WO2006074954A1

WO2006074954A1 - Method for determining the neutral position of a femur in relation to a pelvic bone, and device for carrying out said method

Info

Publication number: WO2006074954A1
Application number: PCT/EP2006/000299
Authority: WO
Inventors: Benoit Mollard; Cyril Perot; Sergej Kammerzell
Original assignee: Aesculap Ag & Co. Kg
Priority date: 2005-01-17
Filing date: 2006-01-14
Publication date: 2006-07-20
Also published as: DE102005003317A1

Abstract

The invention relates to a method for determining the neutral position of a femur in relation to a pelvic bone. Said method is characterized by the following steps: determining the anterior pelvic plane from the three points of the pelvic bone 1) left spina iliaca anterior superior, 2) right spina iliaca anterior superior, 3) symphysis pubis (pubic bone); determining a femur sagittal plane from the position data of the hip joint center, the knee joint (100) and the ankle joint at bent lower leg; calculating the angle modifications required to transfer the connecting line of the hip joint center with the knee joint (mechanical femur axis) to a line that in a plane parallel to the anterior pelvic plane runs through the hip joint center and at a right angle to the connecting line of the two spinae iliacae anteriores (150) superiores; and additionally calculating the angle modifications required to orient the femur sagittal plane at a right angle to the anterior pelvic plane.

Description

METHOD FOR DETERMINING THE NEUTRAL POSITION OF A

THOROUGH BIT RELATIVELY TO A BECKENKNOCHEN AND

DEVICE FOR CARRYING OUT THIS PROCEDURE

The invention relates to a method for determining the neutral position of a femur relative to a pelvic bone.

In the implantation of an artificial hip joint, among other things, it is necessary to mathematically simulate the mobility of the femur relative to the pelvic bone after insertion of the implant components in order to predict whether the use of certain implant components and their specific orientation and positioning in the bone to the desired lead maximum mobility. For example, it is checked whether a rotation of the femur inward and outward to a sufficient extent is possible with the leg extended, also with angled leg pivoting inwards and outwards. The axes of rotation that are the basis of this review, are relative to the pelvic bone fixed axes, and therefore it is essential that the thigh and thus implanted implant parts to determine this mobility have a particular orientation to the pelvic bone. It is believed that a neutral position is suitable, that is, a position that substantially corresponds to the orientation of the thigh in a standing patient and leg extended.

In order to determine this neutral position of the thigh relative to the pelvic bone in practice, the thighbone of a patient has been brought as accurately as possible into this neutral position during an operation, for example. However, this succeeds only very imperfect, as in a Surgery often pelvic bone is pivoted and since the body parts of the patient are covered by surgical drapes and difficult to access during surgery, also such a precise arrangement is problematic in a recumbent patient. For this reason, it has hitherto been only approximately possible to produce a neutral position, from which then the desired simulation calculations can be carried out.

It is an object of the invention to provide a method by which the neutral position of the femur relative to the pelvic bone can be determined in a simpler manner.

This object is achieved by a method of the type described above, which is characterized by the following process steps:

• It is determined from the three points of the pelvic bone

1) left spina iliaca anterior superior (left upper iliac spine)

2) right anterior superior iliac spine (right upper iliac spine)

3) Symphysis pubis (pubis)

the anterior pelvic plane.

• Determine the location of the hip joint center relative to the pelvic bone and relative to the femur.

• Determine the position of the knee joint relative to the femur,

• Flex the lower leg about 90 ° with respect to the thigh and then determine the position of the ankle relative to the thighbone.

• A femoral sagittal plane is determined from the position data of the hip joint center, the knee joint and the ankle in the angled lower leg.

• Calculates the angle changes necessary to align the line connecting the hip joint center with the knee joint (mechanical axis of the femur) in a plane parallel to the anterior pelvic plane through the midpoint of the hip joint and perpendicular to the connecting line of the two anterior superior iliac spines.

• Additionally, one calculates the angle changes necessary to orient the femoral sagittal plane perpendicular to the anterior pelvic plane.

As a result of these method steps, one obtains a data set of location coordinate transformations which describe how the thigh must be pivoted and rotated in order to reach the neutral position. This shift will not be carried out physically, but only mathematically, and in this way also mathematically the shifts - A -

and calculate rotations of implant parts that are actually implanted in the thigh or even theoretically assumed in the femur in a previous model. It is therefore mathematically possible to convert the implant parts into a position and position that correspond to the neutral position, and based on this relative position of the thigh-side implant parts on the one hand and the pelvic bone-side implant parts on the other hand, calculate their mobility relative to each other in the usual way.

Essential to the method described is that no opening of the body is necessary, all the described method steps can be found without intervention in the body simply by movements of the limbs and scanning certain landmarks, regardless of the position in which the patient is and in which position the limbs are arranged relative to the pelvic bone. It suffices in this method, in some position of the thigh the lower leg about right angles zuwinkein to then determine the position of the ankle relative to the thigh, all other steps are determinations of endogenous marking points and calculations, so it is not necessary in fact the thigh actually to the neutral position.

The determination of the femoral sagittal plane is based on the finding that, when the lower leg is bent, the ankle is pivoted in the femoral sagittal plane, which in the neutral position of the thigh is actually perpendicular to the anterior pelvic plane and perpendicular to the connecting line of the two anterior superior iliac spines. It is beneficial to palpate the three pelvic bone points to determine the anterior pelvic plane.

The hip center can be determined by pivoting the femur relative to the hip joint. Assuming that the hip joint is a ball joint, all points of the thigh that are spaced apart from the hip joint center move on a ball cup around the center of the hip joint. This ball socket can be determined by measurement, for example by means of a navigation system, and from this the ball center can be determined, which coincides with the hip joint center.

The position of the knee joint can preferably also be determined by palpation of the patella, and the position of the ankle can also be determined by palpation, for example by palpation of the two lateral ankle projections and / or bony prominences on the front of the lower leg.

The invention also relates to a device for carrying out this method, wherein at the pelvic bone and the femur in each case a marking element is set, these marking elements are in terms of their location, so in terms of position and orientation in space, monitored by a navigation system, so that at any moment the location of these marking elements in the room can be determined.

Since the marking elements are fixed to the pelvic bone and the thigh, there is a permanent relationship between the position data of the marking elements on the one hand and the position data of the above-described NEN marking points on the pelvic bone on the one hand and the mechanical femur axis and the sagittal plane on the thigh bone on the other hand, once this relationship is established, it remains the same and by determining the position of the marking can then calculate the respective location of said marker points, connecting lines and levels.

It is advantageous if a button provided with a marking element is used to determine the marking points, the position of which is also monitored by the navigation system. This makes it possible in a simple manner, to capture the described marking points in terms of their location from the navigation system and to create a corresponding record.

The following description of preferred embodiments of the invention is used in conjunction with the drawings for further explanation. Show it:

FIG. 1 shows a schematic view of the pelvic bone, of the thigh bone and of the lower leg bone of a patient and of a navigation system with a data processing system for determining the position data of endogenous marking points and further geometric data;

Figure 2 is a view of the patient similar to the representation of Figure 1 with additional indication of the mechanical femur axis of the femur and

FIG. 3 shows a view of the pelvic bone, the thigh bone and the lower leg bone angled at 90 ° Patients indicating the anterior pelvic plane, the mechanical femoral axis and the femoral sagittal plane.

To determine the neutral position of the thigh of a patient, a navigation system 1 is used, which emits infrared radiation through three mutually spaced transmitters 2, 3, 4, which impinges on reflector elements of marking elements 5, 6, 7 and from there on as recipients working transmitter 2, 3,4 is reflected back. From the transit time differences and the directions of the reflected radiation, the navigation system at any time determine the exact position and orientation, ie the location of each marking element 5, 6, 7 in space and generate a corresponding record, which are then fed to a data processing system 8 for further processing can. Among other things, the data processing system is assigned a display unit in the form of a screen 9.

Such navigation systems are known per se and can be deviating in a known manner, for example, instead of infrared radiation electromagnetic radiation or ultrasound radiation can be used etc. It is only essential that the navigation system can determine the location of the marking elements in the room at any time and can generate a record.

A first marking element 5 is firmly connected to a femur 10 of a patient, for example by means of a bone screw screwed into the bone, to which the marking element 5 is rigidly fastened. Similarly, the marker 6 is fixedly connected to the pelvic bone 11 of a patient, and finally the marker 7 is rigid with a Tastinstrument 12 connected, which has, for example, a needle-shaped stylus tip 13. With this probe tip 13 striking points on the body of a patient can be approached, and from the position of the Tastinstruments and the geometric data of the Tastinstruments, so the relative position of the probe tip 13 relative to the marker 7, then the exact location of the probe tip in space and thus one of the probe tip 13 approached point of the patient are detected.

To determine the neutral position of the thigh relative to the pelvic bone, the following parameters are recorded:

With the palpation instrument 12 three marking points are approached on the pelvic bone, namely the left anterior superior iliac spine 14 (left iliac spine), the right anterior superior iliac spine 15 (right iliac spine) and the pubic symphysis pubis 16 (pubis). From the data sets which describe the position of these three marking points, the data processing system 8 calculates a plane, which is referred to below as the anterior pelvic plane. This is arranged almost vertically in a standing patient and forms a reference plane for the pelvic bone.

In a further step, the position of the hip joint center 17 is determined. For this purpose, the thigh bone 10 is pivoted relative to the pelvic bone 11. In this pivoting movement, the marking element 5 moves on a spherical shell around the hip joint center point 17. This spherical shell is measured by the navigation system, and the data processing system 8 can determine the position of the hip joint center 17 therefrom, relative to the femur 10, that is, to the marrow. kierelement 5, and relative to the pelvic bone 11, that is to the marking element. 6

In a further step, the position of the knee joint is determined. Since this is not initially opened in the operation, this position is approximately determined by taking a certain point on the patella 18 and defines this as the knee center.

The data processing system 8 calculates from the position data of the hip joint center 17 and the knee joint a connecting line, which is referred to as a mechanical femur axis 19 (FIG. 2). Thus, the orientation of this mechanical femur axis relative to the femur 10 and thus against the marking element 5 is determined.

In a further step, the lower leg of the patient is angled relative to the thigh by approximately 90 °, as shown in FIG. In this position of the lower leg, the position of the ankle 20 is determined. This can also be done by palpation with the stylus 12, for example, the most prominent points of the two hocks of the foot or on the front of the leg a prominent bone point in the ankle is palpated and from these data, the position of the ankle is determined. The data processing system 8 calculates a plane from the position data of the hip joint center 17, the knee joint and the ankle, this is referred to as femoral sagittal plane 21. The geometric data of this Femursagittalebene 21 relative to the femur 10 are thus known, and thus also relative to the marking element. 5 In the measurement described, the patient's leg will normally not be oriented relative to the pelvic bone, that is, it will not be in the neutral position.

It is now assumed that the neutral position is characterized in that the mechanical femoral axis 19 is parallel to the anterior pelvic plane 22 and perpendicular to the connecting line 23 of the two iliac spine anteriores superiores and that the femoral axis 21 is perpendicular to the anterior pelvic plane 22. This assumption is essentially true in most patients, so this description is a very good representation of the neutral position.

Since this position of the leg was not taken when taking the measurement, deviations arise, and these deviations can easily be calculated by the data processing system 8, that is, the coordinate transformations necessary to derive from the actually measured orientations of the femoral axis plane 21 and the mechanical femur axis 19 to reach the corresponding positions in the neutral position. From this transformation data can then also calculate the transformation data describing the transition of the position of the marking element 5 from the actual measurement position to the neutral position or the transition of an inserted into the femur and fixedly connected to this implant. The position of this implant in the femur 10 is either mathematically simulated before the operation, it is said that a certain position of the implant in the femur, for example, using image data of the femur and image data of the implant part, which are copied one above the other, or receives one the position of the implant part after implantation in that also the implant part is navigated, for example by a temporarily rigidly connected to the implant part marking. In any case, it is possible in this way the data processing system 8, the position of the implant in the neutral position of the femur from the actual position of the implant, which can be determined at any time by determining the position of the thigh bone own marker 5, relative to the pelvic bone 11th

Thus, without having actually brought the thighbone 10 into this neutral position, a position of the implant part in the femur relative to the pelvic bone corresponding to the neutral position of the femur can be given for the simulation of the movement sequences, and thus the simulation of the mobility can be carried out in a realistic manner. For this procedure, it is neither necessary to perform any interventions on the body, nor must the leg be brought to the neutral position. The measured values described are easy for the surgeon to absorb and lead to reliable, easily reproducible values for determining the neutral position of the thigh.

Claims

A method for determining the neutral position of a femur relative to a pelvic bone characterized by the following method steps:

• It is determined from the three points of the pelvic bone

1) left spina iliaca anterior superior (left upper iliac spine)

2) right anterior superior iliac spine (right upper iliac spine)

3) Symphysis pubis (pubis)

the anterior pelvic plane.

• Determine the position of the knee joint relative to the thighbone. • Flex the lower leg about 90 ° with respect to the thigh and then determine the position of the ankle relative to the thighbone.

• Calculate the angle changes necessary to align the line connecting the hip joint center with the knee joint (mechanical axis of the femur) in a plane parallel to the anterior pelvic plane through the midpoint of the hip joint and perpendicular to the connecting line of the two anterior superior iliac spines.

2. The method according to claim 1, characterized in that the three

Pelvic bone points determined by palpation for determination of anterior pelvic plane.

3. The method according to claim 1 or 2, characterized in that one determines the hip joint center by pivoting of the femur relative to the hip joint.

4. The method according to any one of the preceding claims, characterized in that one determines the position of the knee joint by palpation of the patella.

5. The method according to any one of the preceding claims, characterized in that one determines the position of the ankle by palpation.

6. Apparatus for carrying out the method of one of claims 1 to 5 with a navigation system (1), with the femur

(10) and marking elements (5, 6, 7) fixed on the pelvic bone (11) of a patient whose position and orientation can be determined by the navigation system (1), with a stylus element connected to a marking element and with a data processing system (8) for processing the position data supplied by the navigation system (1) of the marking elements (5, 6, 7) and thus of the femur (10), the pelvic bone (11) and the Tastinstruments (12), characterized in that the data processing system is programmed so that they from the three points of the pelvic bone

(11) Left anterior superior iliac spine (14), right anterior superior iliac spine (15), and pubic symphysis (16) determines the anterior pelvic plane (22) and is determined from the location of the hip joint center (17) relative to the pelvic bone (11). and relative to the femur (10), the position of the knee joint relative to the femur (10), and the position of the ankle (20) relative to the upper leg (10). femur bone (10) at about 90 ° angled lower leg Femursagittalebene (21) determines that it calculates the angular changes necessary to the connecting line (19) of the hip joint center (17) with the knee joint (mechanical femur axis) in a Line passing in a plane parallel to the anterior pelvic plane (22) through the hip joint center (17) and perpendicular to the line connecting the two spine iliacae anteriores superiores (14, 15), and that additionally calculates the angle changes that are necessary to orient the femoral axis (21) perpendicular to the anterior pelvic plane (22).