Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1998-09-16
2001-02-27
Milano, Michael J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
Reexamination Certificate
active
06193760
ABSTRACT:
The invention relates to a thigh prosthesis and more particularly, to a thigh prosthesis with a shaft that can be inserted into the upper end of a femur.
DISCUSSION OF RELEVANT ART
A thigh prosthesis of this type is disclosed in DE 36 15 655A, corresponding to U.S. Pat. No. 5,002,579. It comprises an anchoring shaft formed by anchoring pillars suspended from the support plate. The anchoring pillars each support a plurality of axially successive annular anchoring collars. Spongiosa can grow into the intermediate spaces between the individual anchoring pillars. In this manner, the prosthesis is securely connected to the femur following healing without the use of cement.
In order to adapt the prosthesis to differently sized cavities in the proximal end of the femur, free ends of anchoring pillars can be shortened as required. However, this can only be effected without difficulty in the case of anchoring pillars which end freely or are unattached. In the case of anchoring pillars which are connected to one another, a separation of parts of the cage structure would be associated with such an intensive intervention into the mechanical support structure with consequences which could not be overlooked by the surgeons, that the durability and loading capacity of the prosthesis could no longer be guaranteed. Also in the case of shaft prostheses which are connected to the corticalis of the femur using cement, it is clearly difficult to obtain an improved adaptation to the bone geometry by mechanical reworking of the prosthesis during the course of the operation. However, it is particularly desirable in the case of cemented prostheses that the cement layer does not vary locally to an excessive degree, which means that the anchoring section must closely match the bone geometry at the stage of manufacture.
By way of the present invention, a thigh prosthesis according to the field of invention is therefore to be further developed in such a manner that it more closely matches the geometry of the corticalis in the upper end shaft of the femur without mechanical reworking.
SUMMARY OF THE INVENTION
This object is attained according to the invention by a thigh prosthesis having the following features.
It is recognised that the geometry of the corticalis in the upper end section of the femur can generally be better taken into account by constructing the shaft of the prosthesis from two shaft sections which are tilted relative to one another.
Using a set of prostheses which differ between the two shaft sections in respect of the bending angle but which otherwise have the same dimensions, it is possible to take into account a very large number of different implantation conditions.
Consequently, it is no longer necessary to compensate the misfitting of the prosthesis external surface and the internal surface of the corticalis by means of cement layers of a thickness which varies greatly locally.
Advantageous developments of the invention are laid out in the subclaims.
Advantageously, the acute angle (b) measures between 5° and 30°, preferably between 10° and 20°. The angles given are most suitable for the most commonly occurring thigh geometries. If the bending angle in a prosthesis set is graded in stages of 5°, then there is always one prosthesis in the set which is well adapted to the geometry of the upper end of the thigh with only slight residual thickness variations in the cement layer.
Advantageously, the line of intersection between the main surfaces of the two shaft sections lies at a distance of between 50 and 70% of the overall length of the shaft, preferably approximately 60% of the overall length of the shaft from the free end of the distal shaft section. This gives preferred values for the distance of the shaft bending site from the distal end of the shaft. Again, prostheses can be provided in a prosthesis set in which the shaft bending line lies at different distances from the distal end of the shaft, the grading preferably being effected in stages of 5 mm.
Advantageously, the support plate extends in a plane lying substantially perpendicular to the proximal axis (P). In a thigh prosthesis according to this feature, the support plate extends substantially in the horizontal direction when the prosthesis is implanted.
Advantageously, the support plate projects in the circumferential direction substantially uniformly beyond the proximal end of the proximal shaft section. In a thigh prosthesis according to this feature, the edge of the support plate can form a substantially flush continuation of the external surface of the proximal end of the corticalis. The support plate can then form a lid, by means of which the upper end of the femur, which is open following resectioning, is sealed again.
Advantageously, the shaft sections comprise a non-circular, preferably substantially rectangular cross section, taper in the direction from proximal to distal and at least one shaft section comprises a lower section, which is twisted about the longitudinal axis of the shaft section in question. With the cross sectional shape for the shaft sections according to this feature, it is possible to attain a particularly good adaptation to the transverse cross section of the cavity, which is obtained by removing spongiosa from the upper end section of the femur. In this respect, the torsion also disclosed in claim
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of at least one lower section of at least one of the shaft sections allows for particularly good adaptation to the internal surface of the corticalis.
Advantageously, the angle of torsion of the lower section in question measures between 5 and 30°, preferably between 10 and 15°, a lower section of the proximal shaft section again being preferably twisted through a smaller angle than a lower section of the distal shaft section. Preferred torsion angles used for a shaft section lower section of this type are given by these features.
Advantageously, the shaft sections comprise a substantially smooth, continuous surface. The development of the invention according to this feature is also advantageous in that the cement layer between the external surface of the shaft and the internal surface of the corticalis has a substantially constant thickness.
Advantageously, the surfaces of the shaft sections and preferably, also of the support plate comprise microirregularities produced by sandblasting, which are preferably additionally etched. With the development of the invention according to this feature, it is attained that the cement used for the implantation adheres particularly well to the outside of the shaft.
Advantageously, laterally the support plate comprises a raised lateral smooth section, whose plane preferably forms an angle of 100° to 150° with the main section of the support plate. As a result of the development of the invention according to this feature, it is possible to merely partially resection the greater trochanter of the femur, which can therefore be partially left in place. This is advantageous with a view towards a good transmission of transverse forces from the prosthesis to the corticalis.
Advantageously, the element is a forged element or cast element or biocompatible material, more particularly titanium. The development of the invention according to this feature is advantageous with a view towards high mechanical loadability of the prosthesis and with a view towards low manufacturing costs.
REFERENCES:
patent: 4435854 (1984-03-01), Keller
patent: 4546501 (1985-10-01), Gustilo
patent: 4608053 (1986-08-01), Keller
patent: 4713076 (1987-12-01), Draenert
patent: 4738681 (1988-04-01), Koeneman
patent: 4743263 (1988-05-01), Petrtyl
patent: 4808186 (1989-02-01), Smith
patent: 4978359 (1990-12-01), Wilhelm
patent: 5002579 (1991-03-01), Copf et al.
patent: 5032130 (1991-07-01), Schelhas
patent: 5507829 (1996-04-01), Thongpreda
patent: 5897592 (1999-04-01), Caldarise
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