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Hip stem centralizer datum guide and method

Hip stem centralizer datum guide and method description/claims

The present invention relates to total hip arthroplasty. More particularly, the present invention relates to a proximal centralizer for a cemented hip stem and a method for its use.

Total hip arthroplasty is often used to restore function to a diseased or injured hip joint. Positions and directions relative to the hip joint may be described in terms of proximal being nearer the hip joint, distal being further from the hip joint, anterior being nearer the front of the body, posterior being nearer the back of the body, medial being nearer the centerline of the body, and lateral being further from the center line of the body. In total hip arthroplasty (FIGS. 1-2), the articular surfaces of the femur and pelvis are cut away and replaced with prosthetic implant components. In a typical case, the implants can include a hip stem component 10, a femoral head component 12, an acetabular component 14, and bone cement 16. The hip stem component includes a stem portion 18 extending down into the intramedullary canal 20 of the femur 22 and a neck portion 24 extending away from the femur 22 to support the femoral head component 12.

The femur 22 is prepared by reaming the intramedullary canal 20 down into the bone along an axis 26 from a proximal position near the hip joint at the upper end of the femur 22 toward a distal position nearer the knee joint at the lower end of the femur 22. The pelvis 28 is prepared by reaming the acetabulum 30. Bone cement 16 is introduced into the prepared intramedullary canal 20 and acetabulum 30 and the prosthetic components are seated in the bone cement 16 so that it hardens around and locks the components in place. Alternatively, the hip stem component 10 and the acetabular component 14 may be positioned in intramedullary canal 20 and acetabulum 30, respectively, without the use of cement. Positioning the hip stem component 10 in the correct orientation within the cement 16 is important for proper biomechanical functioning and long term stability. It is desirable to have a uniform and strong cement mantle 16 proximally and distally around the anterior 34, lateral 36, posterior 38, and medial portions of the stem component 10. Proper placement further results in appropriate loading of the implants.

The present invention provides a hip stem centralizer datum guide and method for positioning a proximal portion of a hip stem component within bone cement in an intramedullary canal of a femur.

In one aspect of the invention, a combination includes a datum guide for being positioned in a predetermined position relative to the intramedullary canal and for creating a datum that records a predetermined hip stem component position relative to the intramedullary canal. The combination is further capable of referencing the datum to position the hip stem component in the predetermined hip stem component position in the bone cement in the intramedullary canal.

In another aspect of the invention, a combination includes a datum guide and a hip stem inserter. The datum guide includes a base positionable adjacent to the intramedullary canal in a predetermined position relative to the intramedullary canal and a cut guide mounted to the base. The cut guide is able to guide a cutter to cut a datum into the proximal portion of the femur that records a predetermined hip stem component position relative to the intramedullary canal. The hip stem inserter is engageable with the hip stem component in axial, medial/lateral, and anterior/posterior force transmitting relationship. The hip stem inserter includes a portion engageable with the datum. The hip stem inserter is simultaneously engageable with the hip stem component and the datum to position the hip stem component in the predetermined hip stem component position in the bone cement in the intramedullary canal.

In another aspect of the invention, a method includes positioning a datum relative to the intramedullary canal; creating a datum on the femur using the datum guide, the datum recording a desired hip stem component position in persistent manner such that the datum remains after the datum guide is removed; introducing bone cement into the intramedullary canal; inserting the hip stem component into the bone cement in the intramedullary canal; and referencing the datum to position the hip stem component in the desired position.

In one form, the present disclosure provides a combination for establishing a datum on a femur and for referencing the datum during implantation of a hip stem component into bone cement in an intramedullary canal of the femur, the femur having a proximal portion nearer the hip joint, a distal portion nearer the knee joint, an anterior portion toward the front of the body, a posterior portion toward the rear of the body, a medial portion toward the midline of the body, and a lateral portion further from the midline of the body, the datum being able to guide positioning of the proximal portion of the hip stem component within the bone cement to provide a predetermined bone cement thickness around the hip stem component, the femur having a proximal portion including a calcar region, a greater trochanter, and medial, lateral, anterior, and posterior sides and the intramedullary canal defining a longitudinal axis, the combination including a datum guide including means for positioning the datum guide in a predetermined position relative to the intramedullary canal; and means for creating a datum that records a predetermined hip stem component position relative to the intramedullary canal in persistent manner such that the datum remains after the datum guide is removed; and means for referencing the datum to position the hip stem component in the predetermined hip stem component position in the bone cement in the intramedullary canal.

The means for positioning the datum guide may include a rasp having a shape corresponding to the shape of the hip stem component and a cement mantle thickness around the implant, the rasp being insertable into the intramedullary canal to form an opening to receive the bone cement and the hip stem component, the rasp having a proximal portion with reference marks able to guide forming corresponding datum marks on the femur, the means for referencing the datum comprising alignment marks formed on the proximal portion of the hip stem component, the position of the alignment marks on the hip stem component being related to the position of the marks on the rasp to produce a hip stem component position corresponding to a predetermined cement mantle thickness around the hip stem component.

The means for creating a datum may include means for guiding a cutter to cut a datum into the proximal portion of the femur and wherein the means for referencing the datum comprises a hip stem inserter engageable with the hip stem component in axial, medial/lateral, and anterior/posterior force transmitting relationship, the hip stem inserter comprising a portion engageable with the datum, the hip stem inserter being simultaneously engageable with the hip stem component and the datum. The means for creating a datum may include means for guiding a cutter to cut a proximal/distally oriented datum slot in the proximal femur and wherein the inserter comprises a tab engageable with the datum slot in axial sliding relationship. The means for creating a datum may include a cut guide having a base engageable with the calcar region of the proximal femur and a guide portion defining a cut guide slot and extending upwardly at an angle from the base to position the cut guide slot adjacent to the greater trochanter, the cut guide slot being oriented to guide a cutter to form the proximal/distally oriented datum slot in the greater trochanter.

The inserter tab may have anterior, posterior, lateral, and distal surfaces, the anterior and posterior surfaces being engageable with the datum slot to establish the anterior/posterior position of the hip stem component, the lateral surface being engageable with the datum slot to establish the medial/lateral position of the hip stem component, and the distal surface being engageable with the datum slot to establish the hip stem component insertion depth.

The means for creating a datum may include means for guiding a cutter to cut a datum hole in the proximal femur and a datum pin insertable into the datum hole, the inserter comprising an opening engageable with the datum pin to position the inserter and hip stem component relative to the intramedullary canal of the femur.

The means for creating a datum may include a drill guide having a base engageable with the calcar region of the proximal femur and a drill guiding portion extending upwardly and laterally from the base to position the drill guiding portion above the greater trochanter, the drill guiding portion being oriented to guide a drill to form a proximal/distally oriented datum hole in the greater trochanter.

The inserter may include an extension projecting radially outwardly and defining the opening engageable with the datum pin, the opening extending into the extension to form an elongated socket having a side wall and an end wall, the side wall being engageable with the datum pin to establish the medial/lateral position of the hip stem component and the end wall being engageable with the datum slot to establish the hip stem component insertion depth.

The means for creating a datum may include a drill guide having a base engageable with the calcar region of the proximal femur and a drill guiding portion extending upwardly at an angle from the base to position the drill guiding portion adjacent to the greater trochanter, the drill guiding portion defining a plurality of drill guide bores oriented to guide a drill bit to form a plurality of datum holes in the greater trochanter, the means for creating a datum further comprising a plurality of datum pins insertable into the plurality of datum holes, the inserter comprising a plurality of openings engageable with the datum pins to position the inserter and hip stem component relative to the intramedullary canal of the femur.

The drill guide bores may be directed distally and laterally to form datum holes oriented distally and laterally transverse to the intramedullary canal axis.

The means for creating a datum may include a datum sleeve defining a bearing surface having an axis, the datum sleeve being mountable to the datum cut into the femur to position the bearing surface in predetermined relationship to the intramedullary canal, the hip stem inserter further comprising a portion engageable with the bearing surface in axial sliding relationship.

The means for guiding a cutter may include a drill guide having a base engageable with the calcar region of the proximal femur and a drill guide portion extending upwardly at an angle from the base to position the drill guide portion adjacent to the greater trochanter, the drill guide portion defining a plurality of drill guide bores oriented to guide a drill bit to form a plurality of datum holes in the greater trochanter, the datum sleeve including a plurality of legs engageable with the plurality of datum holes.

The means for positioning the datum guide may include a spigot engageable with the opening of the intramedullary canal.

In another form, the present disclosure provides a combination for establishing a datum on a femur and for referencing the datum during implantation of a hip stem component into bone cement in an intramedullary canal of the femur, the femur having a proximal portion nearer the hip joint, a distal portion nearer the knee joint, an anterior portion toward the front of the body, a posterior portion toward the rear of the body, a medial portion toward the midline of the body, and a lateral portion further from the midline of the body, the datum being able to guide positioning of the proximal portion of the hip stem component within the bone cement to provide a predetermined bone cement thickness around the hip stem component, the femur having a proximal portion including a calcar region, a greater trochanter, and medial, lateral, anterior, and posterior sides and the intramedullary canal defining a longitudinal axis, the combination including a datum guide including a base positionable adjacent to the intramedullary canal in a predetermined position relative to the intramedullary canal; and a cut guide mounted to the base, the cut guide being able to guide a cutter to cut a datum into the proximal portion of the femur that records a predetermined hip stem component position relative to the intramedullary canal in persistent manner such that the datum remains after the datum guide is removed; and a hip stem inserter engageable with the hip stem component in axial, medial/lateral, and anterior/posterior force transmitting relationship, the hip stem inserter comprising a portion engageable with the datum, the hip stem inserter being simultaneously engageable with the hip stem component and the datum to position the hip stem component in the predetermined hip stem component position in the bone cement in the intramedullary canal.

• Provisional Patent
• Utility Patent

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