Surgery – Instruments – Orthopedic instrumentation
Patent
1991-04-29
1992-12-08
Hafer, Robert A.
Surgery
Instruments
Orthopedic instrumentation
606 79, A61B 1756
Patent
active
051694026
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a surgical instrument for use in preparing a bone cavity for the subsequent implantation of a joint replacement prosthesis.
The invention has been developed primarily, though not exclusively, in relation to a surgical instrument for enlarging and shaping the natural medulla of a femur for the subsequent implantation of the femoral component of a hip prosthesis.
Conventionally, this is done by using a broach or rasp which comprises a handle and a serrated shank joined to the handle, the serrated shank being shaped to correspond to the shape of the stem of the femoral component to be implanted.
The disadvantage of such a conventional rasp is that, for accuracy, the rasp must be moved in a straight line, preferably parallel to the shaft of the femur. However, such a direction of movement does not produce a proper cutting action on the bone surfaces which are far from parallel to the direction of movement of the rasp, particularly the medial cortex, but also anterior and lateral cortices, and sometimes the posterior cortex.
According to the invention there is provided a surgical instrument for use in the shaping of a bone cavity prior to the implantation of a joint replacement prosthesis, in which the instrument comprises a shank having serrations on at least a part of its outer surface and a handle mounted at one end of said shank, said shank being divided into a main body member and a slidable member which is engageable with said main body member in such a manner as to allow relative sliding motion between the slidable member and the main body member during use of the instrument, in order that the serrations can carry out the required shaping of the bone cavity.
A surgical instrument according to the invention is applicable generally to the shaping of a bone cavity in preparation for the subsequent implantation of a replacement joint prosthesis, but is particularly suitable for use in preparing i.e. enlarging the medullary cavity of a femur prior to implantation of a femoral component of a hip prosthesis.
Preferably, the sliding movement between the main body member and the slidable member of the shank is limited at each of its two extreme positions by a pair of stops located on the slidable member and engagable by a protrusion carried on the body member. Alternatively, the stops are provided on the body member and are engagable by a protrusion carried on the slidable member.
Conveniently, a single slidable member is provided, which is arranged relative to the main body member such that its outer, bone cutting surface prepares the medial surface of the cavity in the femur. However, additional slidable members may be provided, arranged appropriately to prepare the anterior, posterior and lateral surfaces of the cavity.
The sliding member is preferably located at the end of the shank closest to the handle, such that as the instrument is inserted into the femoral medulla the outer surface of the sliding member will engage the calcar and will be retained whilst the main body member is caused to penetrate deeper within the medulla, with the result that the sliding member slides along the main body member towards the handle.
By applying force to the exposed end of the sliding member, the latter can be forced into the femoral medulla, and these two actions are repeated alternately until the whole shank of the instrument has been fully inserted in the femoral medulla. This ensures that the medulla is enlarged to exactly the right size and shape to fit the stem of the femoral component, without cutting too much bone away in the process of preparing the femur. Preferably, the main body member and the sliding member each include guide means which cooperate to restrict said relative sliding movement to a single plane. However, the sliding movement may alternatively be along an arc. In either case, the choice of slide angle, either plane or arc, should be such that it avoids overcutting of the bone during operation. A good compromise is to restrict the sliding movement to a plane tangential to t
REFERENCES:
patent: 4466429 (1984-08-01), Loscher et al.
patent: 4777942 (1988-10-01), Frey et al.
Chas. F. Thackray Ltd.
Hafer Robert A.
Rooney Kevin G.
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