Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-09-08
2001-05-08
Mancene, Gene (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S018110, C623S019110
Reexamination Certificate
active
06228120
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns a surgical device for the implantation of a total shoulder prosthesis. It covers a total shoulder prosthesis of the type including a prosthesis stem designed to be implanted in the humeral canal of a patient and a head intended to fit the prosthetic socket of the shoulder or the glenoid cavity of the patient.
BACKGROUND OF THE INVENTION
Initially, the first shoulder prostheses, so-called NEERs, consisted of monobloc prostheses, i.e., they comprised a prosthesis stem and a head in a single piece. However, experience has shown that such prostheses have two major disadvantages.
As a matter of fact, and in the first place, the one-piece nature of these prostheses requires a large inventory of different implants that can adapt to the anatomical requirements of various patients. Furthermore, since the relative position of the head and the prosthesis stem are fixed, and also because of the one-piece nature of the prosthesis, the only solution available to the practitioner in order to accurately reproduce the anatomy of the upper end of the humerus consists of fitting the humerus to the prosthesis, an operation that proves to be quite tricky and a source of failures, or at least future traumatisms, for the patient.
Several solutions have been proposed to mitigate these disadvantages, as described in particular in French patents FR-2 685 633, FR-2 727 002, FR-2 727 857, and FR-2 731 612, aimed at providing prostheses with heads and prosthesis stems linked through connecting devices whose relative position can be adjusted by rotating the head around two or three axes of rotation with respect to the prosthesis stem, then locking these elements in the desired configuration.
Compared to the NEER prostheses, these prostheses have the advantage of making it possible to approximate the exact anatomy of the upper end of the humerus. However, they also have two major disadvantages.
As a matter of fact, and in the first place, due to the design of the systems for the related locking of the head and the prosthesis stem, they first require that the practitioner uses trial prostheses in order to determine the ideal relative positioning of the head and the prosthesis stem, and then duplicates the geometry of the trial prosthesis in order to construct the final prosthesis that is to be implanted.
But this surgical technique leads to an increase in the length of the operation during which the patient is under anesthesia. Furthermore, it can be the source of errors prejudicial to the patient during the duplication of the trial prosthesis, which must be done during the operation, i.e., as quickly as possible. It should also be noted that due to the obligation of duplicating the trial prosthesis, any increased possibility of adjustment that would advantageously make it possible to provide a better reproduction of the anatomy of the upper end of the humerus leads to complicating the step of duplicating this test prosthesis. Thus, it appears in particular that this duplication step is most difficult for the prostheses described in patents FR-2 727 002 and FR-2 727 857, which offer the best-performing range of adjustments.
The second disadvantage of these prostheses results from the fact that anatomical studies have made it possible to reveal the existence of a double eccentricity, called combined offset, between the proximal metaphysical axis of the humerus and the parallel axis that passes through the center of the humeral head. This combined offset has a medial component, called medial offset, that is relatively constant from one individual to another, and a posterior component, called posterior offset, that is relatively variable from one individual to another, between which there is no relationship. And none of the current prostheses as described in particular in the aforesaid French patents makes it possible to adjust the medial offset and the posterior offset independently, so that an exact reproduction of the upper end of the humerus cannot be achieved to this day. Furthermore, this impossibility of independent adjustment of the two offsets may lead the practitioner to artificially increase the humeral retro-torsion during implantation.
SUMMARY OF THE INVENTION
The purpose of this invention is to mitigate the disadvantages of the current shoulder prostheses and its primary objective is to provide a shoulder prosthesis offering multiple continuous adjustments of the position of the head relative to the prosthesis stem, in which said prosthesis stem can be sealed directly without using trial prostheses.
Another objective of the invention is to provide a shoulder prosthesis that permits continuous independent adjustments of the medial offset and the posterior offset.
To that end, the invention first involves a surgical device comprising:
a shoulder prosthesis stem with a humeral rod and a metaphysical section angled in relation to said humeral rod that has an upper frontal face inclined in relation to the humeral rod, in which a hemispherical cavity centering on an axis (&agr;) is provided, and a tapped bore opening into the bottom of the hemispherical cavity and centered on axis (&agr;),
a humeral plate comprising:
a hollow hemispherical ball joint with an axis of rotation D, featuring an external face made to fit the cavity of the prosthesis stem, and an internal face that defines a hemispherical bearing and has an axially drilled tapered bore,
a tapered swivel with an axis of rotation D′, eccentric by a distance d in relation to axis D, connected to the ball joint through a connecting section with a cross-section no larger than the maximum cross-section of the ball Joint, which tapered swivel and connecting section have a through hole drilled through them into the extension of the ball joint cavity,
a locking unit comprising the following, arranged axially:
a rod with a threaded lower section and a diameter matching that of the bore of the prosthesis stem and smaller than the minimum diameter of the tapered bore of the humeral plate ball joint,
a hemispherical ball joint made to fit the hemispherical portion of the humeral plate ball joint,
and a screw head for the locking unit.
the hemispherical cavities in the prosthesis stem, the external and internal faces of the humeral plate ball joint, and the locking unit ball joint being concentric around a point O when the locking unit is in locked position,
a head with a concave upper wall designed to fit the glenoid cavity of the shoulder and a lower wall with a tapered recess of a shape that matches the tapered swivel,
a so-called trial head comprising a lower wall of the same size as that of the lower wall of the cap with a tapered recess of a shape that matches that of the tapered swivel, and an upper wall with a hole drilled in it that opens into said recess.
(Note that ball joints and hemispherical bearings are understood to mean components of a general hemispherical shape defining an arc of circle equal to or slightly greater than 180°.)
According to the invention, the surgical device comprises first a shoulder prosthesis stem whose component elements, humeral stem, humeral plate, and unit for related locking of said humeral rod and humeral plate have hemispherical contact bearings and are designed and arranged so that the ball joints of the humeral plate and the locking unit can oscillate in all directions around a point
0
representing the center of the hemispherical cavity in the humeral rod. This surgical device also includes trial heads with a bottom wall of the same dimensions as those of the permanent caps and designed to make it possible to adjust the position of the humeral plate and to lock the locking unit, thereby locking the humeral plate in the desired position in relation to the humeral stem.
Such surgical device first has the advantage of making it possible to directly seal the final prosthesis stem and to make adjustments in the head position using specific trial heads once this seal is made. In effect, it is therefore not necessary to use trial stems that have to be duplicated,
Flurin Pierre
Leonard Alain
Mancene Gene
Priddy Michael B.
Young & Thompson
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