Patent Description:
This invention relates to a reamer for cutting the acetabulum, in preparation for receiving an acetabular implant, and processes or methods of manufacturing thereof.

Current reamers are stamped of metal and then drilled to create cutting edges. The stamping process, however, creates recesses into which bone and soft tissue matter can become trapped, making cleaning difficult. In addition, accuracy and precision of the reamer is often difficult to obtain by stamping.

There exists a need for a reamer which is easier to clean. In addition, there exists a need for a reamer that is precise and easier to manufacture.

Related background references are represented by documents: patent <CIT> and patent <CIT>.

Document <CIT> discloses an acetabular reamer, for producing a well-rounded recess in a bone. The reamer presents a hemisphere having protrusions that extend from the hemisphere for forming the cutting elements responsible for removing bone material. The cross-section of these cutting elements does not have a cutting-edge apex.

Analogously, document <CIT> discloses an orthopaedic reamer for cutting bone which has a head with a plurality of cutting teeth that protrudes from the hemispheric head.

The present invention refers to an acetabular reamer according to claim <NUM>. The acetabular reamer of the invention meets these needs via a reamer driver device having a domed external surface, a domed internal surface being concentric to the domed external surface and a rim thereby defining a hollow dome. At least one cutting tooth is disposed on the hollow dome. The cross-section of the cutting tooth has a cutting-edge apex on the crest which extends from the domed external surface, wherein the crest is defined by the tooth domed surface which connects the domed external surface to the cutting-edge apex. The cross-sectional thickness T measured substantially perpendicular to the crest of the at least one tooth between the tooth domed surface and the domed internal surface is greater than the radial distance t between the external and internal domed surfaces. Preferably, the reamer further comprises a reamer connection which has an internal anular rim that will be contacting the domed internal surface once assembled and a base rim that will be contacting the rim of the hollow dome once assembled.

The reamer includes a domed internal surface in which a plurality of cutting edge facing surfaces extend completely to the domed internal surface. The cutting edge facing surfaces are formed by drilling or milling. This avoids pockets that trap bone chips or soft tissue and so eases cleaning of the reamer between uses and should improve cutting efficiency as well.

In a preferred embodiment, the reamers of the invention are made by injection molding of metal powder (MIM) and sintering. Other materials like plastics, plastics filled with carbon fibers or glass fibers, resins, ceramics can be used as well. The present invention differs from the prior art reamers where teeth are made by deformation of a sheet of metal of constant thickness and where the connecting bars are assembled onto the reamer shell afterwards by a welding process.

The present invention also describes methods of making the acetabular reamer according to claims <NUM>-<NUM>.

The attached drawings represent, by way of example, different embodiments of the subject of the invention.

Those skilled in the art will appreciate that elements in the Figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, dimensions may be exaggerated relative to other elements to help improve understanding of the invention and its embodiments. Furthermore, when the terms 'first', 'second', and the like are used herein, their use is intended for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. Moreover, relative terms like 'front', 'back', 'top' and 'bottom', and the like in the Description and/or in the claims are not necessarily used for describing exclusive relative position. Those skilled in the art will therefore understand that such terms may be interchangeable with other terms, and that the embodiments described herein are capable of operating in other orientations than those explicitly illustrated or otherwise described.

In <FIG> and <FIG>, the acetabular reamer <NUM> is shown after injection molding and assembling of the components, sintering and machining of the cutting edges. The acetabular reamer <NUM> comprises typically a domed external surface <NUM>, a rim <NUM>, and a domed internal surface <NUM> which together define a hollow dome. The domed external surface and the domed internal surface are concentric with each other and therefore spaced apart by a constant distance. The domed has cutting teeth <NUM> disposed around the dome to insure an even reaming of a socket when rotated around its main axis. Connecting bars <NUM> allow the acetabular reamer to be connected to an instrument holder, also called a reamer handle.

Note that although a hollow dome is suitable for the cutting of the acetabulum, many of the benefits of the invention can be obtained using other shapes (see e.g., <FIG>), depending on the application. A hollow cone or other surface of revolution would also be used in particular applications.

In an embodiment, the four connecting bars are disposed at <NUM>° from each other to form a cross bar. A reinforcement portion <NUM>, having at least one of its cross-section dimensions larger that the diameter of the connecting bars, is located at the center of the cross bars. A hole or opening <NUM> is located at the center of the cross bar (or the reinforcement portion <NUM>). Undercuts <NUM> along the connecting bars <NUM> reduce the cross-section of the connecting bars and decrease the deformation of the rim <NUM> during the sintering process.

In another embodiment, a window <NUM> along a connecting bar <NUM> is added for the identification of the size of the reamer.

In another embodiment, the connecting bars <NUM> are adjacent to the rim <NUM> of the acetabular reamer and located fully inside the internal surface <NUM> of the hollow dome. In a different embodiment, the connecting bars may be located above or below the rim <NUM>. In a still further embodiment, the connecting bars have different shapes and cross-section shapes. In fact, the number of connecting bars can be increased or reduced to be adapted to the reamer driver used.

Now referring to <FIG>, the domed internal surface <NUM> has a larger cross-sectional thickness in the equator area, forming a circular reinforcement rim <NUM>.

Referring to <FIG>, the size of the reamer or any other information <NUM> can be displayed in the window <NUM> of the connecting bar.

Referring to <FIG>, a different embodiment of the reamer is shown where the center of the cross bar is solid and allows the display of information.

Now referring to <FIG>, and according to the invention, the cross-section of the cutting tooth <NUM> has a cutting-edge apex <NUM> on the tooth domed surface or crest <NUM> which extends from the domed external surface <NUM>, <NUM>. A tooth domed surface or crest <NUM> is essentially a radial projection of a line centered on a tooth <NUM> oriented along the cutting trajectory of the tooth and projected onto the top of the tooth. The tooth domed surface or crest <NUM> connects the domed external surface <NUM> to the cutting-edge apex <NUM>. A tooth cutting surface <NUM> facing the cutting direction is disposed at an angle <NUM> to the domed internal surface <NUM>, <NUM>. The perpendicular distance t between the external surface <NUM> and the internal surface <NUM> is equivalent to the thickness of the reamer hollow dome. The perpendicular distance T between the tooth domed surface <NUM> and the internal surface <NUM> is significantly larger than the perpendicular distance t between the external surface <NUM> and the internal surface <NUM>. Tooth holes <NUM> are made through the external surface <NUM>, the tooth domed surface <NUM> and the internal surface <NUM> to form the cutting edges of the tooth. The tooth holes <NUM> may be cylindrical, elliptical, polygonal, even square, and/or tapered or have a specific geometry depending on the desired cutting properties. The tooth holes <NUM> are usually machined at an angle <NUM> between <NUM>° to <NUM>° from the axis parallel to the surface of the hollow dome. The angle <NUM> corresponds to what we can refer to herein as the cutting angle of the tooth. Consequently, a <NUM>° angle would be blunt, and a <NUM>° angle would be very sharp considering the direction of cutting.

In the prior art tooth shown in <FIG>, the tooth <NUM> is formed by deformation of a constant thickness sheet of material. A punching tool is typically usually used to deform the shell and create the tooth geometry. A small cavity <NUM> is therefore formed on the inside of the shell, which may be problematic when cleaning the acetabular reamer after surgery. It is sometimes difficult to access this cavity <NUM> for cleaning. The perpendicular distance between the external surface <NUM> and the internal surface <NUM> of the hollow dome <NUM> is essentially equal to the perpendicular distance t between the cutting-edge apex <NUM> and the tooth internal surface <NUM>. That is because typically, as mentioned above, a sheet metal blank of set thickness is used to form the hollow dome <NUM>.

Referring again to <FIG>, on the other hand, the tooth <NUM> of the present invention is not formed by deformation of a constant thickness sheet of material but by injection molding. Therefore, the cross-sectional thickness of the tooth <NUM> is not constant and offers a flat internal domed surface <NUM> without recesses <NUM>, eliminating bone chip collection areas and thus allowing easier cleaning of the instrument.

Although a single tooth <NUM> is mentioned, it should be evident that typically, more than one tooth <NUM> is required to properly cut the acetabulum. In fact many teeth <NUM>, typically formed in a spiral orientation from the apex of the hollow dome <NUM> to the rim <NUM>, <NUM> are used. Generally, between <NUM> and <NUM> teeth are used depending on the size of the reamer and the size and geometry of the teeth. The teeth may be oriented in a spiral orientation or disposed in any convenient manner which cuts the desired rotational surface of the dome or other shape when the reamer is rotating thereby cutting the bone evenly.

Referring now to <FIG>, the acetabular reamer is shown at an intermediate step of the manufacturing process where the acetabular reamer <NUM> is composed of two injection molded pieces, the reamer hollow dome <NUM> and the reamer connection <NUM>. The reamer connection <NUM> is preferably made from the same injection molding process as the reamer hollow dome <NUM> and assembled together before sintering and machining of the holes. The reamer hollow dome <NUM> has tooth domes <NUM> that will be used to form the teeth <NUM>. A positioning feature <NUM>, located around the rim <NUM> of the hollow dome <NUM>, guarantees a correct orientation with the positioning feature <NUM> of the reamer connection <NUM> once assembled. According to the invention, the reamer connection <NUM> has an internal annular rim <NUM> that will be contacting the domed internal surface <NUM> once assembled and a base rim <NUM> that will be contacting the rim <NUM> of the hollow dome <NUM> once assembled. Since important internal constraints and deformations may occur during the sintering process, the internal annular rim <NUM> and the base rim <NUM> may be designed with different shapes, thicknesses and dimensions. The interfacing surfaces may be tapered. The undercuts <NUM> along the connecting bars <NUM> are also important for partially reducing the cross-section of the connecting bars and therefore decreasing the internal constraints generated during the sintering process and causing eventual deformations of the rim. The undercuts <NUM> may be replaced by different geometries of the connecting bars <NUM> allowing an increase or decrease of the cross-section in that area. The hole or opening <NUM>, located at the center of the cross bar (or the reinforcement portion <NUM>) gives direct access to the internal apex surface of the hollow dome. Specific fixtures will be used to support the apex of the hollow dome from the inside during the sintering process to avoid its deformation or sagging.

Referring now to <FIG>, the assembly of the reamer hollow dome <NUM> and the reamer connection <NUM> is shown. After sintering of the assembly <NUM>, the two pieces will be fully fused together, showing only a parting line <NUM>. The positioning features <NUM> and <NUM> are coincident, showing a parting line <NUM>.

Referring now to <FIG>, the reamer hollow dome <NUM> after injection molding (and without the reamer connection <NUM>) is shown. The internal surface <NUM> is smooth.

Referring now to <FIG>, a cross-section of the assembled and sintered reamer hollow dome <NUM> and reamer connection <NUM>, where the two pieces will be fully fused together is shown. <FIG>, referring as well to a close-up view of the cross-section of a tooth dome is shown prior to drilling or milling of the cutting edge. The thickness of the tooth dome <NUM> is larger than the thickness of the reamer dome shell.

Referring now to <FIG>, the method <NUM> for manufacturing the acetabular reamer <NUM> includes several steps. In a first step <NUM>, the reamer hollow dome <NUM> and the reamer connection <NUM> are made by injection molding of metal (MIM). In a second step <NUM>, the reamer hollow dome <NUM> and the reamer connection <NUM> are assembled together. A positioning feature <NUM> insures correct positioning of the two components. In a third step <NUM>, the assembly of the two components is sintered at high temperature, which fuses the components together to form only one piece. In a fourth step <NUM>, tooth holes <NUM> are machined into the sintered assembly to create the cutting edges of the teeth. In a fifth step <NUM>, the assembly is optionally heat treated to give the material the desired hardness properties.

Referring to <FIG>, an alternative method <NUM> for manufacturing the acetabular reamer includes several steps. In a first step <NUM>, the reamer hollow dome <NUM> and the reamer connection <NUM> are made by injection molding of metal (MIM). In a second step <NUM>, tooth holes <NUM> are machined into the green hollow dome <NUM> to create the cutting edges of the teeth. In a third step <NUM>, the reamer hollow dome <NUM> and the reamer connection <NUM> are assembled together. A positioning feature <NUM> insures correct positioning of the two components. In a fourth step <NUM>, the assembly of the two components is sintered at high temperature, which fuses the components together to form only one piece. In a fifth step <NUM>, the part is optionally heat treated to give the material the desired hardness properties.

Importantly, machining the cutting edge after molding or even better after sintering enables the forming of a more effective cutting tooth with good cutting properties. The cutting edge of the cutting tooth should not be formed during the molding process (as is the case in the prior art). The reamer of the invention has at least a portion of a visible parting line close to the rim of the reamer.

An advantage of the present invention is to provide an acetabular reamer having a smooth surface on its inside, therefore allowing easier cleaning of the instrument. Another advantage of the invention is to improve the accuracy of the positioning and orientation of the teeth by using a more repetitive process with less manual operations. The spherical form of the reamer is also improved because there is no deformation of the shell when punching the teeth, as was the case with prior art reamers.

It should be appreciated that the particular implementations shown and herein described are representative of the invention and its best mode and are not intended to limit the scope of the present invention in any way.

It should be appreciated that many applications of the present invention may be formulated.

As will be appreciated by skilled artisans, the present invention may be embodied as a system, a device, or a method.

The specification and figures should be considered in an illustrative manner, rather than a restrictive one. Accordingly, the scope of the invention should be determined by the appended claims rather than by merely the examples described above.

Benefits, other advantages and solutions mentioned herein are not to be construed as critical, required or essential features or components of any or all the claims.

Other combinations and/or modifications of the above-described elements, materials or structures used in the practice of the present invention may be varied or adapted by the skilled artisan to other designs without departing from the general principles of the invention.

Claim 1:
An acetabular reamer (<NUM>) comprising a domed external surface (<NUM>, <NUM>) and a domed internal surface (<NUM>, <NUM>) being concentric to the domed external surface (<NUM>, <NUM>) and a rim (<NUM>, <NUM>) thereby defining a hollow dome (<NUM>), wherein at least one cutting tooth (<NUM>) is disposed on the hollow dome (<NUM>), wherein the cross-section of the cutting tooth (<NUM>) has a cutting-edge apex (<NUM>) on the crest (<NUM>) extending from the apex to the domed external surface (<NUM>, <NUM>) and wherein the crest (<NUM>) is defined by the tooth domed surface which connects the domed external surface (<NUM>, <NUM>) to the cutting-edge apex (<NUM>), the reamer characterized in that
the cross-sectional thickness (T) measured substantially perpendicular to the crest of the at least one tooth (<NUM>) between the tooth domed surface and the domed internal surface (<NUM>, <NUM>) is greater than the radial distance (t) between the external (<NUM>, <NUM>) and internal (<NUM>, <NUM>) domed surfaces.