Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2001-11-21
2003-12-02
Robert, Eduardo C. (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
Reexamination Certificate
active
06656188
ABSTRACT:
BACKGROUND TO THE INVENTION
This invention relates to a tamp assembly for use in configuring bone cavity filler material within a bone cavity, in preparation for receiving an implant.
It can be necessary to prepare a bone cavity to receive an implant during replacement of a bone joint. For example, the cavity within a femur has to be prepared to receive the femoral component of a hip joint prosthesis and cavities within the femur and tibia have to be prepared to receive respective components of a knee joint prosthesis.
Joint prosthesis components can be fixed within a bone cavity by means of bone cement materials. They can also be fixed within a bone cavity by relying on the natural bone tissue, especially by providing the components with an appropriate surface finish which promotes bone ingrowth.
It can be important to configure the cavity so that the prosthesis component fits into it with minimum space left empty within the cavity around the component. For this purpose, the cavity is generally prepared by providing a filler material within it. The filler material is compatible with the prosthesis component and the technique by which it is to be fixed in place. It should also be conformable so that it can be shaped to configure the cavity appropriately for the selected component. For example, when the component is to be fixed within the cavity by means of a bone cement, the filler material will be a bone cement. When the component is to be fixed within the cavity relying on natural bone tissue, the filler material can be a bone graft material.
Filler material that is located in the bone cavity needs to be packed densely within the cavity to minimise voids. It also needs to be shaped to match the configuration of the prosthesis. It is known (for example from WO-A-93/1773) to shape bone graft material within a bone cavity by means of a tamp which is forced into the cavity to compress the material so that it adopts the configuration that is desired to suit the prosthesis that is to be implanted. A surgeon might use a number of tamps in sequence, whose configurations tend closer to that of the prosthesis. The tamps slide over a guide wire which is fitted in the cavity in a bone plug. The guide wire defines the path for the tamp to move along when it is being used to compress the bone graft material. When the tamping operation is complete, the guide wire is removed, leaving a cavity whose shape is defined by the shape of the tamps. This technique has been found to be an advantageous technique for making the filler material dense and also match the configuration of the prosthesis component to be implanted. For example, the configuration of a set of tamps for a prosthesis that is tapered gradually towards its tip might change from being tapered sharply so that it is wide at its end facing the handle, to being tapered less sharply so that it is relatively narrow at its end facing the handle.
A disadvantage of using a plurality of separate tamps can arise when a tamp has to be removed from within the bone cavity to be replaced by another tamp. Removal of the tamp can result in the filler material within the cavity being loosened or otherwise disturbed.
SUMMARY OF THE INVENTION
The present invention provides a tamp assembly for use in configuring bone cavity filler material within a bone cavity, in preparation for receiving an implant, which comprises:
1. a distal tamp portion which has a substantially constant cross-section over at least part of its length,
2. a proximal tamp portion which has a through bore extending through it with a size which is such that the proximal tamp portion is a sliding fit over the distal tamp portion, and which has an tamping surface extending from the through bore which faces generally towards the distal tamp portion, and
3. a hammer for transmitting impact to the bone cavity filler material which is contacted by the tamping surface of the proximal tamp portion.
The assembly of the invention has the advantage that the configuration of the tamp (which is made up of the distal and proximal tamp portions together) can be changed by replacing one proximal tamp portion with another which has a different shape. The distal tamp portion which defines the shape of the cavity at the distal end thereof can therefore remain in place throughout the tamping operation, which means that the filler material within the cavity at is distal end is not disturbed by unnecessary movement of the distal tamp portion.
The references to components of the assembly as “distal” and “proximal” should be understood as being relative to the resection of the bone which is to receive the implant and not in accordance with conventional anatomical uses of these terms. Accordingly, the distal tamp component is located further from the bone resection than the proximal tamp component.
Preferably, the assembly includes a guide shaft which is aligned with the distal tamp portion. The hammer can then have a through bore extending through it with a size which is such that it is a sliding fit over the guide shaft. This enables the impact that is imparted to the filler material through the proximal tamp portion (and often also the distal tamp portion) to be properly directed.
The hammer can be arranged so that it is moved to contact the proximal tamp portion which is stationary, in contact with the bone cavity filler material, to transmit impact to the filler material. In a different arrangement, the proximal tamp portion and the hammer can have mating formations which enable them to be fastened to one another so that they are moved together to contact the bone cavity filler material in order to transmit impact to it. For example, the formations might take the form of threads, or a spring loaded catch or the like; the fastening which is provided by the formations should be such that it does not become loose when the hammer and the proximal tamp portion are moved to impact the bone cavity filler material.
The configuration of the distal tamp portion will often be generally cylindrical (which can involve a slight inward taper towards the distal end to ease withdrawal of the tamp after use). When the distal tamp portion has a cross-section which changes significantly along its length, it can be preferred for the assembly to include more than one distal tamp portion, for example which differ by the cross-section and its variation along the length of the tamp portion. Different distal tamp portions within an assembly can have different cross-sectional configurations. Generally, they will be generally rounded, especially circular. The distal tamp portion that is selected for a particular patient will depend on the transverse dimensions of the cavity within the bone, which often will have been reamed so a predetermined diameter using known reaming techniques. In this case, the distal tamp portion will be selected so that its transverse dimensions are consistent with those of the reamer and of course of the implant that is to be used. The diameter of the distal tamp portion will generally be at least about 5 mm, preferably at least about 7 mm, more preferably at least about 10 mm. For some patients, the diameter of the distal tamp portion will be at least 12 mm, or even up to 15 mm or more.
The configuration of the proximal tamp portion will be selected according to the shape of the cavity within the bone in which the filler material is to be compressed, and to the shape of the implant which is to be fitted within the filled cavity. When the volume within the cavity which is to be filled with filler material is large so that the layer of the filler material is thick (at least in a part of the cavity), it can be preferred for progressively smaller tamp portions to be used so that the filler material is compressed within the bone cavity in layers. The assembly can include a proximal tamp portion whose tamping surface is tapered outwardly from its distal end towards its proximal end. It can include a proximal tamp portion with a tamping surface facing towards the distal tamp portion which is generally planar.
Moore David
Naybour John
Depuy Products, Inc.
Robert Eduardo C.
Wagley John S.
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