Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1993-07-27
1995-01-24
Isabella, David
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 18, A61F 238
Patent
active
053839331
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an endoprosthesis having two prosthesis parts which are connected by an overlapping connection.
The problem frequently exists of connecting two prosthesis parts rigidly to one another after they have been implanted separately. An example of this is a prosthesis for the rigid connection of two bone fragments or for the arthrodesis of two tubular bones which are otherwise connected by a joint. At the site of the fracture or joint, the two bones can be angled towards one another so that the shafts of the two prostheses can be inserted in the bones. The bones are then aligned relative to one another and the parts of the prostheses facing one another are connected to one another. This can be done, for example, in a positive-locking manner using a cone or pin at the end of one shaft which is inserted in a corresponding sleeve at the end of the other shaft. However, this has the disadvantage that, for inserting the cone or pin in the associated sleeve, the two bones must firstly be distracted by the length of the cone or pin, which can be difficult or harmful. A connection is therefore desired which can be closed without substantial distraction. For this purpose, the lug connection is available, in which two lugs, provided at the ends of the prosthesis shafts, are screwed to one another, which has the disadvantage, however, that the reliability of the connection depends on the screws which may become loose, and that the transition from the lugs to the shafts forms a weak point.
The invention avoids these disadvantages in a lug connection due to the fact that the ends of the mutually overlapping lugs are received in a positive-locking manner by pockets on the respective other prosthesis part. In order to couple the lugs to one another, only a small distraction is required, whose length corresponds to the length of the engagement of the lug ends in the associated pockets. This length is far shorter than in a pin or cone connection, in which distraction is required over virtually the entire length of the connection region.
According to the invention, an engagement length of the lug ends in the associated pockets of no more than 1/5, preferably no more than 1/10, of the overall overlapping length, is sufficient.
Devices for securing the lugs in the engagement position are expediently provided, which merely need to ensure that no longitudinal displacement of the lugs relative to one another can take place, by means of which the lug ends could come out of the associated pockets. The pertinent technology provides various types of such means. The simplest method is to screw the lugs to one another. It is notable in this case that the screw connection prevents longitudinal displacement even if a screw may have loosened slightly. In contrast to the known screwed lug connections, the safety of the connection is therefore not impaired by screws becoming loose.
According to a further feature of the invention, the lugs are thicker near to their transition into the associated prosthesis part than at their free end, in that the contact surface with which they face one another runs at an inclination to the common longitudinal axis of the connection region of the prosthesis parts. Due to the fact that the lugs are thickest at that end at which they are firmly connected to the associated prosthesis part, they can merge into the prosthesis part with equal cross-section without forming dangerous notches, while their end which engages in the pocket of the other prosthesis part is correspondingly thinner. The taper allows the lug ends and the pockets surrounding them to become wedged in one another, thus resulting in a self-locking, clearance-free engagement position.
The invention is explained in greater detail below with reference to the drawing which shows an advantageous exemplary embodiment of a prosthesis or rail for the arthrodesis of the knee joint.
FIG. 1 shows a lateral view of the connection region of the prosthesis,
FIG. 2 shows a lateral view transversely to that according to FIG. 1,
FIGS. 3 and 4
REFERENCES:
patent: 4578081 (1986-03-01), Harder
patent: 4938768 (1990-07-01), Wu
patent: 5129898 (1992-07-01), Brusasco
Isabella David
Waldemar Link (GmbH & Co.)
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