and the two upper frame sections could be attached to a stationary fixture, without departing from the spirit of the invention. The upper section of each frame is attachable to a first bone structure by means of a relatively stiff wire, called a k-wire, which is run through the first bone structure and through tapered slots in the upper sections of the two frames. Similarly, the lower section of each frame is attachable to a second bone structure by means of a second k-wire, which is run through the second bone structure and through tapered slots in the lower sections of the two frames. Each frame has a releasable ratcheting mechanism formed on its upper and lower sections, to maintain the degree of extension of the frame.
In performing the method of using the apparatus, once the frames have been located one on either side of the bone structures, a k-wire is run through the first bone structure and through the tapered slots in the upper frame sections. Similarly, a second k-wire is run through the second bone structure and through the tapered slots in the lower frame sections. Alternatively, the k-wires could be run through the bones first, followed by assembly of the frames onto the k-wires. The handles are then grasped and pulled in opposite directions, pulling the bone structures in two directions as desired. This pulling action causes the k-wires to seat into the narrow ends of the tapered slots, which results in gripping of the k-wires by the frame sections.
The pulling action is continued until the relative displacement of the two bone structures is as desired for diagnosis or treatment. This pulling can be in a straight line, to cause equal extension of the two frames, resulting in a linear displacement of the bone structures. Alternatively, the pulling can be at a slight angle, to cause one frame to be extended more than the other, to result in a slight angular displacement of the bone structures. Once the desired displacement has been achieved, the handles can be released, and each frame will be held at its desired degree of extension by the ratcheting mechanism formed on its upper and lower sections. Since the k-wires are installed substantially at right angles to the pulling force, they are subjected to a bending force. This is an advantageous arrangement, because the wires can bend as stress increases, rather than fracturing the bone. The k-wires used for each procedure are selected according to their desired degree of rigidity, so that if manual force beyond a selected level is applied, the k-wires will yield by bending. This prevents excessive displacement of the bone structures. The k-wires used for distraction of a typical adult ankle would bend under the imposition of approximately 30 pounds of force. In addition to the protection afforded by the bendable k-wires, excessive displacement of the bone structures is prevented by the fact that the physician can physically feel the force being applied to distract the bone structures. This feature results from the construction of the present invention, which applies the force manually exerted by the physician directly to the bone structures unassisted. In other words, the present invention provides no mechanical advantage to multiply the manual force, such as a lever or a screw mechanism. This direct, unassisted application of the manual force also results in the transmission of direct feedback to the physician's hands, giving the physician the maximum sensitivity possible in distraction of the bone structures.
The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of a preferred embodiment of the ankle distractor of the present invention, showing the device as intended to be fastened to an ankle; and Figure 2 is a posterior elevation view of the ankle distractor shown in Figure 1.
DESCRIPTION OF PREFERRED EMBODIMENTS As shown in Figures 1 and 2, the ankle distractor 10 of the present invention is intended to be fastened onto two bone structures such as the lower end of the tibia 12 and the body of the calcaneus 14 of a typical ankle. The mode of attachment shown is appropriate for displacing the calcaneus 14 relative to the tibia 12. The device of the present invention could also be configured to be used on various other bone structures without departing from the spirit of the invention.
The ankle distractor 10 includes a relatively rigid left frame 16 and a relatively rigid right frame 18. The left frame 16 and the right frame 18 can be identically shaped, and they can be formed from any relatively rigid plastic, such as ABS or polycarbonate, or from various metals. The upper portions of the left frame 16 and the right frame 18 are fastened to a first bone structure such as the tibia 12 by means of an upper, relatively stiff, wire called a k-wire 20. Actually, as shown in the instance of the tibia and the fibula, the frames 16, 18 can be fastened to more than one bone structure by a single k- wire 20. For the purposes of this invention, however, this upper attachment point can be considered an attachment to a single bone structure. In a similar way, the lower portions of the left frame 16 and the right frame 18 are fastened to a second bone structure such as the body of the calcaneus 14 by means of a lower, relatively stiff, k-wire 22.
The fastener wires 20, 22 are commonly called k-wires, and they are well known in the art as means of attachment to bone structures. The k-wires 20, 22 are available in various diameters, and hence various degrees of stiffness. A typical k-wire for use in attaching the device of the present invention to an adult ankle would have a diameter of 0.0625 inch, and it would remain relatively straight until subjected to a bending force of approximately 30 pounds. An upper handle 24 is pivotably attached to the upper portion of each of the frames 16, 18, and a lower handle 26 is pivotably attached to the lower portion of each of the frames 16, 18. The upper and lower handles 24, 26 can be formed from a relatively strong material such as high density polyethylene, or from various metals. The upper and lower handles 24, 26 are shown attached to the frames 16, 18 in line with the points at which the k-wires 20, 22 penetrate the frames 16, 18, but the handles could alternatively be attached to the frames 16, 18 out of alignment with the k-wires 20, 22. Such non-aligned attachment would result in a reduction of the force experienced by the bone structures, or in the generation of a transverse displacement of the bones.
Each extendable frame 16, 18 consists of an upper section 28, 32 and a lower section 30, 34. On the left extendable frame 16, the upper section 28 is a flat, rigid, longitudinal bar slidably inserted within the lower section
30, which is a flat, rigid, hollow tube. Similarly, on the right extendable frame 18, the upper section 32 is slidably inserted within the lower section 34. Other well known slidable attachments could alternatively be used, such as a pin and groove arrangement. Further, rather than rendering the frame 16, 18 extendable by means of a slidable attachment, a well known alternative extendable structure which would not depart from the spirit of the invention would be the use of pivotably attached sections to form the extendable frames 16, 18.
A ratchet pawl 36, 38 is formed on each lower frame section 30, 34, and a set of ratchet teeth 40, 42 is formed on each upper frame section 28, 32. The ratchet pawls 36, 38 are biased inwardly to mesh with their respective sets of ratchet teeth 40, 42 to maintain the extended length of the frames 16, 18. Of course, if desired, a rotating ratchet mechanism could be used, for instance, if pivotable frame sections were used. A plurality of tapered slots 44 are formed in each of the upper frame sections 28, 32 and in each of the lower frame sections 30, 34. It is through the tapered slots44 that the k-wires 20, 22 pass to fasten the frames 16, 18 to the bone structures. Placement of a plurality of slots 44 on each frame section 28, 30, 32, 34 allows each k-wire to be inserted through the bone structure at the desired location, with the frames 16, 18 in the non-extended position. Each tapered slot 44 has a larger end and a smaller end, with the smaller end being smaller than the diameter of the k-wires 20, 22. The smaller end of each tapered slot is oriented toward the center of the frame 16, 18. When force is applied to extend the frames 16, 18, this causes the k-wires 20, 22 to seat firmly in the smaller ends of the tapered slots 44 through which the k- wires 20, 22 are inserted, causing the frames 16, 18 to grip the k-wires 20,22. This gripping action aids in preventing the frames 16, 18 from sliding either outwardly or inwardly on the k-wires 20, 22. The frames 16, 18 are also held substantially in place on the k-wires 20, 22 by the stiffness of the handles 24, 26.
OPERATION
To use the ankle distractor of the present invention, the frames 16, 18 are positioned on opposite sides of the two bone structures to be displaced. Once the frames 16, 18 have been located one on either side of the bone structures, the upper k-wire 20 is run through the first bone structure and through the tapered slots 44 in the upper frame sections 28, 32. Similarly, the lower k-wire 22 is run through the second bone structure and through the tapered slots 44 in the lower frame sections 30, 34. Alternatively, the k-wires 20, 22 could be run through the bones first, followed by assembly of the frames 16, 18 onto the k-wires 20, 22. The handles 24, 26 are then grasped and pulled in opposite directions, pulling the bone structures in two directions as desired. This pulling action causes the k-wires 20, 22 to seat into the smaller ends of the tapered slots 44, resulting in gripping of the k-wires 20, 22 by the upper and lower frame sections 28, 30, 32, 34.
The pulling action is continued until the relative displacement of the two bone structures is as desired for diagnosis or treatment. This pulling can be in a straight line, to cause equal extension of the two frames 16, 18, resulting in a selected linear displacement of the bone structures. Alternatively, the pulling can be at a slight angle, to cause one frame 16 or 18 to be extended more than the other, to result in a slightly angular selected displacement of the bone structures.
Once the desired displacement has been achieved, the handles 24, 26 can be released, and each frame 16, 18 will be held at its desired degree of extension by engagement of the ratchet pawls 36, 38 with the sets of ratchet teeth 40, 42. Each upper frame section 28, 32 is held in its extended position relative to its respective lower frame section 30, 34 by the ratchet pawl 36, 38 formed on the upper section 28, 32, which meshes with the set of ratchet teeth 40, 42 formed on the respective lower section 30, 34. When the frames 16, 18 are extended, the ratchet pawls 36, 38 engage with the ratchet teeth 40, 42 to prevent the upper frame sections 28, 32 from sliding back into their respective lower frame sections 30, 34. The resistive force generated by the ankle joint prevents the upper frame sections 28, 32 from sliding farther out of the lower frame sections 30, 34. Therefore, the relative displacement between the two bone structures is maintained. The ratchet pawls 36, 38 can be lifted away from their respective upper frame sections 28, 32 to release them from the sets of ratchet teeth 40, 42 to allow the frames 16, 18 to contract, allowing the bone structures to return to their original positions. Since the k-wires 20, 22 are installed substantially at right angles to the pulling force, they are subjected to a bending force as the bone structures resist the pulling force. If a manual pulling force beyond a selected level is applied, the k-wires 20, 22 will yield by bending. This prevents excessive displacement of the bone structures. In addition, excessive displacement of the bone structures is prevented by the fact that the physician can physically or tactilely feel the ankle resistance to the force being applied to distract the bone structures, and he can physically feel the degree to which the bone structures have been displaced.
While the particular Ankle Distractor and Method of Use as herein shown and disclosed in detail are fully capable of obtaining the objects and providing the advantages hereinbefore stated, it is to be understood that they are merely illustrative of the presently preferred embodiments of the invention, and that no limitations are intended to the details of construction or design herein shown, other than as described in the appended claims.