Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1990-02-21
1993-01-19
Isabella, David
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 16, A61F 234
Patent
active
051803950
DESCRIPTION:
BRIEF SUMMARY
This invention concerns a shaft-part implantable into a tubular bone for use in a joint-end prosthesis or as a bone-shaft replacement.
A large number of shaft parts for joint-end prostheses used in uncemented implants are known which require automatically locking the shaft in the marrow cavity. As an illustration, the patent document WO 86/06954 discloses a hip-prosthesis shaft with medial and lateral legs joined to one another by link structures. The shaft enlarges its cross-section upon bending stress and thereby fastens the shaft against the marrow cavity. Even though this and similar systems of the state of the art do clamp the shaft, the contact with the bone always remains restricted to three points. But these point contacts entail high local stresses.
The object of the invention is palliation. Its purpose is to create a self-locking shaft-part for a joint-end prosthesis of which the surface lends itself to making a real contacts with the bone so that the local stresses shall be relatively slight.
The invention solves this problem by means of a shaft-part evincing the features of claim 1.
Essentially the advantages offered by the invention are that, because of the shaft-part construction, maximum adaptation of the shaft surface to the anatomy of the marrow cavity is achieved and that both implantation and removal of the shaft-part can be carried out rapidly and without complications.
Because of the open and preferably frusto-conical design of the shaft, the marrow cavity remains open--contrary to the case of conventional systems--so that the bone maintains its blood circulation and bone metaplasia continues.
Another advantage lastly is that because the shaft cross-section is essentially circularly or elliptically symmetric, any rotational forces--of the kind that predominantly arise in a rapid, intermittent manner in hip prostheses--are significantly better absorbed and shunted in comparison to the mostly leaf-like shafts of the state of the art.
The drawing shows an illustrative embodiment of the invention and also elucidates the principle of operation. Details are provided below.
FIG. 1 is a lateral perspective of the shaft designed as the femur part of a hip prosthesis,
FIG. 2 is a cross-section along line II--II of the shaft of FIG. 1,
FIG. 3 is a cross-section in the manner of FIG. 2 of a longitudinally slotted shaft part of the invention,
FIG. 4 is a perspective of the shaft part of the invention as yet not clamped, and
FIG. 5 is a perspective of the clamped shaft part of the invention.
As shown by FIG. 1, the femur part designed as a hip prosthesis includes a frusto-conical braid 5 tapering from the proximal to distal ends in harmony with the anatomy of the marrow cavity and is constituted by two mutually crossing series of fibers 2, 3. Preferably the frusto-conical braid 5 assumes a nearly circular cross-section in the distal zone and a nearly elliptical cross-section in the proximal zone. As indicated in FIG. 1, the external contours of the braid 5 are longitudinally concave, i.e., the cross-section is narrower at the center than a regular frustrum of cone which would have straight outer contours. The fibers 2, 3 consist of a body-compatible metal, or of a suitable metal alloy or a plastic. Carbon fibers, illustratively of Pyrocarbon, are preferred. The fibers 2, 3 subtend an angle .alpha. to the longitudinal axis 4 of the hollow frustrum of cone formed by the braid 5. As a rule the angle .alpha. is about the same for both sets of fibers 2, 3. However, in order to achieve a better adaptation or fit of the braid in the proximal femur part, the angle .alpha. also may be variable along each fiber 2 or 3 and preferably becomes smaller from the distal toward the proximal zones.
In a preferred embodiment mode, the gaps 17 in the frusto-conical braid 5 made of fibers 2 and 3 are filled as shown in FIG. 2 with an elastomer 9 such as silicone rubber or Silastic in order to achieve a smooth shaft surface. This circumstance is significant because it has been found that newly formed bone material 1 easi
REFERENCES:
patent: 3893196 (1975-07-01), Hochman
patent: 4441215 (1984-04-01), Kaster
patent: 4459708 (1984-07-01), Buttazzoni
patent: 4610688 (1986-09-01), Silvestrini
patent: 4714467 (1987-12-01), Lechner et al.
patent: 4750905 (1988-06-01), Koeneman
Farley Walter C.
Isabella David
Laboratorium fur experimentelle Chirurgie
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