NL2020309A

NL2020309A - Positioning aid in particular for positioning an acetabular prosthetic component

Info

Publication number: NL2020309A
Application number: NL2020309A
Authority: NL
Inventors: Vermaat Jan
Original assignee: Orpidem B V
Priority date: 2017-01-24
Filing date: 2018-01-24
Publication date: 2018-08-01
Also published as: WO2018139922A1; NL2020309B1

Abstract

A positioning aid 1 has a coupling element 7 for coupling to the prosthetic acetabular component, as well as an auxiliary body 9 that is fixed relative to the coupling element and which is provided with recesses. The center lines of said recesses are at angles relative to each other, in one of the recesses a ball compass 13 is inserted. This recess corresponds to the desired orientation in which the acetabular prosthetic component 3 is to be mounted in the acetabulum 5. Inscriptions are provided on the auxiliary body near each recess indicating two angles at which the recess is relative to two vertical reference planes which are perpendicular to each other. When the auxiliary body 9 is kept level, the angles indicated near the recess in which the circular bubble spirit level compass 13 is inserted defines the position in which the acetabular prosthetic component is oriented.

Description

Positioning aid in particular for positioning an acetabular prosthetic component DESCRIPTION:

Technical field of the invention

The invention relates to a positioning aid for all surgical procedures where direction and angle relative to the body are decisive, for example for positioning a bone in a human body during a surgical procedure. More particularly, the invention relates to a positioning aid. for positioning a prosthesis of which the direction and angle relative to the body are decisive. Even more particularly, the invention relates to a positioning aid for positioning an acetabular prosthetic component of a prosthetic hip in an acetabulum of a patient. The positioning aid comprising: an auxiliary body to be fixed relative to a coupling element connected to the prosthetic acetabular component, which auxiliary body is provided with at least one cylindrical or conical recess, and a. position indicator which is provided with a coupling pin which is detachably provided in the recess.

The coupling element is for example a straight, curved or angled rod.

Several studies (see Arch Orthop Trauma Surg. 2007 Jul; 127(5): 375-379. Published online 2007 Feb 13. doi: 10.1007/s00402-007-0294-y PMCID: PMC 1914284) have demonstrated a correlation between the acetabular cup position and the risk of dislocation, wear, damage and range of motion after total hip arthroplasty. This study was designed to evaluate the accuracy of the surgeon’s estimated position of the cup after freehand placement in total hip replacement. Perioperative estimated abduction and anteversion of 200 acetabular components (placed by three orthopedic surgeons and nine residents) were compared with measured outcomes (according to Pradhan) on postoperative radiographs. Cups were placed in 49.7° (SD 6.7) of abduction and 16.0° (SD 8.1) of anteversion. Estimation of placement was 46.3° (SD 4.3) of abduction and 14,6° (SD 5.9) of anteversion. Of more interest is the fact that for the orthopedic surgeons the mean inaccuracy of estimation was 4.1° (SD 3.9) for abduction and 5.2° (SD 4.5) for anteversion and for their residents this was respectively, 6.3° (SD 4.6) and 5.7° (SD 5.0). Significant differences were found between orthopedic surgeons and residents for inaccuracy of estimation for abduction, not for anteversion. Body mass index, sex, (un)cemented fixation and surgical approach (anterolateral or posterolateral) were not significant factors. Based upon the inaccuracy of estimation, the group’s chance on future cup placement within Lewinnek’s safe zone (5-25° anteversion and 30-50° abduction) is 82.7 and 85.2% for anteversion and abduction separately. When both parameters are combined, the chance of accurate placement is only 70.5%. The chance of placement of the acetabular component within 5° of an intended position, for both abduction and anteversion is 21.5% this percentage decreases to just 2.9% when the tolerated error is 1°. There is a tendency to underestimate both abduction and anteversion. Orthopedic surgeons are superior to their residents in estimating abduction of the acetabular component. The results of this study indicate that freehand placement of the acetabular component is not a reliable method.

Further, Bone Joint J. 2015 Feb;97-B(2): 164-72 indicates that positioning an acetabular prosthetic component of an prosthetic hip in an acetabulum is still an issue. In this study the orientation of the acetabular component is assessed in 1070 primary total hip arthroplasties with hard-on-soft, small diameter bearings, aiming to determine the size and site of the target zone that optimises outcome. Outcome measures included complications, dislocations, revisions and AOHS (the difference between the Oxford Hip Scores pre-operatively and five years post-operatively). A wide scatter of orientation was observed (2sd 15°). Placing the component within Lewinnek's zone was not associated with improved outcome. Of the different zone sizes tested (± 5°, ± 10° and ± 15°), only ±15° was associated with a decreased rate of dislocation. The dislocation rate with acetabular components inside an inclination/anteversion zone of 40°/15° ± 15° was four times lower than those outside. The only zone size associated with statistically significant and clinically important improvement in OHS was ± 5°. The best outcomes (AOHS > 26) were achieved with a 45°/25° ± 5° zone. This study demonstrated that with traditional technology surgeons can only reliably achieve a target zone of ±15°. As the optimal zone to diminish the risk of dislocation is also ±15°, surgeons should be able to achieve this. This is the first study to demonstrate that optimal orientation of the acetabular component improves the functional outcome. However, the target zone is small (± 5°) and cannot, with current technology, be consistently achieved.

Background of the invention A positioning aid according to the preamble of claim 1 is known from EP2644164A1. This known positioning aid for positioning an acetabular prosthetic component in a patient's surgically-prepared acetabulum, comprises: a shaft having a first end configured to be coupled to the acetabular prosthetic component, a handle attached to the shaft at a second end opposite the first end, and a bubble indicator attached to the shaft between the first end and the second end, the bubble indicator having a face and a plurality of markings defined on the face, the plurality of markings including: (i) a first marking indicating a first abduction angle, and (ii) a second marking indicating a second abduction angle and an anteversion angle of the acetabular prosthetic component.

The position indicator of the positioning aid includes a housing having a gravity-based indicator secured thereto. A "gravity-based indicator" is a sensor that indicates position based on gravity. The gravity-based indicator is a bubble indicator including a vial that defines a chamber filled with a fluid. The vial defines a domeshaped chamber. A bubble is trapped within the chamber. Gravity and the physical difference between the gas of the bubble and the fluid in the chamber control the function of the bubble indicator, with the bubble floating toward the side of the vial that constitutes the high side of the vial. The vial has a face plate that is substantially transparent. In that way, a user may look through the face plate to determine the position of the bubble. The bubble indicator has a plurality of markings etched into an outer surface of the face plate. Each of the markings indicates a predetermined position of the acetabular prosthetic component within the patient's surgically-prepared acetabulum.

The markings include a plurality of graphical indicators that correspond to the plurality of predetermined positions of the acetabular prosthetic component. The markings also include a plurality of numerical indicators that are associated with the graphical indicators including rings, and the bubble is configured to align with each of the rings based on the position of the acetabular prosthetic component within the patient's surgically-prepared acetabulum. The markings further include side indicators, which associate the graphical indicators and the numerical indicators with a particular side of a patient's body (i.e. right or left).

Because of the limited surface of the face plate of the spirit level a limited number of marks indicating different orientati ons can be provided on the plate.

Further, the known positioning aid cannot be used in situations the patient is lying on his/her back. In this position of the patient the positioning of the acetabular prosthetic component in one of the directions is in a horizontal plane and therefore does not have influence on the position of the bubble within the bubble indicator

Summary of the invention

It is an objective of the present invention to provide a positioning aid of the type defined in the opening paragraph with more positions/orientations pre-specified and which thus can take more different positions. To this end the positioning aid according to the invention is characterized in that the auxiliary body is provided with a number of further cylindrical or conical recesses, the center lines of said recess and said further recesses are at angles relative to each other, wherein the position indicator with the coupling pin is inserted in one of the recess and further recesses, corresponding to the desired orientation in which the acetabular prosthetic component is to be mounted in the acetabulum. The auxiliary body forms an interface between the position indicator and the coupling element and can be carried out in any desired size of choice. Because the position indicator can be coupled via the auxiliary' body with the coupling element in a large number of different positions / orientations also a large number of pre-defined positions / orientations can be indicated on the auxiliary' body.

In an embodiment the position indicator is a circular buble spirit level provided with a bubble indication. This is a circular device with the liquid under a slightly convex transparent face with a circle at the center.

Preferably, the spirit level has a convex surface window in the middle provided with two concentric circles, wherein the air bubble just fits within the innermost circle and in this position the spirit level is horizontally oriented, and when the air bubble touches the outer circle the spirit level is at a specified angle relative to the horizontal plane.

In another embodiment the position indicator is a circular bubble spirit level compass. With a circular bubble spirit level compass is meant a combination of a circular bubble spirit level and a compass. This enables the use of the positioning aid in situations the patient is lying on his/her back. In this position of the patient the positioning of the acetabular prosthetic component in one of the directions is in a horizontal plane and therefore does not have influence on the position of the bubble within a spirit level. Using the compass function instead of the spirit level function makes it possible to position the prosthetic component in a desired direction in a horizontal plane. Further, with such a position indicator it is possible to retrieve a position and orientation in space (relative to the body of the patient) which has been taken before. This is especially of advantage in. case first a test cup is used for determining the correct position of the cup before the prosthetic cup is positioned. This can be used both in case the patient is lying on his/her back as well as in case the patient is lying on his/her side.

In case no test cup is used then a position indicator that is both a circular bubble spirit level and a compass is still advantageous especially in case the patient is lying on his/her back to find the correct orientation of the cup.

The auxiliary body and coupling elements preferably have no ferromagnetic characteristics that could adversely influence the correct functioning of the compass.

Further, the auxiliary body is provided with a surface in which the recess and the further recesses are present and which is provided with inscriptions indicating angles at which the recesses are relative to two vertical reference planes which are perpendicular to each other.

An embodiment of the positioning aid according to the invention is characterized in that the surface is curved along a spherical surface in which the center lines of the recesses are perpendicular to the surface. As a result, the recesses can easily be applied with a drilling machine in the auxiliary body. A further embodiment of the positioning aid according to the invention is characterized in that the auxiliary body is detachably connected to the coupling element and is provided with a further surface opposite to the surface, which further surface is also provided w'ith cylindrical or conical recesses in which the coupling pin of the position indicator can be inserted, each recess having an axis, the axes of the recesses are at angles relative to each other, wherein the auxiliary body can be connected to the coupling element in two different orientations, namely with the surface or the further surface facing up. As a result, the positioning aid can be applied both for left and for the right-hand side of the patient.

Yet a further embodiment of the positioning aid according to the invention is characterized in that a side of the auxiliary' body is provided with a hole with a rectangular (or other non-rotationally symmetric) cross-section for coupling with a rod with a similarly rectangular (or similarly other non-rotationally symmetric) cross-section which rod is connected to the coupling element, wherein the sides of the hole are inclined with respect to the surface in which the recesses are provided. The angle at which the recess is arranged relative to the surface defines a position in which the acetabular prosthetic component is oriented overall in the desired position when the auxiliary holding body is kept level.

Preferably, the auxiliary body has the shape of a cross. This helps arranging the auxiliary'’ body in the correct orientation with respect to the patient. One axis of the cross should be in line with the length direction of the patient. The other axis of the cross should be kept more or less horizontally.

Brief description of the drawings

The invention will be further elucidated below on the basis of drawings. These drawings show embodiments of the positioning aid according to the present invention. In the drawings:

Figure 1 is perspective view of the positioni ng aid during use,

Figure 2 shows the application of the positioning aid with a patient lying on his/her back;

Figure 3 shows the application of the positioning aid with a patient lying on his/her side;

Figure 4 is a plan view of a first embodiment of the auxiliary body with the circular bubble spirit level compass of the positioning aid; and

Figure 5 is a side view of a second embodiment of the auxiliary body with the circular bubble spirit level compass of the positioning aid.

Detailed description of the drawings

Figure 1 shows an embodiment of the positioning aid I for positioning an acetabular prosthetic component 3 of an prosthetic hip in an acetabulum 5 of a patient according to the invention during use. The positioning aid 1 comprises a coupling element 7 for coupling to the prosthetic acetabular component. Figures 2 and 3 show the application of the positioning aid with a patient lying respectively on his/her back and on his/her side. An auxiliary body 9 is fixed relative to the coupling element and is provided with a number of recesses 11, see figure 4. The center lines 11A of said recesses are at angles relative to each other.

The positioning aid further comprises a circular bubble spirit level compass 13 having a coupling pin 15. This coupling pin is inserted in one of the recesses 11 corresponding to the desired orientation in which the acetabular prosthetic component is to be mounted in the acetabulum. The circular bubble spirit level compass 13 is a circular device with the liquid under a slightly convex surface with a marking at the center, it serves to level a surface across a plane.

The auxiliary body 9 is provided with a surface 17, see figure 2. in which the recesses are provided and which is further provided with inscriptions 19 indicating angles at which the recesses are relative to two vertical reference planes which are perpendicular to each other. The surface is curved along a spherical surface in which the center lines of the recesses are perpendicular to the surface.

In figure 5 a second embodiment of the auxiliary body 9’ is shown in side view. This auxiliary body 9’ is provided with a further surface 21 opposite to the surface 17, and is also provided with recesses 22 in which the coupling pin 15 of the ball compass 13 can be inserted. The axes 22 A of the recesses are also at angles relative to each other. The auxiliary body 9 is detachably connected to the coupling element 7 and can be connected to the coupling element in two different orientations, namely with the surface 17 or the further surface 21 facing up.

In a side 23 of the auxiliary bodies 9 and 9' a hole 25 is provided. This hole has rectangular cross-section for coupling with a rod 27 (see figure 1) with a similarly rectangular cross-section, which rod is attached to the coupling element 7. This coupling element can be straight or angled depending on the position the patient is in. The sides of the hole are inclined with respect to the surface 17 in which the recesses 11 are provided.

The circular bubble spirit level compass 13 has a convex surface window 29 in the middle provided with two concentric circles, wherein the air bubble 31 just fits within the innermost circle 33 and in this position the ball compass is horizontally oriented. When the air bubble 31 touches the outer circle 35 the ball compass is at a specified angle relative (for example 2,5 degrees) to the horizontal plane.

Although the present invention is elucidated above on the basis of the given drawings, it should be noted that this invention is not limited whatsoever to the embodiments shown in the drawings. The invention also extends to all embodiments deviating from the embodiments shown in the drawings within the context defined by the claims.

Claims

A positioning aid (1) in particular for positioning an acetabular prosthetic component (3) of an artificial hip joint in a hip cup (5) of a patient, comprising: an auxiliary body (9) to be fixed with respect to a coupling element (7) connected to the acetabular prosthetic component and which is provided with at least one cylindrical or conical recess (11), and a position indicator (13) which is provided with a coupling pin (15) releasably present in the recess, characterized in that, in addition to said recess, the auxiliary body (9) is provided with a number of further recesses (11), of which recess and further cylindrical or conical recesses the axes (11A) are angled relative to each other, and wherein position indicator (13) with the coupling pin (15) is releasably inserted into one of the recesses and further recesses, corresponding to the desired orientation in which the acetabular prosthetic c omponent (3) must be placed in the hip cup (5).

Positioning aid according to claim 1, characterized in that the position indicator (13) is a circle-shaped bubble level.

Positioning aid according to claim 2, characterized in that the position indicator (13) is a circular bubble level compass.

Positioning aid according to one of the preceding claims, characterized in that the auxiliary body (9) is provided with a surface (17) in which the recess and the further recesses (11) are present and which is provided with inscriptions (19) which are angles indicate below which the recesses are in relation to two perpendicular vertical reference planes.

Positioning aid according to one of the preceding claims, characterized in that the surface (17) is curved along a convex surface, the center lines (11A) of the recesses (11) being perpendicular to the surface.

Positioning aid according to one of the preceding claims, characterized in that the auxiliary body (9) is releasably connected to the coupling element (7) and is provided with a further surface (21) which is present opposite the surface (17) and is also provided with cylindrical or conical recesses (22) into which the position indicator (13) can be inserted with the coupling pin (15) and whose center line (22A) is angled relative to each other, the auxiliary body (9) in two different orientations, namely with the plane or with the further plane upwards, can be connected to the coupling element.

Positioning aid according to one of the preceding claims, characterized in that the auxiliary body (9) is provided in a side surface (23) with a hole (25) with a rectangular cross-section for coupling to a rod (27) with a likewise rectangular cross-section which is connected to the coupling element (7), the sides of the hole being inclined with respect to the surface (17) in which the recesses (11) are present.

Positioning aid according to one of the preceding claims, characterized in that the auxiliary body (9) has the shape of a cross.