Transport distraction apparatus

Abstract

Transport distraction apparatus for performing transport distraction osteogenesis is provided which includes a track capable of being formed into a curvilinear shape with a carriage movable longitudinally along the track. The carriage has a fixation plate secured or securable to it and at least one gear for moving the carriage along the track in order to adjust its position relative to the length of the track. The track has a series of formations extending along one edge of the track and engaged by the gear which is at least partially accommodated within a space between a plane including the front face of the track and a plane including the rear face of the track. Preferably, the apparatus creates a gap between a central region of the track and a patient's bone in use. A fixation plate is also provided.

Claims

1. A transport distraction apparatus suitable for performing transport distraction osteogenesis on the maxilla of a patient, the transport distraction apparatus comprising: a track having a rectangular cross-section with a width greater than its thickness to provide a front and a rear face and two longitudinally extending edges one of which has a toothed rack extending along its length and wherein the track is capable of being formed into a curvilinear shape with a curvature radius suitable for accommodation in the maxilla of a patient; a carriage movable longitudinally along the track and to which a fixation plate is releasably secured, the fixation plate (i) including a hook-shaped attachment formation configured to fit over an edge of the carriage and (ii) configured to extend between the track and a bone of a patient and wherein the carriage includes a first side and a second side, the second side extending in a direction transverse to the first side, and wherein the hook-shaped attachment formation engages the first and second sides; and a worm gear having a helically extending thread which meshes the toothed rack extending along one edge of the track for moving the carriage along the track in order to adjust its position relative to the length of the track, wherein the worm gear is at least partially accommodated within a space between a plane including the front face of the track and a plane including the rear face of the track, and wherein the track itself is made as a separate item from a separate elongate mounting and one end of the track is releasably secured by first fasteners to the separate elongate mounting that is securable by second fasteners to bone in a patient and wherein the first fasteners, track, and separate elongate mounting are configured to enable the track to be removed from the separate elongate mounting in a direction that is transverse to the length of the track so as to enable the track to be (i) removed from a patient as may be required and (ii) reinstalled in a patient without disturbing the secure attachment of the separate elongate mounting to the patient.

2. A transport distraction apparatus as set forth in claim 1, wherein the worm gear has formations at both ends thereof for releasable engagement by a tool for rotating the worm gear and thereby moving the carriage relative to the length of the track.

3. A transport distraction apparatus as set forth in claim 1, wherein the mounting or shaping of the track is such that a central region of the track and the attachment or attachment position for the fixation plate to the carriage are spaced forwardly of the separate elongate mounting that is configured to be operatively secured to bone in a patient.

4. A transport distraction apparatus as set forth in claim 3, wherein the rear face of the central region of the track is spaced forwardly of a rear face of the separate elongate mounting that is configured to be operatively secured to bone in a patient by a distance of the order of the thickness of the elongate mounting.

5. A transport distraction apparatus as set forth in claim 1, wherein the fixation plate is a generally flat plate having the hook-shaped attachment formation attaching the plate to the carriage, and wherein the fixation plate has deep generally sector shaped cut-out portions extending inwardly towards the attachment formation so as to define plural arms capable of independent bending to conform generally to a three-dimensional curve.

6. A transport distraction apparatus as set forth in claim 5, wherein the fixation plate is generally semicircular in shape with two, three, or four sector shaped cut-out portions defining a plurality of arms extending in a generally radial direction from the attachment formation.

7. A transport distraction apparatus as set forth in claim 6, wherein each of the arms is perforated with multiple perforations that can be used for securing the fixation plate in position, in use.

8. A transport distraction apparatus as set forth in claim 1, wherein the track is angularly adjustable relative to the separate elongate mounting.

9. A transport distraction apparatus as set forth in claim 1, wherein the track includes a titanium material configured to be formed into the curvilinear shape.

10. A transport distraction apparatus as set forth in claim 1, wherein the track includes a first end and a second end opposite the first end, the first end releasably secured to the separate elongate mounting by the first fasteners, and the second end being devoid of fasteners.

11. A transport distraction apparatus as set forth in claim 1, wherein the fixation plate and the hook-shaped attachment formation collectively define a U-shape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 is a perspective view of one embodiment of transport distraction apparatus according to the invention;

(3) FIG. 2 is a cross-section taken through the track and carriage of the apparatus illustrated in FIG. 1;

(4) FIG. 3 is a plan view of the apparatus illustrated in FIG. 1;

(5) FIG. 4 is a perspective view of a worm gear utilised in the apparatus illustrated in FIGS. 1 to 3;

(6) FIG. 5 is an enlarged and partly cut away elevation of the central region of the track and carriage of the apparatus illustrated in FIG. 1;

(7) FIG. 6 is an exploded perspective view of the carriage and fixation plate assembly of the apparatus illustrated in FIGS. 1 to 5;

(8) FIG. 7 is a view similar to FIG. 3 but illustrating the incorporation of the second aspect of the invention;

(9) FIG. 8 is an elevation of the apparatus illustrated in FIGS. 1 to 7 showing schematically the application of the apparatus to the maxilla of a human skull;

(10) FIG. 9 is a view similar to FIG. 1 blood of a second embodiment of the invention;

(11) FIG. 10 is a plan view (edge on) of the apparatus illustrated in FIG. 9;

(12) FIG. 11 illustrating elevation adjustments that can be accommodated by connection of the track to a separate elongate mounting;

(13) FIG. 12 illustrating perspective view the attachment of the track and separate elongate mounting of the embodiment illustrated in FIGS. 9 to 11;

(14) FIG. 13 is an exploded perspective view of the carriage and fixation plate of the second embodiment of the invention;

(15) FIG. 14 is a very much enlarged perspective view of the worm gear employed in the second embodiment of the invention; and,

(16) FIG. 15 illustrates the manner in which the various components of the apparatus can be bent in order to be accommodated in a patient.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

(17) As illustrated in FIGS. 1 to 7 of the accompanying drawings, one embodiment of transport distraction apparatus (1) according to the invention, hereinafter referred to as the distractor, includes a track (2) with a carriage (3) movable along at least a central part of its length wherein the carriage carries a perforated or mesh fixation plate (4). The track (2) is of a type generally known in the art and assumes the form of a titanium strip having a plurality of apertures (5) roughly centrally located with respect to the width of the track and spaced apart along its length. The apertures are suitable for receiving fasteners for securing the track directly to the bone of a patient. The track is such that it may be bent to take on a suitable curvilinear shape in use as shown quite clearly in FIG. 15.

(18) The width of the track is greater than its thickness to provide a front face (6) and a rear face (7) (see FIGS. 2 and 3) with two longitudinally extending edges. In the present embodiment of the invention the width is typically about three times the thickness of the track. The one edge of the track has a toothed rack (8) extending along its length.

(19) The carriage (3) is movable longitudinally along at least the central region of the track and carries the fixation plate (4) that is made as a separate component that easily attaches to the carriage. As shown most clearly in FIGS. 2 and 6, the carriage comprises a body part (12) having a recess (13) for accommodating the track and a rotatable worm gear (14) having the usual helically extending thread wherein the worm gear extends parallel to the track and engages the toothed rack that extends along the one edge of the track. Each end of the worm gear extends out of the body part of the carriage and is formed into a polygonal shaped head (15) for engagement by a socket carried by a tool (not shown).

(20) This arrangement enables the worm gear to be engaged from either end, as may be dictated by ease of access, and therefore the carriage can be moved in either direction by rotating the appropriate end of the worm gear in order to adjust the position of the carriage relative to the length of the track.

(21) The construction of the carriage and fixation plate is extremely simple so that assembly is greatly facilitated.

(22) To this end, the fixation plate has an extension (17) terminating in a hook (18) that extends from the part of the fixation plate forming the attachment formation. The hook fits over the outside of one edge of the body part of the carriage and the attachment formation bridges the opening to the recess (13) in the body part to close it. As illustrated in FIG. 2, the extension (17) of the fixation plate (4) is configured to extend between the track and a bone of a patient. The fixation plate is secured to the other side of the recess in the body to thereby hold the worm gear captive in its operative position and the carriage captive relative to the track. This part of the fixation plate thus forms the attachment formation mentioned above.

(23) With this arrangement the worm gear is substantially accommodated within the space between a plane including the front face of the track and a plane including the rear face of the track to provide an extremely low profile carriage with respect to the track.

(24) The fixation plate, as provided by this invention, is a generally flat plate of titanium having a multitude of perforations (19) therethrough with deep, generally sector shaped cut-out portions (21), extending inwardly towards the attachment formation so as to define plural arms (22) capable of being bent independently of each other to conform generally to a three-dimensional curved surface. In this particular instance there are four sector shaped cut-outs so that five generally radially extending arms are provided in a generally semicircular arrangement.

(25) The fixation plate has an angled connection zone (24) interconnecting the two parts of the fixation plate. In this manner the rear face of the central region of the track is spaced forwardly of the rear face of the end regions of the track by a distance that may typically be of the order of 1 mm depending on the thickness of the track. This offset accommodates the difference in thickness of the track and the diameter of the worm gear and would typically be slightly more than half the difference between the track thickness and the diameter of the worm gear.

(26) It is generally possible, although not necessarily convenient, to ensure that the relevant part of the track along which the carriage is to move in a particular instance is adequately spaced from the bone to ensure that the bone does not interfere with movement of the carriage, or, on the other hand, the carriage does not damage the bone. However, it is preferred that the second aspect of the invention be employed to facilitate this.

(27) In this instance, as shown most clearly in FIG. 7, the central region (2a) of the track is spaced forwardly of the rear face of the two end regions (2b) of the track such that attachment of said end regions to bone in a patient can more easily be achieved with the central region of the track and the carriage being out of contact with the bone.

(28) In use, detailed measurements of a patient's anatomy may be made and a three dimensional model is preferably constructed, conveniently using rapid prototyping or stereolithographic printing technology. This permits the trajectory of the track (2) to be carefully calculated and the track to be bent into the basically required shape beforehand. It may be necessary to use further fixation plates to secure the track (2) in position and these too can be prepared ahead of time.

(29) In calculating the trajectory of the track (2) it will be taken into consideration that it must be sufficiently spaced from other bones to permit uninhibited movement of the carriage and that it not have unacceptably sharp curves and the construction of the central region of the track described above greatly facilitates this.

(30) After proper planning it is relatively straightforward to secure the distractor in position on a patient during a surgical procedure using conventional fasteners, such as implantable titanium bone screws. FIG. 8 illustrates schematically the basic installation of the distractor.

(31) The important benefit that the distractor (1) exhibits is that it can be easily used on a range of curved trajectories.

(32) In this embodiment, the worm gear has a pitch of 1 mm, a threaded length of 6.6 mm, an outer diameter of 4.2 mm and a thread height of 0.6 mm. The toothed rack of the track has a pitch of 1 mm. The prescribed distraction rate and rhythm is 0.75 mm twice a day or 1.5 mm once a day, which, with a thread pitch of 1 mm, corresponds to one and a half turns of the worm gear per day. The patient is usually required to perform the daily distractions. In order to ensure that the healing tissue is not overstrained by more than 10%, it is assumed that patients are capable of rotating the worm gear in increments of half a turn to an accuracy of within 36. To assist the patient, a tool (not shown) is provided, the tool being configured to indicate through a ratchet mechanism when a half turn has been completed.

(33) The distractor is easy to assemble and use; is robust and cost effective and, most importantly, permits distraction on curved trajectories.

(34) It will be appreciated, however, that many other embodiments of the invention exist which fall within the scope hereof, particularly regarding the configuration and shape of the track, fixation plate and carriage. For example, the gear need not be a worm gear but could, for example, be a pinion gear.

(35) The distractor can achieve bilateral locomotion and the traction is accomplished by the worm propagating either on top of the rail or at the bottom (depending on its placement), thus providing a low profile, almost as thick as the rail itself. Due to the low profile and the design parameters the distractor of this invention can follow a spiral path and a curvature having a radius of as little as 20 mm.

(36) Referring now to the embodiment of the invention illustrated in FIGS. 9 to 15, one of the main differences is that the track (31) is made as a separate item from a separate elongate mounting (32) and is attached to one end of the latter by means of a pair of fasteners. This arrangement has a number of advantages in that the track can be removed from a patient as may be required and he reinstalled without disturbing the secure attachment of the separate elongate mounting to the patient. Removal may take place in a direction that is transverse to the length of the track so as to enable the track to be (i) removed from a patient as may be required and (ii) reinstalled in a patient without disturbing the secure attachment of the separate elongate mounting to the patient.

(37) Also, as shown clearly in FIG. 11, the arrangement enables the angular attachment of the track to the separate elongate mounting to be varied within certain limits that provides an advantage in orientating the various components suitably. As shown most clearly in FIG. 12, the track is secured to the separate elongate mounting using a pair of screws (33).

(38) The use of a separate elongate mounting has an additional advantage in that it enables the track, at least in the region of attachment to the mounting, to be spaced from the bone of the patient with the advantages indicated above.

(39) In this embodiment of the invention the fixation plate (35) has narrower arms (36) each with a single row of perforations (37) in order to provide additional flexibility for contouring the arms for attachment to a patient. A contoured set of arms is illustrated simply by way of example in FIG. 15.

(40) The attachment of the fixation plate to the carriage (38) is simplified in that it uses two screws (39), as shown in FIG. 13. The hook of the first embodiment of the invention is therefore omitted.

(41) As regards the formations whereby the worm gear (41) can be rotated by a suitable socket on a tool (not shown), these assume the form of square cross-sectioned heads (42) with rounded front and rear faces such that a socket can be effectively engaged with such a head whilst not being coaxial and rotation can be achieved somewhat in the manner of a universal joint.

(42) This embodiment of the invention therefore has a number of advantages over the embodiment described with reference to FIGS. 1 to 7.

(43) It will be understood that numerous other variations may be made to the embodiments of the invention described above without departing from the scope hereof. Also, the different aspects of the invention may be used either individually or in any combinations of two or all of the aspects, as design considerations may dictate.