Centering Means for Holes of Intramedullary Nails

This invention relates to centering means for holes of intramedullary nails, of the type used in bone surgery.

For the surgical repair and stabilization of fractures of long bones, such as the femur, tibia, humerus and fibula, it has long been known to insert an intramedullary nail of appropriate length into the medullary cavity, and to anchor bone fragments to the nail. Anchorage is achieved by means of bolts or pins which are screwed into the walls of the bone on opposite sides of the medullary cavity, and these bolts or pins pass through transverse holes located in the vicinity of the proximal and distal ends of the intramedullary nail. The anchoring bolts are held in position until confronting edges of the broken bone have completely grown back, and are then extracted to allow the intramedullary nail to be removed. The procedure for inserting the bolts requires (a) accurate location of the transverse holes in the intramedullary nail, (b) drilling through the cortical and spongy tissue of the bone to provide passages for the bolts, and (c) inserting bolts in such a way as to secure the nail in a suitable position with respect to the bone fragments.

The most critical part of this procedure is to determine, from outside, the location and center of so-called blind holes in the nail; this must be done with the maximum possible accuracy in order to avoid any misalignment of drilled holes and repeated drilling of the bone.

The known method of centering provides for the use of a drilling mask or frame consisting of a longitudinal template which can be attached to the intramedullary nail at its proximal end and which is provided with holes to house bushes for drilling the bone at positions aligned with the holes in the nail.

The centering of holes toward the proximal end of the intramedullary nail, close to the area of attachment to the frame, is a relatively simple operation which does not give rise to any special problems. On the other hand, the centering of blind holes near the distal end of the intramedullary nail is very much more difficult because of the elasticity of the template, and play in the vicinity of coupling between the frame and the intramedullary nail.

A great many centering devices have been proposed, using orientable drilling bushes or a more rigid drilling template with less play in the frame/nail coupling. However, none of these proposed arrangements have been sufficiently rigid; as a result, these proposed arrangements do not ensure the accuracy which is needed for repeatable precision drilling at the distal end of the nail.

It should also be noted that all the known centering devices mentioned above require an X-ray source, which is used by the surgeon to check the hole location with respect to the outer surface of the patient's limb.

The known techniques are hazardous because they require the patient and healthcare personnel surrounding him to suffer repeated and prolonged exposure to X-rays, which are well known to be harmful beyond certain limits, but which cannot be switched off without compromising the final result of an operation. Also, X-rays cannot be used to accurately establish the axial orientation of a hole with respect to the external surface of the limb because the X-ray image is projected onto a plane and cannot be used for a clear determination of any errors in the inclination of the hole.

U.S. Pat. No. 4,667,664 discloses a centering device for the blind holes of an intramedullary nail, wherein a bar supports an X-ray aiming device at one end and the intramedullary nail at the other end; the device is provided with a stabilizing member comprising an arm which connects a median portion of the bar to an intermediate point, between the proximal and distal ends of the nail. But even this device is not sufficiently stable with respect to the distal end of the nail, and therefore the device does not offer maximum assurance of accuracy and stability in the drilling of bone at a distal location. Also, this device again makes use of X-rays, and is therefore unreliable and unsafe.

The principal object of this invention is to overcome the above-mentioned disadvantages by providing a hole-centering device and technique which offers high reliability and accuracy, without requiring the use of X-rays.

Another object is to meet the above object with a device and technique of extreme simplicity and accuracy.

The invention achieves these objects, for the case of an intramedullary nail having proximal and distal ends, with plural transverse holes close to these ends, by providing a frame for supporting transverse bolts from outside the involved limb. The frame comprises a longitudinal template having transverse guide bores for drilling tools, and these guide bores are spaced to accord with the spacing of the transverse holes of the intramedullary nail. The frame further comprises at its proximal end a transverse arm for removable attachment of the proximal end of the nail, such that the template is parallel to the nail, with template bores at approximately equal offset from and potential alignment with holes of the nail. At the distal end of the frame, provision is made for limited displacement of the frame in a plane that is substantially perpendicular to the transverse holes and bores, and such limited displacement is guided by a stabilizing member which can be anchored to the distal bone fragment that contains the distal end of the intramedullary pin, the anchorage being distally beyond the distal end of the intramedullary nail. Preferably, the stabilizing member includes a bar that is threaded for screwed anchorage to the bone, in the proximity of a distal metaphysis, such that the axis of the bar is substantially perpendicular to the axis of the bone. A metal-detecting instrument carried by the frame is capable of detecting the location of a blind hole in the intramedullary nail, in the course of stabilized and guided displacement of the distal end of the frame; when this instrument detects alignment of the guide bore with the blind hole, the distal end of the frame is clamped to the stabilizing member, and guided drilling can proceed.

The invention will be described in detail, for a preferred embodiment, in conjunction with the accompanying drawings, in which:

FIG. 1 is a side elevation of a device of the invention, namely, centering means for an intramedullary nail, shown in application to a bone having a fracture between distal and proximal fragments of the bone;

FIG. 2 is a front elevation of a distal feature of the device and bone of FIG. 1;

FIG. 3 is a plan view, from above, of the feature of FIG. 2;

FIG. 4 is a perspective view of the distal feature of FIGS. 2 and 3, on a slightly enlarged scale;

FIG. 5 is a simplified view in perspective to illustrate a control assembly which can be attached to the centering device of FIG. 1; and

FIGS. 6a, 6b, and 6c diagrammatically illustrate three successive stages in a procedure for using the device of the invention.

With initial reference to FIG. 1, hole-centering means of the invention is generally indicated at 1, in application to a bone having a fracture F between longitudinal ends of the bone, and an intramedullary nail 9 is positioned in the medullary cavity for repair of the fracture F; nail 9 is of metal, preferably stainless steel. The device 1 comprises a frame 2, formed from an elongate template 3 which can be secured in fixed positions to an offsetting arm 4. Arm 4 carries a chuck sleeve 5 having an adjustment grip 6. The chucking end 7 of sleeve 5 includes elements for releasable chucking engagement to the proximal end 8 of the intramedullary nail 9, the distal end of which is indicated at 10. Nail 9 has distal-end holes 11, 12 and proximal-end holes 13, 14 designed to receive transverse bolts (not shown), which can be placed in the cortical or spongy tissue of the bone after the nail has been positioned in the medullary cavity M. Intermediate holes 15, 16 for further stabilization of the stumps close to the fracture may also be provided in nail 9, and the axes of all transverse holes will be understood to be parallel to each other and perpendicular to the axis of nail 9.

Transverse passages or guide bores 17, 18, 19, 20, 21, 22 are designed to receive bushes 23 for drilling tools, suggested by dashed lines in FIG. 1 and are provided along the longitudinal length of template 3. Suitably, the distances from transverse member 4 for passages 17, 18, 19, 20, 21, and 22 and for corresponding holes 11, 12, 15, 16, 13, 14 are identical, so that their alignment depends only on the fact that the template 3 and the nail 9 are parallel, although this may vary because of elasticity of the template and its attachment to transverse member 4. An alignment device, which is indicated as a whole by reference number 25 (FIG. 5), is provided to ensure that these two can be adjusted to be parallel, and therefore that the passages in the template are centered on the blind holes in the intramedullary nail.

In particular, the alignment means 25 comprises a stabilizing member which can be anchored at the distal end of the bone, in a longitudinal position beyond the distal end 10 of the intramedullary nail, and the stabilizing member can be secured to the distal end of template 24 by attachment means of adjustable length.

More specifically, the stabilizing member comprises a bar 26 with a threaded end 27 which can be anchored in a distal condyle of the bone and has an exposed or free end 28 which forms a solid reference and abutment member for the distal end 24 of the template.

The attachment means of adjustable length comprises transverse guide means which extend between the distal end 24 of the template and stabilizing bar 26. Such guide means may comprise a guide block 29 which can be secured at the free end 28 of bar 26 by means of a screw clamp 30, at the same height as template 3. The block 29 has a guide bore 31 which slidably houses the free end 32 of a transverse rod 33 that is fixed to a supporting block 34; and block 34 is rigidly fixed to the distal end 24 of template 3 by means of a bolted connection 35. A stop or set screw 36 has threaded engagement at 37 (FIG. 4) to slide 29, whereby to lock an adjusted position of rod 33 with respect to block 29; and it will be understood that the functions of guide block 29 and of supporting block 34 can be reversed, without altering the operation of the device. Translational movement of the distal end 24 of the template may be effected manually or by mechanical, electromechanical or other actuating means.

From structure thus far described, it will be seen that the transverse extent of the connection between the distal end 24 of template 3 and the free portion of stabilizing bar 26 can be selectively varied to vary the axial alignment of the template with respect to the intramedullary nail, as viewed in plan and shown diagrammatically in FIGS. 6a, 6b, 6c; this is an adjustment within a geometric plane that is normal to the axis of every hole (11 to 16) in nail 9 and to every guide bore (17 to 22) in template 3. Measurement means are provided to measure in this plane the transverse distance between the distal end of the template and the stabilizing bar 26, thus providing an indirect measurement of the required adjustment to achieve alignment. Such measurement means may consist of an electronic comparator 38, comprising a sensitive member 39 in which a slidable rod 40 having an end plate or foot 41 is spring-urged against the confronting wall of guide block 29. The distance measured by comparator 38 is converted into an electrical signal transmitted via a cable 42.

A metal-detector device, susceptible to the presence of the conductive material of nail 9, and generally indicated by reference number 43, may be advantageously used for the non-invasive determination of template alignment with the intramedullary nail and, therefore, for the alignment of template bore axes at 17, 18 with the corresponding blind distal holes (11, 12) in the intra medullary nail, all without using an X-ray source. Metal-detector device 43 is preferably of the magnetic variety and may be generally as described in U.S. Pat. No. 4,526,177 or in German OS 2,842,203. Specifically, the metal-detector device comprises a head 44 and an elongate cylindrical sensor unit 45 dependent from head 44, which includes electronic components for excitation and detection of signals via sensor 45. Sensor 45 is seen to be sized for accurate mounting via one of the guide passages, e.g., 17, 18 in the distal end 24 of template 3, with orientation toward a corresponding hole 11, 12 in nail 9. Means 43 can be further stabilized in a given position on template 3, by means of a guide bar 46 which is generally L-shaped and is self-stabilizing in flat abutment with a side wall of the template.

When the basic material of the template is present, the metal-detector device detects a specific value for the magnetic field which varies as the sensor axis approaches nail 9 and thus the axis of the hole. The value of the field measured by device 43 and the changes in it are converted into electrical signals which are transmitted via a cable 47.

The signals transmitted by cables 42, 47 are sent to a control center 48 and are displayed on corresponding analog or digital displays at 49, 50.

The procedure for using the described device of the invention is as follows.

After correcting the fracture and after inserting nail 9 into medullary cavity M, the surgeon fixes stabilizing bar 26 in a distal hypophysis of the bone and connects the distal end of template 3 to bar 26. The template is then stably attached to the intramedullary nail, so that the instantaneous directions of the axes of these members can then be adjusted with extreme accuracy. And sensor 45 of the detection means 43 is stably inserted into one of the distal guide passages in the template, e.g., passage 17.

The distal end of template 3 is then moved laterally, in what is effectively a scanning sweep in the geometric plane which is parallel to nail 9 and to which all hole and guide-bore axes are normal. Such movement may be first to the left, as seen in FIG. 6a, namely, to a position A in which guide passage 17 is out of alignment with respect to the corresponding hole 11 in nail 9. In this position, the surgeon records a measurement d.sub.A for the distance measured by electronic comparator 38, as well as the value F.sub.A of the field measured by metal-detector device 43. The surgeon then moves the distal end 24 of template 3 in the opposite direction, i.e., toward the right, as shown in FIG. 6b, to reach position B where the value F.sub.B of the field determined by metal-detector device 43 is

and he records the distance d.sub.B measured by electronic comparator 38. Alignment position C corresponds to distance d.sub.C, wherein

By moving the distal end until the value d.sub.C measured by comparator 38 is displayed (at 50), passage 17, into which sensor 45 of metal-detector device 43 is inserted, will have been moved into a position which is axially aligned with the corresponding hole 11 in nail 9. Then, by immobilizing shaft 33 on block 29 by means of set screw 37, the surgeon can remove the metal-detector device and insert guide bushes 23 for drilling tools into passages 17, 18, in the certainty of finding corresponding blind holes 11, 12 in nail 9 and accurately drilling the bone for insertion of anchoring bolts.

The means according to the invention may be subjected to many modifications and variants falling within the scope of the invention described in the appended claims. All components may be replaced by their technical equivalents without going beyond the scope of the invention. For example, metal-detector device 43, which is based on the change in the magnetic field when a metal material is present, may be replaced by any device which is based on changes in other force fields, e.g., of an electrical or electromagnetic nature.