Patent Application
20060241608
The present invention relates to the general technical field of surgical devices for fixing together and aligning the two bony parts of a joint relative to each other, and in particular a metatarso-phalangeal joint, in order to perform arthrodesis.
Arthrodesis or fusion of the first metatarso-phalangeal (MTP) joint is often the treatment of choice for several indications, such as hallux valgus, hallux limitus or rigidus, degenerative joint disease, severe dislocation or subluxation, and degenerative deformities. Fusion can be used to correct deformities associated with these indications or to alleviate joint pain associated with movement of the MTP joint. Fusion of the first MTP joint allows the patient to walk without discomfort, usually with minimal impact on gait pattern. In fact, where the indicated pathology led to a significant disruption in the patient's ability to walk, fusion may actually improve the patient's gait pattern.
As a general rule, arthrodesis can be problematic because it results in a joint position that is defined and irreversible. Thus, it is very important for arthrodesis of an MTP joint to be performed carefully so that the two bones will be accurately positioned relative to each other to avoid any subsequent difficulty and to preserve the patient's ability to walk as normally as possible.
In one common fusion procedure, the articulating aspects of the metatarsal bone and phalanx are prepared as necessary so that the bones can be positioned at appropriate dorsi-flexion and varus-valgus angles. Then a pair of bone fasteners, such as 4-0 cannulated screws, are implanted across the MTP joint to fix the joint position. Bone graft may be introduced in areas of bone separation to facilitate complete fusion of the joint.
In one alternative, a fixation plate is implanted across the joint and is typically fastened to the opposing bones by bone screws. The fixation plate is bent by the surgeon to achieve an angle in the dorsi-flexion plane that is specific to the patient, thereby reducing difficulty for the patient while walking and minimizing possible future complications. Many prior plates are unsuitable for bending through a varus-valgus angle, which means that they are not capable of implementing arthrodesis that is sufficiently close to the optimum anatomic orientation of the two bones to be fused together.
More recently, fixation plates have been provided that are pre-formed with a fixed varus-valgus angle and a fixed dorsi-flexion angle. An example of this type of plate is the HALLU®-C Plate offered by Newdeal SA. This plate constitutes two linear plate sections aligned at a fixed ten degree varus-valgus angle relative to each other. The plate is also bent at its mid-line to form a ten degree dorsi-flexion angle. Each linear plate section includes an elongated slot flanked by two screw holes arranged along the longitudinal axis of the section. Other details of this plate appear in published application US2003/0060827, published on Mar. 27, 2003, the disclosure of which is incorporated herein by reference.
Fixation plates of this type represent an improvement over prior plates that required the surgeon to bend the plate at the dorsi-flexion angle during the surgical procedure and that do not permit any varus-valgus angle. However, there is still room for improvement in fixation plates for the MTP joint, especially for the first MTP joint. In particular, there is a need for a fixation plate that provides greater flexibility in positioning the bone fasteners fixing the plate to the associated bones, especially the phalanx. There is also a need for a fixation plate that presents a lower profile to minimize soft tissue irritation.
The present invention satisfies the need for an improved fixation plate for arthrodesis of the metatarsal-phalangeal joint. In one embodiment of the invention, the plate includes a metatarsal portion that is generally elongated to extend along the distal length from the head of the metatarsus bone. A series of chamfered screw holes extend along the axis of the metatarsal portion.
The plate further includes a phalanx portion connected to the metatarsal portion by an intermediate portion of the plate. The phalanx portion is enlarged and asymmetric relative to the elongated metatarsal portion. In the preferred embodiment, the phalanx portion includes a medial wing and an opposite lateral wing that is axially offset from the medial wing. Each wing supports a chamfered screw hole. A central region between the two wings also supports thee screw holes, laterally and axially offset from each other.
In a further aspect of the invention, the entire plate is curved to provide a curved bone engaging surface that generally follows the contour of the metatarsal bone and phalanx. Rather than incorporate a pre-determined varus-valgus angle offset between the metatarsal portion and phalanx portion of the plate, the fixation plate of the present invention is configured so that the phalanx portion cups the proximal end or base of the phalanx and the metatarsal portion simply overlays the distal portion of the metatarsus bone to be fixed to the bone at whatever angle is dictated by the orientation of the phalanx portion fixed to the base of the phalanx. In the preferred embodiment, the plate is bent at the intermediate portion to an appropriate dorsi-flexion angle.
In order to minimize the profile of the plate, the present invention contemplates a plate thickness of about 1 mm. In addition, the perimeter of the plate is contoured about the screw holes to reduce the amount of material across the surface of the plate.
One benefit of the present invention is that it provides a plate for arthrodesis of the MTP joint that can be firmly fixed to the bones of the joint. Another benefit is that the plate provides for a variety of screw fixation points, especially across the base of the phalanx.
A further benefit achieved by the fixation plate of the present invention is that is exhibits a minimal profile to reduce its prominence over the bones and minimizes tissue irritation. These and other benefits of the invention will be appreciated upon consideration of the following written description together with the accompanying figures.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains.
The distal bones of the first toe, or great toe, are shown in
The distal portion 12 is generally elongated with at least two, and most preferably three, holes 22 positioned substantially along the longitudinal axis of the portion. The holes 22 are configured to receive the shank of a bone fastener, such as a bone screw. In one aspect of this embodiment, the holes 22 include a circumferential chamfer 24. This chamfer allows the use of two different sizes of bone screw. In a specific embodiment, the holes 22 have a diameter of 3.8 mm with a 120 degree chamfer 24 to produce a proximal diameter of 5.3 mm. This specific screw hole is configured to receive either 2.7 mm or 3.5 mm cortical screws.
In the illustrated embodiment, the screw holes 22 are configured to receive non-locking screws. In an alternative embodiment, the screw holes are designed to receive locking screws, such as by the incorporation of locking threads (not shown) within the screw hole. The locking threads can be of a variety of known configurations as dictated by the particular cortical locking screw. In a specific embodiment, the locking threads may be at 0.5 mm pitch, with a 4.0 mm major diameter and a 3.6 mm minor diameter.
In the preferred embodiment of the invention, the screw holes 22 are spaced at 6.0 mm intervals. In one aspect of the invention, the perimeter 28 of the distal portion 12 is contoured around the screw holes to reduce the plate material in the area around the holes that does not carry any appreciable load.
The proximal or phalanx portion 14 of the plate is asymmetric, as best seen in
Each wing supports a corresponding screw hole 32, 36. The screw holes are preferably configured like the screw holes 22 described above to include the circumferential chamfer 24. The screw holes 32, 36 may accept locking or non-locking cortical screws, as described above. As with the screw holes in the distal portion 12, the perimeter of each wings 30, 34 is contoured around the corresponding screw holes 32, 36, to reduce the plate profile or prominence above the bone and minimize soft tissue irritation.
The proximal portion 14 includes a central region 38 between the two wings. In the preferred embodiment, the central region 38 includes three screw holes 40, 42 and 44. The center of each of these screw holes is axially and transversely offset relative to each other, as well as relative to the screw holes 32, 36 in the wings. The screw hole 42 may be axially aligned with the screw holes 22 in the distal portion 12 of the plate 10 and/or along the longitudinal axis of the distal portion.
In the preferred embodiment, the proximal portion 14 of the plate includes five screw holes 32, 36, 40, 42 and 44. The screw holes are arranged so that a screw can be threaded into the phalanx through each hole without conflict. The surgeon may select all or any subset of the screw holes for fixation of the plate 10 to the phalanx. This flexibility in screw placement is particularly beneficial for patients with osteopenic bone, where a portion of the bone has been resected or in cases where the base of the phalanx has been fractured. Moreover, the arrangement of the screw holes across the proximal portion 14 allows the surgeon to select a minimum of two screw positions that optimally affixes the plate 10 to the bone. In other words, with the five screw holes in the proximal portion, the surgeon can introduce two bone screws in ten different orientations (e.g., placing a screw in holes 32 and 36, or in holes 40 and 36, or in holes 42 and 44).
It can be appreciated that the arrangement of screw holes in the plate 10 accommodates any varus-valgus angle at the time of implantation. In one method for implanting the plate 10, the surgeon determines the number of screws necessary for strong attachment of the plate to the phalanx. The proximal portion 14 of the plate is positioned on the phalanx and the bone screws are driven into the bone to attach the plate to the bone. (It is understood that the bone is prepared to receive the bone screws according to accepted practice, such as by pre-drilling and tapping a bore in the bone). With the proximal portion attached to the phalanx, the phalanx can be positioned at an acceptable varus-valgus angle. In so doing, the distal portion 12 of the plate 10 will shift position relative to the metatarsal bone, but will always maintain sufficient contact with the bone.
Once the acceptable phalanx-metatarsal bone angle has been achieved, the distal portion 12 may then be attached to the metatarsal bone using any combination of bone screws in the screw holes 22. It can therefore be appreciated that the fixation plate 10 of the present invention eliminates the difficulty associated with prior fusion plates in achieving or accommodating an acceptable varus-valgus angle. The plate 10 accepts any angle desired by the surgeon and does not enforce a pre-determined varus-valgus angle like prior plates. With the screw hole arrangements of the plate 10 of the present invention, the surgeon can produce valgus angles ranging from about five degrees to about ten degrees for fixation of the first toe.
This aspect of the plate 10 also facilitates manufacture of the plate. In one manner of making the plate, a sheet of material may be stamped into the flat pattern shape shown in
In a further feature of the fixation plate 10, the bone engaging surface 18 of the plate may be contoured at a radius approximating the surface of the bone, as shown in
In addition to the contour of the surface 18, the plate may also incorporate a curvature of the upper surface 19 along the length of the plate, as best seen in
The fixation plate 10 preferably incorporates a pre-determined dorsi-flexion angle α, as shown in
The plate 10 is formed of any medical grade material that is sufficiently strong to support the toe until fusion is achieved. In the preferred embodiment, the plate is formed of a titanium alloy, such as TI-6AL-4V. In order to maintain a minimal profile, the plate has a thickness of about 1 mm.
In the illustrated embodiment, the plate 10 is configured for the right foot of the patient. It is of course understood that a plate for the left foot will assume a mirror image of the plate shown in
While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.
