Patent Abstract:
A low insertion profile surgical reamer for cutting a bone socket comprises a cutting structure. The cutting structure is rotatable about a longitudinal axis. The structure has a static profile area upon insertion of the reamer into the bone socket and a dynamic profile area generated upon rotation, both profile areas lying transverse to the axis. The static profile area is substantially smaller than the dynamic profile area. The reamer includes centrally located holes, allowing it to be fixed to a tool holder.

Full Description:
BACKGROUND OF THE INVENTION 
     The subject of this invention is a surgical reamer fitted with a device allowing it to be fixed to a tool holder so that it can be driven in rotation and with at least one cutting edge made up of the edge of a plate containing the reamer&#39;s rotary axis. 
     A reamer of this sort is known under U.S. Pat. Nos. 3,633,583 and 5,290,315. On these reamers, the cutting edge is formed on a half-disk inserted into a diametric split made in a monolithic head which is noticeably hemispherical. The disk is held in the head by a screw and the head has gashes, like a drill bit, for the formation of shavings. In operation, there is an increased risk of these reamers becoming off centre due to the lack of homogeneity of the osseous matter. 
     From document EP 0 947 170, the content of which is incorporated herein by reference, a surgical reamer is shown, particularly intended for the processing of the cotyloid cavity when replacing the hip joint with a total prosthesis, in the shape of a revolving hollow body, in particular a hemispherical cap stretching from one side of the rotary axis and whose edge, over half of its circumference, constitutes the cutting edge. The surface of the cap itself may be fitted with teeth as with reamers of the rasp type which are commonly seen in previous practice, as described, for instance, in patents FR 2 281 025, EP 0 704 121 and 0 782 890, the content of which is incorporated herein by reference. However, it is very difficult to form an exact hemisphere using the usual processes, such as stamping. 
     What is needed is a surgical reamer allowing the centring to be maintained whilst in operation, using simple means. In addition, what is needed is a reamer that has a small insertion profile, compared to its swept cutting area. 
     SUMMARY OF THE INVENTION 
     A surgical reamer according to the invention has a cutting structure rotatable about a longitudinal axis. The structure has a static profile area upon insertion of the reamer into the bone socket and a dynamic profile area generated upon rotation, both profile areas lying transverse to the axis. The static profile area is substantially smaller than the dynamic profile area. The reamer includes centrally located holes ( 18 ), allowing it to be fixed to a tool holder. The invention therefore has a low insertion profile permitting entry into an incision of a relatively small size. 
     The reamer form may be spherical, conical or of some other shape. At least one cutting edge can be fitted with teeth. 
     According to the preferred mode of production for the invention, the reamer is made up of two plates which are split down the middle according to their axis of symmetry and housed at right angles to and inside one another. This is particularly simple to manufacture and also stands out due to its good rigidity and by how easy it is to clean. 
     The plates constitute the cutting structure. The plates are angularly arranged around the rotary axis in such a way as to form three edges including at least one which is a cutting edge. The distribution of at least three edges around the rotary axis ensures that centring is maintained during milling. If only one of the edges is a cutting edge, the other edges are used only for guiding, that is to say for maintaining the centring. 
     The disk, whose split leads out onto the top of the reamer, can usefully be cut so as to release the profile of the other disk at the top and thus allow a cut in the centre when milling. 
     The plates have holes used for fixing the reamer onto a tool holder or an adapter with a head fitted with frontal slots extending radially in relation to the support axis and oriented in such a way as to allow them to house the reamer plates. The devices used to hold the reamer in the slots are usefully made up of balls which engage in the holes on the reamer&#39;s plates and a ball locking device keeping the balls engaged in the holes in the plates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       As an example, the appended drawing shows a mode for producing the invention. 
         FIG. 1  is a perspective view of the reamer. 
       FIGS  2   a – 2   c  shows three examples of teeth formed on the disks. 
         FIGS. 3   a – 3   i  show examples of disk cutting profiles. 
         FIG. 4  shows the same reamer mounted on an adapter. 
         FIG. 5  shows the adapter in the reamer release position. 
         FIG. 6  is a side view of the adapter. 
         FIG. 7  is an axial view of the adapter. 
         FIG. 8  is an exploded view of the adapter. 
       FIGS  9   a – 9   b  show a cup for recovering the shavings before being mounted on the reamer. 
         FIG. 10  shows the same cup mounted on the reamer. 
         FIGS. 11   a – 11   b  show variants for point or centering stock production. 
         FIG. 12  shows an embodiment in which the plates are not equally spaced about the rotational axis. 
         FIG. 13  shows the static profile area vs. the dynamic profile area of the invention. 
         FIG. 14  shows the static profile area vs. the dynamic profile area of a prior art product. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The reamer shown in  FIG. 1  is made up of two disks or plates  1  and  2  perpendicularly assembled. The plates  1  and  2  make up a cutting structure  50 . The cutting structure  50  is rotatable about a longitudinal axis X—X when mounted to a holder  6 . 
     For this purpose, the plates are split down the middle, that is to say according to a radius leading into a central circular cut  3  and they are housed in one another by means of these slots and laser welded so as to give a spherical case of which edges  4  and  5  make up meridians. Edges  4  and  5  present sharp edges forming cutting edges. 
     In the example shown, disk  1  has a split which leads to the top  30  of the reamer and is cut so that the sides of its split  31  diverge from one another on the plane of the other disk  2 , on both sides of the reamer&#39;s rotary axis X—X. The effect of this is to release the edges of the disk  2  at the top  30  and to thus allow a centre cut when milling. 
     At least one of the edges  4 ,  5  of the plates can be fitted with cutting teeth. Examples of teeth shapes are shown in  FIG. 2 , either teeth in a U shape (a), an “N” shape (b) or sloping slot teeth (c). The four edges of the reamer should preferably be fitted with teeth and these teeth are offset, respectively alternated, from one disk to the other or from one half-disk to the next, in relation to the trajectory of these teeth, so as to obtain a full sweep, without grooves, when milling a spherical cavity. 
     The cutting edges  4  and  5  may show various cutting profiles examples of which are shown in  FIG. 3 
         a) half-moon profile on the topside,   b) elliptical profile generating a positive cut,   c) half-moon profile on the cutting side of the plates with a neutral cutting angle   d) half-moon profile on the cutting side of the plates with a positive cutting angle   e) diagonal profile generating a positive cutting angle,   f) neutral profile,   g) half-moon profile on the topside with two relief angles per disk,   h) half-moon profile on both sides of the plates,   i) tenon profile which can synthesise profiles a} to h}.       

     A reamer of this sort cannot be fixed directly onto a tool holder as described in the applicant&#39;s patent EP 0 704 191 (U.S. Pat. No. 5,658,290), the content of which is incorporated by reference herein, which has a head intended to house a cross held by a bayonet fixture. In order to be able to use the same tool holder for reamers fitted with a fixing cross, the new reamer is fixed onto an adapter  6  shown in  FIGS. 4 to 8 . This adapter could obviously constitute a full tool holder. 
     The holder  6  has a cylindrical body  7  fitted, at one end, with a head  8  designed to house the reamer and, at the other end, with a fixing cross made up of four cylindrical branches  9  forced radially through the body  7 . The head  8 , generally cylindrical in shape, is split diametrically so as to have four slots  10  which are at right angles to one another, whose width corresponds to the thickness of plates  1  and  2 . These slots  10  are limited on one side by a relatively thin wall  11  and, on the other side, by a rather thicker wall  12 . The walls  12  are pierced by a circular hole  13 , which is cylindrical over most of the walls. The balls  14 , whose diameter is greater than the thickness of the walls  12  are held in these holes. These balls  14  can also be moved into the holes  13   50  as to release the slots  10  or not. 
     A locking ring  15 , with four pins  16  is mounted, sliding, onto the body  7  stretching out in parallel to the axis of the ring. These pins  16  are engaged in the head  8 , more precisely in the spaces left free by the walls  11  and  12 . Each of these pins  16  has one flat side  17  which at least approximately slides onto the side of a wall  12  opposite the corresponding split  10 , so as to keep the corresponding ball engaged in the split  10 , as shown in  FIG. 7 . If the reamer is engaged in the slots  10 , the balls  14  are then engaged in the holes  18  on plates  1  and  2  so that the reamer is held onto the head  8 . 
     The ring  15  is held in this locking position by a spring  19  which rests on a supporting ring  20  which is mounted on the body  7  of the adapter, as shown in  FIG. 4 . In order to release the reamer all that must be done is pull out the locking ring  15  by constricting the spring  19 , as shown in  FIG. 5 . The reamer can then be removed from the head  8  by pushing back the balls  14 . The same method is used to fix the reamer onto the adapter. This type of locking/unlocking mode is described in the Swiss patent application No 409/00, the content of which is incorporated by reference herein. To lock the balls  14  into the reamer, all you have to do is release the ring  15 . 
     In order to allow the adapter to be cleaned properly, the supporting ring  20  is mounted in such a way that it can be pulled out backwards as far as the cylindrical branches  9 , which allows you to also bring back the locking ring  15  and to release the spring on the ring  15 . For this purpose, the supporting ring  20  is fitted with a radial pin directed internally (not shown in the drawing) and the body  7  of the adapter has a longitudinal groove  21  into which this pin can slide. The upper end of the groove  21  leads to a notch  22  into which the pin on the ring  20  can be bayonet fixed by means of a slight rotation. 
     The reamer can usefully be fitted with a device allowing the shavings to be recovered. The plates offer a particularly simple and effective solution shown in  FIGS. 9   a ,  9   b  and  10 . 
     The recovery devices are made up of a cup  32  in the shape of a hemispherical dome supported by a ring  33 . The diameter of the cup  32  is slightly less than the diameter of the plates  1  and  2  and this cup has four splits  34  stretching according to the meridian levels at right angles to one another and over a part of the height of the ring  33 , over a part  35  of the latter which has the same diameter as the cup  32 . The width of the splits  34  is noticeably greater than the thickness of the plates  1  and  2  and these splits are asymmetrical in relation to the corresponding meridian plane, in such a way that when the cup  32  is mounted on the reamer ( FIG. 10 ) the plates  1  and  2  cross the splits  34  leaving a split  34 ′ behind the plates in relation to the reamer&#39;s direction of rotation, so as to allow the shavings to penetrate into the cup  32  through these splits  34 ′. It will be noted that the reamer plates shown in figures  9   a  and  9   b  and  10  are fitted with U-shaped teeth  50   a ,  50   a ′,  50   b , and  50   b ′ which project over the surface of the cup  32 . 
       FIG. 11  illustrates a variation in which the two plates  1  and  2  are totally flat and form a cross at the end of the reamer. The reamer is fitted with a drill bit  36  fixed axially onto this cross. For this purpose, the bit  36  has two slots running crossways by means of which it is fitted onto the plates. The bit is laser welded onto the plates  1  and  2 . 
     Instead of a bit, a simple centre point or a trocar point  37  could be fitted. 
     A drill bit or a point could be fixed in the same way onto a reamer made up of three, five or more plates. 
       FIG. 12  depicts an reamer  38  in which the plates  40  and  42  are spaced about the rotational axis so as to result in unequal spaces  44  between plates. The spaces  44  encompassed by angle β are smaller than the spaces encompassed by angle β, thus resulting in X and Y dimensions which are different. 
       FIG. 13  illustrates a cutting structure  50 , made up of the two plates  1  and  2 . When viewed statically and axially, the cutting structure  50  presents a two dimensional static profile area  52  in the form of a cross. The square  53  inscribed on the corners of this cross represents the minimum size of an incision which will allow passage of the reamer. The square  53  is therefore the effective profile seen by an incision upon insertion of the reamer into the bone socket and covers approximately 80% of the area of the circular profile area  54 . When this static profile  52  is rotated during cutting, it sweeps out the circular profile area  54  inscribed by the phantom line circle  56 . 
       FIG. 14  shows a conventional reamer  60 , in which the static profile area  62  is essentially a circle with small protrusions  64  constituted of cutting divots. When rotated during cutting, the static profile area  62  sweeps out a dynamic profile area  66 , inscribed by the phantom line  70 , only insubstantially larger. 
     Thus, an advantage of having a substantially smaller static profile area  52  than dynamic profile area  54  is that the size of the incision required in order to receive the reamer is much smaller than that required for conventional reamers. 
     The invention is not limited to the modes of production described. Instead of the two fitted plates, the reamer could be made up of plates fixed radially on an axis, by means of welding, for instance. There do not have to be exactly four plates, but there must be at least one. 
     Whether these are plates fitted as shown or plates welded onto an axis, these plates could be of a different shape, for example a shape limited by a truncated or other form of case. 
     Although illustrative embodiments of the invention have been shown and described, a wide range of modification, change and substitution is contemplated in the foregoing disclosure and in some instances, some features of the present invention may be employed without a corresponding use of the other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.

Technology Classification (CPC): 0