Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-09-22
2001-09-18
Isabella, David J (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S022390
Reexamination Certificate
active
06290727
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an acetabular cup which is supported by a pelvic bone and includes an outer surface resting in a cavity, and a bearing surface receiving an articular body of an artificial hip joint and bounded in surrounding relation by a receiving edge.
An acetabular cup of this type is known, for example, from U.S. Pat. Nos. 4,883,490 and 4,123,806. These conventional acetabular cups suffer shortcomings when implanted in a leg or femur because undesired luxations have been experienced during certain movements. In order to reduce the risk of dislocation of the articular head from the acetabular cup, the depth of the spherical segment in the acetabular cup could be increased. This, however, would be accompanied at the same time by a restriction of movement and a resultant undesired functional limitation of the acetabular cup or of the entire hip joint endoprosthesis.
SUMMARY OF THE INVENTION
It is thus an object of the present invention, to so improve the conventional acetabular cups that the risk of an undesired luxation is reduced, on the one hand, and to substantially eliminate an undesired restriction of movement.
This object is attained in accordance with the present invention by providing the receiving edge at least at one area with an elevation which partially surrounds the articular head received by the bearing surface.
By providing the receiving edge with an elevation, it is possible to create in this region the acetabular cup with a depth which is greater than the radius of the spherical section, so that an inserted articular head is form-fittingly enclosed by the bearing surface of the acetabular cup and snaps into the acetabular cup. In the imperiled movement range, an intended blocking is thus realized that prevents a luxation. The region that is not affected by the elevation does not experience an unnecessary blocking or undesired restriction of movement.
According to a preferred embodiment of the invention, the elevation is provided in an area of least obstruction to the freedom of movement of the articular head. In this way, luxations are greatly diminished, on the one hand, and, on the other hand, the freedom of movement of the articular head is impeded only in those zones in which only very rare movement patterns occur.
According to a further preferred embodiment of the invention, the elevation has at its apex, projecting furthest from the receiving edge, a distance from a lowest point of the bearing surface which guides the articular head in a substantially surrounding relation. In this way, the articular head can snap into the bearing surface, so as to be able to execute within the bearing surface movements which are merely impaired by the elevation, but otherwise allows the relevant part of the freedom of movement desired for a femur.
According to a further preferred embodiment of the invention, the elevation extends from the lowest point of the bearing surface to the apex in a direction in which a femur which receives the artificial hip joint extends slantingly backwards with respect to a stretched standing leg and thereby intersects at an acute angle an imaginary movement plane which is defined by the standing leg in straight alignment. Such a movement direction is uncommon for a femur and is rarely executed. An impairment with respect to this movement direction is thus barely noticeable for a bearer of a hip joint and thus hardly interfering. Still, the elevation has the crucial advantage of substantially preventing luxations of the hip joint.
According to a further preferred embodiment of the invention, the bearing surface is designed as a spherical section of an inner surface which is circumscribed by a hollow sphere and which is formed by a part of a sliding surface of the elevation, confronting the articular head which is configured as spherical head. This sliding surface formed at the elevation fits in the bearing surface formed as hollow sphere, so as to enable optimum guiding conditions for an articular head configured as spherical head.
According to a further preferred embodiment of the invention, the receiving edge is formed in a first segment as edge region of a spherical section extending substantially in a horizontal plane and defining a plane upon which a cup axis is oriented perpendicular and extending through the lowest point. Following a first segment of the receiving edge is a second segment which includes the elevation and ascends from a junction end, adjacent the first segment, of the second segment to the apex of the elevation. The rise of the elevation in the second segment enables an optimization between luxation risk, on the one hand, and freedom of movement, on the other hand.
According to a further preferred embodiment of the invention, the first segment has a first end distal to the junction end of the second segment, wherein between the first end of the first segment and the apex of the elevation of the second segment there is arranged a third segment in which the receiving edge is depressed in the direction to the lowest point for clearing a pivot space within which a stem, secured to the femur, of the spherical head is swingably supported. This pivot space realizes that the stem, connected to the articular head, is not interfere with by the receiving edge when carrying out swivel motions. The guidance of the articular head is diminished in the area of the pivot space and is sufficiently compensated by the elevation. Therefore, the pivot space drops immediately in the direction toward the first end of the apex. Moreover, the receiving edge in the area of the pivot space is slanted in a plane which extends at an acute angle to a plane oriented perpendicular to the cup axis. This plane defined by the pivot space is so configured as to allow in this area an unimpeded movement of the stem secured to the articular head.
According to a further preferred embodiment of the invention, the receiving edge has in the pivot space with respect to the lowest point a height for guiding the spherical head in a form-fitting manner, and a cut-off edge which permits the insertion of the spherical head in the bearing surface. In this manner, the receiving edge can be moved up in the area of the pivot space to a relatively high location at the articular head, without complicating the insertion of the articular head which is inserted via the cut-off edge into the bearing surface.
According to a preferred embodiment of the invention, the receiving edge is formed in a first segment as edge of a spherical section which substantially extends transversely to a cup axis. The first segment of the receiving edge terminates in a second segment which includes the elevation and which ascends from a junction end, adjacent the first segment, of the second segment to an apex of the elevation. The rise of the elevation in the second segment realizes an optimum between luxation risk and freedom of movement.
According to a further preferred embodiment of the invention, the first segment has a first end distal to the junction end of the second segment, wherein between the first end of the first segment and the apex of the elevation of the second segment there is arranged a third segment which forms the edge of a spherical section arranged at an acute angle to the cup axis so as to generate in this area a depth which is less than the depth of the first segment and smaller than the radius of the spherical section. The spherical section in the less imperiled third segment realizes an increased freedom of movement as a consequence of the reduced depth, without increasing the luxation risk compared to the known state of the art.
According to a further preferred embodiment of the invention, the outer surface has a plurality of spacers in substantial concentric relation to the cup axis. When cementing the acetabular cup, the spacers effect a more even layer thickness of the bone cement being used.
Further specifics of the invention will now be described in more detail with reference to the attached drawing in which preferred embodiment
Keller Arnold
Otto Karl Bernahrd
Feiereisen Henry M.
GMT Gesellschaft für madizinische Technik mbH
Isabella David J
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