Patent Application
20080009871
Turning now to
Referring to
The second arm 14 has a V-shaped clamping surface 40 oriented to support the bone at two points 42, 44 on the opposite side of the bone from the clamping end 26 of the clamping screw 24 such that the bone clamp securely holds the bone and the bone plate together at three points. The surface 40, preferably at least at points 42, 44 is provided with a bone engaging structure such as teeth or ridges 46. An opening 48 is positioned at the apex of the V-shaped clamping surface 40. The opening 48 is preferably oblong (longer in the direction in which the second arm 14 extends) and sized for passage of a drill bit that may be extended through the axial bore 32 in the clamping screw 24. As described in more detail below, the opening 48 is preferably oblong to accommodate passage of the drill bit even when the bridge portion 16 flexes when the frame 11 is subject to a pre-load, as now described.
The bridge portion 16 is structured by material and dimension to flex when the clamp 10 applies a compressive force between the first and second arms 12, 14; i.e., by axial movement of the clamping end 26 of the clamping screw 24 toward the second arm 14 to apply a force against the bone 18 and the plate 20 sufficient to deform the bridge portion 16. Such flexing of the bridge portion 16 applies a preload that allows the frame 11 to function as a spring and the clamp 10 to maintain compression over a range of bone-plate dimensions. By way of example only, the bridge portion 16 may flex by approximately up to 6°, and that may correspond to an approximately 2 mm change in the distance between the first and second arms 12, 14. Thus, if the clamp 10 is inadvertently moved such that the clamp 10 and plate 20 are turn moved along the bone a small distance in which the bone decreases in diameter up to 2 mm, the clamp will maintain compression on the bone and the plate at the new location. It is appreciated that adjustment of the material and/or dimension of the bridge portion 16 operates to adjust the spring rate of the clamp. In exemplar embodiments, the bridge has a cross-sectional area of 0.018 in2 to 0.055 in2 but may be larger or smaller depending on the overall size of the clamp in view of the bone(s) for which it is intended. The geometrical cross-section of the bridge portion 16 is such that the force applied by the clamping screw to induce the stress sufficient for the above described flexing is less than the yield strength of the material. In view of the above, the clamp 10 is preferably adapted to apply 30 to 100 lb·f.
As indicated above, the opening 48 is oblong. The oblong configuration of opening 48 allows at least a portion of the opening to remain in alignment with the longitudinal bore 32 of the clamping screw 24 for passage of a drill even after the bridge portion 16 flexes by up to several degrees.
The bone clamp 10 may also include a handle 50 removably coupled to the frame 11. The frame 11 preferably includes handle mount 52 at the upper end of the bridge portion 16 extending opposite the first arm 12. The mount 52 includes a threaded bore 54 and a flat stop 56. A set screw 58 is provided in the threaded bore 54 for coupling the handle 50 to the mount 52 and preferably remains coupled to mount 54 at the bore 54 even when the handle 50 is decoupled. The set screw 58 includes a lower threaded shank 60, an upper knob 62 and an shoulder 64 therebetween. The knob 62 is preferably provided with driver engagement means, such as corners 66 in a hex arrangement. The handle 50 includes a gripping end 68, a shaft portion 70 and a coupling end 72. Coupling end 72 includes a lateral slot 74 having an angled side wall 80, and a rear edge 76 spaced a fixed distance from the slot 74. In assembly, the set screw is provided in the threaded bore with the bottom of the shoulder 64 substantially level with the top surface of the mount 52. The slot 74 of the coupling end 72 of the handle 50 is positioned about the shoulder 64, with the edge 76 located between the shoulder 64 and the stop 56 and the shoulder 64 contacting the angled wall 80 of the slot 74. This configuration accommodates a range of part tolerances and assures a tight fit. When the knob 62 is rotated and tightened down on the coupling end 72, the handle 50 is rigidly held relative to the frame 11. A driver may be coupled at driver engagement means 66 for final tightening. The handle 50 can be used to facilitate placement of the clamp, movement of the clamp and plate along the bone after the clamping screw is partially located within a screw hole but before a clamping force is applied, and removal of the clamp from the surgical site. However, during the surgical procedure the handle can be quickly disassembled to provide increased visual and physical access to the surgical site. In addition, removal of the handle such allows manipulation of the arm under fluoroscopy with minimal inconvenience.
One method of using the clamp is now described with reference to
A K-wire 90 may be drilled through a preferably strategically located fixed angle K-wire hole 92 in the plate 20 and into the bone therebeneath (not shown) to stabilize the fracture reduction. As indicated above, a recess 30 in the head 28 of the clamping screw 24 provides additional clearance for the K-wire. The K-wire 90 holds the plate 20 over the fracture at the location where the surgeon has anticipated it should be implanted. The plate location is then confirmed by viewing the location of the plate and the K-wire relative to the bone under fluoroscopy. If indicated by fluoroscopy, the plate 20 can be repositioned to a new location by removing the K-wire 90, loosening the clamp 10, and then repositioning the plate 20. The K-wire can then be redrilled and the new location again confirmed relative to the anatomy under fluoroscopy. The use of K-wires through strategically located fixed angle holes in a plate is described in detail in U.S. Pub. Nos. 20050065524 and 20050182406 to Orbay, which are hereby incorporated by reference herein in their entireties.
Once the location is approved by the surgeon, a hole is drilled through the longitudinal bore 32 of the clamping screw 24 and the bone screw hole 88 in the plate aligned therebeneath. The clamp 10 is then removed and a screw (not shown) is inserted through screw hole 88 in the plate and into the bone. With the plate fixed relative to the bone, the remaining screws and other fasteners, if any, are then inserted through the plate and into the bone in a conventional manner.
It is appreciated that it may be desirable to facilitate quickly dropping the clamping end of the clamping screw onto the plate (as opposed to rotating the clamping screw all the way down) from a clamp-release position into an initial plate contact position prior to applying a clamping force. Turning now to
In addition, while the bridge portion of the frame of the clamp is adapted to flex for pre-load by controlling its dimensions and materials,
The clamp and handle are preferably constructed of stainless steel, with the clamp made from 17-4 stainless steel for its mechanical properties. The clamp and handle may be constructed by electrical discharge machining (EDM), water jet machining, or laser cutting, among other means. As such, the clamp is relatively easy and inexpensive to manufacture.
There have been described and illustrated herein embodiments of a bone plate clamp and a method of using the same. While particular embodiments of the invention have been described, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise. Thus, while particular dimensional tolerances have been related to the angular displacement of the bridge portion under pre-load, it is recognized that the actual dimensional tolerances provided by a particular angular displacement will be related to the overall size of the frame and that clamps of different sizes may be able to accommodate a different tolerance for dimensional change under pre-load. In addition, the clamp frame and handle may be constructed of materials other than those described. Furthermore, while several alternate embodiments have been described, it is appreciated and the intention of this disclosure that features of the several embodiments may be used with each other, without limitation. It will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided invention without deviating from its scope as claimed.
