CZ305756B6 - Centering element for hip pin - Google Patents

Abstract

In the present invention, there is disclosed a centering element for hip pins intended for cemented pins comprising a ring (1) with an opening (4) compatible with a hip pin (9) neck-down (11), and provided on its outer circumference with three ribs (2) in the form of a trapezoid, the longer base (6) on the ring (1) circumference of which is longer than the ring (1) height and overlaps the ring (1) on the side of the trapezoid shorter arm (8). The overlapping section of the rib (2) forms a fixing element (7), which fits into a groove (10) of the hip pin (9) for attaching the centering element, whereby the beveled shorter edge (3) directs towards the bevel (5) of the ring (1). After insertion thereof in the neck-down (11), it is possible to insert the hip pin (9) along with the centering element through cement into a cavity of the thighbone.

Description

(57) Annotation:

The centering element for the hip stems intended for cemented stems is formed by a ring (1) with an opening (4) compatible with the recess (11) of the hip stem (9) and provided on the outer circumference with three trapezoidal ribs (2) whose longer base ( 6) on the circumference of the ring (1) is longer than the height of the ring (1), and extends beyond the ring (1) on the side of the shorter arm (8) of the trapezoid.

The protruding part of the rib (2) forms a fixing element (7) which fits into the groove (10) of the hip shaft (9) for fixing the centering element, the bevelled shorter edge (3) facing the chamfer (5) of the ring (1). After its insertion into the recess (11), the hip shaft (9) and the centering element can be inserted together into the femur cavity via cement.

Centering element for hip stems

Field of technology

The invention relates to a centering element for the hip stems, which precisely centers the stem of the endoprosthesis in its distal part when it is positioned in the stump of the femur.

Prior art

As people's lifestyles change and their life expectancy increases, the number of artificial joint replacements, especially of the hips and knees, is constantly increasing. The number of hip replacements in the Czech Republic alone is approximately 6,000 to 7,000 operated endoprostheses per year. Operations are performed by standard procedures:

- the upper part of the femur (head and neck) is removed

- a hole is drilled in the axis of the femur stump to the specified depth

- in the proximal part of the femur stump, the opening widens according to the shape of the hip shaft

- cement is applied to the bone cavity

- the hip shaft is implanted.

During the actual implantation and positioning of the hip shaft into the femoral cavity, it is advantageous if the shaft is regularly surrounded by the same layer of cement around the entire circumference.

In the distal part of the hip shaft, this can be achieved by so-called centralizers. Currently used, they are inserted by a pin into a hole in the lower part of the hip shaft. They have several disadvantages. When implanting and moving the hip shaft out of the bone cavity, they may fall out. When not implanted, the centralizer is difficult to remove, for example by drilling and the like.

A) Patent according to WO 99/48443 A

The solution disclosed in WO 99/48443 A is a centralizer in the form of a hollow body with a rectangular or oval cross-section, with ribs projecting from the outer surface. In the example, 4 ribs are shown in particular. This document does not address protection against rotation or axial displacement of the implant.

B) Patent according to document US 2005/0 060 043

Another solution disclosed in US 2005/0 060 043 describes the medial / distal tip of an artificial joint for an uncemented insertion method. The tip is made of absorbable material. The patent claims are only for the uncemented shaft. The document does not address protection against rotation or axial displacement of the implant.

In the uncemented method of anchoring the stem, a smaller cavity is made in the stump of the proximal part of the femur than the hip stem. The implant is inserted with a smaller overlap, of the order of tenths of a millimeter, with a so-called press fit.

In the cemented method, on the other hand, a larger cavity is produced in the femur, of the order of 1.5 to 4 mm on each side, which is filled with so-called cement. The cement should fill the cavity evenly between the bone and the stem, with the stem in the middle. The centering element is used for this.

The purpose of the centralizer for the uncemented method is to eliminate unevenness (the size of the unevenness can be up to a tenth of a millimeter) in a narrower cavity, because even at the point of unevenness the bone mass should be adjacent to the surface. The material of the centralizer is absorbable. This document does not address protection against rotation or axial displacement of the implant.

- 1 CZ 305756 B6

C) Centralizer from the Zimmer brochure

Also known is the Centralizer from the Zimmer brochure. The product attaches to the tapered end of the hip shaft, creating a tip of the hip shaft that is adapted to be inserted into a cavity in the femur (see above). Even in this case, protection against rotation or axial displacement of the implant is not addressed.

In contrast to the above-mentioned inventions, the centering element according to the invention provides protection against rotation or axial displacement of the implant.

The essence of the invention

The above-mentioned disadvantages are eliminated by the centering element for the hip stems according to the invention, the essence of which consists in that it is formed by a ring provided on the outer circumference with at least three ribs. They are in the shape of a trapezoid, the other base of which is on the circumference of the ring and the bevelled longer edge leads to the collapse of the ring, which is located in its lower part. The inner diameter (hole) rings compatible with the cylindrical part of the transverse groove - the groove of the hip shaft.

In a preferred embodiment, the base of the trapezoidal rib is longer than the height of the ring. Thus, the ring extends beyond the shorter edge of the trapezoid. A transverse groove is formed on the distal lead-in portion of the hip shaft to position the inner hole of the centering member ring and prevent it from sliding relative to the hip shaft, and there may be one or more longitudinal grooves to prevent rotational movement of the centering member relative to the hip shaft. In this embodiment, the centering element simultaneously firmly fixes the hip shaft in its distal part (rotationally and slidably) and at the same time, after the insertion of the shaft with the centering element, centers its distal part in the interior of the femur space.

The centering element is made of an implantable material, such as Chirulene. The main advantage of the centering element is its simplicity of universal construction. The centering element firmly fixes the hip shaft both axially and possibly also against rotation and thus increases the overall stability of its bearing. Furthermore, it is easily attached to the hip shaft or is simply removed from the hip shaft. In the event of reoperation, the centering element does not prevent the removal of the hip shaft from the cemented package. After removing the shaft with a drill or cutter, the centering element is easily removed.

Explanation of drawings

The invention is further elucidated by means of the drawings, in which Fig. 1 is a simple variant of a centering element, Fig. 2 is a centering element with higher ribs and Fig. 3 is a centering element mounted on the hip shaft before implantation.

Examples of embodiments of the invention

Example 1

The centering element shown in Fig. 1 is made of an implantable material, for example Chirulen according to ISO 5834-2 and is formed by a ring L. It is provided around the circumference with at least three ribs 2 having a chamfered shorter edge 3 for easy insertion of the shaft into the cement. In the lower part, the ring 1 is provided with a chamfer 5, so that after its attachment to the hip shaft 9 a smooth transition is formed between the shaft 9 and the centering element. The ring 1 is provided with an opening 4 through which it fits in the recess H of the hip shaft 9. After its insertion into this recess, it is possible to insert the hip shaft with the centering element together into the femoral cavity via cement.

The centering element is inserted into the recess 11 in the cylindrical (distal) insertion part of the hip shaft 9. When the shaft moves during implantation towards the femur cavity or outwards, or by rotation, the centering element remains in the recess 11 of the hip shaft 9.

-2EN 305756 B6

During reimplantation, the shaft 9 is removed either together with the centering element and the cement, or the shaft 9 is removed separately without the centering element. In this case, an opening is then made in the cement with a drill, thereby removing the centering element together with the cement.

Example 2

The centering element according to the invention, shown in Fig. 2, is formed by a ring 1 with three ribs 2 as in Example 1, with the difference that the trapezoidal ribs 2 have a longer base 6 longer than the height of the ring 1 and thus extend beyond the ring 1. on the side of the shorter arm 8 of the rib 2. The elongated parts of the ribs 2 on the side adjacent to the body of the shank 9 form shaped fixing elements 7 which have a wedge shape and fit into longitudinal grooves 10 on the cylindrical part of the shank 9.

At the same time, the centering element firmly fixes the hip shaft 9 in its distal insertion part both axially and against rotation and thus increases the stability of the bearing of the hip shaft 9 in the femoral cavity after cementation.

After making the cavity into the proximal part of the femur and deciding that the surgeon will use the centering element, the centering element is first placed on the distal part of the hip shaft 9. After introducing the cement into the femoral cavity, the shaft 9 with the centering element is inserted into the femur . In the event of a reoperation, the centering element does not prevent the removal of the hip shaft 9 from the cemented package. After removing the shaft 9 with a drill or cutter, the centering element is easily removed.

The centering element with a fixed fixation in the distal part of the stem 9 according to Fig. 2 is extended compared to the basic embodiment by a modification of the ribs 2. It is an extension of the rib 2 by a shaped fixing element 7 which fits into a longitudinal groove 10 on the hip stem 9. and the setting of the cement then the centering element prevents the rotation and axial displacement of the entire implant in the bone and thus increases the stability of the implant. At the same time, it prolongs the life of the implant against loosening and subsequent rotation.

Industrial applicability

The centering element according to the invention is used in particular in orthopedic wards, traumatology wards, or in surgical wards for total or partial hip replacements. It is used for cemented shaft.

Claims (2)

Hip stem centering element for cemented stems, formed by a ring (1) with an opening (4) compatible with the recess (11) of the hip stem (9) and provided on the outer circumference with at least three ribs (2), characterized in that the ribs (2) are in the shape of a trapezoid, the further base (6) of which on the circumference of the ring (1) is longer than the height of the ring (1) and extends beyond the ring (1) on the shorter arm (8) of the trapezoid. 2) forms a fixing element (7) which fits into the longitudinal groove (10) of the hip shaft (9) for fixing the centering element, the chamfered shorter edge (3) facing the chamfer (5) of the ring (1). Centering element according to claim 1, characterized in that it is made of an implantable material.