Patent Application
20060064885
Metal rods are used as orthopedic prostheses in a variety of applications. One particular application involves rods used as spinal prostheses. In this application, the rod is surgically implanted adjacent to the patient's spine and attached to individual vertebrae with screws, wires, etc. Titanium and stainless steel are most often used as the materials from which these metal rods are made.
When preparing to implant a prosthetic rod, the surgeon will frequently bend the rod to conform to the individual patient's physiological condition. After bending, it is important to be able to determine the angular orientation of the rod. Because the surface finish of these rods is uniform and without markings, surgeons sometimes in the past have had problems in determining the angular orientation of the rod during the implanting procedure.
Time spent determining the angular position of the rod during the surgery is undesirable. This extra time causes problems for the patient who must be in surgery for a longer time, and less importantly, reduces the surgeon's productivity. For this reason, it would be helpful to have markings on prosthetic rods to allow the surgeon to quickly determine the orientation of the rod after bending.
The industry has found it desirable to place a line or other marking the length of the rod to help determine the angular position of the rod. However, a suitable means to apply these markings has not been available.
The invention comprises a specialized tool for scribing a longitudinal linear mark on such an elongate cylindrical rod. The tool includes a frame made of a rigid material. The frame has a bed having a surface and ii) a linear groove on the bed extending for a predetermined distance and adapted to receive a rod in a predetermined position.
A track is mounted on the frame and runs parallel to the groove. A carrier is mounted on the track and slides on the track in constant spaced relation to and along the groove. A scribe mounted on the carrier extends toward the groove to contact a rod in the predetermined position.
A preferred version of the tool has a frame including a bed, with a groove in the bed. A clamp is mounted on the bed for clamping the rod in the predetermined position. Additional features allow for precise angular positioning of the rod and for scribing a dashed line on the rod.
In use, the tool operator places the rod in the predetermined position in the groove. The scribe is then pressed into contact with the rod. While the scribe is in pressed contact with the rod, the operator slides the carrier along the track.
Frame 11 further includes a pair of track supports 18a and 18b made for example from aluminum and mounted on the ends of bed 13 to project at substantially right angles from flat surface 15 of bed 13. A pair of constant outer diameter round steel tubes or bars 25 are mounted between supports 18a and 18b to extend parallel to each other and form a guide track. The guide track can have other designs as well. One potential option is the traveler track units such as used in sailboats for adjusting sheets, which can be directly mounted on bed 13.
A carrier 30 is slidably mounted on tubes 25 with bearing holes through which tubes 25 pass. The bearing holes may have low friction inserts so that an operator can shift carrier 30 smoothly and easily along tubes 25.
A carriage block 38 is fastened to carrier 30 with convenient fasteners such as cap screws. A scribing unit 22 is fastened to block 38. In some embodiments, scribing unit 22 may be attached directly to carrier 30. Referring to
Groove 27 is adapted to receive a rod 20 to be scribed. A typical rod 20 has a rotational aid 41 comprising six walls forming a hexagonal cross section cylinder as shown in
A rod 20 preferably has two lines 44 scribed 180 apart. Fitting 50 allows lines 44 to be placed almost exactly 180° apart by simply reorienting rod 20 within slot 53.
To insure accurate and firm support for rod 20 within groove 27, tool 10 includes clamp jaws 32 that slide in wide transverse slots within bed 13. Jaws 32 are in horizontal alignment with groove 27, so that jaws 32 will bear directly on a rod 20 within groove 27. Handles 35 operate jackscrews that press jaws 32 against rod 20 lying in groove 27. Preferably, pairs of jaws 32 oppose to allow precise centering of rod 20 within groove 27 without bending rod 20. Jaws 32 should be limited strictly to transverse translation by guide elements as is well known in the machine tool arts.
In one embodiment, fitting 50 is omitted. The near end of rod 20 is temporarily clamped or otherwise attached to the far (left) end of a shaft 70 that extends toward and projects through a hole 73 in support 18b. A knob 77 is attached to the end of shaft 70 that allows angular orientation of rod 20 to be easily changed. Preferably, knob 77 includes a pointer that cooperates with an angle indicator or dial 80 carried on an outer surface of frame 11 to indicate the angular orientation of shaft 70. Of course, jaws 25 must not be clamping rod 20 while the operator is using knob 77 to change the angular orientation of rod 20.
In use, the operator slides carrier 30 to the left against support 18a and places a rod 20 to be scribed with a line in groove 27. Next the operator turns handles 35 to securely clamp rod 20 within groove 27 with jaws 32. Experience shows that the operator can visually control the position of each jaw 32 to prevent excessive bending of rod 20.
Once rod 20 is secured in groove 27, the operator shifts carrier 30 to place stylus 23 directly above the point where the line 44 is to start. The operator smoothly strokes carrier 30 along the length of rod 20 while simultaneously maintaining downward force on arm 47. Typically, one to three strokes will create the desired width of line 44.
The operator can then loosen jaws 32 and rotate rod 20 to a new angle using either fitting 50 or knob 77. The scribing step described above is then repeated. When scribing is complete, the rod is polished and cleaned to prepare for implantation.
For example, the line 44a on rod 20 as shown in
For example, suppose the operator desires 25 mm. dashes with 25 mm. spaces, and pin 69 has a diameter of 5 mm. Then the width of each notch 63 must be 25 mm. plus the diameter of pin 69, or 30 mm. The space between adjacent notches 63 must be 20 mm.
Obviously, bar 60 can be mounted on carrier 30 to achieve a similar function. However, this is less convenient in that the bar 60 then translates with carrier 30. When non-dashed lines 44 are to be formed, it is likely that the operator may wish to remove bar 60 from carrier 30, whereas a bar 60 mounted on support 18a can be simply rotated out of the way.
While the embodiment described above is preferred, many other embodiments can use the same concepts for positioning and securing rod 20. As just one example, bed 13 need not have a machined groove 27. Rather, the groove may be on the surface 15 and formed between a number of aligned clamp jaw pairs or between a pair of linear bars mounted on surface 15. The meaning of “groove” in this instance should be interpreted expansively.
Similarly, the function of other components of tool 10 can be provided in a variety of ways. In particular, a guide track can be formed in many ways besides the two tubes 25 shown, as previously discussed.
It will be understood that this disclosure, in many respects, is only illustrative. Changes may be made in details, particularly in matters of shape, size, material, and arrangement of parts without exceeding the scope of the invention. Accordingly, the scope of the invention is as defined in the language of the appended claims.
