Calibrated Joint Head Prosthesis And Insertion Instrument Assembly

Abstract

The instrument has a straight line shaft which is provided with a calibrated cylindrical hook at one end and a pistol grip at the opposite end. The hook is sized to engage in an eye on a shaft of a prosthesis with a snug fit and is set perpendicularly to the instrument shaft. A hammering element is also slidably mounted on the instrument shaft to impact against an anvil on the hook.

Description

This invention relates to an instrument for use with prostheses. More particularly, this invention relates to an instrument for insertion or removal of a joint head prostheses shaft in or from a femur.

Heretofore, instruments have been known for inserting and for removing joint head prostheses in and from a femur. Usually, these instruments have been constructed with a relatively long rod, which is bent at its end into a pointed hook, and which carries at its other end a knoblike handle. These known instruments moreover have a hammering element which can slide longitudinally on the rod while surrounding it concentrically, and which serves for hammering the joint head prosthesis out of the femur.

While in use to remove a joint head prosthesis, the hook of these instruments have been engaged in an eye on the shaft of the joint head prosthesis. After repeated blows of the hammering element against a suitable counter surface of the knob, the prosthesis is first loosened and is finally, by means of the knob, pulled out of the bone. These known instruments, however, have not been suitable for the introduction of the prosthesis into the bone and for its alignment, because the relatively loose connection between the hook and the eye do not permit turning of the instrument without play on the shaft of the prosthesis.

Accordingly, it is an object of the invention to provide an instrument for accurately placing a prosthesis in a bone.

It is another object of the invention to provide an instrument which is capable of accurately aligning a joint head prosthesis in a bone and of removing the prosthesis.

Briefly, the invention provides an instrument which has an elongated rod, a pistol grip handle at one end of the rod for manipulating the instrument, a hook at the opposite end of the rod for engaging in a cooperating eye of a joint head prosthesis, and a hammering element slidably mounted on the rod between the hook and handle.

The pistol grip handle allows handling of the instrument so as to introduce and align the engaged prosthesis in a bone.

The hook is cylindrical in shape and is calibrated to engage with a snug fit in the likewise calibrated eye of the prosthesis. In addition, the axis of the hook is set perpendicularly to the axis of the rod as well as perpendicularly to the plane of the handle so that the middle plane of the handle forms a reference or sighting plane.

Because the hook is made as a calibrated cylinder which fits into a similarly calibrated eye in the prosthesis, there is obtained on the one hand, a rigid connection between the instrument and the prosthesis for turning about the longitudinal axis of the instrument, while, on the other hand, the instrument can be rotated freely relatively to the prosthesis about the axis of the hook. Thus, it is possible to transmit without play turning movements of the instrument about its longitudinal axis to the prosthesis introduced into the bone, for the purpose of turning the prosthesis in the bone into its correct angular position. The instrument can, however, be moved freely by the handle in the plane defined by and containing its longitudinal axis, for the purpose of bringing the instrument into the most favorable position for the operator relatively to the patient, without a movement in the plane producing an alteration of the position of the prosthesis in the bone.

The reference plane which is formed by the handle can be brought into a definite angular position relatively to a suitable reference line during the introduction and alignment of the prosthesis. For example, the axis of the knee joint of the patient can be used as the reference line so that the prosthesis can be put into its correct position in the bone.

The hook element is further provided with an anvil surface for the hammering element should a supplementary hammering of the prosthesis into the bone be needed. The fabrication of the instrument becomes particularly simple when the hammering element is an investment casting.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a view of the instrument according to the invention;

FIG. 2 illustrates to a larger scale the engagement of the hook into the eye of a prosthesis; and

FIG. 3a to 3c schematically illustrate the introduction and correct positioning of the prosthesis in a femur by the aid of the instrument of the invention.

Referring to FIG. 1, the instrument has an elongated rod 1, some 30 to 50 cm. long, which carries at its front end a hook element 2. This hook element 2 consists of a fundamental cylindrical element 3, having an anvil surface 4 to the rear for a hammering element 5 that slides on the rod 1. The hook element 2 also consists of a conical intermediate piece 6 which eccentrically adjoins the cylindrical element 3 and a hook 7. The entire hook element 2 can be made in one piece with the rod 1, or can be made separately to be fastened at a later time on the rod 1, for example, by threading and by pinning, so as to be secured against turning accidentally on the rod 1. The peripheral surface of the hook 7 is made cylindrical and is calibrated.

The instrument further has a pistol griplike handle 12 attached to the other end of the rod 1 which has a stop 10 for the hammering element 5. The middle plane (plane of the drawing in FIG. 1) of the handle 12 forms a sighting or reference plane, to which the cylinder axis of the hook 7 stands perpendicularly, as shown in FIG. 1. The handle 12 is also secured (not shown) against turning relative to the rod 1, so that the cylinder axis of the hook 7 always remains positioned perpendicularly relative to the reference plane of the handle 12.

Referring to FIG. 2, the hook 7 engages with a snug fit in an eye 11 of a prosthesis shaft 9. For this purpose the inner bore in the eye 11 is likewise made cylindrical and is calibrated. The shaft 9 of the prosthesis, which is slightly curved as is known, has a tonguelike projection 13 for the eye 11 which is situated on the outer curve line of the shaft 9.

The instrument can be made of a material known to be suitable for the fabrication of surgical instruments, for example, of rust-free steel or of an alloy that withstands corrosion. Additionally, the handle can be made of a synthetic substance as is known. Also, the hook element 2 and the shaft 9 of the joint head prosthesis may be investment castings.

Referring to FIGS. 3a, in order to place the prosthesis shaft 9 into a cut 15 made in a femur 16, the handle 12 of the instrument is aligned in a plane K" parallel to the axis K of the knee joint and parallel to the axis K' through the cut 15. As is well known, with most people, the femur neck is turned forward relatively to the knee axis. The femur neck axis H hereby does not intersect the knee axis K, but forms a spatial angle with it, the so-called antetorsion angle AT, which as shown is plotted as the angle between the femur neck axis H and the axes K' and K" corresponding to the knee axis. Its magnitude differs from person to person, and varies within a certain range. It can be determined, prior to the operation, by X-ray photographs.

Referring to FIG. 3b, once the femur neck 17 has been removed, the marrow hole in the femur 16 is cleaned out in order to receive the prosthesis shaft 9 and is filled with a cement mass. The prosthesis shaft 9 is then introduced into the marrow hole by the aid of the instrument. The handle 12, which serves as a reference plane, is situated parallel to the axis K". Through the association of the axis of the hook 7, relative to the middle plane of the handle 12, and the rigid connection between the instrument and the prosthesis shaft 9 for turning about the longitudinal axis of the instrument, the axis of the joint head (not shown) received on the pin 8 of the prosthesis, and corresponding with the femur neck axis H (which must therefore coincide with the axis H in the final position), corresponds in the first place to axis K'. Thereafter, during the insertion of the prosthesis, the handle 12 is turned through the angle AT in the direction of the arrow (FIG. 3c), and this turning is transmitted without play to the prosthesis shaft 9, so that the axis of the pin 8 is brought into the correct position. By the aid of the hammering element 5, which is hammered a number of times against the anvil surface 4 (not shown) of the hook element 2, the prosthesis shaft 9 is driven into the femur 16 while retaining the angle AT between the axis K" and the plane of the handle 12.

It is again noted that because of the cylindrical form of the hook 7 and the correspondingly formed eye 11 in the prosthesis shaft 9, the instrument is free to turn about the axis of the hook 7, so as to be turned about that axis without changing the position of the axis of the pin 8, or the position of the reference plane provided by the handle 12, relative to the axes K' and K".

The invention thus provides an instrument which makes possible a precise introduction and alignment of a prosthesis shaft with a correct adjustment to the antetorsion angle AT. The instrument moreover facilitates, by its free mobility about the axis of the hook, the work of the operator.

Claims

1. An assembly comprising a joint head prosthesis having a shaft, a projection extending from said shaft and a calibrated cylindrical eye within said projection; and an implanting instrument connected to said eye, said instrument for implanting said prosthesis in a bone comprising an elongated rod having a longitudinal axis, a handle mounted on said rod at one end thereof, said handle being disposed in a plane containing said axis of said rod and extending perpendicularly from said rod, and a hook mounted on the opposite end of said rod, said hook having an axis perpendicular to said plane of said handle and said axis of said rod and being of cylindrical shape calibrated to fit with a snug fit into said calibrated cylindrical eye in said prosthesis to form a rigid connection between said prosthesis and said instrument for turning about said longitudinal axis of said instrument while simultaneously allowing free rotation of said instrument relative to said prosthesis about said axis of said hook.

2. An assembly as set forth in claim 1 wherein said hook is integrally formed on a one piece hook element further having an anvil surface at the rear thereof, and which further comprises a hammering element slidably mounted on said rod for hammering against said anvil surface.