This is a 35 U.S.C. 371 application based on PCT/US94/00445, filed Feb. 16, 1994.
The invention relates to an apparatus for lengthening bones.
Apparatuses of this kind, which not only lengthen bones but in addition serve to transport bone fragments within part of a limb, to restore the mobility of joints, to correct congenital or acquired axial misalignments of the limbs, to treat fresh or slowly healing bone fractures, to aid the healing of artificial joints and to stiffen joints by acting as an external stabilizer or fixator, are sufficiently well known. Each such apparatus for lengthening bones comprises at least two frame elements at a distance from one another, which at least partly enclose the bone, to receive and fasten both fixation elements and tensioning elements or the like. The fixation elements, which transfer force to the bone and take the form of wires such as Kirschner wires, screws, Schanz's screws etc., transfix the bone about perpendicularly to its long direction or are drilled into and/or through the bone under aseptic, sterile conditions and fixed to the external frame elements. The tensioning elements or the like, which can be extended telescopically and which connect the frame elements to one another and establish their relative positions, are provided to produce controllable and continuous tractive and pressure forces to lengthen bones, treat bone fractures, and mobilize or stabilize joints.
All these apparatuses present the disadvantage of decidedly elaborate construction. For example, their frame elements are generally constructed as closed rings provided with a single row of holes to receive and fasten the fixation elements on the one hand and the tensioning elements or the like on the other hand. Apart from the fact that such closed rings are not needed in the treatment of every case, they complicate the manipulation of the whole apparatus, particularly for placement and removal during the surgical operation. Furthermore, such closed rings prevent direct access to the bone concerned. In addition, the arrangement of the fixation elements and tensioning elements or the like at each of the frame elements is largely predetermined by the single row of holes, so that it cannot be altered as desired. As another example, the tensioning elements or the like in these apparatuses are in many cases formed by a threaded sleeve with two threaded rods, one at each of its ends, which can be screwed into the threaded sleeve. By rotation of the threaded sleeve, in many cases both of the threaded rods fastened to the associated frame element are simultaneously lengthened or shortened. With this arrangement, fine adjustment of the distance between the frame elements is very difficult. Moreover, the threaded sleeve in such an apparatus has a fixed, unalterable length, so that a tensioning element or the like intended for a relatively short distance between the associated frame elements cannot be used for a larger distance between the associated frame elements. Such tensioning elements or the like, and hence these apparatuses, cannot be employed in a versatile manner when it is desired to vary the distance between the frame elements, unless the tensioning elements or the like are exchanged for others of different length.
Not the least result of these disadvantages is that manipulation of these apparatuses is relatively difficult, both during the operation phase and during the subsequent healing phase.
Finally, in practice such apparatuses have additionally proved to be very heavy, which severely affects acceptance by the patient.