Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
1999-06-22
2001-01-30
Buiz, Michael (Department: 3731)
Surgery
Instruments
Orthopedic instrumentation
Reexamination Certificate
active
06179842
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a blocking system for the medullary canal of a tubular bone in which a prosthesis shaft can be fastened with bone cement, with the blocking system having a blocking element which can be anchored in the medullary space prior to the introduction of the bone cement in order to prevent an advance of bone cement.
The previous teaching for the formation of the cement jacket about the shaft of a cemented in prosthesis starts from as uniformly thick a cement jacket as possible which completely surrounds the shaft, with at most a somewhat greater accumulation of bone cement being tolerated under the shaft end in order to compensate the fluctuations between the setting depth of a mechanical medullary space blocking and the penetration depth of the shaft end.
A mechanical medullary space blocking of this kind is described in the patent specification U.S. Pat. No. 4,293,962 with an associated setting tool. A similar medullary space blocking is shown by the patent specification U.S. Pat. No. 4,245,359 or U.S. Pat. No. 4,344,190 in which the material of the mechanical medullary space blocking can be decomposed in the body. A disadvantage of an arrangement of this kind consists in that relatively large drawing tensions can arise in the transition from the cement socket to the cement plug lying under the shaft end when the shaft moves slightly downwards within the hardened cement socket.
SUMMARY OF THE INVENTION
The object of the present invention is to keep the drawing tension small in the direction of the shaft prosthesis in the lower region of the cement socket. This object is satisfied in that a plug of a deformable material is placed on the blocking element which prevents an advance of liquid bone cement in the capacity of a fill-in or dummy and which permits a penetration of the end of the prosthesis shaft.
An advantage of this arrangement consists in that the shaft end can sink slightly within the tube-shaped socket in accordance with the creep movements of bone cement. Furthermore, there is no cement plug present which can come off or be pushed away to one side as a result of such a creep movement. Also, there is no cement plug present which must be tediously removed in a re-operation. In addition a greater accumulation of bone cement is avoided without it being necessary to observe narrower tolerances between the mechanical medullary space blocking and the shaft end. Because the plug is deformable between the shaft end and the mechanical medullary space blocking, the shaft tip can penetrate, while the still flowable bone cement is displaced backwards. Since the plug is still deformable even after the hardening of the bone cement, it can follow slight sinkings of the shaft, with the cement socket which is supported in the bone being pressed together more strongly. The increase of the drawing tension which extends around in ring shape in the lower socket turns out in this situation to be low, since a small axial sinking of the shaft causes a substantially lesser enlargement of the diameter due to the weak cone angle, which is on the order of magnitude of a few degrees.
A further advantage is present when the deformable plug decomposes in the body and in this manner the body's own tissue can grow in up to the end of the shaft in the form of bone marrow and fat. If the material of the blocking element also decomposes in the body in the medium term, no more parts which are foreign to the body are present beneath the shaft end by the dimensions of which a re-operation shaft would have to be set more deeply. In addition, in a re-operation a removal of the tubular cement socket is considerably simpler after the removal of the shaft which protrudes beyond the socket. Furthermore, it is prevented with this arrangement that a hitherto usual cement plug is torn off from one side of the socket and wanders under the slowly sinking shaft laterally into the tubular bone and weakens the latter. The deformable plug can consist of a plastically deformable, gelatinous or pasty material which gives way while largely preserving its volume when a shaft tip penetrates therein. It can however also consist of a foamed material, the volume of which collapses at the location of the penetration of a solid object. This does not exclude that the foamed plug has a certain elasticity, which permits it, compressed to a smaller diameter, to be introduced with a setting apparatus into a medullary canal where it can assume a larger diameter after being deposited. If a foam is used which easily solidifies on being released, then a plug of this kind can be deposited directly onto the blocking element with a spray can and an extension tube in this manner and can be used as the mentioned fill-in after a corresponding solidification. Hydrolysable materials containing gelatine can be decomposed in the body within hours to days. There are likewise bio-absorbable materials which the body can decompose with its enzymes in days to weeks so that it is possible with such plugs to have a space beneath the shaft immediately after the operation which permits a sinking of the shaft corresponding to the creep movements in the cement socket, at the latest during the first loading attempts, without additional loading peaks arising at the socket and at the transition from the latter to the supporting bone tissue.
The deformable plug must be applied to the blocking element as a fill-in prior to the introduction of the bone cement. A plastically deformable plug can also be positioned together with a mechanical medullary space blocking by a setting apparatus and then be uniformly distributed with a stopper. It is however also possible to lower a deformable plug using a separate setting apparatus and to thrust it out with a piston. It is likewise possible to surround the plastically deformable plug with a membrane which is elastic and can be decomposed in the body in order that it can be pushed into the medullary space in the form of an elongate cartridge and occupies the cross-section of the medullary space with respect to the following bone cement when it arrives at the mechanical medullary space blocking. Because the pressure of the bone cement on the plastically deformable plug is equally large everywhere, the latter experiences no substantial change of form, but merely lies everywhere in contact with the same pressure, whereas the shaft which follows outwardly displaces first the bone cement and then the mass of the plastic plug. In the use of a membrane about the plug it can be advantageous to provide the end of the shaft with a point. This can be pushed on or be a component of the shaft in order to puncture open the membrane.
REFERENCES:
patent: 4245359 (1981-01-01), Stuhmer
patent: 4293962 (1981-10-01), Fuson
patent: 4344190 (1982-08-01), Lee
patent: 4627434 (1986-12-01), Murray
patent: 4865609 (1989-09-01), Roche
patent: 5006071 (1991-04-01), Carter
patent: 5314493 (1994-05-01), Mikhail
patent: 3314210A1 (1984-01-01), None
patent: 87 17 349 U (1989-02-01), None
patent: 0143847 (1985-06-01), None
patent: 0338981A1 (1989-10-01), None
patent: 0652016A1 (1995-05-01), None
patent: 2708192 (1995-02-01), None
patent: WO 94/01063 (1994-01-01), None
patent: WO 95/34331 (1995-12-01), None
patent: WO 97/25940 (1997-07-01), None
Frick Willi
Heller Mathias
Spotorno Lorenzo
Buiz Michael
King Anthony S.
Sulzer Orthopaedie AG
Townsend and Townsend / and Crew LLP
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