DE9005819U1 - Isometer - Google Patents

Description

HOEGER, STELLRECIHT.&'RAJRJNE&Rgr;*:..:

PATENT ATTORNEYS UHLANDSTRASSE 14 c · d 7ooo Stuttgart &igr;

A 49404 u Applicant: AESCULAP AG

d - 223 Möhringer Str.

25 April 1990 7200 Tuttlingen

DESCRIPTION BB MC

ISOMETERS

The innovation concerns an iso-aevo for determining an isometric positioning of a ligament transplant, which is to be placed in a bore through the two articular bones between two attachment points on either side of the joint to connect a pair of articular bones, with a support foot for attachment to one of the two articular bones, with a spring which, on the one hand, engages a holder connected to the support foot and, on the other hand, with a tension element passing through the bore of the two articular bones, and with an indicator element which indicates the elastic deformation of the spring and is connected directly or indirectly to the tension element by means of a gear.

The aim of isometric positioning is to ensure that the ligament transplants are stretched very little when the joint, such as the knee, is bent. This is possible if the transplant is correctly applied, since e.g.

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the movement of the knee joint consists of a rolling and a sliding movement: The isometer is used to determine whether and, if so, how strong the transplant is when it is inserted into the holes provided.

is laid, would be stretched when the joint is bent. If the measured stretch exceeds a specified value, drilling must be carried out again.

Isometers for the above-mentioned purpose are described, for example, in US patent 4,712,542 and in EP application 0 280 572. In the isometers disclosed in both documents, a thread is stretched between the attachment point on one bone and the isometer attached to the attachment point on the other bone using spring force (in the US patent) or gas pressure (in the EP application), whereby in both cases the tension can be varied. If the distance between the attachment points changes when the joint is bent, the displacement of a movable carriage to which the thread is attached is read directly relative to the isometer housing, or - according to the US patent - is first transferred via a rack to a pointer connected to an effective gear and only then read. In both known isometers, the carriage can be fixed in any position relative to the isometer housing. Both devices are too complicated for intraoperative use. An accurate reading of the changes in the current is not easy.

Also in the article "Isometric Placement of Substitutes for the Anterior Cruciate Ligament" by den Graf published in the book "The Anterior Cruciate Deficient Knee" edited by D. W, Jackson is an isometer

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It differs from the other known isometers mainly in that measurements are only taken at a fixed thread tension and that the direct measurement of the displacement of the carriage relative to the isometer housing is carried out in such a way that the zero point of a scale attached to the housing is aligned with a pointer on the carriage before the measurement. In this respect, the isometer described in the article is less complicated than the other two known ones, but the precise reading of the distance changes is only slightly easier with it.

The aim of the innovation is therefore to provide a simple, intraoperatively usable isometer with which it is possible to measure simply and precisely how much a ligament transplant, which has been inserted into a joint in a certain way, is stretched when the joint is bent.

This task is solved with an isometer of the type mentioned at the beginning in that the transmission ratio of the gearbox over the displacement path of the tension element is not proportional to the displacement path of the tension element and that the distance of the support foot from the holder is adjustable.

The isometer according to the invention can be used particularly advantageously if - which is desirable - the extension is very small, because with it, provided it is correctly adjusted, small displacements of the tension elements cause disproportionately large changes in the display of the display element. The displacements of the tension element can therefore be measured very precisely in a simple manner.

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P.'.e Adjustment is carried out in
simply by changing the distance
between the support leg and the holder.
According to the invention, the isometer only works with a fixed thread tension, which simplifies
The structure of the isometer according to the invention compared to the
most known isometers, and also its handling
becomes very simple, so that the inventive
Isometer is particularly suitable for intraoperative use.

i It is advantageous if the support leg rests on the holder. J

This design facilitates the ge- J

targeted change of the distance between support foot and ^

Holder and the fixation of a certain distance.

Applying the isometer according to the invention to the bone
is simplified if the support foot surrounds the tension element in a sleeve-shaped manner .

It is advantageous if the gearbox has a linear drive J

movement of the pulling element into a pivoting movement of the 1

display element is a crank drive. The mechanical ^: ,

see stability of the isometer according to the invention increased |

if the tension element is movable on buckets in the holder
mounted carriage, to which in turn the
spring attacks.

For reasons of mechanical stability and also hy- &iacgr;

giene it is advantageous if the holder as the tension element '

and a housing enclosing the spring.

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A non-proportional transmission ratio can be implemented in a particularly simple manner if the indicator element is rotatably mounted on the holder and the tension element or a part that can be moved with it is rotatable at a distance from this bearing point and acts on the indicator element in a radial direction. It is advantageous if the indicator element is a pointer and a scale that is swept over by this is attached to the holder.

When fixing the isometer to the joint, it is advantageous to have a removable fixation for holding the slide in a fixed position in which the spring is compressed more than during measurement. A favorable design of the fixation is when it consists of a spring catch attached to the holder, a locking bolt connected to it and a locking hole on the slide. Fixing in the above-mentioned position makes it easier to tighten the tensioning device.

It is advantageous if the isometer has a tube that surrounds the tension element, which protrudes from the housing, fits into the hole in one of the joint bones, and is guided in a tube guide connected to the support foot. This design of the isometer makes it easier to position it at the exit of the hole on one of the joint bones.

In order to prevent the pipe from turning when the distance between the housing and the support foot is changed, it is advantageous if the pipe is attached to the slide by means of a fitting which forms a positive connection with the slide.

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It has proven to be advantageous if, in the displacement position of the tension element, in which the non-proportional nature of the transmission ratio is maximum, the spring is compressed with a force of 25 N

The following description of a preferred embodiment of the isometer according to the invention serves to explain the invention in conjunction with the drawings. They show:

Fig. 1: an overall view of the measuring arrangement using the isometer according to the invention when determining the most favorable placement of the holes for the ligament transplant through two joint bones,

Fig. 2: the isometer shown in Fig. 1 in an enlarged view,

Fig. 3: the isometer shown in Fig. 2 in front view from the bone,

Fig. 4: a longitudinal section through the isometer shown in Fig. 3 along line 4-4,

Fig. 5: a cross section through the isometer of Fig. 4 along line 5-5,

Fig. 6: a cross section through the isometer of Fig. 4 along line 6-6.

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Fig. 1 shows an isometer 1 which is inserted with a tube 16 into a hole 4 through a first joint bone 2, e.g. the tibia. The hole 4 has a counterpart on a second joint bone 3, e.g. the femur. A tension element in the form of a tensioned thread 13 runs through the holes, which is fixed on the one hand to a thread holder 14 which is located at the end of the hole through the joint bone 3 facing away from the joint, and on the other hand is led through the tube 16 into the isometer 1 and is held on a thread attachment 15 at the end facing away from the bone. The details of the isometer 1 are described below with reference to the other figures.

The isometer 1, which Figs. 2 and 3 show from the outside in a side and a front view, has a cylindrical housing 5, which is connected by means of a support foot 18 to a pipe guide 17 for the pipe 16. The pipe _guide is located on the joint bone 2 when determining the isometric positioning. A sleeve 41 (Fig. 3) with a tangential extension is pushed onto the housing 5, to which a scale disk 6 with a curved scale 7 is attached. A pointer 10 points to the scale 7. The pointer 10 is rotatably attached to the sleeve 41 by means of a first pointer attachment 11 and also rotatably attached to a slide 31 inside the housing 5, which can be moved in the direction of the housing axis, by means of a second pointer attachment 12. The pointer attachment 12 runs in a slot θ in the housing that is parallel to the housing axis. 5 and in the

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Sleeve 41. Only the end of the slide 31 protruding from the housing 5 can be seen in Fig. 2. The pointer 10 is rotatable about the second pointer fastening 12 and can also be moved relative to it linearly in the direction of the connecting line between the two pointer fastenings, which is made possible by means of an elongated hole 40 in the pointer 10, in which the pointer fastening j.2 is guided. A handle 9 on the end of the housing i> applied by the support foot 18 is connected to the slide and serves to move the slide relative to the housing 5 by hand.

As the sections through the isometer 1 in Fig. 4 to 6 show, the housing 5, which has a circular cross-section, is connected coaxially to the support foot 18 by means of a screw connection 34. The pipe guide 17, which guides the pipe 16, is coaxially attached to the support foot 18. The housing 5 has a cylindrical cavity 30, the axis of which coincides with the housing axis. In the cavity 30 and guided in it are the cylindrical slide 31, which can be moved in the direction of the housing axis, and a spring 32, which is a pressure spring and has one end resting on the front side 33 of the slide 31 facing the support foot 18, and which has its other end resting on a sealing point 43 of the cavity 30.

The pipe 16, which is guided axially in the pipe guide 17, runs axially through the support foot 18 and the cavity 30 into an axial hole 44 in the slide 31. A molded part 35, which sits in the hole 44 and forms a positive connection with the slide 31 (see Fig. 6), holds the pipe 16 firmly.

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and prevents rotation of the tube 16 when the screw connection 34 is turned. Rotation of the slide 31 relative to the housing 5 is prevented by the pointer fastening 12 guided in the gap 8.

The slide 31 also has a locking bore 37 (see Fig. 5) into which, when the slide 31 is correctly positioned relative to the housing E, a locking bolt 36 engages, which is axially attached to a spring catch 38 and guided in a bore 45 extending axially through the sleeve 41 and the outer wall of the housing 4. The spring catch 38 is accommodated in a housing 20 which is attached to the tangential extension of the sleeve 41. A holding button 19 for actuating the spring catch 38 is located axially at the end of the spring catch 38 facing away from the locking bolt 36 and protrudes from the housing 20.

The main advantages of the isometer described here are the manner in which the displacement of the carriage 31 is transmitted to the pointer 10 _and the simple positioning of the pointer 10 in a desired position relative to the scale 7 when the thread 13 is tensioned.

When the slide 31 is moved, the pointer attachment 12 and thus also the pointer 10 also move - as can be seen from Fig. 2 and 4. Since the pointer is also attached to the fixed pointer attachment 11, the pointer performs a rotary movement around the pointer attachment 11. When the slide is moved, the distance between the pointer attachments 11 and 12 changes. If the two pointer attachments 11 and 12 are the smallest distance from each other, which

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This is the case when the connecting line and thus also the direction in which the pointer 10 points runs perpendicular to the direction of movement of the slide, then the pointer deflection is relatively greatest when the slide is moved. Measurements are therefore taken in this pointer position. The scale 7 shown in Fig. 2 shows these conditions: the distance between the lines, which always corresponds to the same slide displacement, is greatest in the middle of the scale and becomes smaller towards the ends of the scale. If the thread attached to the slide 13 is tensioned by means of the spring 32, the pointer 10 can easily be brought into the vertical position by turning the support foot 18. The distance between the tube guide 17, which rests on the bone, and the housing 5 is changed by means of the screw connection 34. Since the thread 13 has a fixed length, the change in the distance between the pipe guide 17 and the housing 5 must be compensated by a corresponding displacement of the slide 31 and thus a rotation of the pointer 10. In other words, by turning the support foot 18, the pointer 10 can easily be brought into the vertical position. In the isometer described here, the thread tension is 25 N when the pointer 10 points in the direction perpendicular to the direction of displacement of the slide 31. It has been found that with this thread tension, all measurements can be carried out with good results.

The following describes the procedure for determining isometric positioning of a ligament graft in a knee joint.

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First, the distance between the tube guide 17 and the housing 5 is set to the maximum value by turning the support foot 18 and the isometer 1 is put into the tensioned state. To do this, the slide 31 is pressed against the spring 32 into the cavity 30 in the housing 5 using the handle 9 until the locking bolt engages in the locking hole 37 in the slide 31. The pointer 10 moves on the scale 7 in the direction of the joint. Then the end of the tube 16 protruding from the tube guide 17 is inserted into the tibial hole until the tube guide 16 stops on the tibia.

A loop at one end of the thread 13 is pushed through the femoral hole into the interior of the knee, for example using a thread fork. For example, using a thread catcher that is inserted through the isometer and through the tibia into the interior, the loop is grasped, pulled through the tibia into the isometer 1 and hooked into the thread attachment 15. The other end of the thread 13, which protrudes from the femoral hole, is manually tightened and fixed to the side of the femur facing away from the knee using the thread holder 14, for example a clamp. The locking bolt 36 is released by applying light pressure against the spring 32. The spring force of the spring 32 is now applied to the thread 13. At a fixed angle position from the tibia to the femur, the pointer 10 is now set to the middle of the scale 7 by turning the support foot 18 - in such a way that the distance between the tubular sleeve and the housing is reduced. The resulting thread tension is 25 N.

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The angle between the tibia and femur is varied five times between 0° and 90° and any misalignment caused by moving the thread 13 in the holes is readjusted at the initially determined angle position, i.e. the pointer is set back to the middle of the scale 7. During the subsequent measurement, the increase or decrease in the distance between the tube guide 17 and the thread holder 14 is determined from the deflection of the pointer 10 at any angle position. The difference between the determined and the measured distance must not exceed 2 mm at any angle position. If the amount exceeds 2 mm, the distance must be re-guided. The method described is so simple and the reading of the change in distance is so precise that the measurement can be carried out without any problem during an operation.

Claims (1)

HOEGER, STELLRECNT _# Ä RARTisTE)^ '·..' PATENT ATTORNEYS UHLANDSTRASSE M c D 70OO STUTTGART 1 A 49 404 u Applicant: AESCULAP AG d - 223 Möhringer Str. 25 April 1990 7200 Tuttlingen PROTECTION CLAIMS 1. Isometer for determining an isometric positioning of a ligament transplant, which is used to connect a pair of articular bones in a hole through the two bones between two attachment points on either side of the joint. ji lenks is to be laid, with a support foot for Attachment to one of the two goniometric bones, with a spring that on the one hand engages a holder connected to the support foot and on the other hand a tension element passing through the bore of the two joint bones, and with an indicator element that indicates the elastic deformation of the spring and is connected directly or indirectly to the tension element by means of a gear, characterized, that the transmission ratio of the gear over the displacement path of the tension element is not proportional to the displacement path of the tension element and that the distance of the support foot (18) from the holder is adjustable. .AESCULAP AG 25 April 1990 A 49404 u u-223 -14- 2. Isometer according to claim 1, characterized in that the support foot (18) is screwed onto the holder. 3. löOiflötöi TiöCii AnSpxTUCii &khgr;&Ogr;<&agr;«5&Ggr; t,, uäuüICn ySrvSnri - characterized in that the support foot (�Lgr;8) surrounds the tension element in a sleeve-like manner. 4. Isometer according to one of the preceding claims, characterized in that the gear is a crank drive that converts the linear movement of the pulling element into a pivoting movement of the display element. 5. Isometer according to one of the preceding claims, characterized in that the tension element is mounted on a scale (31) displaceably mounted in the holder. attacks. 6. Isometer according to one of the preceding claims, characterized in that the holder is designed as the tension element and the spring (32) enclosing the housing (5). Isometer according to one of claims 2 to 6, characterized in that the display element is rotatably mounted on the holder and, at a distance from this bearing point, the tension element or a part displaceable therewith is rotatably attached to the display element and displaceable in the radial direction relative to the display element. AESCULAP AG 25 April 1990 .·* .*' · * '/' I '"l>'· A 49404 u ¹⁽ * " u-223 -15- 8. Isometer according to claim 7, characterized in that the display element is a pointer (10) and a scale (7) swept by the pointer is attached to the holder. 9. Isometer according to one of claims 5 to 8, characterized in that a releasable fixation for holding the carriage (31) in a fixed position relative to the holder is provided. 10. Isometer according to claim 9, characterized in that the fixation consists of a spring catch (38) attached to the holder, a locking bolt (36) connected thereto and a locking bore (10) in the slide (31). 11. Isometer according to one of claims 6 to 10, characterized in that it has a tube (16) which protrudes from the housing (5) and fits into a bore (4) in one of the joint bones (2) and which is guided in a tube guide (17) connected to the support foot (18). 12. Isometer according to claim 11, characterized in that the tube is attached to the carriage (31) by means of a shaped piece (35) which forms a positive connection with the carriage (31). 13. Isometer according to one of the preceding claims, characterized in that in the displacement position of the tension element in which the non-proportionality of the transmission ratio is maximum, the spring (32) is compressed with a force of 25 N.