AU2021104083A4

AU2021104083A4 - A femoral stem for hip implant prosthesis having a particular medial to lateral width ratio

Info

Publication number: AU2021104083A4
Application number: AU2021104083A
Authority: AU
Inventors: Declan Brazil; Christopher Burgess
Original assignee: Signature Orthopaedics Europe Ltd
Current assignee: Signature Orthopaedics Europe Ltd
Priority date: 2021-04-02
Filing date: 2021-07-13
Publication date: 2021-08-26
Anticipated expiration: 2029-07-13

Abstract

A femoral stem having a stem portion has a superior portion cross section normal to a longitudinal curve of the stem. The superior portion cross section has a medial:lateral width ratio across more than 80% of a mediolateral length thereof of less than 0.7, preferably less than 0.6. As such, the superior portion of the current stem has a quite pronounced wedge shape which was found by cadaver, patient and computer modelling studies to provide a better fit within the femoral canal. 7 Cr) soo 00

Description

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A femoral stem for hip implant prosthesis having a particular medial

to lateral width ratio

Field of the Invention

[0001] This invention relates generally to a femoral stem for hip implant prosthesis and, more particularly, to a femoral stem having a particular medial to lateral width ratio.

Background of the Invention

[0002] Hip implant prosthesis comprises a femoral stem having a stem portion which fits within the canal of a resected femur and which has a neck protruding therefrom which supports a liner bearing which articulates within an acetabular cup.

[0003] The present invention seeks to provide a way to better fit the stem portion within the femoral canal, which will overcome or substantially ameliorate at least some of the deficiencies of the prior art, or to at least provide an alternative.

[0004] It is to be understood that, if any prior art information is referred to herein, such reference does not constitute an admission that the information forms part of the common general knowledge in the art, in Australia or any other country.

Summary of the Disclosure

[0005] There is provided herein a femoral stem having a stem portion having a superior portion cross section normal to a longitudinal curve of the stem. The superior portion cross section has a medial:lateral width ratio across more than 80% of a mediolateral length thereof of less than 0.7, preferably less than 0.6.

[0006] As such, the superior portion of the current stem has a quite pronounced wedge shape which was found by cadaver, patient and computer modelling studies to provide a better fit within the femoral canal.

[0007] Other aspects of the invention are also disclosed.

Brief Description of the Drawings

[0008] Notwithstanding any other forms which may fall within the scope of the present invention, preferred embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:

[0009] Figure 1 shows a side elevation view of a femoral stem in accordance with an embodiment;

[0010] Figure 2 shows a superior portion cross section of the stem of Figure 1; and

[0011] Figure 3 shows a further superior portion cross section of the stem of Figure 1.

Description of Embodiments

[0012] A femoral stem 100 comprises a stem portion 101 and an integrally formed neck 102. The neck 102 may define a trunnion 103 for friction fit engagement within a tapered blind bore of an acetabular cup liner (not shown). Figure 1 shows three trunnion 103 configurations for different sized stems 100.

[0013] The stem 100 may define a longitudinal curvature 104 which tends medially superiorly.

[0014] The stem portion 101 may be approximately divided in half into a superior portion 107 and a distal portion 108. The superior portion 107 may lie between a resection line 105 and a half way line 106 approximately halfway along the medial curvature 104 between the resection line 105 and a distal end 109 of the stem portion 101.

[0015]The stem portion 101 defines a superior portion cross section 110 being generally orthogonal to the longitudinal curvature 104.

[0016] Figure 1 shows a first superior portion cross section 11OA being approximately mm from the resection line 105 and a further superior portion cross section 11OB being approximately 25 mm from the resection line 105. The first and second superior portion cross sections 110 are shown in Figures 2 and 3 respectively.

[0017] The superior portion cross section 110 has a medial width 111 and a lateral width 112 between respective anteroposterior sides 113 of the superior portion cross section 110. The superior portion cross section 110 further has a mediolateral length between a medial edge 115 and a lateral edge 114.

[0018] The superior portion cross section 110 has a medial:lateral width ratio across

more than 80% of the length thereof of less than 0.7, preferably less than 0.6.

[0019] Specifically, Figure 2 shows a side fit lines 116 fitting sides of the superior

portion cross section 110. Figure 2 shows a side fit lines 116Afor a larger sized stem

100, side fit lines 116B fora smaller sized stem 100 and respective medial and lateral

widths 111, 112 therefor.

[0020] Specifically, forthe largersized component 100, the lateralwidth 112Ais 22.45

mm whereas the medial width 111A is 11.06 mm. The ratio of the medial width 111A

to the lateral width 112A is 11.06 : 22.45 which is 0.49.

[0021] Similarly, for the smaller size component 100, the ratio of the medial width

111B to the lateral width 112B is 7.59 : 14.71 which is 0.53.

[0022] Similarly, for the further superior portion cross section 11OB shown in Figure

2, the ratio is 6:59 : 12.10 = 0.54 for the smaller sized component 100 and 10.50

19.79 = 0.54 for the smaller size component 100.

[0023]An angle 117 defined by the side fit lines 116 may be greater than 18, such

as approximately 21° is shown in the figures. The angle 117 may remain relatively

constant (such as within 3° or less) between the first and further superior portion

cross sections 110A and 110B and for the different sized stems 100.

[0024] The medial width 111 and the lateral width 112 may be measured apart more

than 80% of the mediolateral length of the superior portion cross section 110.

[0025] In the embodiment shown, the medial width 111 and the lateral width 112 may

be measured as the maximum and minimum width between the side fit lines 116 of

the superior portion cross section 110 at points where the sides 113 start to converge

inwardly.

[0026] The foregoing description, for purposes of explanation, used specific

nomenclature to provide a thorough understanding of the invention. However, it will

be apparent to one skilled in the art that specific details are not required in order to

practise the invention. Thus, the foregoing descriptions of specific embodiments of the invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed as obviously many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the following claims and their equivalents define the scope of the invention.

[0027] The term "approximately" or similar as used herein should be construed as

being within 10% of the value stated unless otherwise indicated.

Claims

Claims 1. A femoral stem having a stem portion having a superior portion cross section

normal to a longitudinal curve of the stem having a medial:lateral width ratio across

more than 80% of a mediolateral length thereof of less than 0.7.
2. The femoral stem as claimed in claim 1, wherein the ratio of less than 0.6.
3. The femoral stem as claimed in claim 1, wherein the ratio of less than 0.55.
4. The femoral stem as claimed in claim 1, wherein the medial:lateral width ratio

is a maximum medial:lateral width ratio.
5. The femoral stem as claimed in claim 1, wherein the medial:lateral width ratio

is a maximum medial:lateral width ratio between the straight side fit lies fitting sides

of the superior portion cross section at respective points where the sides start to

converge inwardly.
6. The femoral stem as claimed in claim 1, wherein the superior portion has a

length less half the length of the longitudinal curve between a resection line and a

distal end of the stem portion.
7. The femoral stem as claimed in claim 1, wherein the stem defines a resection

line and wherein the superior portion cross section is less than 30mm from the

resection plane.
8. The femoral stem as claimed in claim 7, wherein the stem defines a resection

line and wherein the superior portion cross section is approximately 25mm from the

resection plane.
9. The femoral stem as claimed in claim 1, wherein the stem defines a resection

line and wherein the superior portion cross section is less than 10mm from the

resection plane.
10. The femoral stem as claimed in claim 9, wherein the stem defines a resection

line and wherein the superior portion cross section is approximately 5mm from the

resection plane.
11. The femoral stem as claimed in claim 1, wherein the stem defines a resection

line and wherein the superior portion cross section is less than 10mm from the

resection plane and wherein the stem further defines a further superior portion cross section less than 30 mm from the resection plane and greater than 10 mm from the resection plane and wherein angles defined between straight side fit lines fitting sides of the superior portion cross sections is constant to within 3°.
12. The femoral stem as claimed in claim 1, wherein an angle defined between

straight side fit lines fitting sides of the superior portion cross section is greater than

180.
13. The femoral stem as claimed in claim 12, wherein an angle defined between

straight side fit lines fitting sides of the superior portion cross section is

approximately 210.