FLEXIBLE MEDULLARY REAMER

Abstract: A flexible medullary reamer for shaping the medullary space of bones has a shaft (1) formed as a single monolithic element. To permit the use of an elongated guide element, the shaft may be axially bored (2) throughout its length. A cutting head (3) and an adaptor (4) to connect the shaft to a drive mechanism are provided at opposite ends of the shaft. To complement the shaft, the cutting head and adaptor may be centrally bored.

Description: This invention relates to instruments for the treatment of the medullary space of bones, and specifically to an improved flexible medullary reamer for bones. Medullary canal reamers of this type are used to enlarge the medullary canals of bone in preparation for the insertion of fixation devices, performing an intramedullary osteotomy, stimulating bone growth, the insertion of a plug to preclude bone cement from migrating while it is in its viscous state, and for other reasons. The medullary canals of bone are seldom straight. More typically the canal will have some degree of curvature to it. Should a straight and rigid series of reamers be employed to enlarge the canal there is considerable likelihood that the reamer, in not being capable of following the curvature of the bone, will not remove the desired uniform amount of bone tissue. In such a situation, excessive tissue removal occurring in at least one plane will be experienced as the reamer is advanced. For this reason medullary canals are almost always prepared with reamers having a flexible shaft. Heretofore, flexible medullary reamers have been of two types. The first to come into common usage consisted of spiral or helically wound metal wire(s) or strip(s), which comprised the shaft of the reamer. A disadvantage of this design is that these reamers can be operated only in the forward mode of rotation. If operated in the reverse mode, which occasionally is required in order to free a lodged reamer and to facilitate normal removal, the shaft unwinds, thus rendering the reamer permanently deformed, unusable and unrepairable. This adds considerably to the cost of maintaining a serviceable set of medullary reamers. Further, a lodged cutting head may subsequently be extremely difficult, if not impossible, to remove without further violation of the involved bone and surrounding tissues. Another disadvantage of this known design is the extreme difficulty of proper and thorough cleaning after use. The spiral or helically wound metal shafts contain many voids of various sizes. Blood and tissue readily infiltrate such voids and become trapped within the confines of the shaft. When the reamer is in use the voids are considerably distorted and enlarged as the reamer is advanced towards and within the medullary canal, thus providing ready access for the particles of tissue. Prior to use, all medullary reamers are sterilized and, hopefully, the blood and tissue particles not evacuated during the cleaning process and remaining within the interstices of the reamers are at least rendered harmless. However, depending upon the amount and composition of the extraneous particles and their degree of isolation from the sterilizing process, the particles may not be rendered sterile. Even in a sterile condition these foreign particles may still cause problems of infection should they become dislodged from the confines of the reamer and come into contact with the patient's internal tissues. Medical professionals recognize this problem but acquiesce to using these reamers for lack of an acceptable alternative. A further disadvantage of this medullary reamer is that the torsional load it is subjected to when in use results in poor power transfer and varying degrees of distortion of the shaft. If the power source providing the rotational energy to the reamer is great enough, the coils may tighten sufficiently in order adversely to affect the intended flexibility of the shaft. Another disadvantage associated with a spiral or helically wound reamer is the trauma it imposes on surrounding tissues. This results when the shaft of the reamer is not completely within the medullary canal, as would occur during the initial reaming process. As the shaft rotates, that portion remaining outside the medullary canal can become excessively flexed and distorted, thus enlarging the voids between the coils of the shaft. As the flexed shaft rotates, tissue lying outside the canal and not intended for removal becomes trapped within the voids and is torn from the underlying structures. A second distinct type of flexible medullary reamer is described in the literature. The shaft of this reamer embodies a plurality of parallel, flexible elements joined together at opposite ends by means of a welded or soldered connection. A disadvantage of this shaft is that proper cleaning is difficult to accomplish. Towards its opposite ends, where the individual elements converge, the elements come into close contact with each other until the final termination point is reached where they are permanently welded or soldered together to form a solid mass. Where these elements begin to converge, blood and tissue can readily become trapped and prove difficult to remove during the cleaning process. Another disadvantage of this flexible reamer is the excessive noise generated in its use which is caused by the individual elements being twisted and forcefully whipped into contact with each other. A further disadvantage of this flexible reamer occurs during usage. As rotation occurs, the individual elements spirally tighten around each other causing the shaft to become more rigid and thereby reducing the shaft's flexibility and increasing the likelihood of the attached cutting head not properly following the central path of the medullary canal. Another disadvantage of this flexible reamer is the tendency of the shaft, as it rotates but not yet fully within the confines of the medullary canal, to tear tissue from underlying structures as the individual elements are torsionally loaded and unloaded, thereby enlarging and contracting the spaces between the individual elements sufficiently to trap uninvolved tissue between the individual wires and tearing them free. Another disadvantage of this flexible reamer occurs in attempting to utilise the central bore of the reamer. The central bore is intended to receive a long, small-diameter guide pin which has previously been inserted into the medullary canal to act as a track for the advancing reamer. Except at its respective ends, this reamer lacks a well-defined and bordered central bore. Therefore, it is difficult to prevent the guide pin from exiting the reamer in the area of the free standing wires during the initial positioning of the guide pin within the reamer. A further disadvantage of this flexible shaft is the inefficient transfer of energy from the power source to the cutting head, which is caused by the twisting and wrapping together of the individual elements as the reamer is rotated. From DE-A-2542056 is known a manually operated instrument which comprises a tap for creating a thread in a bone channel. The instrument shaft is flexible and may be made of "Teflon", a relatively weak material. A thread cutter is fitted at one end of the shaft and a hand-grip is fitted at the other end of the shaft by which the shaft is manually rotated. This known instrument is intended to cut a thread, and not to ream bone, and can therefore use a shaft of relatively weak material. It would not be appropriate however for the reaming of bones. From FR-A-2366826 is known a surgical reamer comprising an elongate tube of plastics material, such as polyethylene, which is very flexible. At the operative end of the instrument it is formed like a brush with a plurality of projecting elements. The reamer is used manually. In US-A-3554192 is described a medullary drill comprising a flexible shaft having a drill head at one end and an adapter for connection to a power drive source at the other end. The shaft is made from a plurality of parallel flexible elements with a guide element extending therethrough. It is an object of this invention to provide a medullary reamer which is adapted to be power driven and which is more appropriate to surgical use in that it can be easily cleaned, thus ensuring a sterile and biologically safe instrument when properly autoclaved. Other objects include the reduction of trauma to extraneous tissue, a more easily used instrument, one that is more efficient in transferring power from the energy source, more durable than existing reamers, less expensive to manufacture, operable in the reverse mode of rotation, and retaining the required degree of flexibility under maximum load. In accordance with the present invention there is provided an instrument for the treatment of the medullary space of bones, comprising a flexible rotatable shaft having a cutting head at one end, with the other end of the shaft being provided with an adapter for the connection of the shaft to a power drive mechanism thereby to cause rotation of the shaft and head, characterised in that the shaft is a monolithic shaft of thermoplastics, thermosetting or fibre-reinforced composite material having the strength to permit the instrument to be used as a power-driven reamer for clearing, enlarging and reaming the medullary space of bones. Flexible medullary reamers in accordance with the invention maintain the basic ability of enabling the attached cutting head to follow the curvature of the bone in an unimpeded manner as it is advanced within the medullary canal, and remaining unaffected by the inevitable misalignment of the reamer shaft. To achieve this and eliminate the many shortcomings of existing reamers, the invention provides for the utilization of a shaft made of a solid material. The selected material must possess the required degree of flexibility, torsional strength, resistance to abrasion and the ability to be repeatedly steam sterilized. Said shaft may contain a central longitudinal bore for the purpose of receiving an elongate guide pin previously positioned within the medullary space of the bone. The improved shaft eliminates the voids and interstices where tissue may become trapped and hidden from view, thereby providing a more appropriate instrument for surgical procedures. Although unremoved particles may be sterilized during the autoclaving process, their subsequent dislodgement in an ensuing patient may prove to be quite detrimental. Infections within the bone are of a most serious nature and extremely difficult and expensive to treat. The shaft of the invention in having a solid and continuous surface is quickly and easily cleaned. The well-defined central bore, if provided, is readily cleansed by passing a bristle brush through its length. A visual examination will quickly verify the cleanliness of the reamer. Thus, subsequent sterilization is assured when properly performed. The smooth outer surface of the shaft will minimize the trauma and disruption of surrounding tissues as the reamer is used. The shaft maintains its original flexibility under torsional loading and does not in itself create any noise when used. Power transfer from the drive mechanism to the cutting head is very efficient with the present invention. With a smooth inner bore, this facilitates the insertion of the generally used guide pin into the bore of the reamer. This reduces operational time which is significant to the well-being of the patient and helps to reduce the financial charges to the patient. This shaft also permits the reamer to be operated in the reverse mode of rotation with optimum efficiency and no adverse effects. Occasionally, a reamer will become firmly lodged within the medullary space. Forward rotation then seldom frees the reamer and extensive extractive efforts must be employed to remove the offending device. With a reversible reamer, a lodged cutting head is quickly removed. Manufacturing and labour costs associated with this shaft are less due to the few parts, ease of assembly and a lower unit cost of the shaft. The instrument is easy to use and not prone to becoming damaged or abused. Consequently, replacement reamers will seldom need to be purchased, thus increasing the cost effectiveness of the reamer. An embodiment of reamer in accordance with the invention will now be described by way of example and with reference to the drawings, in which: Fig. 1 is a side, partial cross-sectional view of the flexible medullary reamer; and, Fig. 2 is a view of the flexible medullary reamer in a deflected position. Referring to Figs. 1 and 2, the shaft 1 in its preferred embodiment comprises a flexible elongate cylindrical body which may be centrally bored along the longitudinal axis to receive an elongate guide pin (not shown). The diameter and length of the shaft may be varied to meet specific requirements. A typical embodiment utilizing a 13 mm cutting head 3 will have a shaft 7 mm in diameter and be 508 mm (20 inches) in length. The shaft may be made of a composite material of filamentous fibres and an appropriate resin. Alternatively, the shaft may be made of a synthetic plastic material. The fibres or the synthetic plastic material may be of the thermoplastic or thermoset type. The shaft may be formed by extrusion, pultrusion, moulding, laminating, wrapping, machining or bonding. The outer diameter of the cutting head should be greater than the shaft diameter. If centrally bored to receive a guide pin, a typical bore diameter will be .144 inch (3.66 mm) which will be sufficient to accept the frequently-used one-eighth inch (3.17 mm) diameter guide pin. Cutting head 3 is attached to shaft 1 by means of a suitable bonding agent or other method as known to those skilled in the art. Generally, cutting heads for medullary reamers are produced from stainless steel or tungsten carbide. The cutting head 3 may have a central channel to receive a guide pin. The cutting head may be secured to the shaft by adhesive bonding, by heating the end of the shaft sufficiently to permit the shaft material to become softened and directed to flow into the inner spaces of the metal cutting head, by incorporating the connector end of the cutting head into the flexible shaft during the manufacturing of the shaft by embedding said connector end into the shaft material by means of extending the filaments and resin which comprise the shaft to include said connector end, by mechanical means or a combination of the aforementioned methods. An alternative embodiment would utilize removable cutting heads which are mechanically attached to a suitable adaptor connected to the flexible shaft by any of the methods previously described. The diameter and configuration of said cutting head may vary. Adaptor 4 is a separate body, usually of stainless steel, attached to the shaft 1 by any of the methods previously described for the attachment of the cutting heads. The function of adaptor 4 is to be the means of connecting the reamer to a complementary drive mechanism of the power source. It follows that the requirements of the driving mechanism will dictate the configuration of adaptor 4. Adaptor 4 may be centrally bored to receive a guide pin. However, it will generally be found that an adaptor will minimize wear and damage to the end shaft of the reamer and also be of great convenience in permitting a quick and positive means of securing the reamer to the driver mechanism. Adaptor 4, if used, may be secured to shaft 1 by adhesive bonding or mechanical means.

Claims: An instrument for the treatment of the medullary space of bones, comprising a flexible rotatable shaft (1) having a cutting head (3) at one end, with the other end of the shaft (1) being provided with an adapter (4) for the connection of the shaft to a power drive mechanism thereby to cause rotation of the shaft and head, characterised in that the shaft (1) is a monolithic shaft of thermoplastics, thermosetting or fibre-reinforced composite material having the strength to permit the instrument to be used as a power-driven reamer for clearing, enlarging and reaming the medullary space of bones. An instrument as claimed in claim 1, characterised in that the shaft (1) has an axial bore (2) to receive a guide element. An instrument as claimed in claim 1 or 2, characterised in that the adaptor (4) and/or the head (3) are secured to the shaft (1). An instrument as claimed in any preceding claim, characterised in that the shaft (1) is formed by extrusion, pultrusion, moulding, laminating, wrapping, bonding or machining.

Inventors: DIPIETROPOLO, AL
Applicants: DIPIETROPOLO, AL
Application year: 1987
Main classification: A61B17
IPC codes: B23Q5, A61B17