Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-06-30
2001-03-13
Isabella, David J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
Reexamination Certificate
active
06200349
ABSTRACT:
This invention relates to a prosthetic component for insertion in a bone cavity of a patient. In particular the invention is described in the form of a prosthetic hip stem for insertion in a femur, although the prosthetic component of the invention could be for a shoulder, knee or other application.
In the case of prosthetic hip stems, cementless prosthetic hip stems are known in which a prosthetic hip stem is inserted in a patient's femur without surrounding bone cement. The distal portion of the hip stem gives initial stability within the bone cavity. In the long term, bone growth holds the proximal portion of the hip stem in place. In order to suit different patients, five different sizes of proximal portions of the hip stem are usually available to the surgeon. In addition, four different sizes of distal portions of the hip stem are also available. This results in a range of 20 differently shaped and sized hip stems from which the surgeon can choose the correct size for a particular patient.
If the distal diameter of the hip stem can be modified during an operation, this removes the need for hip stems with different distal portions to be available to the surgeon. The number of hip stems could be reduced to five for the five different proximal portions.
A known form of hip stem with an expandable distal portion has a distal portion with at least two slots extending from the distal end of the hip stem. Mandrels are forced into the slots to bend the distal portion of the hip stem outwardly thereby expanding the diameter of the distal portion of the hip stem.
A disadvantage of distal slots of this nature is that they limit the length of the leg due to stress at the end of the slots where bending occurs. Up to 2.5 mm expansion to the diameter of the distal portion of the hip stem has been found to be possible. Hip stems of this type also have the disadvantage that each leg defined by the slots must be strong enough to take the force of the patient's weight to avoid breaking.
According to the present invention there is provided a prosthetic component for insertion in a patient's bone, the prosthetic component comprising a first portion and a second portion having an end, wherein the second portion is hollow with at least two longitudinal slots formed therein, and wherein the slots are closed at the end of the second portion of the component.
Preferably, the first and second portions are proximal and distal portions respectively wherein, in use, the distal portion has a distal end which is inserted further into the patient's bone.
The prosthetic hip stem may be a hip stem and the patient's bone is a femur. Preferably, the prosthetic hip stem is a cementless hip stem.
Preferably, there are provided at least four slots in the second portion of the component. The slots may be staggered such that alternate slots are displaced longitudinally in the component. Alternatively, the slots may be level in the longitudinal direction of the component.
Preferably, the slots are equally disposed circumferentially around the component.
The length of the slots in a component in the form of a hip stem may be in the range of 35 to 65 mm or larger. The slot width may be 0.5-2 mm or wider. Preferably, the distal portion of the hip stem can expand to a diameter of 21 mm and larger.
The slots may end in terminating holes. The holes may have a tear-drop shape.
Preferably, the end of the second portion of the component is closed. Preferably, the component is formed of titanium alloy or a similar material. Preferably, the second portion of the component is plastically deformable such that it holds its deformed position.
The prosthetic component may be a shoulder or knee component.
According to a second aspect of the present invention, there is provided a method of manufacture of a prosthetic component for insertion in a patient's bone comprising providing a component with a first portion and a second portion ending in an end; cutting slots in a second portion of the component; removing cut material from inside the second portion of the component.
Preferably, the first and second portions are proximal and distal portions respectively wherein, in use, the distal portion has a distal end which is inserted further into the patient's bone.
The prosthetic component may be a hip stem. Alternatively, the prosthetic component may be for use in a shoulder or knee application.
Preferably, the method includes the step of applying pressure externally to the distal end of the component to compress the distal portion of the component.
Preferably, the slots are machined through a side of the distal portion of the component. Preferably, at least two slots are formed in the distal portion of the component. Most preferably, at least four slots are formed.
REFERENCES:
patent: 3902775 (1990-08-01), None
patent: 0243298 (1987-10-01), None
patent: 2549717 (1985-02-01), None
Isabella David J.
Johnson & Johnson Professional Inc.
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