Prosthetic Bone Joint Having A Spacer Device

Abstract

The intramedullary or equivalent stem of a prosthetic bone joint device is uniformly spaced within a bone canal during implantation using gap-filling cement. This achieved by using a spacer device having an annular base with at least three spring members extending from spaced points around the base, the spring members extending in a direction having radially outward and common axial components relative to the base. The base is formed to engage around and partway along the stem with its spring members facing forward. When the stem/spacer combination is implanted the springs act to centralise the position of the stem.

Description

This invention concerns prosthetic devices of the kind including a tapered stem which is to be secured by use of a gap-filling acrylic cement or similar medium in a medullary canal or a pre-prepared bore in a bone.

The tapering of the stem of such a device is advantageous in promoting extrusion of the cement into which it is pushed, so that the cement is forced into the adjacent bone and fills the space between the stem and bone to provide a secure bond. However, it is possible for the stem to be significantly off-set in the longitudinal sense relative to the canal or bore, and so give rise to potential weakness in the eventual bond because of the longitudinal region of thin cement which can result from the off-setting. The point to be appreciated in this last connection is that it is normally desirable that the stem be surrounded by a layer of cement having a certain minimum thickness. Certainly the stem should not contact the wall of the bone to any significant extent and, ideally, the stem should be centrally located within its canal or bore.

In this context the present invention provides a spacer device for use with a prosthetic device of the kind in question, which spacer device comprises a generally annular base member having at least three spring members extending from mutually spaced positions around the base member, the spring members extending in directions having an outward radial component and a common axial component relative to the base member.

In use of such a spacer device, the base member is threaded over the tip of the stem of the associated prosthetic device and passed partway therealong with the spring members directed away from the tip of the stem. This relative disposition of a spacer device and prosthetic femoral head device is shown in the accompanying drawing with the former device denoted at 10 and having base and spring members 11 and 12, respectively, and the latter device denoted at 13 and having a stem 14. The base member is of generally rectangular form, as is the cross-sectional form of the stem, and four spring members extend from central positions of the respective sides of the base member. Clearly, the spring members will engage the wall of the medullary canal when the stem is inserted therein and act to maintain the stem generally centrally disposed in the canal.

Naturally, the base member of the spacer device needs to be dimensioned and shaped to accommodate the stem of an associated prosthetic device and to be slidable only partway therealong.

Claims

We claim:

1. A prosthetic bone joint device comprising: a component having a tapered intramedullary stem extending therefrom; and a spacer device including an annular base member engaged around and partway along said stem, and at least three spring members extending from mutually spaced positions around said base member away from the free end of said stem in directions having an outward radial component and a common axial component relative to said base member.

2. A prosthetic bone joint device according to claim 1 wherein said stem has a generally rectangular cross-sectional form, and wherein said base member is of similar rectangular form and has four like spring members individually extending from respectively different sides thereof.