Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2002-09-03
2003-12-02
Philogene, Pedro (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S079000
Reexamination Certificate
active
06656187
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to the field of orthopaedics, and more particularly, to an implant for use in arthroplasty
BACKGROUND OF THE INVENTION
The invention relates to implantable articles and methods for manufacturing such articles. More importantly, the invention relates to bone prosthesis, bone prosthesis instrumentation and processes for manufacturing the same.
There are known to exists many designs for and methods for manufacturing implantable articles, such as bone prosthesis. Such bone prosthesis includes components for artificial joints, such as elbows, hips, knees and shoulders. An important consideration in the designing or manufacturing of any implantable bone prosthesis is that the prosthesis has adequate fixation when implanted within the body.
Earlier designs of implantable articles relied upon the use of cements, such as polymethylmethacrylate (PMMA) to anchor the implant. The use of such cements can have some advantages, such as providing a fixation that does not develop free play or does not lead to erosion of bone faces post-operatively. However, the current trend is to use these cements to a lesser extent because of their tendency to lose adhesive properties over time and the possibility that the cement contributes to wear debris within the joint. When utilizing these cement implants, the implants are designed to be smaller than the respective cavity. The implant is placed in the cavity and a mantel or layer of cement is applied between the cavity and the implant.
Recently, implantable bone prosthesis have been applied and designed such that they encourage growth of hard tissue (ie. bone) around the implant. The bone attachment usually occurs and growth is promoted when the surface of the implantable bone prosthesis is irregular or textured. The bone attachment usually occurs and growth is promoted when the surface of the implantable bone prosthesis has been found to provide a good fixation of the prosthesis with the body. A greater degree of bone fixation interaction of newly formed hard tissue in and around the texture can usually be achieved when bone-engaging surfaces of an implantable bone prosthesis are more porous or regular. For prostheses designed to encourage bone in-growth, the cavity into which the prosthesis is implanted closely conforms to the periphery of the bone prosthesis. Such bone prostheses are press-fitted into the bone cavity.
One of the considerations as to whether to use a cemented stem or a pressed-fitted stem in a prosthetic joint implant is the overall health or condition of the patient's bone. Long bones, particularly the femur, are typically classified into three general classifications of bone structure. These classifications are related to the health of the bone. The health of the bone is typically attributable to the progression of disease within the long bone. The typical long bone diseases that lead to total hip arthroplasty are ostoarthritis, avascular necrosis, and rheumatoid arthritis.
The three distinct classifications of bone structure of the femur can be identified between the metaphysis and the diaphysis. These three types of bone structures are type A, type B, and type C bone structure. These types of bone structure are more fully described in an article by Dorr, L D., Faugere, M C., Mackel, A M., Gruen, T A., Bogner, B., Malluche, H H. “Structural and Cellular Assessment of Bone Quality of Proximal Femur.”
Bone
1993: 231-242 hereby incorporated by reference in its entireties.
In Type A bone structures thick medial and posterior cortices are evident. They begin at the distal end of the lesser trochanter and are quite thick immediately. This creates both a narrow diaphyseal canal and a funnel shape to the proximal femur. The thicker cortices and less porosity result in a lower canal to calcar isthmus ratio. This type of bone is found more often in younger patients.
In Type B bone structures both the medial and posterior cortices exhibit bone loss. The medial cortex is thinned compared to Type A bone but a funnel shape is still present. The funnel shape of the canal remains good for implant fixation. The posterior cortex is especially thinned, or absent, and causes the width of the intramedullary canal to increase. The shape of the bone is proportional at the top and bottom.
In Type C bone structures the bone has lost nearly all the medial and posterior cortices, which result in a “stovepipe” shape of the intramedullary canal. It has the thinnest cortices of the 3 types of bone, a wide intramedullary canal, and appears somewhat “fuzzy” in x-rays. This type of bone is seen most often in older patients.
Cemented implants are more often used in patients with the type C bone structure, while cementless implants are more commonly used in patients with type A bone structure. Further, in many cases cemented implants are used in cases where the ratio where the proximal canal width to the distal canal width is less than the ratio for cases in which the cementless implants might be used.
Stem components for total joint arthroplasty typically have a wedge shape with the distal portion of the stem being smaller in cross section than the proximal cross section. Typically, the stem has a continually decreasing cross-sectional area in the direction from the proximal portion to the distal portion of the stem.
Due to the differences in the types of bone for which the cemented and cementless stems are designed, the shapes of the stems vary widely from one type of prosthetic stem to another. As mentioned before, some cemented stems have a larger difference between the cross-sectional area or width of the proximal portion of the stem to the distal portion of the stem.
Cemented and uncemented stems are implanted into a canal or cavity prepared in a resected long bone. The cavity in the long bone may be prepared utilizing at least one of several types of instruments. For example, the cavity may be prepared by a drill, reamer, or broach. A hip stem cavity may typically be prepared by a combination of drilling, reaming, and broaching. The broaching includes teeth or cutting edges which remove material from the bone. The broach generally has a shape equal to the shape of the stem.
In order to prepare a cavity for a particular stem, a unique broach with a unique profile must be available for preparing that cavity. Even for a particular stem, the surgeon may have patient-specific reasons or general-practice preferences for a cement mantel or thickness of the cement along the profile of the stem which may be different than that provided by the manufacturer of the stem and accompanying broaches. Thus, the prior art requires a vast number of broaches, namely, one for each particular size of a particular design of stem. And even with such a variety of stems, the configuration of a broach limits the surgeon to one particular cement mantel pattern for a particular hip stem and hip stem broach combination.
SUMMARY OF THE INVENTION
According to the present invention, an orthopedic implant tool includes a feature which permits a portion of the periphery of the instrument to be adjustable so that the tool may prepare more than one type of cavity for an orthopedic implant stem. The tool could be expanded or contracted to accommodate either a type A or a type C bone structure. Preferably, the expansion or contraction of the instrument is done in a controlled fashion such that a plurality of different feature sizes could be accommodated by one particular instrument.
The adjustable instrument permits the ideal sizing of the cavity for a particular implant. The adjustable instrument is able to replace separate instrument sets for cemented and cementless implants and reduces both cost and complexity for the manufacturer and the consumer of the instruments.
The present invention allows the same instrument or broach to create an envelope more conducive to the anatomical femur shape via either type A, type B, or type C bone structure and allows the implant to be ideally designed accordingly.
The adjustable
Bonderer David A
Depuy Products, Inc.
Philogene Pedro
LandOfFree
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