Orthopaedic cutting block having a chemically etched metal insert

An orthopaedic surgical instrument comprising an orthopaedic cutting block includes a metallic bearing insert configured to support a bone cutting tool and a body molded to the bearing insert. The bearing insert includes a plurality of chemically etched holes, and the body is molded to the bearing insert such that each of the plurality of chemically etched holes is at least partially filled by a portion of the body. The body of the orthopaedic cutting block may include a bone-facing surface adapted to contact a portion of a patient's bone, and the bearing insert may be positioned to allow a surgeon to perform a cut on the patient's bone using the bearing insert for support. A method of manufacturing an orthopaedic surgical instrument is also disclosed.

Cross-reference is made to co-pending U.S. Utility Patent Application Ser. No. 12/345,133 entitled “Orthopaedic Cutting Tool Having a Chemically Etched Metal Insert and Method of Manufacturing” by Jon Edwards, which is assigned to the same assignee as the present application, filed concurrently herewith, and hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to orthopaedic surgical instruments, and more particularly to an orthopaedic cutting block having a metallic bearing insert with chemically etched holes.

BACKGROUND

Joint arthroplasty is a well-known surgical procedure by which a diseased and/or damaged natural joint is replaced by a prosthetic joint. Typical artificial joints include knee prostheses, hip prostheses, shoulder prostheses, ankle prostheses, and wrist prostheses, among others. To facilitate the replacement of the natural joint with the prosthesis, orthopaedic surgeons use a variety of orthopaedic surgical instruments such as, for example, saws, drills, reamers, rasps, broaches, cutting blocks, drill guides, milling guides, and other surgical instruments. Typically, orthopaedic surgical instruments are fabricated from metal using traditional manufacturing processes, such as machining, turning, and drilling, and require sterilization between surgical procedures.

SUMMARY

According to one aspect, an orthopaedic cutting block may include a metallic bearing insert and a body molded to the bearing insert. The bearing insert may have a plurality of chemically etched holes and may be configured to support a bone cutting tool. The body may be molded to the bearing insert such that each of the plurality of chemically etched holes is at least partially filled by a portion of the body.

In some embodiments, the bearing insert may have an interface surface which contacts the body and a guide surface opposite the interface surface. The guide surface of the bearing insert may be configured to support a bone cutting tool. Each of the plurality of chemically etched holes in the bearing insert may extend from the interface surface to the guide surface of the bearing insert. The portion of the body which at least partially fills each chemically etched hole may fill at least half the volume of the hole. The bearing insert may be embodied as a bushing, and the guide surface may be configured to support a bone drill bit. The bearing insert may be embodied as a non-captured cutting guide, and the guide surface may be configured to support a bone saw blade. The body may be formed of an injection-molded polymer.

The body of the orthopaedic cutting block may include a bone-facing surface adapted to receive a portion of an anterior side of a patient's tibia, and the bearing insert may be positioned to allow a surgeon to perform a proximal cut on the patient's tibia using the bearing insert for support. The body may include a bone-facing surface adapted to receive a portion of an anterior side of a patient's femur, and the bearing insert may be positioned to allow a surgeon to perform a distal cut on the patient's femur using the bearing insert for support. The body may include a bone-facing surface adapted to contact a resected distal surface of a patient's femur, and the bearing insert may be positioned to allow a surgeon to perform at least one of an anterior cut, a posterior cut, and a chamfer cut on the patient's femur using the bearing insert for support. The body may include a first bone-facing surface adapted to contact a resected anterior surface of a patient's femur and a second bone-facing surface adapted to contact a resected distal surface of the patient's femur; the guide surface of the bearing insert may include a medially-facing section, a laterally-facing section, and a distally-facing section; and the bearing insert may be positioned to allow a surgeon to perform a notch cut on a patient's femur using the bearing insert for support.

In another aspect, an orthopaedic surgical instrument may be embodied as an orthopaedic cutting block. The orthopaedic surgical instrument may include a first metallic bearing insert, a second metallic bearing insert, and a body molded to the first and second bearing inserts. The first bearing insert may have a first plurality of chemically etched holes and may be configured to support a bone cutting tool. The second bearing insert may have a second plurality of chemically etched holes and may be configured to support the bone cutting tool. The body may be molded to the first and second bearing inserts such that each of the first plurality of chemically etched holes and each of the second plurality of chemically etched holes is at least partially filled by a portion of the body.

In some embodiments, the first bearing insert may have an first interface surface which contacts the body and a first guide surface opposite the interface surface. The first guide surface may be configured to support the bone cutting tool. Each of the first plurality of chemically etched holes may extend from the first interface surface to the first guide surface of the first bearing insert. The second bearing insert may have a second interface surface which contacts the body and a second guide surface opposite the interface surface. The second guide surface may be configured to support the bone cutting tool. Each of the second plurality of chemically etched holes may extend from second interface surface to the second guide surface of the second bearing insert. The first bearing insert may oppose the second bearing insert with a gap therebetween. The first and second bearing insert may be embodied as a captured cutting slot configured to support a bone saw blade.

According to another aspect, a method for manufacturing an orthopaedic surgical instrument is disclosed. The method may include chemically etching a plurality of holes into a metallic bearing insert. The method may also include molding a body to the bearing insert to form an orthopaedic cutting block. The method may include chemically etching each of the plurality of holes through the entire thickness of the bearing insert. The method may further include chemically etching a groove into the bearing insert. The method may also further include bending the bearing insert along the groove prior to molding the body to the bearing insert.

In some embodiments, the method may include forming a mask on the bearing insert. The mask may define a plurality of exposed areas on the bearing insert. The method may include placing the bearing insert having the mask in a chemical bath whereby the plurality of exposed areas are chemically etched into the plurality of holes. The method may also include removing the bearing insert having the mask from the chemical bath and removing the mask from the bearing insert. The method may include applying a photoresist material to the bearing insert, selectively exposing portions of the photoresist material to a light source using a patterned photomask, and selectively removing portions of the photoresist material using a developer to define the plurality of exposed areas on the bearing insert.

In some embodiments, the method may include loading the bearing insert into a mold. The bearing insert may contact a wall of the mold. The method may also include injecting a polymer into the mold. The bearing insert may be pressed against the wall of the mold by the polymer. The polymer may at least partially fill the plurality of holes.

DETAILED DESCRIPTION OF THE DRAWINGS

Terms representing anatomical references, such as anterior, posterior, medial, lateral, superior, inferior, etcetera, may be used throughout this disclosure in reference to both the orthopaedic surgical instruments described herein and a patient's natural anatomy. Such terms have well-understood meanings in both the study of anatomy and the field of orthopaedics. Use of such anatomical reference terms in the specification and claims is intended to be consistent with their well-understood meanings unless noted otherwise.

The present disclosure relates generally to orthopaedic surgical instruments which include one or more metallic inserts and a body molded to the metallic inserts. The metallic inserts may be positioned at or near areas of the orthopaedic surgical instrument which are subjected to the greatest forces during use. In some embodiments, the body may be an injection-molded polymer. The metallic inserts include a plurality of chemically etched holes. The chemically etched holes have distinctive structural characteristics and create adhesion between the metallic inserts and the body. The concepts of the present disclosure are applicable both to orthopaedic cutting blocks, which employ metallic bearing inserts, and to orthopaedic cutting tools, which employ metallic cutting inserts.

Referring generally toFIGS. 1-4, one illustrative embodiment of an orthopaedic surgical instrument according to the present disclosure is an orthopaedic cutting block100designed to function as a notch guide for use by a surgeon with a surgical bone saw. Similar components are labeled using similar reference numerals in these and all other figures. The orthopaedic cutting block100includes several metallic bearing inserts118,120and a body102molded to the bearing inserts118,120.

As shown inFIGS. 1 and 2, the body102of orthopaedic cutting block100includes an anterior plate104and two distal plates106, generally giving the body102the shape of an inverted “L” when viewed from the side and an inverted “U” when viewed from the top. The body102further includes a central notch opening108defined by a medially-facing wall110, a distally-facing wall112, and a laterally-facing wall114. The anterior plate104includes a bone-facing surface142which is adapted to contact a resected anterior surface of a patient's femur10. Each of the two distal plates106includes a bone-facing surface144adapted to contact a resected distal surface of the patient's femur10. The body102also includes six guide holes116(four of which can be seen in each ofFIGS. 1 and 2). The number and placement of the guide holes116may be varied, and not every guide hole116may require a bearing insert118.

The body102may be formed of any material which may be molded to the bearing inserts118,120, including, but not limited to, polymers and resins. In some embodiments, the body102may be formed of a material which is less capable than the bearing inserts118,120of withstanding external forces, but which is less expensive, lighter, and/or more easily fabricated into complex shapes. The body102may be heterogeneous in nature or may be a composite material. In one illustrative embodiment, the body102is formed of an injection-molded polymer.

The metallic bearing inserts118,120are generally positioned at or near areas of the orthopaedic cutting block100which are subjected to the greatest forces during use. The bearing inserts may be formed of a metal or metallic alloy; in one illustrative embodiment, the bearing inserts118,120be formed of Type 316 or Type 17-4 grade stainless steel. Each bearing insert includes an interface surface122, which contacts the body (visible in partially exploded view ofFIG. 2). Opposite the interface surface122, each bearing insert also includes a guide surface124,126, which is configured to support a bone cutting tool. Each bearing insert118functions as a bushing for one of the guide holes116. Thus, a drill bit or pin passing through one of the guide holes116will only, or at least mostly, contact the guide surface124of the bearing insert118and not the body102. The bearing insert120functions as a non-captured cutting guide for the central notch opening108. The guide surface126includes a medially-facing section128, a distally-facing section130, and a laterally-facing section132, which correspond, respectively, to the medially-facing wall110, the distally-facing wall112, and the laterally-facing wall114of the body102. Thus, a bone saw blade12(shown inFIG. 4) cutting along the central notch opening108will only, or at least mostly, contact the guide surface126of the bearing insert120and not the body102. In another embodiment, two or more separate bearing inserts may be used in place of the single, multi-sectioned bearing insert120.

Each bearing insert118,120includes a plurality of chemically etched holes134. In one illustrative embodiment, each of the plurality of chemically etched holes134extends from the interface surface122to the guide surface124,126of the bearing insert118,120. The chemically etched holes134have distinctive structural characteristics, which will be further described below with reference toFIGS. 3A-D, and create adhesion between the bearing inserts118,120and the body102. It is contemplated that the chemically etched holes134may consist of a variety of shapes and may be arranged in numerous patterns on the surface of the bearing inserts118,120. The chemically etched holes134, in one illustrative embodiment, are circular in shape and approximately 1/50 of an inch in diameter. The bearing inserts118,120may also include other chemically etched features in addition to the chemically etched holes134. In one illustrative embodiment, bearing insert120may further include one or more chemically etched grooves136and/or chemically etched indicia138, such as reference markings, trade names, and product names or numbers, among others.

As will be discussed in more detail below, chemically etched holes134, as well as chemically etched grooves136, chemically etched indicia138, and other features, may be formed by placing the metallic bearing inserts118,120in a chemical bath which dissolves exposed metal. The bearing inserts118,120may be selectively etched to form features, such as the plurality of chemically etched holes134, by forming a mask14, including a plurality of exposed areas18, around the bearing inserts118,120prior to placement in the chemical bath, as shown inFIG. 3A. The mask14may be formed of any material which is not substantially dissolved by the chemical bath.

In one illustrative embodiment, the mask14is a polymeric photoresist material which is formed around the bearing insert120, but includes a plurality of exposed areas18(seeFIG. 3A). A cross-section of the bearing insert120ofFIG. 3Aafter removal from the chemical bath but prior to removal of the polymeric photoresist mask14is depicted inFIG. 3B. In areas which were exposed to the chemical bath on both sides of the bearing insert120, the resulting structure is a chemically etched hole134. The distinctive structural characteristics of the chemically etched hole134are due in part to the isotropic nature of the wet, or liquid, chemical etch. As can be seen inFIG. 3B, as the chemical bath dissolves the metal of the bearing insert120in a vertical direction, it also dissolves the metal in horizontal directions at approximately 20-25% the rate of the vertical direction. In areas which were exposed to the chemical bath on only one side of the bearing insert120, the resulting structure is a chemically etched groove136. The groove136may run the entire width of the guide surface126of the bearing insert120. As will be discussed in more detail below, the groove136allows for bending of the bearing insert120—between the medially-facing section128and the distally-facing section130and between the distally-facing section130and the laterally-facing section132of the guide surface126—prior to molding of the body102to the bearing insert120.

The chemically etched holes134create adhesion between the bearing insert120and the body102, as shown inFIG. 3C. As the body102is molded to the bearing insert120, a portion of the body102at least partially fills each of the plurality of chemically etched holes134. After molding, the body102contacts the bearing insert120at the interface surface122and the sidewalls of the chemically etched holes134, but generally does not contact the guide surface126, providing a substantially all metallic guide surface126configured to support an orthopaedic cutting tool. In one illustrative embodiment, the portion of the body102which at least partially fills each chemically etched hole134may fill at least half the volume of each hole134. In another illustrative embodiment, the portion of the body102which at least partially fills each chemically etched hole134may fill between 70-80% of the volume of each hole134.

In another illustrative embodiment, shown inFIG. 3D, the chemically etched holes134of bearing insert120may also be formed by exposing areas on only one side of the bearing insert120, but allowing the bearing insert120to remain in the chemical bath for a longer period of time. This results in a chemically etched hole134with its own distinctive structural characteristics, including a tapered sidewall140. Again, a portion of the body102at least partially fills each chemically etched hole134, but generally does not contact the guide surface126, providing a substantially all metallic guide surface126configured to support an orthopaedic cutting tool. It should be noted that each of the features described with respect to bearing insert120andFIGS. 3A-D, may apply equally to the bearing inserts118and the chemically etched holes134thereof. Furthermore, for these and all other embodiments hereinafter disclosed, while a plurality of the chemically etched holes134are at least partially filled by portions of the body102, it is contemplated that some of the chemically etched holes134may not be filled at all.

Placement and use of the orthopaedic cutting block100on the distal end of the patient's femur10during surgery can be best seen inFIG. 4. Typically, the surgeon will have performed anterior and distal cuts or resections on the patient's femur10prior to using the orthopaedic cutting block100to perform a notch cut. The orthopaedic cutting block100is positioned such that the bone-facing surface142of the anterior plate104contacts the resected anterior surface of the patient's femur10and the bone-facing surfaces144of the two distal plates106contact the resected distal surface of the patient's femur10. The orthopaedic cutting block100is secured to the patient's femur10by the placement of one or more (typically, three or more) surgical pins16through the guide holes116. Once the orthopaedic cutting block100is secured, the surgeon may use a typical bone saw having a bone saw blade12to perform the notch cut using the bearing insert120to support the bone saw blade12.

Referring generally now toFIGS. 5 and 6, another illustrative embodiment of an orthopaedic surgical instrument according to the present disclosure is an orthopaedic cutting block200designed to function as an anterior/posterior/chamfer cutting guide, also known in the art as a 4-in-1 cutting block, for use by a surgeon with a surgical bone saw. The orthopaedic cutting block200includes several metallic bearing inserts218-226and a body202molded to the bearing inserts218-226.

The body202of orthopaedic cutting block200may be formed of any material which may be molded to the bearing inserts218-226, such as the materials discussed above with respect to orthopaedic cutting block100. As shown inFIG. 5, the body202includes a pair of body components204,206, which when combined give the orthopaedic cutting block200a generally cuboid, or rectangular parallelepiped, outer shape. Both the body component204and the body component206include bone-facing surfaces238which are adapted to contact a resected distal surface of a patient's femur10. The body component204further includes an elongated opening208, generally parallel to an imaginary line drawn between the medial and lateral sides of the body component204. The elongated opening208is defined by a first pair of tapered walls210which open toward the distal side of the body component204and by a second pair of tapered walls (not shown) which open toward the proximal side of the body component204. The second pair of tapered walls are designed to receive the body component206, as indicated inFIG. 5. The body202may also include guide holes216, on both the body component204and the body component206. The number and placement of the guide holes216may be varied, and not every guide hole216may require a bearing insert218.

Similar to the bearing inserts118,120of orthopaedic cutting block100, the bearing inserts218-226may be formed of a metal or metallic alloy and are generally positioned at or near areas of the orthopaedic cutting block200which are subjected to the greatest forces during use. Each bearing insert includes an interface surface236, which contacts the body202. Opposite the interface surface236, each bearing insert also includes a guide surface228-232(and others not shown), which is configured to support a bone cutting tool. Each bearing insert218functions as a bushing for one of the guide holes216. A drill bit or pin passing through one of the guide holes216will only, or at least mostly, contact the guide surface of the bearing insert218and not the body202. The bearing insert220functions as a non-captured cutting guide for performing an anterior cut on the patient's femur10. A bone saw blade12cutting along the anterior side of the orthopaedic cutting block200will only, or at least mostly, contact the guide surface232of the bearing insert220and not the body202. Similarly, the bearing insert222functions as a non-captured cutting guide for performing a posterior cut on the patient's femur10. A bone saw blade12cutting along the posterior side of the orthopaedic cutting block200will only, or at least mostly, contact the guide surface (not shown) of the bearing insert222and not the body202. In another illustrative embodiment, the anterior and posterior cutting guides of orthopaedic cutting block200may alternatively be captured cutting slots, similar to those described below, rather than non-captured cutting guides.

The orthopaedic cutting block200also includes two captured cutting slots which may support a bone saw blade12when performing a pair of chamfer cuts on the patient's femur10. As discussed above, the body component204includes an elongated opening208, which is in part defined by a second pair of tapered walls which open toward the proximal side of the body component204. A metallic bearing insert is disposed on each of the second pair of tapered walls: bearing insert224on the lower tapered wall, and another bearing insert (not shown) on the upper tapered wall. The body component206also has a bearing insert226. The guide surface of the bearing insert226includes a downwardly-facing section228and an upwardly-facing section230. When the body component204and the body component206are assembled, these bearing inserts form two captured cutting slots. The downwardly-facing section228of bearing insert226opposes the bearing insert224with a gap therebetween to form a downwardly-angled, captured cutting slot. The upwardly-facing section230of bearing insert226opposes the other bearing insert (not shown) with a gap therebetween to form a upwardly-angled, captured cutting slot. A bone saw blade12(shown inFIG. 6) cutting along the elongated opening108through one of the captured cutting slots will only, or at least mostly, contact the guide surfaces of the bearing inserts224,226and not the body202. In another embodiment, two or more separate bearing inserts may be used in place of the multi-sectioned bearing insert226. In yet another embodiment, any of the captured cutting slots may be formed by a single bearing insert functioning as an elongated bushing, rather than by a pair of opposed bearing inserts.

Each bearing insert218-226includes a plurality of chemically etched holes234which create adhesion between the bearing inserts218-226and the body202. The chemically etched holes234have the same distinctive structural characteristics as the chemically etched holes134, described above with respect to the orthopaedic cutting block100and shown inFIGS. 3A-D. As the body202is molded to the bearing inserts218-226, a portion of the body202at least partially fills the chemically etched holes234. After molding, the body202contacts the bearing inserts218-226at the interface surfaces236and the sidewalls of the chemically etched holes234, but generally does not contact the guide surfaces, providing substantially all metallic guide surfaces configured to support an orthopaedic cutting tool.

The bearing inserts218-216may also include other chemically etched features in addition to the chemically etched holes234, such as chemically etched grooves or indicia. In one illustrative embodiment, a chemically etched groove may run the entire width of the interface surface236of the bearing insert226. This chemically etched groove would allow for bending of the bearing insert226between the downwardly-facing section228and the upwardly-facing section230prior to molding of the body202to the bearing insert226.

Placement and use of the orthopaedic cutting block200on the distal end of the patient's femur10during surgery can be best seen inFIG. 6. Typically, the surgeon will have performed a distal cut or resection on the patient's femur10prior to using the orthopaedic cutting block200to perform one or more of an anterior cut, a posterior cut, or a chamfer cut. The orthopaedic cutting block200is positioned such that the bone-facing surfaces238of the body component204and of the body component206rest on the resected distal surface of the patient's femur10. The orthopaedic cutting block200is secured to the patient's femur10by the placement of one or more (typically, two) surgical pins16through the guide holes216of the body component204and the body component206. Once the orthopaedic cutting block200is secured, the surgeon may use a typical bone saw having a bone saw blade12to perform an anterior resection using the bearing insert220for support (shown completed), to perform a posterior resection using the bearing insert222for support (also shown completed), or to perform two chamfer resections using the captured cutting slots, as shown inFIG. 6. When the surgeon uses one of the captured cutting slots, the bone saw blade12is guided by the bearing inserts224,226, and avoids contact with the body202, including the first pair of tapered walls210.

It should be noted that an orthopaedic surgical instrument according to the present disclosure may be embodied as additional or different orthopaedic cutting blocks, other than those discussed above. By way of illustrative example, a distal femoral cutting block might include an injection-molded body and a metallic bearing insert having a plurality of chemically etched holes and positioned to allow a surgeon to perform a distal cut on a patient's femur using the bearing insert for support. As a further illustrative example, a proximal tibial cutting block might include an injection-molded body and a metallic bearing insert having a plurality of chemically etched holes and positioned to allow a surgeon to perform a proximal cut on a patient's tibia using the bearing insert for support. Indeed, it is believed that there are few, if any, orthopaedic cutting blocks to which the principles of the present disclosure would not be applicable.

Referring generally now toFIGS. 7-8, another illustrative embodiment of an orthopaedic surgical instrument according to the present disclosure is an orthopaedic cutting tool300designed to function as drill bit for use by a surgeon with a surgical bone drill. The orthopaedic cutting tool300includes a plurality of metallic cutting inserts322and a body302molded to the plurality of cutting inserts322.

The body302of orthopaedic cutting tool300may be formed of any material which may be molded to the plurality of cutting inserts322, such as the materials discussed above with respect to orthopaedic cutting block100. In one illustrative embodiment, the body302of the orthopaedic cutting tool300is formed of an injection-molded polymer. As shown inFIG. 7, the body302is generally cylindrical in shape, having a longitudinal axis L. The body302may be a generally solid cylinder or may optionally include voids312, such as those shown inFIG. 7, in order to decrease the amount of material used to create the body302. The body302includes a cutting segment314, on which the plurality of cutting inserts322are disposed. The body302may also include an integrally formed coupling feature304, at the end opposite the cutting segment314along the longitudinal axis L. The coupling feature304may include narrower sections306, wider sections308, and/or non-cylindrically-shaped sections310to allow a typical surgical bone drill (not shown) to couple to the orthopaedic cutting tool300.

The cutting segment314of the body302of orthopaedic cutting tool300, which is shown in detail inFIG. 8, includes a plurality of cutting flutes316. The plurality of cutting flutes316are arranged radially outward around the longitudinal axis L of the orthopaedic cutting tool300. A channel318is situated between each pair of adjacent cutting flutes316to allow bone fragments removed by the orthopaedic cutting tool300to exit the patient's bone. In operation, a surgeon may couple the orthopaedic cutting tool300to the surgical bone drill to cause rotation of the cutting segment314about the longitudinal axis L in the direction of arrow R indicated inFIG. 8. The cutting segment314of the body302may also include a pointed tip320to assist in guiding the orthopaedic cutting tool300.

Similar to the bearing inserts118,120of orthopaedic cutting block100, the cutting inserts322of the orthopaedic cutting tool300may be formed of a metal or metallic alloy. Each of the plurality of cutting inserts322is disposed on one of the plurality of cutting flutes316and is generally aligned with a leading edge of the cutting flute316on which it is disposed. It is also contemplated that some, but not all, of the plurality of cutting flutes316may have a cutting insert322disposed thereon. Each cutting insert322includes an interface surface328, which contacts the body302. Opposite the interface surface328, each cutting insert322also includes a work surface324which is configured to contact and remove portions of the patient's bone during rotation of the orthopaedic cutting tool300in the direction of the arrow R.

Each cutting insert322includes a plurality of chemically etched holes326which create adhesion between the plurality of cutting inserts322and the body302. The chemically etched holes326have the same distinctive structural characteristics as the chemically etched holes134, described above with respect to orthopaedic cutting block100and shown inFIGS. 3A-D. As the body302is molded to the cutting inserts322, a portion of the body302at least partially fills each of the plurality of chemically etched holes326. After molding, the body302contacts the plurality of cutting inserts322at the interface surfaces328and the sidewalls of the chemically etched holes326, but generally does not contact the work surfaces324, providing substantially all metallic work surfaces324configured to remove portions of a patient's bone.

Referring generally now toFIGS. 9-10, another illustrative embodiment of an orthopaedic surgical instrument according to the present disclosure is an orthopaedic cutting tool400designed to function as a rasp for use by a surgeon in manually removing portions of a patient's bone. The orthopaedic cutting tool400includes a metallic cutting insert412and a body402molded to the cutting insert412.

The body402of orthopaedic cutting tool400may be formed of any material which may be molded to the metallic cutting insert412, such as the materials discussed above with respect to orthopaedic cutting block100. In one illustrative embodiment, the body402of the orthopaedic cutting tool400is formed of an injection-molded polymer. As shown inFIG. 9, the body402includes a cutting segment404, on which the cutting insert412is disposed. The body402also includes an integrally formed handle406, at the end opposite the cutting segment404, which may be gripped by the surgeon during use. The handle404may be ergonomically shaped and the body402may also include bulges408near the ends of the handle406so that the orthopaedic cutting tool400may be more easily grasped by the surgeon. The body402may be generally solid or may optionally include voids410, such as those shown inFIG. 9, in order to decrease the amount of material used to create the body402.

The cutting segment404of the body402of orthopaedic cutting tool400, which is shown in detail inFIG. 10, is molded to the cutting insert412. Similar to the bearing inserts118,120of orthopaedic cutting block100, the cutting insert412of the orthopaedic cutting tool400may be formed of a metal or metallic alloy. The cutting insert412includes an interface surface422, which contacts the body402. Opposite the interface surface422, the cutting insert412also includes a work surface414, which is configured to remove portions of the patient's bone during motion of the orthopaedic cutting tool400in the direction of the arrow M indicated inFIG. 10. In operation, a surgeon may grip the orthopaedic cutting tool400at the handle406, place the work surface414in contact with the patient's bone, and move to the orthopaedic cutting tool400reciprocally in the direction of arrow M.

The cutting insert412includes a plurality of chemically etched holes416which create adhesion between the cutting insert412and the body402. The chemically etched holes416have the same distinctive structural characteristics as the chemically etched holes134, described above with respect to orthopaedic cutting block100and shown inFIGS. 3A-D. As the body402is molded to the cutting insert412, a portion of the body402at least partially fills each of the plurality of chemically etched holes416. After molding, the body402contacts the cutting insert412at the interface surface422and the sidewalls of the chemically etched holes416, but generally does not contact the work surface414, providing substantially all metallic work surface414configured to remove portions of a patient's bone.

To assist in the removal of portions of the patient's bone, the work surface414of the cutting insert412includes a plurality of chemically etched cutting teeth418. In one illustrative embodiment, shown inFIG. 10, the plurality of chemically etched cutting teeth418are etched into the work surface414of the cutting insert412to have a cross-section consisting of two steps with sharp, generally right-angled edges configured to remove portions of the patient's bone. The chemically etched cutting teeth418span the entire width of the cutting insert412and are arranged perpendicularly to the length of the cutting insert412. The work surface414also includes a relief surface420situated between each pair of adjacent cutting teeth412. In this embodiment, the plurality of chemically etched holes416extend from the interface surface422to the relief surfaces420of the cutting insert412. It is contemplated that the work surface414may take other forms, such as a single relief surface420with a plurality of chemically etched cutting teeth418raised above the relief surface420and arranged in various patterns. Various configurations of the work surface414may be formed by selectively exposing areas on one or both sides of the cutting insert412to the chemical bath in a single or multi-step etching process, as discussed below.

It should be noted that an orthopaedic surgical instrument according to the present disclosure may be embodied as additional or different orthopaedic cutting tools, in addition to those discussed above. By way of illustrative example, an orthopaedic surgical reamer might include an injection-molded body and a plurality of metallic cutting inserts having chemically etched holes and disposed at the cutting edges of the instrument to allow a surgeon to ream an intramedullary canal of a long bone using the cutting inserts. As a further illustrative example, an orthopaedic surgical broach might include an injection-molded body and a metallic cutting insert having chemically etched holes and cutting teeth to allow a surgeon to prepare a femur for placement of a femoral component during a hip arthroplasty. Indeed, it is believed that there are few, if any, orthopaedic cutting tools to which the principles of the present disclosure would not be applicable.

Referring generally now toFIGS. 11-13, an illustrative embodiment of a method for manufacturing an orthopaedic surgical instrument according to the present disclosure is illustrated as a series of simplified flow diagrams. The manufacturing process500may be used to fabricate an orthopaedic cutting block, in which case one or more metallic bearing inserts would be used, or may be used to fabricate an orthopaedic cutting tool, in which case one or more metallic cutting inserts would be used. In describing the illustrative embodiments of this method, the term “insert(s),” without a modifier, shall be used to signify either one or more metallic bearing inserts or one or more metallic cutting inserts. The manufacturing process500includes a number of process steps502-512, as shown inFIG. 11.

The manufacturing process500begins with process step502, in which the insert or inserts to be used in forming the orthopaedic surgical instrument are chemically etched to include a plurality of holes and any other desired features. The chemical etching may be performed with any chemical which dissolves metal, including, but not limited to, hydrochloric acid, ammonium persulfate, and ferric chloride. As will be described in more detail below with respect toFIG. 12, process step502will include chemically etching a plurality of holes into the insert in every embodiment, but may also include etching additional features, including grooves, indicia, cutting teeth, and/or relief surfaces, in some illustrative embodiments. Process step502may involve a single chemical etch or may involve multiple chemical etches, as needed.

After process step502, the manufacturing process500optionally proceeds to process step504, in which the insert or inserts may be bent into the approximate shape needed for the orthopaedic surgical instrument, if necessary. Process step504may be used when a single insert will occupy multiple planes in the finished surgical instrument. For instance, bearing insert120in orthopaedic surgical block100and bearing insert226in orthopaedic surgical block200is bent prior to process step506. Bending of the insert may be facilitated by one or more chemically etched grooves, such as the groove136described above and shown inFIG. 3B. The insert need only be bent to its approximate shape, as process step508will further form the insert to the correct shape, as discussed below.

After process step502, or optional process step504, the manufacturing process500proceeds to process step506, in which the insert or inserts are loaded into a mold. In one illustrative embodiment, the insert is loaded into the mold such that a guide surface (if a bearing insert) or a work surface (if a cutting insert) contacts a wall or walls of the mold. The inserts may be held in place in the mold in a number of ways, including gravitational, magnetic, or other forces.

After process step506, the manufacturing process500proceeds to process step508, in which the body material is injected into the mold. As discussed above, the body material may be any substance which may be molded to the inserts, including, but not limited to, polymers and resins. In some illustrative embodiments, the body material may be a substance which is less expensive, lighter, and/or more easily fabricated into complex shapes than the metallic inserts. Process step508may include heating the body material to make the material suitable for injecting into the mold. In process step508, the force of the body material injected into the mold presses the inserts to the walls of the mold, further shaping inserts which were bent during optional process step504into the proper shape. A portion of the body material may at least partially fill the plurality of holes in the insert which were chemically etched in process step502. In some embodiments, the body material will substantially fill all of the holes in the insert. In other embodiments, many or most of the holes will be filled, while others will be left unfilled.

After process step508, the manufacturing process500proceeds to process step510, in which the body material is allowed to set into its final, rigid form. Process step510may involve allowing the heated body material to cool to a temperature lower than its temperature when injected into the mold. In some illustrative embodiments, the body material will reach the wall of the mold during injection in process step508and be flush with the guide surface (if a bearing insert) or the work surface (if a cutting insert). During process step510, the body material may retract slightly while setting, resulting in the portion of the body only partially filling the hole, as shown in the cross-sections ofFIGS. 3C and 3D.

After process step510, the manufacturing process500proceeds to process step512, in which a formed body and insert(s) are removed from the mold. At this point, another insert or set of inserts, which have been chemically etched according to process step502, may be loaded into the mold according to process step506and the process may be repeated. It is also contemplated that the manufacturing process500may include additional process steps. For instance, in some embodiments, after the formed body and insert(s) are removed from the mold in process step512, additional assembly of the orthopaedic surgical instrument may be required.

One illustrative embodiment of process step502of the manufacturing process500is shown in detail inFIG. 12as a chemical etching sub-process consisting of process steps520-526. In every embodiment, the chemical etching sub-process502will include chemically etching a plurality of holes into an insert. In some illustrative embodiments, the chemical etching sub-process502may also include etching additional features, including grooves, indicia, cutting teeth, and/or relief surfaces into the insert. These features may be chemically etched into the insert along with the holes simultaneously, that is during a single iteration of the chemical etching sub-process502. Alternatively, the process steps520-526may be repeated, as needed, to form the appropriate chemically etched features before returning to manufacturing process500.

The chemical etching sub-process502begins with process step520, in which a mask is formed on the insert or inserts. As shown in the cross-section ofFIG. 3A, the mask14is formed around the metal to be chemically etched into the inserts, but includes a plurality of exposed areas18. The mask may be formed from any material which is not substantially dissolved by the chemical bath of process step522. As will be described in more detail below with respect toFIG. 13, one illustrative embodiment of process step520may include forming a layer of polymeric photoresist around the inserts to act as a mask during etching. The mask may be formed on one side, both sides, or neither side of the insert at various positions, depending on the desired feature at that position.

After process step520, the chemical etching sub-process502proceeds to process step522, in which the insert or inserts having the mask or masks are placed in a chemical bath. The chemical bath may include any chemicals which dissolve the metal of the inserts, but do not substantially dissolve the mask material, including, but not limited to, hydrochloric acid, ammonium persulfate, and ferric chloride. During process step522, the chemical bath selectively attacks and dissolves the metal of the inserts at the plurality of exposed areas18(FIG. 3A). As a wet, or liquid, chemical etch is isotropic in nature, the chemical bath dissolves the metal of the inserts in horizontal directions, as well as the vertical direction, resulting in the structures shown inFIG. 3B-D. Etching occurs in the horizontal directions at approximately 20-25% the rate of the vertical direction.

After process step522, the chemical etching sub-process502proceeds to process step524, in which the insert or inserts having the mask or masks are removed from the chemical bath after a predetermined amount of time. In addition to the pattern of the mask applied in process step520, the form of the inserts will also be determined by the amount of time elapsed between process steps522and524. If the chemical etch is allowed to proceed for approximately the time required to dissolve half the thickness of an insert, areas which were exposed to the chemical bath on both sides of the insert will result in a hole which extends through the entire thickness of the insert, while areas which were exposed to the chemical bath on only one side of the insert will result in a groove, as shown inFIG. 3B. If the chemical etch is allowed to proceed for approximately the time required to dissolve the entire thickness of an insert, areas which were exposed to the chemical bath on only one side of the insert will result in a hole with a tapered sidewall, similar in structure to that shown inFIG. 3D. It is contemplated that holes and other features of various other cross-sections may formed by chemically etching a particular distance into the insert from one side using a first mask, then repeating the chemical etching sub-process502using a second mask and chemically etching the remainder of the thickness of the insert from the opposite side.

After process step524, the chemical etching sub-process502proceeds to process step526, in which the mask applied in process step520is removed from the insert or inserts. At this point, the chemically etching sub-process502may be repeated, if necessary, or the manufacturing process500may proceed to one of process step504or process step506. It should also be noted that the chemical etching sub-process502may be applied to one insert at a time, or multiple inserts may be chemically etched in parallel. In one illustrative embodiment, a large metallic sheet of appropriate thickness, containing multiple rows and columns of inserts, may proceed through the chemical etching sub-process502. The mask formed in process step520may include an outline around all or substantially all of each insert, such that the inserts either fall out of the sheet during chemical etching or may be easily removed afterward.

One illustrative embodiment of the process step520of the chemical etching sub-process502is shown in detail inFIG. 13as a mask forming sub-process consisting of process steps530-536. The mask forming sub-process520is a photolithography process in which one or more patterned photomasks are used to form a light-sensitive material into a mask having a plurality of exposed areas on the insert or inserts.

The mask forming sub-process520begins with process step530, in which a photoresist material is applied to substantially cover the exterior of the insert or inserts. The photoresist material is a polymeric substance which changes its structure in response to exposure to an ultraviolet (“UV”) light source. The coating of photoresist material may be a positive photoresist, which becomes more soluble when exposed to UV light. Alternatively, the coating of photoresist material may be a negative photoresist, which becomes polymerized and less soluble when exposed to UV light. The coating of photoresist material may be applied in numerous ways, including high-velocity spin coating. The photoresist material may also need to be heated slightly before becoming light-sensitive.

After process step530, the mask forming sub-process520proceeds to process step532, in which a first patterned photomask is positioned between a UV light source and a first side of the insert covered in photoresist material. The first patterned photomask includes both translucent and opaque portions. If a positive photoresist is used in process step530, the translucent portions of the photomask will correspond to the plurality of exposed areas18in the mask14(FIG. 3A). If a negative photoresist is used in process step530, the opaque portions of the photomask will correspond to the plurality of exposed areas18in the mask14(FIG. 3A).

After process step532, the mask forming sub-process520proceeds to process step534, in which the UV light source is turned on and areas of the photoresist material are selectively exposed to the light source through the translucent portions of the first patterned photomask. In response, the chemical structure of the exposed areas of photoresist will change, becoming more or less soluble depending on the type of photoresist used. Process steps530and532may be repeated using a second photomask and a second side of the insert, if needed. Alternatively, the first and second photomasks may be positioned at the same time, each with its own light source, and the first and second sides of the insert may be exposed simultaneously.

After process step534, the mask forming sub-process520proceeds to process step536, in which a developer is applied to the insert to selectively remove areas of the photoresist material to define the plurality of exposed areas on the insert. The developer is a chemical solution which dissolves the more soluble areas of the photoresist material, but not the less soluble areas. The developer may be applied in numerous ways, including high-velocity spin coating. After developing, the remaining photoresist material may again need to be heated to harden into a mask that can withstand the chemical bath. At this point, the mask forming sub-process520is complete, and the chemically etching sub-process502may proceed to process step522.

Cross-reference is made to co-pending U.S. Utility patent application Ser. No. 12/345,133 entitled “Orthopaedic Cutting Tool Having a Chemically Etched Metal Insert and Method of Manufacturing” by Jon Edwards, which is assigned to the same assignee as the present application, filed concurrently herewith, and hereby incorporated by reference.