Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-05-28
2001-07-03
Smith, Jeffrey A. (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S023150
Reexamination Certificate
active
06254640
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a shaft prosthesis in accordance with the preamble of the independent patent claim.
Shaft prostheses, especially those for the implantation in the femur, are available on the market in numerous different embodiments. With regard to the manner of the anchoring of the prosthesis in the femur, one can distinguish, the shaft prostheses into cemented and cement-free prostheses. In this it is determined in the planning of the operation whether a cemented or cement-free anchoring of the prostheses comes under consideration as a result of the information about the bone, e.g. on the size of the femur and on its condition, which the orthopedist receives from X-ray photographs, etc. In addition the size of the respective prosthesis which is to be implanted is also determined.
During the operation it is then assumed that a given kind of anchoring is carried out, e.g. a cemented anchoring. Prostheses which are suitable for an anchoring of this kind are known for example from DE-B2-25-37 807 or from EP-A-0,672,396. During the operation the femur is first prepared by the orthopedist. Simply expressed, in this situation a cavity is produced into which the cement is then introduced. Subsequently the prosthesis is introduced into the cement and held in place until the cement hardens and the prosthesis is thus fixed. The introduction of the prosthesis into the cement must take place in such a manner that no inclusions of air arise in the cement. This introduction requires a certain skill on the part of the orthopedist since the cement is so constituted by its flow properties at the time point of the introduction into the femur that a flowing back of cement which has once been displaced practically does not take place. This is correspondingly reflected in the design of the shaft—the design of prostheses to be cemented differs considerably from the design of prostheses to be anchored without cement because the anchoring of cemented prostheses takes place in the cement jacket which surrounds the prosthesis, whereas in prostheses to be anchored without cement the anchoring takes place directly in the bone tissue surrounding the prosthesis.
The decision as to whether a prosthesis is anchored with cement or without cement in the implantation is thus made prior to the operation, namely in the pre-operative planning. The decision on the size of the prosthesis to be implanted is also already made prior to the operation. These decisions then also decide how the cavity to be produced by the orthopedist for the reception of the cement must look or which dimensions it must have respectively.
In several cases it turns out during the operation, namely during the preparation of the femur, however, that, for example as a result of the condition of the bone material, it is possible or even desirable to provide a cement-free anchoring although a cemented anchoring had been planned. At this time point however a change in the decision for the cemented prosthesis is no longer possible because for this a new operation planning must take place as a result of the different shaft design of the prostheses to be anchored with cement and without cement.
SUMMARY OF THE INVENTION
An object of the invention is thus to propose a shaft prosthesis which enables a decision with respect to the anchoring which had already taken place in the operation planning to be changed once again without a new planning being required for this. This means in other words that the prosthesis must be suitable by virtue of its design both for a cemented and for a cement-free anchoring.
In accordance with the invention this object is satisfied by a shaft prosthesis which has a distal section which has a substantially circular cross-section. This means that this distal section is preferably designed to be completely circular, but that slight deviations from the circular shape such as e.g. flattenings in order to ensure a sufficiently thick cement jacket in cemented anchorings are however possible. At this distal section there adjoins a proximal section at which a rib which protrudes in the ventral direction is provided at the lateral side. The proximal section of the shaft prosthesis enlarges in the upward direction and a neck is provided in the upper end region on which a joint ball can be attached. The diameter of the shaft prosthesis enlarges substantially conically on all sides (see above), preferably conically on all sides, starting from the distal end of the shaft prosthesis. A shaft prosthesis of this kind is basically suitable for a cemented as well as for a cement-free anchoring in the bone.
The substantially all-sided conical extension starting from the distal end of the shaft prosthesis means that the prosthesis has no undercuttings which can otherwise lead to air enclosures in a cemented anchoring due to the poor flow properties (high viscosity) of the bone cement. In addition the enlargement of the shaft in the proximal direction leads to a compression of the bone cement and thereby to better distribution of the cement into cavities in the often porous bones (spongiosa). Moreover, a conical enlargement which already starts from the distal end of the prosthesis corresponds to the natural shape of the marrow chamber in the diaphysary bone region. In shaft prostheses with non-conical cylindrical distal end regions, namely, stoppages of prostheses of this kind can partially arise in the cement-free anchoring, the anchoring of which prostheses should however preferably take place in the proximal region of the prosthesis. A stoppage of this kind then means an additional work step for the orthopedist since he must then in addition bore open the marrow chamber, which had been prepared with a conical rubbing awl, in order that the prosthesis can be introduced still further into the marrow chamber in order that it can be anchored in the proximal end region.
In an advantageous exemplary embodiment of the shaft prosthesis in accordance with the invention the opening angle in the region of the conically enlarging distal section lies in the range from 1° to 10°; in particular it amounts to about 2°. Practically all shapes of the marrow chamber in the diaphysary bone region which occur are covered by this range; a not infrequently occurring shape has an opening angle of 2°.
In a further advantageous exemplary embodiment of the shaft prosthesis in accordance with the invention the angle between the longitudinal axis of the shaft and the neck axis lies in the range from 120° to 150°; in particular it amounts to approximately 135°. In the case of this angle one also speaks of the so-called “CCD angle” (
C
entrum
C
ollum
D
iaphysis angle). The important cases occurring in practice are likewise covered by the named region. A CCD angle of 135° is frequently encountered in younger patients; however a prosthesis with a CCD angle of this size is also implantable for patients of advanced age. With such a CCD angle e.g. a tautening of the partially slackened ligament apparatus can be effected because the natural CCD angle at the bone of the patient was lower prior to the implantation of the prosthesis and the ligament apparatus is again “tautened” through the greater CCD angle.
In a further exemplary embodiment of the shaft prosthesis in accordance with the invention the shaft prosthesis is inclined in the anterior direction in the proximal section, with this angle of inclination or anteversion (anteversion angle is the frequently encountered designation) lies in the range from 5° to 17°, and amounts in particular to approximately 11°. This angle range includes the most frequently occurring anteversion angle; a very frequently occurring value for this angle amounts to approximately 11°.
A further aspect of the present invention relates to a series of shaft prostheses of different sizes, with the individual shaft prostheses of a series of this kind being formed as described above. The shaft prostheses of different sizes are built up according to the onion skin principle, with the thickness dimensions of two suc
De Cesaris Alessandro
Menzi Manfred
Puhl Wolfhart
Smith Jeffrey A.
Sulzer Orthopaedie AG
Townsend and Townsend / and Crew LLP
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