Hollow reamer for medical applications

[0001] 1. Field of the Invention

[0002] The present invention relates to a hollow reamer for medical applications; and more particularly, to a hollow reamer having a disposable cutter assembly which can be attached to a reusable shaft portion.

[0003] 2. Description of the Prior Art

[0004] Reaming of the internal canal of bones is required in many surgical procedures of orthopedic surgery. These procedures include hip replacement, knee replacement and shoulder replacement. Reamers are also used in procedures that involve the internal fixation of fractures. Prior art reamers typically fall into two major classes: rigid and flexible shaft. Typically, reaming of the internal bone canal is achieved through utilization of a solid cylindrical or tapered reamer. Solid cylindrical or tapered reamers currently utilized are required to cut both cancellous bone (spongy bone) and cortical bone (hard bone). Cortical bone is generally denser and stronger, requiring an efficient cutter to machine the canal for a proper fit of the implant. Conventional reamers can cut cortical bone initially but can quickly dull after a single use, or at best a few uses. Once the reamer has dull cutting edges, it reduces the efficiency of bone cutting and in addition generates sufficient friction/heat to damage or kill the surrounding bone. These prior art solid cylindrical or tapered reamers are intended for multiple uses and therefore become less efficient after each surgery, resulting in poor cutting performance and bone necrosis.

[0005] There remains a need in the art for a hollow reamer for medical applications having a disposable hollow cutter assembly which can be attached to a reusable shaft portion that provides means for reaming of the internal canal of bones whereby after one or more uses of the reamer a new hollow cutter assembly is utilized and the old hollow cutter assembly is discarded.

[0006] The present invention provides a hollow reamer for medical applications having a disposable cutter assembly which can be attached to a reusable shaft portion. Preferably, a fresh cutter assembly is used with each new application. Alternatively, the cutter assembly is used several times and, after it has become worn, is discarded. The cutter assembly includes a plurality of apertures and is hollow to allow space for bone debris. This therefore reduces heat generated during cutting by removing the bone debris from the outer surface of the cutter to the inside of the cutter, and further provides space for bone debris to be collected and later removed for bone grafting for the specific surgical procedure. A further advantage of the hollow design is that by allowing the removal of the bone debris from the outer surface of the cutter to the inside of the cutter, the reamer is less likely to raise the intramedulary pressure in the long bone being reamed, thereby lessening the chance of fat embolism during these procedures.

[0007] Generally stated, the reamer for medical applications comprises: (a) a shaft portion having an elongated body with a distal end and a proximal end, said distal end having a coupling portion appointed for attachment of said reamer to a drilling device, said proximal end having a threaded portion; and (b) a disposable hollow cutter assembly comprising: (1) a disposable hollow cutter sleeve portion having an outer surface and a hollow construction, said disposable hollow cutter sleeve portion further comprising a plurality of cutting teeth and a plurality of apertures on said outer surface; and (2) a pilot tip having a threaded inner surface and being attached to said disposable hollow cutter sleeve portion; said disposable hollow cutter assembly being adapted to slide over said proximal end of said elongated shaft portion and extend over a portion of said elongated body thereof, thereby enabling said pilot tip to be threaded with said threaded portion of said proximal end of said shaft portion.

[0008] The present invention solves the problems associated with the reuse of prior art reamers. In accordance with the present invention, the hollow reamer for medical applications has a disposable cutter assembly which can be attached to a reusable shaft portion that allows for a fresh cutter assembly to be used with each new application of the reamer. The hollow reamer of the present invention reduces heat during its application and is more efficient and safe when compared to prior art reamers.

[0023] Reaming of the internal canal of bones is required in many surgical procedures of orthopedic surgery. These procedures include hip replacement, knee replacement and shoulder replacement. Other surgical procedures that see the use of reamers include internal fixation procedures for fractures. Typically, reaming of the internal bone canal is achieved through utilization of a solid cylindrical or tapered reamer, illustrated in FIG. 1. Prior art reamers typically include a driver coupling 11 (shown as a Jacob chuck connector), a size designation 12, a pilot tip 13, a shaft 14, and cutting flutes 15. FIG. 1 shows a tapered reamer, however cylindrical reamers of similar design also exist in the prior art. Those solid cylindrical or tapered reamers currently utilized are required to cut both cancellous bone (spongy bone) and cortical bone (hard bone). Cortical bone is generally denser and stronger, requiring an efficient cutter to machine the canal for a proper fit of the implant. Conventional reamers can cut cortical bone initially but can quickly dull after a single use, or at best a few uses. Once the reamer has dull cutting edges, it reduces the efficiency of bone cutting and in addition generates sufficient friction/heat to damage or kill the surrounding bone. Currently utilized solid cylindrical or tapered reamers are intended for multiple uses and therefore become less efficient after each surgery, resulting in poor cutting performance and bone necrosis.

[0024] FIG. 2 depicts the hollow reamer assembly of the present invention which provides hollow reamers appointed for use in medical applications. The hollow cutter assemblies are disposable, so that the cutting performance of the hollow reamer is not compromised through repeated use. Several improvements towards the clinical problems seen with prior art reamers are overcome through utilization of the hollow reamers herein. Novel design features of the hollow reamers of the present invention and improvements to prior art reamers are multifaceted and include a reusable shaft 22 with a disposable hollow cutter assembly 21. Preferably, the hollow cutter assembly 21 is discarded after a single use to ensure a sharp cutter during surgery. Alternatively, the hollow cutter assembly is used several times and after becoming worn is discarded. Various techniques may be used to determine if the hollow cutter assembly is worn enough that it requires disposal. Such techniques may include measurements of the sharpness of the cutter assembly. Moreover, when dealing with revision hip surgery, the hollow reamers have also been designed to cut bone cement (PMMA) in a more efficient manner by providing internal space to capture the debris and thereby reducing both the cutting temperature and time required to remove the remnant cement mantle. Both these features are important in reducing heat to the bone and reducing O.R. (operating room) time required for revision surgery. FIG. 2 illustrates a hollow reamer having a tapered cutter portion of the present invention. Alternatively, a hollow reamer having a cylindrical design may be utilized. The hollow reamer comprises a shaft portion 22 and a disposable hollow cutter assembly 21. The shaft portion 22 can either be solid or cannulated.

[0025] FIGS. 3A, 3B, 3C, collectively, provide an assembly view depicting the hollow reamer in FIG. 3A that is formed by the disposable hollow cutter in FIG. 3B and reusable shaft in FIG. 3C in accordance with the invention. FIG. 3A depicts the modular design of the hollow reamer at 31. FIG. 3C depicts a reusable reamer shaft 22. The reamer shaft 22 may be flexible or rigid depending on the particular medical application. FIG. 3B depicts a disposable, one-time use hollow cutter assembly 21.

[0026] FIG. 4A is a perspective view depicting the disposable hollow cutter in accordance with the invention. FIG. 4B is a side view depicting the disposable hollow cutter in accordance with the invention. FIG. 4C is a front view depicting the disposable hollow cutter in accordance with the invention. FIG. 4C depicts the disposable hollow cutter assembly which comprises: (i) a disposable hollow cutter sleeve portion having an outer surface and a hollow construction, the disposable hollow cutter sleeve portion further comprising a plurality of cutting teeth 41 and a plurality of apertures (also at 41) on the outer surface; and (ii) a pilot tip 43 having a threaded inner surface and being attached to the disposable hollow cutter sleeve portion. The non-cutting pilot tip 43 is designed for guidance, and the tip 43 matches the diameter of the previous cutter sleeve end to achieve this guidance feature. The pilot tip 43 further helps to keep each successive reamer centered, thereby resisting the tendency of the reamer to drift and cut eccentrically, particularly when there is eccentric cement in the canal. Preferably, the pilot tip 43 is tapered at about the same angle as the hollow cutter sleeve. Alternatively, the pilot tip 43 is generally cylindrical. Preferably, the hollow cutter assembly is discarded after a single use to ensure a sharp, efficient cutter for every surgery. Alternatively, the hollow cutter assembly is used several times and, upon becoming worn, is discarded. FIG. 4B further depicts the hollow cutter which provides space 42 for bone debris offering multiple benefits, including reducing heat generated during cutting by removing the bone debris from the outer surface of the cutter to the inside of the cutter and providing space 42 for bone debris to be collected and later removed for bone grafting for the specific surgical procedure. A further advantage of the hollow design is that by allowing the removal of the bone debris from the outer surface of the cutter to the inside of the cutter, the reamer is less likely to raise the intramedulary pressure in the long bone being reamed, thereby lessening the chance of fat embolism during these procedures. The hollow cutter sleeve is provided with a plurality of apertures 41 on its outer surface. Preferably, the cutting teeth 41 protrude from the outer surface of the disposable hollow cutter sleeve, consequently forming the plurality of apertures. Alternatively, the plurality of apertures can be separate and distinct from the cutting teeth on the outer surface of the disposable hollow cutter sleeve.

[0027] FIG. 5 illustrates a family of disposable cutter assemblies. The family of disposable cutter assemblies addresses a wide range of bone sizes, including sizes ranging from 7 mm through 20 mm in one (1) mm increments; and being tapered and having a 7 mm tapering to a larger diameter in one (1) to three (3) mm increments and having size options from a 7 mm base dimension to a 20 mm base dimension in one (1) mm increments. Preferably, and as shown in FIG. 5, the hollow cutter assemblies are tapered. Alternatively, the hollow cutter assemblies are cylindrical and have diameters ranging from 7 mm through 20 mm. Preferably, there are provided two shafts of each size in the instrument set, thereby allowing the surgeon to go back one size during the procedure, if necessary, without having to break off the disposable cutter.

[0028] Multiple disposable cutter assemblies can be attached to a single shaft, as is illustrated in FIG. 6. Preferably, a single shaft will attach to at least three different sized disposable hollow cutter assemblies. This provides for the ability to combine various sized shafts with various sized disposable hollow cutter assemblies.

[0029] FIG. 7 shows the reamer shaft appointed with graduated markings 72. The reamer shaft incorporates graduations 72 to determine the depth of insertion of the cutter assembly into the canal of the bone. The reamer shaft further incorporates markings 71 to identify the proper assembly between the shaft and the cutter assembly. Alternatively, this method could be further enhanced through color coding the shafts and the disposable hollow cutters. A shaft size designation marking 71 informs the user as to what sized disposable hollow cutter assemblies will fit the shaft. A cutter assembly size designation 73 is indicated on the pilot tip of the disposable hollow cutter assembly.

[0030] FIG. 8 illustrates the shaft cutter assembly, showing flats on the reamer shaft end and flats on the disposable cutter assembly pilot tip, which are provided to facilitate assembly of the disposable hollow cutter assembly to the shaft using simple wrenches found in the prior art.

[0031] FIG. 9 shows an embodiment of the shaft/disposable hollow cutter assembly wherein the inner surface of the pilot tip 93 is threaded. One method for assembling the disposable cutter assembly 91 to the shaft incorporates a left-hand thread on the end of the shaft and a left-hand thread in the inner surface of the pilot tip of the disposable hollow cutter assembly. With this assembly arrangement, the assembly tightens during operation (hand or power reaming is right-hand rotation) thereby providing stability of the cutter assembly 91 to the shaft. The assembly method between the reamer shaft and the disposable cutter assembly 91 is further shown in FIG. 9, where the reamer shaft has a taper 92 incorporated into the body of the shaft, which closely mates with the internal taper of the hollow disposable cutter sleeve 91, thereby establishing stability to the opposite end of the cutter from the thread attachment.

[0032] FIG. 10 illustrates the shaft drive coupling. A reamer shaft having a driver end 101 compatible with currently available hand and power instruments in the medical field is provided. The hollow reamer could also be coupled with a flexible drive shaft.

[0033] FIGS. 11A and 11B each illustrate an alternative embodiment of the disposable hollow cutter assembly which incorporates a disposable hollow cutter break-away feature which prevents reuse of the disposable hollow cutter assembly. The pilot tip 111 of the disposable hollow cutter assembly includes a flat portion 112 in order to enable the assembly and disassembly of the disposable hollow cutter assembly to the shaft by using a simple wrench or the like. The disposable hollow cutter assembly is assembled with a wrench. Following use of the disposable hollow cutter assembly, it is disassembled from the shaft by using the wrench. The disposable hollow cutter assembly is preferably manufactured in such a manner so that the break away torque that is required for disassembling the disposable hollow cutter assembly from the shaft will cause the pilot tip 113 to shear away from the hollow cutter sleeve portion. Then, the pilot tip may be unthreaded from the drive shaft, and the hollow cutter sleeve portion may be slid off the end of the shaft. Once the reamer is disassembled in this manner, the disposable hollow cutter assembly can not be reused. Therefore, the optional break away feature prevents the re-use of the same disposable hollow cutter assembly, thereby assuring the proper function that can only be provided by the use of a new disposable hollow cutter assembly.

[0034] Having thus described the invention in rather full detail, it will be understood that such detail need not be strictly adhered to, but that additional changes and modifications may suggest themselves to one skilled in the art, all falling within the scope of the invention as defined by the subjoined claims.