Angled reamer spindle for minimally invasive hip replacement surgery

A reamer for use in minimally invasive hip replacement surgical approaches is provided. The reamer spindle includes an elongate housing portion that extends along a first axis and a neck or distal portion that extends along a second axis, wherein the second axis extends at an angle of between about 35 degrees and about 65 degrees relative to the first axis. A reamer head is removably connectable to the distal neck portion and has a surface configured to cut bone.

BACKGROUND OF THE INVENTION

Nearly 200,000 hip replacements are performed each year in the United States and the number is expected to continue to grow as the population ages. The usual reasons for hip replacement are osteoarthritis, rheumatoid arthritis and traumatic arthritis, all of which can cause pain and stiffness that limit mobility and the ability to perform daily living activities. Hip replacement surgery is usually performed when other measures (e.g., physical therapy, medications, and walking aids) are unable to overcome the chronic pain and disability associated with these conditions.

Various techniques are used by orthopedic surgeons to perform hip replacements. These include the following approaches: anterior, antero-lateral, anterior, posterior, and postero-lateral. The posterior and posteolateral approaches account for approximately 60% to 70% of hip replacement surgeries.

Traditional hip replacement surgery involves an open procedure and extensive surgical dissection. However, such procedures require a longer recovery period and rehabilitation time for the patient. The average hospital stay for open hip replacement procedures is 4-5 days, followed in most cases by extensive rehabilitation.

More recently, there has been considerable interest and research done in Minimally Invasive Surgery (MIS), including the use of MIS procedures in connection with hip replacement surgery. In comparison with the traditional open surgical approach, MIS hip replacement surgeries involve fewer traumas to the muscles surrounding the hip joint. Specifically, fewer muscles that help to stabilize the hip joint are cut in MIS hip replacement surgeries, reducing the risk of dislocation of the hip surgery and speeding recovery. Patients spend less time in the hospital and return to normal life activities more quickly.

MIS approaches use smaller surgical fields, which require smaller instruments to perform the hip replacement procedures. One such instrument is a reamer spindle detachably connected to a surgical reamer. The surgical reamer is used to shape the bone of the acetabulum. However, reamer spindles have typically been straight and used in surgical exposures that cut quite a bit of muscle and are, therefore, unsuitable for MIS approaches. Accordingly, there is a need for an improved reamer spindle for use in MIS hip replacement surgical approaches.

SUMMARY OF THE INVENTION

In accordance with one embodiment, a reamer for use in minimally invasive hip replacement surgical approaches is provided. The reamer spindle includes an elongate housing portion that extends along a first axis and a neck or distal portion that extends along a second axis, wherein the second axis extends at an angle of between about 35 degrees and about 65 degrees relative to the first axis. A reamer head is removably connectable to the distal neck portion and has a surface configured to cut bone.

In accordance with another embodiment, the reamer neck can have a length of between about 25 mm and about 35 mm from the intersection of the first and second axes and the distal end of the reamer head.

In accordance with still another embodiment, the elongate housing portion meets the distal neck portion at a rounded low profile surface configured to inhibit trauma to muscle tissue during use of the reamer spindle.

In accordance with yet another embodiment, the reamer can be driven by a source of rotational power, which may be an electric source. A housing is configured to enclose a rotatable shaft connectable to the reamer with the proximal end of the shaft being removably connectable to the source of rotational power. The housing can be a metal (e.g., stainless steel), super alloy or composite casing.

In accordance with another embodiment, the reamer spindle is configured in a way that it can be sterilized between uses.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings,FIGS. 1 to 3,3A to3F and4to9illustrate a reamer spindle10according to the present invention. The reamer spindle10is shown connected to a reamer12(FIGS. 4 and 7) for performing a minimally invasive hip replacement surgery. The reamer spindle10generally comprises a drive train14disposed within a housing16. A handle assembly18is adjustably connected to the housing16spaced from the reamer12.

The housing16had a length that extends from a proximal housing section20to a distal neck section22with an intermediate housing section24there between. The intermediate housing section24comprises spaced apart right and left side walls24A and24B extending upwardly from a bottom wall24C to an upper opening26. This construction provides the intermediate section24with a generally U-shaped cross-section perpendicular to a longitudinal axis A-A extending along the proximal and intermediate housing sections20and24, but not along the distal section22. A pair of aligned slots28A,28B extends from the upper opening26part-way into the height of the respective side walls24A,24B.

The side walls24A,24B and the bottom wall24C of the intermediate housing section24meet the proximal housing section20having a partially annularly shaped side wall20A. The annular side wall20A has an upper opening30aligned with the upper opening26of the intermediate handle section24.

The distal neck section22of the housing16is angled in a downwardly direction away from the longitudinal axis A-A and the upper opening26of the intermediate section24. In that respect, the right and left side walls24A,24B of the intermediate housing section22seamlessly form into the right and left side walls22A and22B extending distally and downwardly to form the distal neck section22. However, the bottom wall24C of the intermediate section24ends spaced from the distal neck section22. This provides an intermediate lower open slot32that is vertically below the aligned slots28A,28B.

The right and left side walls22A,22B meet an upper wall22C of the distal neck section22. Potions of a lower distal side wall22D extend from the right and left walls22A,22B. This forms a distal open slot34that is not as wide as the intermediate slot32in the intermediate section24or a forward opening36formed by the right and left side walls22A,22B, the upper wall22C and the partial lower wall22D at the end of the distal neck section22. The significance of the open slots32and34will be described hereinafter with respect to partial disassembly of the drive train14from the housing16for cleaning.

As particularly shown inFIGS. 2 and 2Ato2F, the drive train14comprises a major shaft38as a cylindrically-shaped member having a proximal portion40and a distal end38A with a length there between. The proximal shaft portion40comprises a series of two cylindrical sections40A,40B and40C that step down in diameter as they progress toward the shaft38and its proximal end38B. The proximal shaft end38A has a hexagonal or similar type structure that provides flats for detachable connection to the chuck of a source of rotary drive power (not shown).

A partially cylindrical sleeve42is positioned on the major shaft38in an axially slidable relationship therewith. Preferably, a polymeric inner sleeve44is disposed between the shaft38and an inner surface of the sleeve42to facilitate sliding movement of the sleeve42along the shaft38. The outer sidewall of the sleeve42is provided with diametrically opposed planar surfaces42A and42B that support respective pins46A,46B. The pins46A,46B extend outwardly from the sleeve42. They are received in the respective vertically aligned slots28A,28B in the side walls24A,24B of the intermediate section24of the housing16with their respective axes aligned with each other and perpendicular to the longitudinal, axis A-A of the major shaft38. The pins46A,46B received in the slots28A,28B provide stability to the drive train14as it rotates during a MIS procedure.

As particularly shown inFIGS. 2A and 2B, a first or proximal U-joint48is supported at the distal end38A of the shaft38. The proximal U-joint48is comprised of a proximal cylindrical side wall48A supporting a pair of yoke plates48B and48C having respective openings50B,50C. Connection of the U-joint48to the shaft38is made by a screw52, and the like. The screw is received in an opening54in the sidewall48A and seats against a flat56at the distal shaft end38A. In the alternative, the proximal U-joint could be welded or otherwise secured in place or, the U-joint and shaft could be machined from a single piece of material.

As shown inFIGS. 2C and 2D, the drive train14further includes an H-shaped joint58comprising a cylindrical intermediate section58A supporting opposed first and second pairs of yoke plates58B,58C and58D,58E. Respective openings60B,60C and60D,60E are provided in the yoke plates. A proximal pivot block62(FIG. 2) resides between the yoke plates48B,48C of the proximal U-joint48and the first pair of yoke plates58B,58C of the H-joint58. The proximal pivot block62comprises two pairs of perpendicularly opposed openings62A and62B.

Pins64A are received in the openings50B,50C in the yoke plates48B and48C of the U-joint48and the opening62A in the pivot block62, and a pin64B is received in the opening62B of the pivot block62and the openings60B,60C of the yoke plates58B,58C of the H-plate58to thereby pivotably secure the proximal U-joint48to the first end of the H-joint58. It is noted that only one of the pins64A or64B extends completely from one face of the pivot block62to the other face. As passage from one face to the other is blocked by the first pin, the other of the two pins64A or64B is two “half pins”.

As shown inFIGS. 2E and 2F, the drive train14also includes a distal U-joint66that comprises a distal cylindrical side wall66A supporting a pair of yoke plates66B and66C having respective openings68B,68C. Opposite the yoke plates, the cylindrical side wall66A meets a base plate70having an enlarged diameter. A plurality of pins72extending outwardly from the base plate70have their respective axes aligned parallel to each other and co-axial with, but spaced from, a longitudinal axis B-B of the distal U-joint66.

A distal pivot block74, similar in structure to the proximal pivot block62, comprises two pairs of perpendicularly opposed openings74A and74B. Pins76A are received in the openings68B,68C in the respective yoke plates66B,66C of the distal U-joint66and the opening74A in the pivot block74, and a pin76B is received in the openings60D,60E of the respective yoke plates58D,58E of the H-joint and opening74B of the pivot block74to thereby pivotably secure the distal U-joint66to the second or distal end of the H-joint58. As with the pivotable connection between the H-joint58and the proximal U-joint48, only one of the pins76A,76B extends the full width of the pivot block74from one face to an opposite face thereof. The other pin is provided as two partial length pins.

In this manner, the drive train14comprising the drive shaft38, the proximal. U-joint48, the first pivot block62, the H-joint58, the second pivot block74and the distal U-joint66provides for transmission of rotational motion imparted to the proximal end of the shaft38to the base plate70and its supported pins72through a wide range of angles. The extent of this angular motion will be discussed in further detail hereinafter.

As particularly shown inFIG. 3, the base plate70of the distal U-joint66includes a central opening78completely through the thickness of the plate. A reamer connection crown80comprises a base plate80A supporting a plurality of angled fingers80B. Preferably, there are four angled fingers80B. The plate80A is provided with openings82that receive the pins72extending from the base plate70of the distal U-joint66.

An abutment pin84is a cylindrically shaped member having a first section84A of a lesser diameter, an intermediate section84B of an intermediate diameter and a larger diameter third section84C. A coil spring86is received on the abutment pin84surrounding the intermediate section84B. The spring86abuts against the third section84C. The first section84A of the pin84is received in a central opening88in the base80A of the reamer connection crown80in a fixed manner.

One end of the coil spring86biases against the base plate70of distal U-joint66. That is on the side of the plate70opposite the pins72. The other end of spring86biases against the larger diameter section84C of pin84. However, since the first section84A of the pin84is fixed to the base80A of the crown80, the crown is thereby tensioned into a secured relationship with the distal U-joint66. The bias of spring86enables the distance between the connection crown80against the distal U-joint66to be manipulated between a closely-spaced relationship and a spaced apart position.

In that manner, the reamer12is removably fixed to the drive train14by manipulating the reamer connection crown80in an axial direction away from the distal U-joint66and against the biasing force of the spring86. This creates separation between the crown80and the U-joint66, which prior to manipulation are in the closely-spaced relationship, and removes the pins72from blocking access to the spaces90provided between the fingers80B and the crown plate80A. The connection structure, such as the cross-bars92(FIG. 7) of the reamer12, is then capable of being received in these spaces90. When the surgeon releases his grip on the crown80, the spring86returns the connection crown to its original closely-spaced relationship against the plate70of the distal U-joint66. The pins72are once again partially residing in the spaces90between the fingers80B and the base plate80A to thereby prevent unintended release of the reamer12from the drive train14of the reamer spindle10. This connection structure is commonly referred to as a “bayonet-type” connection.

In an assembled condition, the base plate70of the distal U-joint66seats against the forward opening36provided at the distal neck section22. That is with the remaining parts of the drive train housed within the proximal and intermediate sections20and24of the housing20. Preferably, a shaped polymeric bushing92is disposed between the base plate70and side walls22A,22B,22C and22D of the distal neck section22to provide a low-friction bearing surface as the drive train14is rotated with respect to the stationary housing16.

Referring back toFIG. 1, the housing16supports a metal ring94on its proximal section20. The ring94abuts up against a step forming a transition to the intermediate housing section24. A plurality of proximally-facing notches96is spaced at regular intervals about the annular extent of the ring94.

As shown inFIGS. 8 and 9, the handle assembly18comprises an outer sleeve98having a handle100fixedly secured thereto and extending in a radial or perpendicular orientation from the longitudinal axis A-A extending through the sleeve98. At least one, and preferably two, protrusions102oriented diametrically opposite each other extend axially outwardly from a distal edge of the outer sleeve98. The protrusions102are received in the notches96of the housing ring94to thereby connect the handle assembly18to the housing. However, it is desirable to be able to change the extending position of the handle assembly18with respect to the housing16. That is so a surgeon can adjust the reamer assembly to a handle position that is ergonomically comfortable to him. For that purpose, any one of the protrusions102can fit into any one of the notches96.

As particularly shown inFIGS. 8 and 9, an inner sleeve104is received inside the bore provided by the outer sleeve98of the handle assembly18. The inner sleeve104is somewhat longer than the outer sleeve98to thereby provide a distally extending portion104A. A pair of diametrically opposed J-shaped channels106is provided through the sidewall thickness of the extending sleeve portion104A. A movable sleeve108comprises a knurled, large diameter portion108A and a lesser diameter portion108B. A pair of bore openings (not shown) extends from the knurled surface to the inner surface of the movable sleeve108. The openings received pins110that extend inwardly past the inner sleeve surface104. A coil spring112is received in an inner step98A of the outer sleeve98. This spring112biases between the step98A and the movable sleeve108. The pins110thereby confine movement of the sleeve along the J-shaped channels106. This structure secures the movable sleeve108to the handle assembly18.

Referring back toFIG. 3, a polymeric bushing114is provided on the drive shaft38between the proximal shaft portion40and the sleeve42. This bushing114has a proximal section114A shaped to fit between the side walls24A,24B of the intermediate handle section24, and an enlarged distal section114B. The larger diameter section114B has a number of axial grooves116positioned at 90° intervals about its periphery. The proximal bushing section has an annular groove118that communicates with the upper one of the axial grooves116.

To connect the handle assembly18to the proximal section20of the housing16, the extending ends of pins110are moved along two of the axial channels116in the polymeric bushing114until the protrusions102fit into the notches96. This puts the handle100in a desired orientation. Then, the knurled portion108A of the movable sleeve108is rotated in a counterclockwise direction against the bias of spring112to move the pins110along the J-shaped channels106until the pins reside in a blind terminus end of the J-channels. In that manner, the handle assembly18is locked to the housing16with the handle100extending outwardly in a desired orientation and the drive train14secured in position inside the housing16. To remove the handle assembly18from the housing16, the movable sleeve108is manipulated in a reverse manner.

One unique aspect of the present reamer spindle10is the structure of the yoke plates comprising the proximal U-joint48, the H-joint58and the distal U-joint. As particularly shown inFIGS. 2A and 2B, the beveled surfaces48D of the yoke plates48B,48C comprising the proximal U-joint48are at an angle of about 15° extending from at or adjacent to the respective openings50B,50C until the plates meet an end surface48E that is substantially perpendicular to a longitudinal axis B-B of the U-joint48. Axis B-B is aligned coaxially with the longitudinal axis A-A when the reamer spindle10is assembled having the drive train14housed inside the housing16is a functional manner.

However, the yoke plates58B,58C,58D and58E of the H-joint58and the yoke plates66B and66C comprising the distal U-joint66have much steeper angular shapes. As shown inFIGS. 2C and 2Dfor the H-joint andFIGS. 2E and 2Ffor the distal U-joint, the beveled surfaces58F of the respective yoke plates58B,58C,58D and58E and the beveled surfaces66D of the yoke plates66B and66C are at angles of about 45° extending from at or adjacent to the respective openings60B,60C,60D,60E and68B,68C until the plates meet respective end surfaces58G and66E.

As shown inFIGS. 2D and 4, the beveled relationship between the proximal U-joint48and the H-joint58enables them to articulate through a range of angles α of from about 10° to about 15°, preferably about 12.5°, measured from axis C-C to the longitudinal axis A-A when the reamer spindle10is assembled.

Further, as shown inFIGS. 2F and 4, the beveled relationship between the H-joint58and the distal U-joint66enables the distal U-joint and, consequently, the reamer12to articulate through a range of angles β of from about 35° to about 45°, preferably about 42.5° measured from axis D-D to the axis C-C. The combined angular range provided by this U-joint/H-joint structure means that the distal U-joint66and reamer12are articulatable at an angle ε of from about 45° to about 60°, preferably about 55°, measured from the axis D-D to the longitudinal axis A-A when the reamer spindle10is assembled.

Another unique aspect of the present reamer spindle10is the length of the intermediate section58A of the H-joint58with respect to the lengths of the yoke plates58B,58C,58D and58E. The length of the intermediate section58A is designated “x” inFIG. 2Cwhile that of the yoke plates58B,58C,58D and58E is designated as “y”. Preferably, the lengths y range from about 9 mm to about 12 mm, preferably about 10.5 mm while the length x of the intermediate section58A is from about 3 mm to about 5 mm, preferably about 4 mm. This structure for the H-joint58in conjunction with the beveled surfaces of the yoke plates comprising the various U-joints48,66and the H-joint58enables the housing16comprising the proximal and intermediate sections20,24to be relatively long and aligned along the longitudinal axis A-A in comparison the length of the distal neck section22. An important aspect of the distal neck section22is that it has a length of from about 25 mm to about 35 mm. That is without a reamer12secured to the drive train14at the end of the distal section22being at an angle of about 55°.

With reference toFIG. 4, what is meant by the term “distal neck section22” is defined by an imaginary plane perpendicular to the axis D-D at the point where that axis intersects axis C-C. In other words, this imaginary plane is perpendicular to the axis of pin76B and aligned along pins76A.

In that manner, the present reamer spindle10is useful for performing MIS procedures with the drive train14rotating at relatively high revolutions per minute without unacceptable wobble or vibration. Having the bevel angles of the yoke plates of the proximal U-joint48being less than those of the H-joint58and the distal U-joint66means that the lesser α articulation angle provides a gradual transition to the greater β articulation angle. It is believed that having the lesser articulation angle α leading into the greater β angle provides greater rotational stability for that portion of the drive train14housed in the distal neck section22than if the combined articulation angle were the sum of two angles α and β being one-half of ε. That is especially the case with the neck section22being of relatively short length in comparison to the proximal and intermediate housing sections20,24.

FIGS. 10 to 12depict some features of the musculoskeletal anatomy of a human hip region. As shown inFIG. 10, there are several muscles that act to stabilize the femoral head of a femur bone in the acetabulum. Those include the short external rotator muscles (i.e., the piriformis, the superior gemellus, the obturator internus, the inferior gemellus obturator externus and the quadratus femoris). The gluteus maximus (seeFIG. 11) extends over the short external rotator muscles. The femoral head is enclosed in a fibrous capsule (seeFIG. 12), which attaches to the bone outside the acetabular lip and to the base of the neck of the femoral head.

The MIS posterior hip replacement approach has traditionally involved first a skin incision, followed by an incision in the fascia lata, and then detachment of the short external rotator muscles of the hip (seeFIG. 10). However, in a modified MIS posterior hip replacement approach, described further below, only the piriformis muscle or conjoined tendon needs to be detached.

FIG. 13is a schematic block diagram illustrating steps in a method200for using the reamer spindle10in a MIS hip replacement surgery. The surgeon begins by making an incision210in a posterior side of a patient's hip (e.g., on the buttocks) on a side proximate the hip joint to be treated. The surgeon then separates220fibers in the gluteus maximus longitudinally (i.e., not cut transversely) using a trans maximus approach to access the capsule. The present approach does not involve an incision in the fascia lata, which is required in other posterior surgical approaches. The surgeon then detaches230the piriformis or conjoined tendon, which is the only short external rotator muscle that is detached. This approach preserves the superior gemellus if it is not conjoined to the pirif tendon, obturator internus, inferior gemellus obturator externus and quadratus femoris, which provide significant additional stability to the hip. It is believed that such preservation also facilitates significantly faster post operative recovery. The surgeon then performs a capsulotomy240(e.g., L-shape or J-shape) to access the acetabulum. Once access to the acetabulum is achieved, the surgeon advances250the distal section22of the reamer spindle10supporting the reamer12through the incision to the surgical site proximate the acetabulum (seeFIG. 14). The reamer spindle10is now operated to cut bone from the acetabulum (e.g. diseased bone) and prepare the acetabulum for implantation of a prosthetic acetabular cup. The femoral head is also removed and a prosthetic hip stem implanted into the femur, the prosthetic hip stem having a femoral ball head configured to articulatingly couple to the acetabular cup prosthesis. Once the prosthesis is in place, the capsule can be closed260, followed by closure in the incisions to the gluteus maximus and skin.

The reamer spindle10is preferably configured for reuse, and can be disassembled for sterilization between uses. Disassembly is done by first manipulating the movable sleeve108in a clockwise direction against the bias of spring112to move the pins110along the J-channels106and the axial channels116in the polymeric bushing114until the pins are free of the J-channels and the bushing. The handle assembly18is then movable in a proximal direction to remove the protrusions102from the notches96of the housing ring94to thereby separate the handle assembly18from the housing16. The proximal portion40of the drive train14is then lifted in a lateral direction with respect to the proximal housing section20. This separates the drive train14from the housing16with the pins46A,46B of sleeve42freeing from the vertically aligned slots28A,28B in the side walls24A,24B of the intermediate housing section24. A further pushing force imparted to the drive train14causes the distal U-joint66to move out through the forward opening36provided at the distal neck section22. The drive shaft38is now capable of relative movement with the housing16along the lower intermediate slot32of the intermediate housing section24and the open slot34of the distal neck section22. However, the size of the sleeve42prevents the drive train14from being completely movable through the upper openings26and30of the respective intermediate and distal neck sections24and22. Thus, the drive train14is separable from the housing16in a manner that is sufficient to clean and sterilize all of their parts without the possibility of there being total separation of one for the other. Total separation could easily lead to lost and misplaced parts.

Additionally, the housing16is preferably made of a durable material that can be washed and sterilized (e.g., with high heat) to comply with sterilization standards known in the art. In one embodiment, the housing16is made of metal, such as stainless or a super alloy material. In another embodiment, the housing10is made of a composite material. Though the illustrated embodiment shows the housing16as being one piece, in other embodiments it can be modular to facilitate disassembly of the reamer spindle10.

Preferably, the reaming angle should correlate as closely as possible to the intended angle of acetabular cup implantation.

Additionally, as discussed above, the length of the distal neck section22is preferably between about 25 mm and about 35 mm. This range is particularly advantageous in MIS hip replacement surgical procedures (e.g., the method illustrated inFIG. 13) in that during the surgical procedure the distal neck section22is in direct contact with the short external rotator muscles, which must be preserved to optimize the clinical outcome. The length of approximately 25-35 mm advantageously allows the reamer12to be positioned within the acetabulum while minimizing contact between the reamer spindle10(e.g., the distal neck section22) and the short external rotator muscles of the hip, which are in the inferior aspect of the wound. Additionally, the thickness (e.g., outer diameter) of the housing16, which is preferably between about 9 mm and about 16 mm also advantageously minimizes soft tissue trauma during advancement of the reamer spindle10through the incision, to position the reamer12within the acetabulum.

Through the reamer spindle10is discussed above in connection with an MIS hip replacement posterior approach, one of the ordinary skill in the art will recognize that the reamer spindle10can be used in other MIS hip replacement surgical approaches, such as the anterior, antero-lateral, and postero-lateral approaches. Additionally, the reamer spindle10may also be usable in applications other than posterior MIS hip replacement procedures such as interior, interior-lateral and postero-lateral approaches, as well as shoulder replacement procedures. Though use of the reamer spindle10is described herein with respect to human hip replacement surgery, one of ordinary skill in the art will recognize that it may also be useful in animal hip replacement surgeries.

Of course, the foregoing description is that of certain features, aspects and advantages of the present invention, to which various changes and modifications can be made without departing from the spirit and scope of the present invention. Moreover, the reamer need not feature all of the objects, advantages, features and aspects discussed above. For example, in some embodiments, the casing of the reamer in the neck portion can be removed and/or replaced with a shield member to inhibit trauma to muscle tissue during operation of the reamer. Thus, for example, those of skill in the art will recognize that the invention can be embodied or carried out in a manner that achieves or optimizes one advantage or a group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. In addition, while a number of variations of the invention have been shown and described in detail, other modifications and methods of use, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is contemplated that various combinations or subcombinations of these specific features and aspects of embodiments may be made and still fall within the scope of the invention.