Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1995-03-20
1997-12-30
Isabella, David
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 18, A61F 230
Patent
active
057024790
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a shank unit for an endo-prosthesis to be implanted into a tubular bone and including a hollow-cylindrical anchoring sub-assembly with a longitudinal axis and an articulating sub-assembly.
BACKGROUND OF THE INVENTION
A large number of shank units especially for hip-joint protheses are already available, however, they all incur the drawback that the anchoring sub-assembly to be implanted into the bone marrow canal is rigidly joined to its neck part projecting from it and ultimately receiving the joint-ball. Accordingly, once the shank unit has been implanted, it is impossible to adjust the position of the neck relative to the now stationary anchoring sub-assembly. As a result the anterior torsion or the neck-shank angle (centrum collum diaphysary angle CCD) cannot not be adjusted subsequently.
The state of the art suffers from another drawback in that a substantial number of shank units must be kept on hand to meet the main requirements and anatomical particulars (shank diameter, shank length, neck-shank angle, neck length) of a particular patient.
SUMMARY OF THE INVENTION
The object of the invention is to create an easily implanted shank unit allowing changing the neck geometry (anterior torsion, neck-stub angle, neck length, trochanter replacement) during the operation and even after it without the need to remove or fit the already implanted anchoring sub-assembly of the shank unit.
Essentially, the advantages of the invention are the optimal matching of the shank unit to the anatomic particulars and the modular bearing being as compact as possible.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention and further developments are elucidated below by means of an illustrative embodiment of a shank unit for the hip joint. However the invention also applies to shank units of other endoprostheses, illustratively for the shoulder and the fingers.
FIG. 1 is an exploded perspective of the shank unit of the invention, and
FIG. 2 is a longitudinal section of a shank unit of FIG. 1 implanted in the femur.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The hip joint prosthesis shank unit shown in FIGS. 1 and 2 substantially comprises a hollow cylindrical and rotationally symmetrical anchoring sub-assembly 2 with a longitudinal axis 1 and of separate articulating sub-assembly 3 detachably affixed to anchoring sub-assembly 2.
At its upper end 25 facing the articulating sub-assembly 3, the anchoring sub-assembly 2 comprises a serrated disk surface 24 mounted perpendicularly to the longitudinal axis 1 and a central borehole 22 with an inner thread 23 of constant diameter. At the other end 26 to be inserted into the bone marrow cavity 61 of the femur 6, the anchoring sub-assembly 2 constricts in the form of telescoping, coaxial, hollow cylinder segments, and as a result allows optimal matching to the anatomy of the bone marrow cavity 61. Furthermore, the anchoring sub-assembly 2 comprises a structured outer surface in the form of a thread 21 and perforations 27 enhancing the growth penetration of bone material. Instead of the perforations and the thread, or in addition to them, the surface also may be fitted with longitudinal channels parallel to the longitudinal axis 1, or with a coating or surface etching. Such structures serve to improve bone bonding.
Thread 21 is made self-tapping for the bone and thereby the use of a separate tap, as required with conventional protheses, is eliminated.
Essentially, articulating sub-assembly 3 has a rotationally symmetrical, annular base element 31 with an axis of rotation 32 and with a preferably conical neck extension 33 mounted eccentrically on base element 31 and subtending an angle .alpha. of 70.degree. to the axis of rotation 32 to receive a joint ball 36. The joint ball also may be rigidly joined to the neck extension 33.
At its lower end facing anchoring sub-assembly 2, articulating sub-assembly 3 comprises a serrated disk surface 34, perpendicular to its longitudinal axis 32, of which the teeth have the same angular spacing apar
REFERENCES:
patent: 4051559 (1977-10-01), Pifferi
patent: 4384373 (1983-05-01), Sivash
patent: 4908032 (1990-03-01), Keller
patent: 5002578 (1991-03-01), Luman
patent: 5002581 (1991-03-01), Paxson et al.
Farley Walter C.
Isabella David
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