DE2627569A1 - Prosthesis for head of femur - has ridge at shoulder and groove reaching to lower end - Google Patents

Abstract

The prosthesis which has a slender neck, on which the ball of the joint is fixed, a broader middle section, and a tapering shaft: the middle section is curved and carries blades extending sideways, which support the prosthesis in position. A triangular ridge is to be added on the outside of the curve, and a groove made along the inside of the shaft at the lower end: the middle line of the profile is, below the medial curve, to be quite straight. The new ridge is pref. highest at the top end, and its height reduces continuously to zero at the lower end of the curve.

Description

Thigh part of a hip joint prosthesis

The invention relates to a thigh part made from an Mta alloy a hip joint endoprosthesis for cementing into the medullary canal of the bone, with a slender neck supporting the joint ball, a wider central part and a tapering shaft towards the free end, which in its upper end extends over about a third of its length extending, curved section on the convex The outer surface is provided with at least one protruding support edge.

In the case of a thigh part known from DT-OS 2 537 807 is such a support edge on one side of the thigh part or on both attached and used to transfer pressure to the cement to prevent the stem sinks deeper and deeper into the medullary canal under load when the bone dissolves in places where the stress is too high. Turns however, the stem in the surrounding cement with simultaneous load, so this can in spite of the support edge to the destruction of the cement socket and to penetration lead into the medullary canal. The invention is based on the object of rotating movements of the shaft to prevent destruction of the cement socket and penetration of the stem into the medullary canal.

In the case of a thigh part, this task becomes the one mentioned at the beginning Type solved according to the invention in that the bearing edge bears a ridge on the outside, whose cross-section is approximately triangular and its height is such that the The ridge line penetrates the trochonal bone that the lower portion of the shaft has on the inner surface a longitudinal groove and that a center line which from the outer surface of the shaft is the same distance as from the inner surface, in the section adjoining the curved section (intermediate area and lower section) runs in a straight line.

The ridge according to the invention penetrates the bone in the area of the large one A rolling mound where enough bone mass is available so that the sharp one Burr cannot compromise the strength of the bone. On the other hand, it doesn't matter if the ridge the cement coating ("cement quiver") of the shaft in the convex area penetrates, as the tensile-loaded cement has no strength there anyway, which could be impaired, and since the cement is not load-bearing in this area Function.

In the same way is in the area of the lower section of the shaft the cement on the inside of the stem relieves pressure. There is inventive A longitudinal groove is provided in the shaft, which is advantageously about a third of the Shaft extends and prevents the lower portion of the shaft in Cement quiver turns. Although this longitudinal groove disturbs the smooth surface of the shaft, similar to the ridge, but any cracks or breaks in the cement, which form on these irregularities do not result in any destruction of the cement socket lead in this area, since the cement is not contaminated there.

Finally, to ensure that the shaft is pointing downward, i. H.

in the direction of its free end, no tensile forces on the cement, but only exerts pressure forces, according to the invention, the center line of the Straight in the middle and lower area. This means that the stem does not have an underhand hook at the free end, as is the case, for example, in the US-PS 3,064,645 shows; For this reason alone, the subject of this US Pat. No. 3,064 would be 645 unsuitable for cementing into the medullary canal of a bone.

The available bone mass in the area of the large rolling mound decreases towards the bottom. For this reason, the height of the ridge advantageously increases downwards (i.e. towards the free end) as continuously as the width of the support edge to end at the lower end of the curved section.

For a firm, non-rotating anchoring of the shaft in the cement sleeve it is advantageous if this cement quiver has as wide an inner surface as possible and the outer surface rests on the cement without any splitting effect on the bearing cement surface exercise.

The outer surface and the inner surface are advantageous for this purpose slightly convex, the thickness of the shaft along its entire length (from the upper Section towards the free end) decreases only slightly, around 20%. In contrast the inner surface of the shaft of the subject of DT-OS 2 537 807 is very narrow and the curvature so strong that - as in Fig. 6 of DT-OS 2 537 807 by arrows indicated - a wedge effect is achieved.

A particularly good, non-rotatable anchoring of the shaft in the cement sleeve is achieved when the cross section of the shaft is advantageous over its entire length Length drawn in on the side surfaces and - apart from the ridge and the longitudinal groove - is approximately rectangular with rounded corners, over the entire length of the shaft the ratio of thickness to depth increases from about 0.5 to about 1.7 to the extent of the decrease the internal cross-section of the medullary canal.

A good central position of the thigh part in the medullary canal and the possibility optional use on a right or left thigh will be advantageous achieved in that the thigh part is symmetrical to the plane which is spanned by its center line.

An advantageous embodiment of the invention is schematic shown in the drawings. 1, 2 and 3 show different views of a thigh part of a hip joint endoprosthesis, FIG. 4 is a view of the object 1 in the direction of arrow IV and FIGS. 5 to 11 different sections in the levels V to XI of FIG. 1.

Fig. 1 shows a thigh part of a hip joint endoprosthesis in Side view, Fig. 2 shows the same thigh part from the right (view of the inner surface 28) and FIG. 3 from the left (view of the outer surface 10).

According to FIGS. 1 to 3, the thigh part has a slender one Neck 2 on which a joint ball attached or formed in one piece can. This slender neck 2 is followed by a wider middle part 4, which has a support edge 5 (collar). The shaft begins below the support edge 6, initially the upper one, which extends over a third of the length of the shaft, curved section 8. This carries on its convex outer surface 10 a right and left, protruding support edge 12. This transfers the pressure loads on the cement quiver, which the space between the shaft 6 and the wall of the Fills the medullary canal of the bone.

On the outside, the support edge 12 has an approximately triangular cross-section Ridge 14, the height h of which is shown in Fig. 4, which shows the view of the thigh part 1 shows in the direction of arrow IV. This ridge is so high that its sharp ridge line 16 cuts into the hillock 18 of the trochontic bone and causes the thigh part to be secured against rotation relative to the bone.

This ridge 14 runs towards the end 20 of the curved section 8 just like the support edge 12. This can be seen more precisely from Figs. 4, 5 and 6, which represent the view IV and the sections V and VI and show how in the area of the curved portion 8 continuously the width b of the support edge 12 and decrease the height h of the ridge 14; in the further FIGS. 7 to 11, which show the sections VII to XI in Fig. 1, the ridge and the support flange are no longer available.

In Fig. 1, the center line 22 is drawn, which of the Outer surface 10 (on the left in Fig. 1) has the same distance as from the inner surface 28 (on the right in Fig. 1). This center line is in the area of the upper section 8 curved, but in the adjoining intermediate region 34 and in the lower section 30 straight to enable the thigh part to be pulled out of the cement holder.

In the lower section 30, extending over about a third of the length of the Shank 6 extending, the inner surface 28 carries a longitudinal groove 32, the width of which slightly expanded towards the free end 31 to allow the manhole to be inserted into the cement to facilitate.

The sectional figures 5 to 11 can be seen that the cross section of the The shaft is drawn in over its entire length on the side surfaces 24 and 26 and is roughly rectangular with rounded corners.

This cross-sectional shape has been used to prevent rotation of the shaft especially proven with the cement quiver. The broad, only slightly convex surfaces 10 (outer surface) and 28 (inner surface) of the shaft provide a secure contact surface between the stem and the cement, which ensures good pressure transmission and an overload of what experience has shown to become brittle over time Cement is avoided. Due to the gentle power transmission to the cement, it remains this is intact and penetration of the shaft into the medullary canal is prevented.

Claims (8)

Claims thigh part of a hip joint endoprosthesis for cementing in into the medullary canal of the bone, with a slender neck supporting the joint ball, a wider middle part and a shaft tapering towards the free end, which in its upper, extending over about a third of its length, curved section on the convex outer surface with at least one protruding Support edge is provided, characterized in that the support edge (12) is on the outside carries a ridge (14) whose cross-section is approximately triangular and whose height (h) is dimensioned such that the ridge line (16) penetrates into the trochonal bone (18), that the lower portion (30) of the shaft (6) on the inner surface (28) has a longitudinal groove (32) and that a center line (20) extending from the outer surface (10) of the Shank (6) has the same distance as from the inner surface (28) in which the section adjoining the curved section (8) (intermediate area 34 and lower section 30) runs in a straight line. 2. thigh part according to claim 1, characterized in that the height (h) of the ridge (14) decreases downwards just as continuously as the Width (b) of the support edge (12) to at the lower end (20) of the curved section (8) to expire. 3. thigh part according to claim 1 or 2, characterized in that that the length of the longitudinal groove (32) is equal to about one third of the length of the shaft (6) is. 4. thigh part according to claim 1 or the following, characterized in that that the outer surface (10) and the inner surface (28) are slightly convex and the thickness (d) the shaft decreases only slightly towards the free end (31). 5. thigh part according to claim 4, characterized in that the decrease in the thickness (d) of the shaft (6) over its entire length about 20 % amounts to. 6. thigh part according to claim 5, characterized in that the Cross section of the shaft (6) over its entire length on the side surfaces (24, 26) is drawn in and - apart from the ridge (14) and the longitudinal groove (32) - roughly rectangular with rounded corners, from the upper section (8) to the free end (31) the ratio (d / t) of the thickness (d) to the depth (t) increases from about 0.5 to about 1.7. 7. thigh part according to claim 3 and 6, characterized in that that the ratio (d / t) in the area of the longitudinal groove (32) increases approximately from 0.7 to 1.7 (Fig. 9-11) and in the intermediate area (34) is about 0.5 (Figs. 7 and 8). 8. thigh part according to claim 1 or the following, characterized in that that it is symmetrical to the plane which is spanned by its center line (22) is.