CONTROLLED FEED SIJRGICAL REAMER
DESCRIPTION
FIELD OF THE INVENTION
The present invention relates generally to instrumentation used in orthopaedic surgery, and more specifically to procedures where surgeons use a powered surgical instrument fitted with a cutting tool to ream bone, and more particularly it relates to the instrumentation employed in hip arthroplasty. The invention provides a mechanism for controlling and varying, as required, the feed rate at which the cutting tools are fed into the bone. It will be readily apparent that the invention disclosed could be employed in any other field where there is a requirement to control the rate at which a cutting tool is fed into a work piece.
Hip arthroplasty or hip resurfacing, is a well-known surgical procedure, involving replacement of defective bearing surfaces of a hip joint. It involves reshaping of the femoral head to receive a prosthetic femoral cap. Such a cap may be fitted directly to the prepared surfaces of the head of the femur without the use of bone cement or it may be secured in position with bone cement.
After exposure of the femoral head and neck a plain guide rod (spigot) is inserted into the head of the femur as nearly as possible along the axis of the femoral neck Presently the procedure then usually requires three separate operations to be performed:-i. the making of what is termed the barrel cut, where the head of the femur is machined into a cylinder by running a cylindrical cutter down the guide rod; ii. the end cut where the surface of the head of the femur is cut off square with the cylinder formed by the barrel cut, usually by use of a saw and a guide clamped around the cylinder already generated; iii. the chamfer cut where the square edge formed by the barrel cut and the end cut is chamfered to receive the femoral implant by means of a chamfer cutter run down the guide rod.
The large bone power tools currently used in resurfacing comprise pneumatic, externally powered electric and battery electric models. Some are dedicated to only one function, whilst others are modular headpieces onto which a variety of attachments can be fitted to permit reaming, drilling, sawing, and various other functions. Given the desirability of achieving a lightweight and small bulk, existing large bone power tools are generally underpowered to perform the machining involved in hip resurfacing. It is not uncommon for such tools to stall under full load 2.
due to a combination of insufficient power and the difficulty experienced by the surgeon in judging and properly controlling the optimum feed (axial) pressure to be applied to the instrument.
Presently femoral reamers vary in diameter from around 36 mm up to some 52 mm.
Clearly a greater torque force is required to drive the larger sizes and the optimum feed rates for the larger sizes will be lower than that for the smaller sizes. Thus it is desirable for the surgeon to be able to vary, at will, the feed rate, that is the rate at which the reamer is advanced into the femur, to achieve the optimum feed rate for each diameter of reamer.
A variety of factors can cause unwanted loosening of the implanted femoral component. One is the failure to achieve the optimum mechanical fit between the prepared surfaces of the femoral head and the implanted femoral cap. Accurate reaming of the femoral head enables the surgeon to achieve reproducible bone apposition to assist in the development and maintenance of optimal fixation for the femoral cap, as a close initial fit is critical to achieving long term stability.
Whilst the accuracy of a prosthetic femoral cap can be achieved and verified in ideal conditions during manufacture the weak link in the resurfacing procedure is the difficulty of accurately machining the femoral head.
THE PROBLEMS TO BE SOLVED
Without control of the rate at which the reamer is fed into the femoral head there is the risk that the surgeon may apply too much axial pressure. The excess force may cause the reamer to dig into the bone and stall the power tooL It may also place an unacceptable torque stress on the neck of the femur. Too little pressure applied to the reamer could cause the reamer to skid over the surface of the bone generating an unwanted increase in the temperature of the reamer and of the subject bone.
The neck of the femur is a highly stressed bone and if it is inadvertently notched during the reaming process that notch can act as a stress raiser and subsequently induce a fatigue fracture of the neck or leave the neck weakened and vulnerable to trauma fracture. It is therefore essential that when carrying out what is termed the barrel cut the surgeon does not permit the femoral reamer to impinge on the neck of the femur.
DESCRIPTION OF THE INVENTION
The present invention seeks to address the shortcomings of existing large bone powered instruments outlined above. There is provided a controlled fed reamer which can be employed as an attachment to existing powered surgical hand pieces or can be configured as a self powered instrument. The rate at which the reamer is fed into the head of the femur is controlled by the surgeon irrespective of the axial force applied.
In the preferred embodiment the feed rate can be varied at will to match the diameter of the cutter and thus make optimum use of the power available. The controlled feed also assists the surgeon in avoiding any overshoot whilst undertaking the barrel cut.
The objectives of the present invention are: i. to eliminate any risk of inadvertently damaging the neck of the femur; ii. To more accurately and safely machine the femoral head than is possible with existing instrumentation; According to the present invention, there is provided a bone reamer assembly comprising a reamer and means that enables the feed rate of the reamer into a bone to be controlled by a surgeon irrespective of the axial force applied, in use, by the surgeon.
Preferably the means to enable the feed rate of the reamer includes a threaded guide rod having a first portion for screwing into a hole formed in a bone and a second portion to which the reamer may be releasably fitted.
The second portion of the guide rod may be threaded, to mate with a corresponding thread of another part associated with the reamer.
Said other part may be a threaded nut coupled in use to the reamer.
The reamer may be releasably fitted to the guide rod by means of a quick-release device.
In accordance with another aspect of the present invention, there is provided a bone reamer adapted to form part of the assembly as defmed above.
In the preferred embodiment of the invention the plain guide rod presently used with conventional reamers is replaced by a threaded guide rod. That is provided with a coarse thread at one end which is screwed into the hole drilled in the femoral head.
The larger part of the remainder of the rod is provided with a thread to match the thread of the feed nut within the controlled feed reamer. After the threaded guide rod had been placed in position in the head of the femur the controlled feed reamer is fitted over the threaded guide rod and suitably positioned.
It is important for the surgeon to be able to release the controlled feed reamer at any time and to reposition the controlled feed reamer at any desired position along the threaded guide rod as required. Those capabilities are provided in the present invention by means of a quick release mechanism which permits the surgeon to release the feed mechanism and reposition the instrument on the threaded guide rod or remove it altogether.
There is also provided an adjusting mechanism whereby the surgeon can vary the feed rate as required to accommodate the particular reamer in use at any one time and to allow for variations in the hardness of the femoral head. "-
For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-Fig. 1 shows the overall layout of the controlled feed reamer when fitted as an attachment to a standard hand piece.
Fig. 2 shows the internal workings of the controlled feed reamer Fig. 3 shows details of the internal mechanism for controlling the feed rate of the controlled feed reamer Fig. 4 shows the top elevation of the controlled feed reamer
DETAILED DESCRIPTION OF THE DRAWINGS
Fig. 1 shows the overall layout of the controlled feed reamer when fitted as an attachment to a standard hand piece.
Fig. 2 shows the internal workings of the controlled feed reamer 1 conical attachment member for attaching the controlled feed reamer to an existing surgical hand piece 2 input gear wheel 3 main gear wheel 8 spindle for feed rate control 9 feed nut release sleeve release sleeve for reaming tool 11 reaming tool 13 feednut 14 outer sleeve needle bearing clutch
SINGLE PASS FEMORAL CUTTER
FIELD OF THE INVENTION
The present invention relates generally to instrumentation used in orthopaedic surgery, and more specifically it relates to the instrumentation employed in that branch of hip arthroplasty commonly known as hip resurfacing. However it will be readily apparent to anyone familiar with the art that the invention can be applied in other fields.
In orthopaedic surgery a total hip replacement involves the acetabulum being reamed out to accept a prosthetic cup whilst the head and neck of the femur are removed and replaced by a prosthetic stem and ball. The more limited hip resurfacing procedure involves replacement of just the defective bearing surfaces of the hip joint.
Sometimes, but not always, that procedure requires the acetabulum to be reamed for a prosthetic cup to be fitted. In all cases the femoral head and femoral neck are retained and the femoral head is machined to receive a prosthetic femoral cap. The present invention relates more particularly to a means of machining the femoral head to receive a femoral cap.
The surgical procedure required to undertake a hip resurfacing is largely dictated by the instrumentation currently available, and typically requires the following machining operations and surgical procedures to be performed on the femoral head: i. a guide hole is drilled into the femoral head as nearly as possible along the axis of the femoral neck and a guide rod is inserted into the head of the femur.
There is a plurality of instruments available to aid the correct positioning of the guide rod; ii. the making of what is termed the barrel cut, whereby the head of the femur is machined into a cylindrical shape by running a cylindrical, or shell cutter, driven by a powered tool, down the guide rod; iii. the end cut, where the surface of the head of the femur is cut off square with the cylinder formed by the barrel cut, often by the application of a saw using a ring guide clamped around the cylinder already generated; iv. the chamfer cut, where the square edge formed by the barrel cut and the end cut is chamfered by means of a chamfering cutter driven by a powered tool, run down the guide rod; vi thereafter the prosthetic femoral cap is fitted over the prepared surfaces of the femur, frequently being cemented in place using bone cement. Many caps in current use are also fitted with a central spigot which is inserted into the previously drilled hole in the femoral head, suitably enlarged as required. The spigot helps to position the cap and assists in maintaining a uniform mantle of bone cement.
THE PROBLEMS TO BE SOLVED
It is common to find that three cutters are required to complete the machining of the femoral head for each diameter of femoral prosthesis. Internal diameters of femoral prosthesis caps range from around 36mm internal diameter up to around 56mm internal diameter involving a range of 6, 8 or even 10 different diameters. Thus a set of surgical instruments to machine the femoral head will comprise many separate cutters. The present invention replaces the multiple cutters presently required for each diameter of femoral prosthesis with a single cutter.
Whilst accuracy of the prosthetic femoral cap can be achieved and verified in ideal conditions during manufacture, a weak link in the resurfacing procedure is the difficulty of accurately machining the femoral head to achieve a good fit in the socket of the femora! cap, particularly where cementless fixation is to be undertaken. It is more difficult to achieve the necessary accuracy if the procedure is undertaken in three separate steps.
Accurate machining of the femoral head is necessary to achieve optimal fixation for the femoral cap, as an accurate initial fit is a prerequisite to long term stability. As can be seen from the description of the procedure above generally three separate cutters are required for each diameter of prosthetic femoral cap to make the barrel cut, chamfer and end cuts. That involves time being spent changing the cutters on the surgical power tool always with the possibility of the wrong cutter being selected.
A further problem is the cutting process can generate unwanted heat which can adversely affect the femoral head bone stock and in extreme cases cause thermal necrosis of the bone structure. The cutting processes also produces bone and tissue debris which have to be removed from the wound.
DESCRIPTION OF THE INVENTION
There is provided by the present invention a single pass cutter which enables all three cuts described above, namely the barrel cut, chamfer and end cut to be carried out in one pass. A further embodiment of the invention permits a tapered barrel cut to be made to accommodate prosthetic caps provided with a tapered socket. Means are provided to permit the cutter to be disassembled for cleaning and sharpening. In a further embodiment of the invention means are provide to enable the length of the barrel cut to be adjusted axially in relation to the cutting edges which generate the chamfer and end cuts, thus enabling the machined head of the femur to exactly match the geometry of the socket in the femoral cap.
In the preferred embodiment of the invention an outer cutting member comprising a broadly cylindrical tube or body is fitted with cutting blades at the distal end, which cutting edges may extend back to the forward edges of an inner cutting member.
Slots or holes can be formed in the walls of the said cylinder to permit bone debris, tissue and any irrigation fluid to be expelled or extracted from the body of the cutter.
The opposite end of the said broadly cylindrical tube is closed by a base plug which may be an integral part of said cylinder or a separate insert permanently fitted to the end of said cylinder, which is pierced to permit a shaft forming part of an inner cutting member to pass through it. Said base plug is further pierced by a hole or holes which enable irrigating fluid or cooling gas to pass into the body of the single pass cutter and provide irrigation and cooling during operation. The inner cutting member comprises a shaft on which is formed a cutting head possessing a number of cutting edges to perform the chamfer cut and end cut on the femoral head. Desirably the shaft of the inner cutting member is hexagonal or rectangular or otherwise irregular in shape and the passage through the base plug is shaped accordingly. There is located in the base plug a sliding releasable locking plate. Said locking plate is pierced to permit the passage of the inner cutting member shaft and is fitted with a locking tooth or teeth which engage in a groove or grooves cut into the outer surface of the shaft of the inner cutting member. Operating the locking plate disengages said locking tooth or teeth from the groove or grooves cut on the outer surface of the shaft of the inner cutting member thereby permitting the inner cutting member to slide axially and adjustably in relation to said base plug and/or to be removed completely for cleaning or sharpening of its cutting edges. The shaft of the said inner cutting member is cannulated for its entire length to permit it to fit over a guide rod or to fIt over a drill bit.
In an alternative embodiment of the invention the portion of the shaft of the inner cutting member immediately behind the cutting head is cylindrical in form and is threaded for part of its length, which thread may be left or right handed, but is preferably a left handed thread. When the shaft of the inner cutting member is fitted into a power tool which rotates the inner cutting member in a clockwise direction the action of the left handed thread is to securely tighten the inner cutting member against the forward face of the base plug, thereby achieving the necessary rigid relationship between the inner cutting member and the cutting edges fitted at the distal end of the said cylinder and also transmitting a rotation force to the complete single pass cutter.
To permit suitable adjustments to be made to allow for variations in the internal geometry of the socket of different types of femoral prosthesis or to allow for variations in the dimensions of the cutting edges introduced through the sharpening of the various cutting edges, a ring piece or ring pieces of differing depths may be interposed between the rear face of the inner cutting member and the front face of the base plug to permit axial adjustment of the cutting edges of the inner cutting member relative to the cutting edges fitted at the distal end of the said cylinder.
In a further embodiment of the invention the outer cutting member is fitted with a cutting edge or cutting edges which extend (s) from the distal end of the said broadly cylindrical tube or body back towards the forward outer edges of the inner cutting member. Said cutting edge or edges is, are inclined relative to the axis of the said broadly cylindrical tube or body so that when applied to the femoral head a tapered cut is produced on the femoral head enabling the femoral head to engage securely with a tapered socket formed in the femoral prosthesis.
In a further embodiment of the invention a removable cooling shroud is provided which enables a fluid or gas to be passed into the body of the single pass cutter and provide irrigation of the femoral head during machining and evacuation of the irrigation fluid together with bone and tissue debris. Said shroud which is broadly cylindrical in shape may be made of metal or non-metallic material. On the rear face of the said shroud there is provided a hollow mounting spigot which fits over a corresponding formed spigot on the rear of the single pass cutter. Said shroud is releasably fitted to the spigot of the single pass cutter, and held in position on said spigot by the action of a resilient ring, such as a cuff spring or 0 ring mounted within a groove formed in the mounting sleeve of said shroud and mating with a groove formed in the spigot of the single pass cutter.
On the rear face of said cooling shroud a connection or connections is/are provided for a vacuum tube/s which provides a means of removing the bone debris, tissue and irrigation fluid from the body of the single pass cutter. Also on the rear face of said cooling shroud are provided a connection or connections for the passage of irrigating fluid or cooling gas. An annular groove formed in the inside face of the shroud permits irrigating fluid or gas to reach a hole or series of holes passing through the base plug of the single pass cutter and thence to pass into the body of the said cutter enabling cooling of the cutting edges of the cutter and of the subject bone to take place. Suitable annular face seals are provided in the base of the cooling shroud in a further embodiment of the invention said shroud is slotted along a portion of its length and provision is made for a vacuum tube with a mating aperture to be attached.
That vacuum connection serving to remove bone debris, tissue produced by the action of the cutter when in use together with any irrigation fluid or gas.
DETAILED DESCRIPTION OF THE DRAWINGS
Fig. 6 shows a cutaway cross sectional drawing of the single pass reamer with sliding inner cutting member I outer body 2 cutting edge 3 hole for evacuation of bone and tissue debris and irrigation fluid 4 base plug inner cutting member shaft 6 inner cutting member cutting head 7 sliding locking plate p 8 cutting edges on inner cutting member 9 grooves cut in outer surface of shaft cannulation of inner cutting member shaft 13 irrigation fluid passage 22 locking tooth on sliding lock plate 24 groove on spigot to accommodate locking ring of cooling shroud Fig.7 Shows a cutaway cross sectional drawing of the single pass reamer with a threaded inner cutting member shaft and spacer ring 1 outer body 2 cutting edge 3 hole for evacuation of bone and tissue debris and irrigation fluid 4 base plug inner cutting member shaft 6 inner cutter member cutting head 8 cutting edges on inner cutting member cannulation of inner cutting member shaft 11 spacing and adjusting ring 12 thread on inner cutting member shaft 13 irrigation fluid passage 24 groove on spigot to accommodate locking ring of cooling shroud Fig. 8 Shows a cutaway cross sectional drawing of the single pass reamer fitted with a threaded inner cutting member shaft and elongated cutters to the outer body to produce a tapered barrel cut on the femoral head.
2 elongated inclined cutting edge 4 base plug inner cutting member shaft 6 inner cutting member cutting head 8 cutting edges on inner cutting member cannulation of inner cutting member shaft 11 spacing and adjusting ring 12 thread on inner cutting member shaft 13 irrigation fluid passage 23 bell mouthing on outer body 24 groove on spigot to accommodate locking ring of cooling shroud Fig. 9 Shows a cutaway cross section of cooling shroud and an end on view of the cooling shroud base plate 14 outer body of cooling shroud locating spigot 16 locking ring 17 vacuum connection 18 inlet connection for irrigation fluid or cooling gas 19 annular face seal annular groove to permit cicualtion of irrigation fluid or cooling gas 21 vacuum scavenging tube
DESCRIPTION OF THE PREFERRED EMBODIMENT
An outer cutting member comprising a broadly cylindrical tube or body as depicted at fig. 6 is fitted with cutting blades at the distal end 2, which cutting edges may extend back to the forward edges of an inner cutting member. Slots or holes 3 can be formed in the walls of the said cylinder to permit bone debris, tissue and any irrigation fluid to be expelled or extracted from the body of the cutter. The opposite end of the said broadly cylindrical tube is closed by a base plug 4 which may be an integral part of said cylinder or a separate insert permanently fitted to the end of said cylinder, which is pierced to permit a shaft 5 forming part of an inner cutting member to pass through it. Said base plug is further pierced by a hole or holes 13 which enable irrigating fluid or cooling gas to pass into the body of the single pass cutter and provide irrigation and cooling during operation. The inner cutting member comprises a shaft 5 on which is formed a cutting head 6 possessing a number of cutting edges 8 to perform the chamfer cut and end cut on the femoral head. Desirably the shaft of the inner cutting member 5 is hexagonal or rectangular or otherwise irregular in shape and the passage through the base plug is shaped accordingly. There is located in the base plug a sliding releasable locking plate 7. Said locking plate is pierced to permit the passage of the inner cutting member shaft and is fitted with a locking tooth or teeth 22 which engage in a groove or grooves 9 cut into the outer surface of the shaft of the inner cutting member 5. Operating the locking plate 7 disengages said locking tooth or teeth 22 from the groove or grooves cut on the outer surface of the shaft of the inner cutting member 9 thereby permitting the inner cutting member to slide axially and adjustably in relation to said base plug 4 andlor to be removed completely for cleaning or sharpening of its cutting edges 8. The shaft of the said inner cutting member is cannulated for its entire length 10 to permit it to fit over a guide rod or to fit over a drill bit.