Abstract
The invention relates to an external fixator device and the method of its use in treating bone fractures and in orthopedic interventions, such as corrective osteotomies.
Claims
1. An external fixator for fixing bone segments into a construct comprising: a frame (1) consisting of a first bar and a second bar (1a, 1b), wherein the first bar and the second bar are opposed to each other in a clamshell fashion and clamped together by a plurality of fasteners; and a plurality of bone pins (2) interposed between the first bar and the second bar, wherein the clamping of the first bar and the second bar results in clamping of a subset of the plurality of bone pins interposed between the bars, wherein the plurality of bone pins are at a multitude of pre-set positions, and wherein at least one unclamped bone pin of the plurality of bone pins is effectively clamped by insertion of one or more fixing elements on a surface of the at least one unclamped bone pin of the plurality of bone pins disposed between the first bar and the second bar.
2. The external fixator of claim 1, wherein the plurality of bone pins (2) can be inserted through the frame (1) between the first bar and the second bar at pre-defined positions, wherein the pre-defined positions comprise at least two different angulations with respect to the frame (1).
3. The external fixator of claim 2, wherein the pre-defined positions include (i) a first plurality of grooves perpendicular to a longitudinal axis of the frame and (ii) a second plurality of grooves at an oblique angle to the longitudinal axis of the frame, and wherein each of the second plurality of grooves has a depth which varies along a width of the frame.
4. The external fixator of claim 2, wherein the pre-defined positions include a first position at a first oblique angle to the longitudinal axis of the frame and a second position at a second oblique angle to the longitudinal axis of the frame, wherein the first position is substantially perpendicular to the second position.
5. The external fixator of claim 1, wherein the clamped subset of the plurality of bone pins are disposed between the first bar and the second bar at an angle perpendicular to the longitudinal axis of the frame, and wherein the at least one unclamped bone pin of the plurality of bone pins disposed between the first bar and the second bar at an oblique angle to the longitudinal axis of the frame remains unclamped.
6. The external fixator of claim 1, wherein each of the plurality of bone pins (2) interposed between the first bar and the second bar is located in at least one of: (i) a mid-plane of the frame, (ii) a first plane transverse to the mid-plane of the frame, and/or (iii) a second plane transverse to the mid-plane of the frame.
7. The external fixator of claim 1, wherein the first bar and the second bar (1a, 1b) are injection molded bars comprising a glass fiber or a carbon fiber reinforced polymer.
8. The external fixator of claim 7, wherein the first bar and the second bar (1a, 1b) are identical.
9. The external fixator of claim 1, wherein the plurality of fasteners comprises bolts and nuts (3).
10. The external fixator of claim 1, wherein the one or more fixing elements are shims (14).
11. An external fixator for fixing bone segments into a construct comprising: a frame (1) consisting of a first bar and a second bar (1a, 1b), wherein the first bar and the second bar are opposed to each other in a clamshell fashion and clamped together by a plurality of fasteners; and a plurality of bone pins (2) interposed between the first bar and the second bar, wherein the clamping of the first bar and the second bar results in clamping of a subset of the plurality of bone pins interposed between the bars, wherein the plurality of bone pins are at a multitude of pre-set positions, wherein the plurality of bone pins (2) can be inserted through the frame (1) between the first bar and the second bar at pre-defined positions, wherein the pre-defined positions comprise at least two different angulations with respect to the frame (1), wherein the pre-defined positions include (i) a first plurality of grooves perpendicular to a longitudinal axis of the frame and (ii) a second plurality of grooves at an oblique angle to the longitudinal axis of the frame, and wherein each of the second plurality of grooves has a depth which varies along a width of the frame.
Description
LIST OF FIGURES
(1) FIG. 1: A perspective view of the external fixator according to the present invention showing the frame and six bone pins
(2) FIG. 2: A frontal and top views of the external fixator attached to a fractured bone
(3) FIG. 3: A perspective view of the bar of the frame showing the inside-facing details of the bone pins clamping features
(4) FIG. 4: A perspective view of a section of the bar of the frame with three bone pins crossing at one of the clamping positions
(5) FIG. 5: Orthogonal views of a section of the bar of the frame with three bone pins crossing at one of the clamping positions
(6) FIG. 6 Cross sectional views of the frame showing the bone pins clamping features of the frame clamped onto the bone pins with the bolts and nuts of the frame
(7) FIG. 7: A perspective and view of the clamping shim for obliquely placed bone pins alone and inserted into the frame
(8) FIG. 8: Two drill sleeves passed through the frame of the external fixator
(9) FIG. 9 A spacer pin protecting the obliquely inserted bone pin from being unintentionally clamped when without the shims
(10) FIG. 10: A transverse or T-bar attached to the axial bar for holding bone pins inserted into short bone segments near adjacent joints
(11) FIG. 11: An external fixator construct comprising a link connecting two separate bone pins-clamping units
DETAILED DESCRIPTION
(12) FIG. 1 shows the perspective view of the external fixator frame with six bone pins 2 according to the present invention. The frame 1 is comprised of two identical bars 1a and 1b opposed to each other in clamshell fashion and clamped together with a multitude of fastening elements, e.g. bolts and nuts 3, nuts being on the lower side of the frame and thus not visible on this view. At each position for bone pins there are preferably recesses that can accommodate three pinsone can be placed perpendicularly to the long axis of the frame and the other two obliquely. Large recesses 4 at each end of the frame can receive and clamp auxiliary elements of the fixator, e.g. a transverse T-bar.
(13) FIG. 2 shows a frontal and a top view of the external fixator attached to a fractured bone 5. While many options exist for placing pins into the bone fragments with a total of 45 choices for the pins, the configuration shown with three pins per bone segment, two of which are perpendicular to the frame, is simple and easy to execute and modulate for overall stiffness. The perpendicular bone pins 2a, 2c, 2d and 2f are in the mid-plane of the external fixatorthe oblique bone pins 2b and 2e are angled in the transverse plane, as shown in the top view.
(14) FIG. 3 shows a segment of a frame bar 1b with the inside facing features that allow clamping of the bone pins at any one of the positions and in any of the three orientations. Between any two pin positions there are holes 6 for passing the clamping bolts. For clamping perpendicular bone pins there are V-shaped grooves 7 and 8 at each edge of the bar 1b. Exactly the same recesses exist in the bar 1a (not shown here). A deep V-shaped groove 9 is placed obliquely to the long axis of the frame and its depth also varies across the width of the bar, being shallower on the side that will face bone. This will result in the bone pin entering the bone at about the same line (close to the middle) as the perpendicular bone pins, provided that the distance to the bone is properly chosen. Elevated features 10 and 11, also with a V-shaped groove on the top, will clamp the bone pins seated in the corresponding deep groove of the frame bar 1a (not shown). The depth of the groove 9 is sufficient to allow interference-free crossing of the pins in the groove 9 and in the perpendicular grooves 7 and 8.
(15) FIG. 4 shows a perspective view of three bone pins 2x, 2y and 2z crossing at a point in mid section of the frame bar 1b, with the corresponding section of the frame bar 1a lifted off and turned by 90 degrees to show the pins.
(16) Between the bone pin positions there are transverse holes 6 for passage of the bolts 3.
(17) FIG. 5 shows orthogonal views of the frame bar 1b and the three bone pins 2x, 2y and 2z. The distance 12 where the axis of the pins cross in the side view is the ideal distance between the frame and the bone, so that all pins enter the bone at about the same transverse positionabout the middle of the bone.
(18) FIG. 6 shows a section of the fixator frame with four different cross sections A-A, B-B, C-C and D-D. The bolts 3 and the nuts 13 are used to clamp the frame and the interposed bone pins together. Nuts are preferably fixed in the frame, by e.g. ultrasonic welding.
(19) FIG. 7 shows a fixing element, e.g. a shim 14 in the perspective view and also inserted between the bone pin 2 and the groove 9 in the frame bar 1a. The holes 15 in the shim are to facilitate its insertion and removal into/from the intended position along the bone pin.
(20) FIG. 8 shows a perspective view of the external fixator according to the present invention with two drill sleeves 16a and 16b clamped in the frame 1 to facilitate pre-drilling of the holes in the bone segments for insertion of the bone pins in the exact positions. The outside diameter of the drill sleeves 16 is the same as that of the pins; the inside corresponds to the diameter of the drill used to pre-drill the bone. The sleeves can be clamped so that their length pointing out from the frame towards the bone is equal to distance 12 of FIG. 5. Before pre-drilling the holes in the bone segments the fracture should be reduced if a single frame as shown here is used to stabilize the fracture.
(21) FIG. 9 shows a perspective view of a segment of the frame 1 with a bone pin 2 inserted in an oblique direction. In this position, the pin is not clamped without a shim. However, deformation of the frame bars 1a and 1b, squeezed by the bolts 3a and 3b, could still cause a partial engagement of the bone pin in the frame. To prevent this, a dummy, short pin 17 can be inserted at the same position as the bone pin 1, in the perpendicular direction. This is not needed if there is another bone pin in that location.
(22) FIG. 10 shows a perspective view of the fixator frame with a T-bar 20 locked in the large recess 4 between the bars 1a and 1b of the main fixator frame. The purpose of this T-bar is to allow placement of bone pins 21a-e into the very end of the fractured, or osteotomized bone.
(23) FIG. 11 shows an external fixator frame consisting of two sections 30 and 31, connected by a universal joint 32, shown only schematically. The sections 30 and 31 are just the shorter versions of the frame 1, otherwise of the same construction and with the same functional features. Use of connecting universal joint is common in the art to facilitate more precise reduction of the fracture, should the first one, obtained in the primary surgical intervention, not be adequate. Unfortunately, the production of such a frame entails much higher production costs, so for the undeveloped countries in may not be economically feasible.
(24) The invention discloses an external fixator frame composed of two identical parts, opposed to each other in a clamshell fashion, clamped over interposed bone pins by a set of nuts and bolts providing a stable fixation of the bone pins against bending and axial loads. The bone pins can be inserted through the frame at a multitude of positions, either perpendicularly, or at an angle to the long axis of the frame. Clamping of the fixator frame locks only the bone pins placed perpendicularly to the framethose inserted at an angle are locked only upon insertion of shims between the pins and the frame. The frame components are injection molded using a high performance, fiber-reinforced polymer. In the proposed method of use, preferably three pins are inserted in each of the bone segments, no more than two parallel to each other. In the initial period of fracture healing, only two pins are locked making the construct stiffness relatively low. After a period of one to two weeks, the third pin is locked by insertion of the shim, increasing the construct stiffness by more than a factor of two in what is referred to as reverse dynamization. In the final phase of the fracture healing, after additional two to three weeks, pins can be either selectively removed, or unlocked in the frame by shim removal to effect conventional dynamization.
