SET OF MECHANIZATION AND PROCEDURE TO PREPARE THE MEDULAR CAVITY OF A FÉMUR IN A HIP ARTHROPLASTYBACKGROUND OF THE INVENTIONThe present invention relates to a milling cutter and a method for preparing a medullary cavity for receiving a stem component of a femoral prosthesis, specifically an improved machining assembly and a method for preparing a medullary cavity that allows the implantation of a femoral prosthesis. which is neutrally aligned within the medullary cavity prepared for improved fixation therein, thereby minimizing any subsequent loosening and pain commonly associated with misaligned prostheses. It is widely known that the success of hip replacement without cementation depends on the correct dimensioning and positioning of the prosthesis within the medullary cavity of the femur. In cases where the failure is due to an aseptic loosening, a common observation is that the implant is not large enough to get support through filling the implant site, and thus to get in contact with the cortical surfaces of the femur. Typically, these undersized prostheses are misaligned and have been placed with some degree of varus inclination, with respect to the medullary axis of the femur.
Consequently, the implant only achieves contact with the cortex of the femur medially, immediately below the surface of the proximal femoral osteotomy, and laterally adjacent to the distal tip of the prosthetic stem. However, contact is not present in other areas, including the anterior and posterior cortices, the medial cortex below the lesser trochanter, or the lateral cortex above the distal tip of the implant. Contact in these areas is necessary to rigidly fix the prosthesis and prevent excessive relative movement in the implant / bone transition, which would eventually lead to pain and loosening. In practice, the prostheses implanted in the femur are under-inflated because the opening formed by the surgeon does not extend far enough laterally into the proximal femur to allow the prosthesis to be aligned with the longitudinal axis of the canal. This occurs because the medullary axis passes through the superior surface of the femur in the vicinity of the medial edge of the greater trochanter, near the posterior cortex of the femoral neck, in a zone of rigid bone that is difficult to intervene using conventional instruments, such as They are strawberries, rasps and reamers. Since the adjacent bone in this area is relatively soft, conventional intervention instruments tend to bend away from the hard bone and into the medullary canal at a location that is located anteriorly and medially. As the posterior instruments enlarge the initial entry point, the bone is progressively extracted from the anterior and medial cavity walls, leading to the development of a poorly aligned implantation site. If a bur or rasp is placed inside the femoral canal through an entry hole that is not aligned with the medullary axis, the rasp or milling instrument will become wedged in the canal because the teeth present in the devices are generally unable to actually extract the areas of hard bone that block them in their advance. The extraction of this bone, generally, can be carried out only by rotating machining tools, such as flexible or rigid reamers, or possibly with a bone chisel. Thus, in conventional hip replacement, the preparation of a neutrally aligned implantation cavity critically depends on the initial entry of the instruments into the femur, and the use of the associated instruments to intervene by extracting the areas of hard bone that block the movement of the strawberry, as it seeks to achieve a neutral alignment within the channel. The anatomical variability of the proximal femur also contributes to the misalignment and infradirnension of the femoral prostheses. The trabeculae of the medullary axis through the upper surface of the femur at a point that varies by ± 5 mm medially-laterally and anteriorly-posteriorly, depending on the precise location of the larnetphysis shape and the orientation of the femoral neck with respect to the rest of the femur. For this reason, it is difficult to determine intraoperatorily if the instruments located in the femoral canal are correctly aligned, and if the entry point for the instruments designed to machine the femur is located sufficiently laterally and subsequently to allow the development of an implantation site. aligned neutrally. The conventional solution to minimize difficulties in the preparation of the femur in the presence of areas of hard bone, has been to insert a reamer, typically a long, tapered reamer, or drill medullarly into the medullary cavity, and assume that the The instrument would be disposed co-axially with the medullary cavity during insertion, effectively forcing the proximal part of the instrument to cut into the greater trochanter to the extent necessary to provide the correct alignment of the prepared cavity. In practice, this solution has not been completely successful due to the following factors: (1) The bone inside the trochanter is usually very hard, fatty, and often covered with a considerable amount of soft tissue that has to counteract the action of cutting of conventional drilling and reaming instruments. (2) This solution assumes that the instrument will be aligned with the medullary cavity without enlarging or cutting the bone distally, thus deforming the cavity itself. In practice, the use of drills and long instruments that do not have a polished tip can lead to misalignment, because the instrument cuts the bone both proxirnally and di ff erently. (3) The complete solution of the use of the intramedullary cavity to guide the alignment of the instruments supposes that the segments of the femur and rnetafisapo of the femur coincide. In practice, however, there is a deviation of up to two degrees in the e eesis and the diaphysis of the medullary cavity. Consequently, the travel machined by the instrument guided distally only provides an approximate indication of where an instrument positioned neutrally within the rnetaphysis should be placed. (4) Instruments and aggressive reamer drills extract a considerable segment of the greater trochanter during insertion. This requires a greater exposure of the surgical site and the removal of excessive bone, and can lead to increased osteolysis in the long term, as the spongy soft bone is exposed to the waste of the generator wear within the joint. There are many devices that help the process of modeling the femoral canal, to adapt to the contours of the femoral implant; however, the successful function of each of these devices is exposed on the assumption that some instrument has been inserted into the spinal canal in a neutral position. This instrument is then used as a platform to position the reamer guides of different designs. These instruments have been commercially available, being used mainly to facilitate the reaming of the medial bone inside the femur, which is often very strong and which can prevent the use of a properly dimensioned prosthesis. The exemplary instruments are manufactured by Biornet, Inc. (U rsa, Indiana), and are described in U.S. Patent Nos. 4,809,689 (flnapliotis), 4,777,942 (Frey et al.), And 4,738. 256 (Freemna and others). The designs of the additional instruments are available for use with modular prostheses, comprising the interchangeable anterior and posterior elements, which are mounted on the center shank of the prosthesis. The firm Richards Medical Cornpany (Mernphis, Tennessee) manufactures a system consisting of a plurality of modular reaming guides, which uses a rail fixed to a rod located in the medullary canal. The function of the rail is to guide the position of the reamer used to machine the anterior and posterior surfaces of the femur to optimize the fit of this prosthesis inside the femur. Another design is that set forth in U.S. Patent No. 5,169,402 (Elloy) and comprising a milling cutter having two separate parts that engage an articulated handle to form a solid, uniform piece. The minor segment of the original drill consists of a medial part of the drill, which extends down from the upper face of the level of the osteotomy. This segment is loaded with a spring so that the surgeon controls the bur within the femur, causing the medial segment to fall somewhere within the medial cortex, consequently, as the surgeon advances the body of the instrument further down the length of the fernur the medial segment slides along the path present in the body and remains in a position that protrudes from the bone. The movement of the segment is restricted by a spring, so that once the rest of the drill has settled into the bone, the surgeon can control that the middle segment fits inside the femur, thereby completing the machining operation to form the implantation cavity.
BRIEF DESCRIPTION OF THE INVENTIONThe present invention is directed in certain aspects to an improved cutter design and to a method for preparing a medullary cavity of a femur, for the subsequent implantation of a neutrally aligned femoral prosthesis. Specifically, the cutter includes a longitudinal axis and the anterior, posterior, medial and lateral faces. The overall configuration of the drill is similar to that of many components of the medial and distal femoral shaft, and in the intermediate zone of the shaft. However, in the proximal zone, the cutter has a groove that is positioned on the side face and extends from the upper end of the cutter downwards. In the most preferred embodiment, this groove extends through the entire side face of the cutter (ie, from the front face to the back face), rather than a part of the side face (i.e., the rear corner). /side). The configuration of the slit allows the drill, in the implantation inside the medullary cavity of the femur, to avoid the hard bone of the greater trochanter. Initially avoiding this area of the hard spindle is important in order to achieve a desired shape of the medullary cavity, in order to receive a femoral stem, since conventional instruments often deviate away from this area of the bone during the machining process. , resulting in a prepared cavity having a shape that does not allow the desired neutral alignment of the prosthesis within it. In the present invention, the ability to avoid this area due to the presence of the proximal lateral groove, allows the milling cutter of the invention to be seated within the medullary cavity in such a way that the longitudinal axis of the milling cutter substantially coincides with the axis medullary, to achieve neutral alignment. Consequently, with the subsequent extraction of a sufficient amount of trochanter bone to allow the implantation of a stem femoral prosthesis (or a finishing cutter prior to the implantation of the prosthesis), the femoral prosthesis is able to achieve alignment. Neutral den of the medullary cavity when implanted. The present invention is also directed to the use of the cutter of the invention, in combination with a machining device that includes a second cutting instrument, the device being designed to extract areas of bone that are immially avoided by the cutter of the invention. , especially the greater trochanter bone and the posterior / lateral corner of the osteotomy part, to allow the subsequent implantation of the femoral prosthesis or the reamer.
BRIEF DESCRIPTION OF THE DRAWINGSThe objects, advantages and features of the invention will become apparent by reference to the drawings attached thereto, in which like numerals indicate like parts and where an illustrated embodiment of the invention is shown, in which : Figure 1 is a rear view of the prosthesis aligned neutrally implanted within a femur. Figure 2 is a rear view of a misaligned prosthesis implanted within a femur. Figure 3 is a front view of a left component of the cutter of the invention. Figure 3A is a front view of the complete cutter used to construct the partial cutter. Figure 3B is a side view of the complete cutter shown in Figure 3a. Figure 4 shows a middle view of the cutter of the invention. Figure 5 is a top plan view of the cutter of the invention. Figure 6 is a front view of a left component of the cutter of the invention, showing the positioning of the preferred cutting teeth. Figure 6fl is a front view of the left component of another embodiment of the cutter of the invention, showing the cutter implanted within the medullary cavity of a femur. Figure 7 is a front view of the machining assembly of the invention, implanted inside the medullary cavity of a femur. Figure 8 is a front view of the assembled machining assembly, including a cutting instrument and the milling cutter. Figures 9-11 are the front, rear and side views of the guide component of the machining assembly. Figures 12 is a medial view of the machining assembly (without the milling cutter and the second cutting instrument). Figure 13 is a cross-sectional view of the machining assembly, taken along lines 13-13 Llof Figure 12, showing the preferred means for fixing the guide to the mounting block. Figure 14 is a bottom plan view of the mechanization set (without the milling cutter and the second cutting tool). Figure 15 is a side view of the machining assembly (without the milling cutter and the second cutting tool). Figure 16 is an enlarged view of the spring piston. Figure 17 is an enlarged view of the locking screw for fixing the guide to the mounting block. Figure 18 is a view of the longitudinal cross section of the mounting block, showing the different channels and holes. Figure 19 is a side view of the machining assembly (without the milling cutter and the cutting instrument). Figure 20 is a cross-sectional view of the machining assembly, turned along the lines 20-20 of Figure 19, showing the preferred means for attaching the milling cutter to the mounting block. Figure 21 is a side view of the machining assembly. Figure 22 is a cross-sectional view of the machining assembly, turned along the lines 22-22 of Figure 21, in which the locking assembly is shown in the initial position and in the retracted position, to fix the strawberry inside the assembly block. Fig. 23 is a cross-sectional view of the machining assembly as shown in Fig. 22, in which the assembly assembly is shown in the open part to allow insertion of the milling cutter into the mounting block. Figures 24A-24B are side views of the second preferred cutting instrument. Figure 25A is an enlarged view of the distal tip of the second cutting instrument shown in Figures 24A-24B. Figure 25B is a bottom view of the second cutting instrument shown in Figures 25B. Figure 25C is a cross-sectional view of the distal tip along the lines 25C-25C of Figures 25B.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS1. Design and partial procedure of the cutter The present invention is directed to a design and method of an improved cutter for preparing the medullary cavity of a femur for the subsequent implantation of a femoral prosthesis in a hip arthroplasty. After having prepared the medullary cavity using the cutter of the invention, a femoral stem component or a hip prosthesis can be implanted within the cavity, in which the longitudinal axis of the stem is aligned neutrally with the medullary axis of the femur, giving This results in an improved rigid fixation of the rod, thereby minimizing the possibility of a subsequent loosening of the implant, as well as the pain associated with said loosening. The phrase "neutral alignment" as used herein, refers to a substantial coincidence of the longitudinal axes, specifically the medullary axis of the femur and the longitudinal axis of the reamer or femoral prosthesis, as it is explained in more detail below. ahead. In order to prepare the implantation site inside the medullary cavity, it is desirable that the site be configured in such a way that when the femoral prosthesis is implanted, a total contact between the outer surface of the rod and the surface of the cavity is achieved. As shown in Figure 1, said contact is achieved when the rod (S) is located in a neutral alignment within the medullary cavity (C) (i.e. substantially coinciding with the longitudinal axis (? I) of the rod (S). ) and the medullary axis (Y) of the femur (F)). Figure 2 shows an undesirable implantation due to the precision milling of the cavity, where only a partial contact between the rod (S) and the medullary cavity (C) is achieved (as shown in the areas marked with circles xey), fldicional entity, there is a free gap between the rod (S) and the lateral cortex (4) in the area (z). Consequently, said milling has led to a misalignment of the shank (S), where the longitudinal axis (Yi) of the shank (S) is located with a certain degree of varus alignment (5) with respect to the medullary axis (Y) of the femur . As discussed above, a problem that often occurs during conventional milling / reaming is that the cutting instrument deviates away from the greater trochanter bone (1), especially in the vicinity of the posterior margin of its medial wall ( 3), where the bone is generally very difficult to machine with conventional instruments, thus altering the course of the instrument towards the softer adjacent bone, in a location that is located anteriorly and medially. As subsequent cutting instruments enlarge the initial entry point, the bone is progressively extracted from the anterior and middle walls of the cavity, leading to the development of a misaligned implant site. The present invention is directed to a design and procedure of the milling cutter to prepare the implantation site within the medullary cavity, to allow a neutral alignment of a subsequently implanted femoral stem prosthesis, that is by employing a design that allows that the strawberry avoids the greater trochanter during the initial milling and the preparation of the implantation site. Referring now to Figures 3-6A, the present invention comprises a partial cutter (10) having a longitudinal axis (X), the anterior (fl), posterior (P), medial (M), and lateral (L) faces. ), a plurality of teeth (17) positioned on one of the faces (shown in Figures 6, 6fl and 7), and a lateral groove (13) located in the proximal segment (11) (ie, approximately one third top) of the strawberry. Although the smaller slit would occupy the rear / side corner of the milling cutter (not shown) to avoid the large area of the larger tronchanter, the most preferred embodiment comprises a lateral groove (13) extending from the front face (fl) to the face posterior (P), as shown in the Figures. It should be further noted that although the inventive arrangement and the related Figures are directed to the left femoral bur, the present invention may also be designed for a right bur, which is simply a mirror image of the left cutter described and illustrated in this. document. Figures 3-6A show a preferred configuration of the slit (13); however, alternative configurations of the slit may be used, assuming that each of them is of sufficient depth and the appropriate location to allow the reamer to avoid the desired bony area, typically the greater truncation zone of the femur. Figures 3 and 5, for example, show a preferred side slit design, which comprises in series a substantially planar rear part (14) (extending from approximately the point of the upper end (12) and a part of the base comprising a cavity (15a), extending from the back and ending at a distal edge (16) .The part of the base further includes a chamfer (15b) extending from the distal edge (IB) to approximately point b, and positioned preferably with an angle (6) of about 30 fat to about 60 degrees, more preferably about 45 degrees, with respect to the longitudinal axis (X) of the milling cutter.The beveled edge (15b) of the slit is a design feature preferred that allows the cutter (10) to avoid the collision against the lateral bone below the greater troncanter, thus minimizing the possibility of a fracture when removing the cutter from the femur. Figures 6-6fl, the milling cutter of the invention comprises a plurality of cutting teeth (17), positioned on at least one medial face (h), but more preferably on all four faces of the milling cutter (10). The configuration of the cutting teeth can be the same on all faces; however, the most preferred types and configuration of the cutting teeth are those shown in Figure 6, as well as those together with the present, serial number 08 / 594,892, and which is incorporated as a reference thereto in its entirety. . Although the preferred embodiment of the cutter described in the serial number document 08 / 594,892, comprises a plurality of diamond-shaped teeth of aggressive cutting on the side face, the presence of a side groove on the partial cutter, minimizes the need for an aggressive cut of the lateral bone. In the preferred embodiment, the partial cutter of the invention eeta prepared from a "complete" cutter (ie, one that does not have a partial groove), as shown in Figures 3A and 3B, whereby the part of the slit, extracting it from the complete strawberry. Preferably, the material is extracted from the proxirnal side face of the milling cutter, such that the "length" of the slit (Ii) (see Figures 3 and 3fl) is about 2.54 cm (1 inch) to about 3 crn. (1.2 inches), more preferably approximately 2.85 cm (1.125 inches). In addition, the preferred depth (d) of the slit, as shown in Figure 3, is from about 2 crn (0.80 inches) to about 3.3 crn (1.3 inches), with a preferred radius of the concavity varying from about 0.88 crn (0.35 inches) to about 1.77 crn (0.70 inches), more preferably from about 1.27 cm (0.5 inches) to about 1.58 c (0.625 inches). Table 1 shows a listing of the preferred depths (d) of the slot and the amount of the radius of the concavity for several sizes in particular of the milling cutter. The cutter of the invention can be supplied in a variety of different sizes to meet the different surgical requirements. Table 2 shows a list of the preferred widths (w) and lengths (1) for different sizes of the strawberry in particular. The values of the width (w) are obtained from a complete milling cutter (Figure 3B) on the front side to the rear face. Additionally, in the coronal plane, the neck (21) of the cutter is positioned at an angle (7) with respect to the longitudinal axis (X) of the cutter, of approximately 36 degrees, as shown in Figure 3. Preferably, the Complete configuration of the drill is the same as the configuration of the femoral prosthesis used (except for the lateral cleft). The Figures show an asymmetric design in which the cutter incorporates a slight back bending, as best shown in Figure .4.
TABLE 1TABLE 2II. Surgical method of using the partial drill: The drill of the invention (10) is generally used in conjunction with a drill or awl (not shown), which are used to form an entrance hole in the upper cortex of the femoral neck preferably in the proximity of the exit point (3) of the medullary axis (Y) (see Figures 1 and 2). Once the hole that is large enough to accommodate the distal tip (22) of a reamer is made, the removable handle (not shown) is firmly fixed to the upper surface of the reamer, which is pressed from the femur (F) with a mallet or similar instrument. As the drill is advanced in the femur, it will generally rotate until contact is achieved with the medial cortex proximally and with the lateral femoral cortex, just below the level of the minor troncanter (2). If necessary, a succession of burs or reamers of increasing size can be passed through the femur, until a rigid fixation is achieved in the appropriate position within the femur, to allow optimal reconstruction of the center of the femoral head. At this point, an intimate fixation between the drill and the medullary cavity will be achieved, and consequently the longitudinal axis (X) of the reamer (10) and the medullary axis (Y) will substantially coincide (ie, be in a neutral alignment). . Once the femur has been prepared using the cutter of the invention, a second finishing cutter can be implanted in the femur to enlarge the implantation site to its final shape. Since the finishing cutter is generally minimally larger than the cutter of the invention with the exception of the sunken zone, all the energy supplied to the finishing cutter can be used exlusively in the extraction of hue in the medial aspect of the troncanter, which It was initially prevented by the partial cutter. The fresae of finishing with cutting teeth of conventional configuration in the form of diamond, can be easily implanted in a neutral orientation, assuming that the cavity of the implantation has been prepared initially with the milling cutter of the invention.
III. Machining Assembly As shown in Figures 7-25C the cutter of the invention can also be used in combination with a machining device, comprising a guide (200) configured to detect a second cutting instrument (208), this tool being designed last instrument to mechanize the additional bone micially avoided by the strawberry. Figure 8 shows the preferred machining assembly, in combination, the cutter of the invention (10) and a machining device comprising a mounting block (101), a guide (200), and a second cutting instrument (208). ). As alternatively, the machining assembly could include other types of cutting tools in place of the partial bur of the invention, for insertion into a bone cavity if desired for a particular procedure, including but not limited to, a cutter complete (for example, Figure 3A), rasp, reamer and the like. Additionally, other means for securing the router guide, in addition to an independent mounting block (101) as shown and described herein, are within the scope of the present invention. A more detailed description of the specific components of the preferred embodiments of the machining assembly, however, will be discussed below. Once the drill has been advanced to the desired position within the medullary canal, the machining device including a guide (200) and a second cutting instrument (208) can be attached to the drill, to extract additional bone micially prevented for the strawberry, such as it is 77shows for example in Figure 8. The shape of the lateral groove (13) of the cutter allows the second cutting instrument (208) to advance inside the cavity (C) to machine the extraction areas of the medial aspect of the greater trochanter (1), to allow the insertion of a second cutter, such as a finishing bur (not shown), or a femoral prosthesis similarly to the cutter of the invention (except in the presence of a lateral groove). Once the second cutting instrument (208) has been advanced into the slit, in order to remove all the bone, the machining assembly, including the cutter, is removed from the femur. At this point, a prosthesis, for example of the suitable shape designed to be coupled to the mechanized cavity, can be implanted in the femur (see Figure 1 for example). As an alternative, a finishing mill with a shape similar to the milling cutter of the invention and to the implantation site can be introduced into the femur, to generate the final shape of the cavity and to extract the discontinuities present between the areas of the femur that were in contact with the milling cutter of the invention and machined by the second cutting instrument (208). The remaining exposure will be directed to the specific components of the preferred machining assembly (100). Referring now to Figures 9-18, the machining assembly (100) comprises a guide (200) for receiving and directing the movement of the cutting instrument (208), more preferably including a means for securing the guide to a block of assembly (L01), and preferably a means for allowing sliding engagement of the guide within the block (101), to allow multiple cutting positions with respect to the block (10)). As an alternative, the guide can be fixed permanently to the mounting block, or even directly to the milling cutter by some other means of fixing. Preferably, the guide (200) comprises a body (201) having an outer surface (201a) and an internal conduit (203) communicating through to receive a second cutting instrument (208). The second cutting instrument (208) preferably includes a means for cleaning the distance that can be displaced through the guide, preferably a collar (208a) attached to the upper end of the instrument, and which lands on the upper edge of the guide, for example as shown in Figure 8. In the preferred embodiment, the cutting instrument is a cylindrical reamer that passes through a cylindrical shaped guide, such as shown in the figures.; however, it is contemplated that other means of machining the bone are within the scope of the present invention, including but not limited to a hollow bore, bone die, or chisel, configured to conform to the shape of the groove. A second preferred cutting instrument (208) is a 90 degree tip knife, such as that shown in Figures 24A-24B and 25A-25C. In this case, the cutting instrument (208) comprises a part of the body that preferably has six grooves (211) and a distal tip (212), comprising a total of six cutting edges, two cutting edges (212a) that converge in a point with a 90 degree angle (8), and four cutting edges (212b) ending in a horizontal plane (212c) perpendicular to the longitudinal axis (Z) of the cutting instrument (208). The guide preferably includes an arm (202) that can be permanently fixed in the mounting block; however, in the most preferred embodiment, the guide arm (202) is coupled in a sliding manner within a complementary transverse chamber (205), which passes through the block (Figure 18). In this embodiment, the arm can be adjusted in different positions laterally for a desired cutting area, as discussed above. The machining assembly includes a means for attaching the arm (202) within the chamber (205), preferably a locking screw (206) having a head (206a) and a lower body (206b) coupled within a conduit complementary longitudinal (207), positioned at the upper end (102) of the block, and in communication with the transverse chamber (205). When the head of the screw (206a) is rotated in one direction, the lower body (206b) of the screw moves downwardly until it comes into contact with the guide arm (202) to prevent any further sliding movement of the guide arm within the camera (205). When the head of the screw is rotated in the opposite direction, the lower body is retracted to release the arm (202), thereby allowing the sliding movement of the guide arm within the chamber. Figure 17 shows an enlarged view of a design of the locking screw, in which the lower body (206b) is further divided into four segments: a narrow segment (206c) underlying the head of the screw (206a); a wide segment (206d) underlying the narrow segment; an elongated segment (206e) underlying the wide segment (206d); and a distal tip (209) having a larger diameter than the upper elongated segment (206e). Finally, to prevent the locking screw (206) from being detached from the mounting lock (101) and possibly lost, a grooved pin (104) is used, which is contained within a complementary chamber (104a) in communication through of the mounting lock (101) adjacent to the locking screw (206), as shown in Figures 13, 18 and 19, for example. With the retraction of the locking screw (206), the upper edge (209a) to the lower tip (209) of the screw comes into contact with the grooved pin (104) to prevent further upward movement and subsequent removal of the screw. blockage of the mounting block (101). With specific reference to Figures 9, 13, 16 and 18, the guide arm (202) preferably includes a means for adjusting the guide in multiple positions relative to the mounting lock, more preferably a plurality of indentations (204) located in the housing. on the upper surface of the guide arm, and a piston pressed with a spring (300) coupled into a complementary longitudinal bore (302) parallel to the locking screw (206), and perpendicular to the transverse chamber (205). The piston (300) includes a lower elastic tip loaded with a spring (301), which overhangs the traneversal chamber (205), so that when an indentation (204) is positioned directly below the rivet, the lower tip (301) engages in the indentation (204). The indentations are separated from each other with the desired intervals, corresponding to the strawberries of different sizes that can be used during the surgical procedure. For example, the guide (200) shown in Figures 9-11 comprises two indentations separated from each other to correspond to two different sizes of milling cutters (ie, milling cutters 4 and 5). Preferably, the sizes are engraved on the guide arm (202) and can be viewed by the surgeon through an opening (105) in the block. Finally, although these guide arms of different configurations may be used, the preferred configuration is that having at least tree flat sides corresponding to a transverse chamber (205) having at least three corresponding sides to prevent rotational movement of the arm around the tranevereal axis (210), defined within the chamber (205). The most preferred embodiment as shown in the figures comprises six sides (2D2b) configured tai as shown in Figures 9-11 for further coupling and disassembly. Referring now to Figures 12-15 and 18-23, the machining assembly of the invention (100) further includes a means for attaching a milling cutter to the mounting lock (101). Although other conventional locking means known to those skilled in the art can be used, the figures show a preferred locking mechanism including a bore (400) present in the lower end (103) of the block, and configured to receive a protrusion or stump (18) located at the upper end (12) of the milling cutter. Also incorporated in the mounting block (101) is a lock pin assembly (101), which comprises a spring-loaded pressure pin (401) engaged within a first complementary transverse chamber (402) located above the drill (400), a locking pin (403) coupled within a second transverse complementary chamber (404) parallel to the first chamber (402), and in communication with the bore (400), the second chamber (404) being located between the drill (400) and the first chamber (401), and a connecting piece (405) that fixes one end of the locking pin (403) to one end of the pressure pin (401). Preferably, the pressure pin (401) is housed inside a helical spring (401a), which has a sufficiently high compression to ensure the stability of the locking system. As shown in Figures 21-23, when the spring pin (401) is actuated (i.e., pressed in the direction of the arrow), the locking pin (403) is disengaged from its corresponding transverse chamber (404). ) to allow the projection or stump of the cutter (18) to enter the duct (400) (Figure 22). With the subsequent release of the pressure pin (401), the locking pin (403) is reintroduced into the conduit (400) to lock the projection (18) thereof, thereby fixing the milling cutter to the mounting block (101) ( Figure 23). Preferably, the locking pin (403) is tapered to slide and received by a corresponding slot (19), located in the stump (18). For additional stability, the mounting block may also include a small key member (406) (Figures 14-15, and 18), which extends downwardly below the conduit (400), being configured to engage a groove. complementary (20) positioned on the upper end (12) of the milling cutter, adjacent to the stump or protrusion (18), as shown in Figure 5 for example. The engagement of the key member (406) within the groove (20) functions to prevent any rotational movement of the mounting lock (101) about the longitudinal axis (X) of the cutter (10). The present invention is particularly advantageous in the preparation of a femoral medullary cavity for the reception of a femoral prosthesis., so that after the subsequent implantation of the prosthesis, the longitudinal axis of the prosthesis coincides substantially with the medullary axis, thus achieving a neutral alignment within the cavity to achieve a more rigid fixation and greater stability. One method for preparing the site of the planned implantation is to press the partial bur within the medullary canal as described above in Section II. Once the medullary cavity has been prepared using the partial bur, a second finishing bur that does not contain a lateral groove can be used to enlarge the implant site to its final shape as well as to remove the bone in the medial aspect of the greater trochanter. In the most preferred embodiment, however, the machining assembly of the invention as described herein, is employed in combination, or instead, with a second finishing bur, at least with respect to bone removal from. the greater troncaterea area of the femur. Figure 7 shows the machining set (100) implanted inside the medullary cavity (O of a mur (F).) Consequently, once the bur is implanted in the medullary cavity at the desired location, the assembly block (101), which has the lateral (H) and medial (Mi) sides, is fixed to the trunnion (18) by means of the lock-pin assembly described above.The guide (200) is then fixed inside the transverse chamber (205) and being located on the lateral side (L *) of the mounting block on the split area (13) of the milling cutter (10) in a position corresponding to the desired size of the milling cutter The second cutting tool (208) it is then placed inside the guide, advancing in the cleft cavity, preferably by means of a straight piston, to machine the medial aspect zones of the greater trochanter, to allow the insertion of another cutter or prosthesis in a similar way to the partial cutter. the invention (but without having the lateral cleft). Once the cutting instrument segment (208) advances to the base portion of the slot (ie, the concavity (15a)), the cutting instrument (208) can be removed from the slot, transferring the guide to a new one. position, and then the cutting instrument (208) is advanced again to the maximum possible depth (i.e., the base of the slit). This process can be repeated until all the oozing has been extracted into the slit. As an alternative, you can advance a side cut reamer (not shown) through the guide, and move it along a curved path of a lateral cut shape, until all the bone has been removed. For ease of explanation, the description of the design and use of the machining assembly of the invention has been confined to the preferred method of use, that is, in the preparation of the femoral medullary cavity to receive a femoral prosthesis during hip arthroplasty. . As set forth above, when the machining assembly includes the partial bur of the invention described herein, it is possible to prepare a medullary cavity which allows the subsequent implantation of a neutrally aligned femoral stem component. However, it is contemplated that a technician of ordinary skill in the art, having the advantage of the expoeicionee and suggestions of the invention, could make the necessary modifications in the mechanization set, including the cutter, for the orthopedic surgical procedures that require the extraction of bone. Preferred materials for manufacturing the components of the machining assembly, including the milling cutter of the invention, are typically employed in orthopedic surgical instruments and implants, including, but not limited to, stainless steels and alloys of cobalt, chromium and molybdenum. Preferred materials including precipitation hardenable stainless steels types 455 and 17-4. To obtain optimal results, the outer surface of the second cutting instrument used within the guide is preferably electropolished and coated with a chromium nitride or similar surface hardening compound. The foregoing description and description of the invention is of the illustrative and explanatory type thereof, and various changes may be made in the dimension, shape and materials, as well as in the details of the construction shown, including, but not limited to, the necessary modifications to accommodate variations to the patient's anatomy, without deviating from the spirit of the invention.