APPARATUS FOR PREPARATION OF A PROSTHESIS

Abstract: A guide for milling the femur of a patient to receive a femoral hip prosthesis includes a guide body (11) having a lower end base portion (12) adapted to extend into intermedullary canal of the femur and an upper end portion comprised of at least one or preferably two spaced apart struts (13,14) whereby the overall configuration of the guide body can be substantially the same as the prosthesis body sought to be implanted in the patient. In the lower end of the guide body base there is provided one or more hemispherical receptacles (15,16) for holding the hemispherical end portion (21) of a spinning mill bit. A removable arcuate, transverse guide rail (30), is connected to a strut to guide the mill bit.

Description: The present invention relates to a modular hip prosthesis system wherein various custom selected component parts of an implant can be selected during the surgical procedure. More particularly the present invention relates to instrumentation for fitting such prosthesis components and systems such as mills or rotary reamer guides, which selected to prepare the femur so that the implant can be custom fitted to a patient. Increasingly, surgeons want to be able to custom fit femoral prostheses to patients. Instead of having to choose a properly sized prosthesis from a group of pre-formed implants, it would be advantageous to have a basic design which can be modified with various component parts. This would eliminate the need to maintain a large inventory and would provide better fitting implants. In addition, the femur of each patient can differ slightly so that some cutting and/or reaming of the intermedullary cavity is desirable for properly preparing the femur to receive the selected prosthesis. Custom fitted implants are particularly important in revision cases where an implant has to be removed and replaced since old cement must be removed and bone resorption occurs in many cases. Unpredictable, proximal and/or distal bone loss or deformity often occurs which must be accomodated by the replacement prosthesis. For initial implants, basic variations in patient anatomy are often confronted by the surgeon. Variations in intramedullary canal diameter can also occur, which if not accompanied by a properly sized implant, can result in distal toggle. In short, it is difficult, if not impossible to predict the exact shape of a hip implant which is suitable for all patients. Since it is impractical and would be prohibitively expensive to maintain an inventory of implants for most patients, compromises must sometimes be made in supplying implants which fit reasonably well but could be improved upon. One type of cutting guide for use with a reamer in preparing the proximal end of the femur for a hip prosthesis is described in US Patent No. 4777942, wherein a milling instrument is disclosed which is inserted into a medullary cavity and a spindle which is linked to the caliper at an angle. The spindle carries a milling cutter as well as a guide shoe at the distal end which slides within a guideway at the distal end of the caliper. The instrument is able to cut a circular arc corresponding to the boundary line between the spongiosa and cortical tissue in the region of the calcar arc. It is an object of the present invention to provide a rotary reamer guide apparatus for preparing the femur for a hip prosthesis which can then be custom fitted to a particular patient by a surgeon prior to surgical insertion of the prosthesis. According to the present invention there is provided a guide apparatus for preparing the femur of a patient with a mill guide to receive a femoral hip prosthesis comprising: a) a body having a lower end base adapted to extend into the intermedullary canal of the femur, and an upper end portion comprised of at least one strut; b) the lower end of the base having receptacle means for receiving and holding the end of a spinning mill; c) an arcuate transverse guide rail having means thereon for forming a connection with the upper end of the guide body, the guide rail having a curved surface that is adapted to guide the mill during preparation of the intermedullary canal of the patient's femur for receiving a hip prosthesis. The present invention also provides apparatus for preparing the femur to receive a prosthesis comprising: a) mill guide in accordance with the invention and b) an elongated mill having a lower end portion with a hemispherical tip thereon and circumferentially spaced apart cutter blades extending between the hemispherical tip and at least the mid-section of the mill the upper end portion of the mill having a tooled end portion receptive of a rotary drill for rotating the bit said hemispherical tip being adapted to be received in a receptacle formed in the lower end base portion of the guide. The apparatus includes preferably a V-shaped guide body having end base portion that is adapted to extend into the intermedullary canal of the femur during use, with an upper end portion comprises of a pair of spaced apart struts. The lower end of the base includes one or more receptacles for holding the end of a mill or rotary reamer. In the preferred embodiment, the mill provides at its lowest end portion a hemispherical surface and the receptacle comprises a pair of spaced apart hemispherical receptacles, for containing the hemispherical portion of the mill in one of two pre-selected cutting positions for the lower end of the reamer. A curved, transverse guide rail is provided which attaches at a removable connection with the upper end of the guide body at one of the struts, the guide rail including a cantilevered arm having a curved surface that is adapted to engage and guide the mill during preparation of the intermedullary canal of the patient's femur before receiving a hip prosthesis. Because the guide rail is removable from the guide body, the present invention provides a modular kit wherein a plurality of different guide rails can be used for creating cuts of different pre-selected configurations in the intermedullary canal. Thus, the surgeon can select a particular guide rail configuration and resultant cut for the intermedullary canal depending upon the particular patient's needs and depending upon a particular selected modular prosthesis that will be implanted. The guide body preferably defines an envelope having a size and shape that corresponds to the shape of the upper end portion of the prosthesis body so that the guide body and cut made by the reamer closely correspond to the actual shape of the prosthesis to be implanted, thus eliminating the problem of a poor fit. In the preferred embodiment, the guide rail provides a cantilevered arm that extends away from the V-shaped guide body, connecting thereto by means of a removable connection, such as, for example, a pair of spaced apart pins that downwardly extends from the cantilevered arm into sockets provided on the guide body. As an alternative construction, the connection can be in the form of a dove-tail shaped connection member carried by the guide rail, arm and slidably interfacing with a dove-tail shaped recess in the guide body. The guide rail can provide connectors on both the superior and inferior surfaces so that each guide rail can be used to make both anterior and posterior cuts as desired. For a further understanding of the nature and objects of the present invention, reference should be had to the following detailed description, taken in conjunction with the accompanying drawings, in which like parts are given like reference numerals, and wherein: Figure 1 is a perspective view of the preferred embodiment of the apparatus of the present invention; Figure 2 is a fragmentary side view of the preferred embodiment of the apparatus of the present invention illustrating the guide body; Figure 3 is a sectional view taken along lines 3-3 of Figure 2; Figure 4 is top view of the guide body of Figure 2; Figure 5 is a fragmentary view of the preferred embodiment of the apparatus of the present invention illustrating the mill portion thereof; Figure 6 is another fragmentary view of the mill portion of the apparatus of the present invention; Figure 7 is a side view of the mill portion of the apparatus of the present invention; Figure 8 is a top view of the preferred embodiment of the apparatus of the present invention, shown in position in the patient's femur with the mill being shown in hard and in phantom lines in multiple cutting positions; Figure 9 is a top view of the preferred embodiment of the apparatus of the present invention illustrating a second construction of the guide rail; Figure 10 is a side view of the preferred embodiment of the apparatus of the present invention showing a second construction of the guide rail; Figure 11 is a sectional view taken along lines 11-11 of Figure 9; Figure 12 is a sectional view taken along lines 12-12 of Figure 9; and Figure 13 is a fragmentary side view of the second construction of the guide rail connection for the embodiment of Figures 9-12. Figures 1 and 8 show generally an embodiment of the apparatus of the present invention designated generally by the numeral 10. Mill apparatus 10 includes a mill guide body 11 having a base 12 portion at its lower end a pair of spaced apart struts 13, 14 extending upwardly therefrom. The guide body 11 has a lower receptacle in the form of a pair of spaced apart hemispherical bearing cups 15, 16 each of which is adapted to receive a hemispherical end portion 21 of reamer 20 (see Figures 1, 7 and 8) during use. The guide body has an overall shape and configuration, as shown in Figures 2 and 4, that corresponds to the shape of the upper end portion of a hip prosthesis to be implanted, so that the strut 13 defines a medial strut and the strut 14 defines a lateral strut. The surgeon prepares the intermedullary canal with a broach, for example, which is generally shaped to the configuration of the prosthesis body to be implanted in the intermedullary canal. The broach (not shown) typically has an envelope that corresponds to the envelope of the prosthesis body to be implanted. After the surgeon prepares the intermedullary canal using the broach, the guide body 11 is inserted into the intermedullary canal and a particular guide rail 30 selected by the surgeon depending upon the shape of the desired cut to be made by the mill, and as selected by the surgeon. It is possible that cutting on one side of the guide body only would be desired, and thus the surgeon may only use the mill to cut on one side, as shown in Figure 1. The guide rail 30 would preferably be reversible in order to cut on both medial and lateral sides of the intermedullary canal. In that respect, the guide rail 30 would preferably be removable from the guide body 11, and reversible, having pairs of attachment pins 31, 32 on both its upper and its lower surfaces. Pin openings 17, 18 in guide body 11 receive corresponding pins 31, 32 of guide rail to form the connection. In Figure 1, the lower surface set of pins 31, 32 is not shown because the lower set of pins are in the openings 17, 18. In the embodiment of Figures 9 - 13, a dove-tail connector 34 would be provided on each side of guide arm 30 for connecting with a corresponding dove-tailed groove 39 milled in the top of the strut 13, so that the guide rail 30 has the same generally horizontal orientation as with the construction illustrated in Figure 1. Thus, when connector 34 registers in groove 39, the rail 30 can be extended either rearwardly of guide body 11 for posterior cuts and forwardly of guide body 11 for anterior cuts. Stop pins 38 limit the movement of guide rail 30 with respect to body 11 during milling or cutting using mill. Once attached, the guide rail 30 provides a generally curved guide surface 35 that extends between the connection end portion 40 of guide rail 30 to the free end 37 portion thereof. The shape of guide surface 35 would vary, depending upon the size of the cut to be made by the mill 20 as selected by the surgeon. Thus, a plurality of guide rails 30 could be provided in kit form to the surgeon, each with a different curvature or configuration of surface 35. The surface 35 would be abutted during operation with bearing sleeve 22 of mill 20, as shown in Figure 1. The sleeve 22 could be removably attached to the central portion 23 of mill 20 which could be in the form of a reduced diameter section 25 of mill 20 as shown in Figure 7. The upper end portion 28 of mill 20 has a tool receptive tip having multiple flat surfaces 27 which are circumferentially spaced (see Figure 6) so that a drill or the like could be attached to drill mill 20. A plurality of circumferentially spaced apart blades 24 would be provided on the lower end of mill 20 for the purposes of cutting away bone tissue during use.

Claims: A guide apparatus for preparing the femur of a patient with a mill guide to receive a femoral hip prosthesis comprising: a) a body (11) having a lower end base (12) adapted to extend into the intermedullary canal of the femur, and an upper end portion comprised of at least one strut (13,14); b) the lower end of the base (12) having receptacle means for receiving and holding the end of a spinning mill; c) an arcuate transverse guide rail (30) having means thereon for forming a connection with the upper end of the guide body, the guide rail (30) having a curved surface (35) that is adapted to guide the mill (20) during preparation of the intermedullary canal of the patient's femur for receiving a hip prosthesis. Apparatus according to claim 1 wherein the guide body (11) comprises a base of a pair of struts (13,14) extending upwardly therefrom. Apparatus according to claim 1 or claim 2 further comprising a receptacle (17,18;39) formed on the upper end portion of the guide body for receiving the connection means portion of the guide rail. Apparatus according to any one of the preceding claims wherein the connection forming means comprises a reversible connector that attaches the guide rail (30) to the guide body (11) in multiple positions. Apparatus according to any one of the preceding claims wherein the guide body (11) includes medial and lateral spaced apart struts (13,14). Aparatus according to claim 5 wherein the connection means forms a connection with the medial strut. Apparatus according to any one of claims 2 to 6 wherein the connection means comprises a receptacle (17,18;39) carried by one of the struts (13,14) of the guide, and pair of opposed pegs (31,32) carried by one end portion of the guide rail (30) for respectively attaching the guide rail to the guide body (11) and pre-selected left and right respective positions so that the guide rail (30) can be used to form posterior and anterior sides of the intermedullary canal. Apparatus according to any one of claims 2 to 7 wherein the guide body (11) includes a pair of spaced apart struts (13,14) including a generally vertically upstanding strut and inclined strut forming an acute angle therewith. Apparatus according to any one of claims 2 to 8 wherein the guide body (11) defines an envelope having a shape corresponding to the shape of an upper end portion of the prosthesis body to be placed in the patient's femur. Apparatus according to any one of the preceding claims wherein the receptacle means includes a pair of spaced apart, anterior and posterior receptacles (15,16) each being sized to receive the lower end portion of the mill (20). Apparatus according to any one of the preceding claims wherein the guide body (11) defines an envelope having substantially the same configuration as the prosthesis body sought to be implanted in the patient. Apparatus according to any one of the preceding claims wherein the guide rail (30) includes an arcuate portion having a bearing surface thereon which allows the mill (20) to track an arcuate path extending generally away from the central axis of the intermedullary canal so that the mill (20) forms a cut in the intermedullary canal that increases the size of the intermedullary canal from the distal end portion thereof to the proximal end portion thereof. Apparatus according to any one of the preceding claims wherein the guide rail (30) includes a cantilevered arm portion extending away from the connection means, the cantilevered arm carrying a curved guide surface (35) that is positioned to engage the mid-section of the mill (20) during use. Apparatus for preparing the femur to receive a hip prosthesis comprising: a) a mill guide apparatus as defined in any one of the preceding claims and b) an elongated mill (20) having a lower end portion with a hemispherical tip thereon and circumferentially spaced apart cutter blades (24) extending between the hemispherical tip and at least the mid-section of the mill the upper end portion (28) of the mill having a tooled end portion receptive of a rotary drill for rotating the bit said hemispherical tip being adapted to be received in a receptacle (15,16) formed in the lower end base portion of the guide.

Inventors: FALLIN, THOMAS WADE
Applicants: SMITH & NEPHEW RICHARDS INC.
Application year: 1991
Main classification: A61F2
IPC codes: A61B17, A61F2