RU232101U1 - Device for determining the level of the joint line for calculating the thickness of the distal and posterior augments when filling defects of the femoral condyles during knee arthroplasty - Google Patents

Abstract

The utility model relates to the field of medicine, namely to traumatology and orthopedics, and can be used in surgical interventions: revision or primary arthroplasty of the knee joint, in cases where it is necessary to compensate for femur defects for optimal location of the joint line level. A device for determining the joint line level, including a bar with a first sponge, a frame with a second sponge mounted on the bar with the ability to move along it, and a main scale applied to the bar with the ability to display in the frame window. The first sponge is pivotally mounted on an axis passing through the bar, the second sponge is pivotally mounted on an axis passing through the frame. The technical result consists in increasing the accuracy of determining the optimal distance from the femoral epicondyle to the joint line level.

Description

The utility model relates to the field of medicine, namely to traumatology and orthopedics, and can be used in surgical interventions: revision or primary arthroplasty of the knee joint, in cases where it is necessary to compensate for defects of the femur for the optimal location of the joint line level.

In knee joint endoprosthetics, both primary and revision, the surgeon faces the problem of compensating for bone defects to restore the optimal level of the joint line and posterior offset of the femur. Their change leads to an inevitable imbalance of soft tissue structures that ensure the stability of the knee joint throughout the entire range of motion and the appearance of instability, limitation of motion and mechanical overload of soft tissue and bone formations, thereby increasing pain syndrome and worsening the functional result of endoprosthetics [1].

Positioning the femoral component to determine the joint line in accordance with the anatomical attachment points of the collateral ligaments during implantation of endoprostheses with preservation of the posterior cruciate ligament allows maximal preservation of proprioception and stability of the knee joint [2]. Deviation of the joint line during implantation of structures with a higher degree of mechanical connection between the components of the endoprosthesis (posteriorly stabilized, varus/valgus connected, hinged) leads to deterioration of the results of arthroplasty [2]. An increase in the level of the joint line by 5–8 mm or more leads to a significant deterioration in functional indicators [3, 4, 5].

A measuring device installed in the femoral fitting component is similar in its functional purpose to the claimed device, which allows estimating the permissible range of the lower pole of the patella, thereby determining the desired level of the joint line. The disadvantage of this method is a fairly wide range of permissible location of the joint line and the lack of consideration of the different anatomical location of the patella and the size of the femur [7, 8].

A known method for determining the level of the joint line is the use of a computerized navigation system during knee joint endoprosthetics, which allows for all calculations to be automatically and accurately performed in accordance with a given program [9].

The disadvantage of the computerized navigation system is its high cost, which significantly limits the possibility of its use outside large medical centers. In addition, such a system requires a high level of training of the operating surgeon: the degree of correspondence of the indicators in the navigator to the real clinical situation depends on how accurately he determines multiple anatomical points during registration. In accordance with the learning curve, the duration of surgical intervention also increases (from 40 minutes at the stage of mastering the technique to 20 minutes when the skills of its use appear). In a number of clinical situations, the use of computer navigation is impossible, for example, in case of ankylosis of the hip joint or severe coxarthrosis due to the fact that rotation will be accompanied by a displacement of the pelvis, due to which an error will arise in determining the proximal point of the axis of the lower limb. At the same time, errors in the operation of the computer navigation system can also be associated with a possible displacement of sensors fixed to the bones during endoprosthetics. Computer navigation cannot be used for hip arthrodesis, femoral head deformities, complex deformities of the femoral and tibial epiphyses, and its use is difficult, including in obese patients [9].

A device is known for determining the position of the joint space during revision knee arthroplasty [10], consisting of a rod with a millimeter scale applied to it, which is installed in a cylindrical housing with the ability to move and fix with a screw element, while a guide element is made on the generating surface of the housing, in which a telescopic probe with a curved end is located with the ability to move and fix with a screw element, and the rod is fixed to the holder. In addition, the end of the telescopic probe is bent at an angle of 120-150°.

The disadvantage of the described device is the impossibility of determining the exact values of the distances from the level of tibia resection to the level of the fibular head, which determine the level of the knee joint space, in case of extensive and extended bone defects. In addition, the use of the device requires mandatory intraoperative selection of an anatomical landmark (the fibular head) for the purpose of clear visualization, which increases the trauma, time, blood loss and frequency of general surgical complications of the performed surgical intervention. In addition to the above, the risk of developing peripheral motor and sensory neurological disorders in the operated lower limb increases due to the high probability of damage to the common peroneal nerve (nervus peroneus communis), located anatomically close to the fibular head. At the same time, this device does not allow determining the level of installation of the endoprosthesis components in accordance with the anatomically correct joint line without additional independent calculations (only based on the scale values).

The closest to the claimed device is a caliper [11], rarely used to measure the level of the joint line, including a bar with a sponge, a frame with a sponge mounted on the bar with the ability to move along it, a main scale applied to the bar, and an auxiliary scale applied to the frame. The measurement is performed as follows: an anatomical landmark (the epicondyle of the femur) is determined empirically intraoperatively and the intercondylar distance (WF) is measured with sponges, after which the desired distance is calculated taking into account the MEMFC and LELFC formulas [12].

The disadvantage of the device selected as a prototype is its low efficiency and complexity of use. This is due to the fact that the user (doctor) must first accurately mark the anatomical landmarks with knitting needles or other auxiliary instruments, which is very difficult in the presence of extensive defects in the area being operated on. Measuring with the device by such anatomical landmarks that do not have strict anatomical boundaries and do not have precise dimensions, which excludes the exact determination of the knitting needle insertion point, leads to a significant measurement error and, as a consequence, to incorrect restoration of the joint space, and therefore to disruption of the knee joint extensor apparatus, limitation of movement and pain syndrome. In addition, the distance (supracondylar) measured with a caliper by landmarks requires further use of pre-prepared calculation tables, or to perform calculations during the operation, which inevitably leads to additional time costs and introduces the possibility of an error in the calculations. Further determination of the joint line level taking into account the values obtained from the calculation tables using the prototype device is extremely inconvenient: the jaws touch the initially installed spokes, cling to the edges of the surgical intervention zone. All of the above causes inconvenience of operation, a high probability of errors in calculations and visual fixation on the anatomical landmark (epicondylus) while simultaneously preventing the displacement of the caliper.

The technical problem is to develop a simple, effective and easy-to-use device for determining the level of the joint line for calculating the thickness of the distal and posterior augments when filling defects of the femoral condyles during knee arthroplasty with significant anatomical abnormalities of the distal femoral epiphysis.

The technical result consists in increasing the convenience of performing measurements by the device with high accuracy in determining the level of the joint line.

The technical result is achieved by using a device for determining the level of the joint line for calculating the thickness of the distal and posterior augments when filling in defects of the femoral condyles during knee arthroplasty, comprising a bar with a first sponge, a removable frame with a second sponge and a window mounted on the bar with the ability to move along it, the first sponge is pivotally mounted on an axis passing through the bar, the second sponge is pivotally mounted on an axis passing through the removable frame, said sponges have the ability to be positioned on the epicondyles of the femur, a main scale with the values of the femur width measurements and with an inverted section for determining the level of the joint line in the downward direction from the epicondyle to the tibia, a first auxiliary scale with the values of the distance from the epicondyle to the level of the joint line in the distal direction, a second auxiliary scale for determining the level of the joint line from the epicondyle in the posterior direction, located perpendicular to said main scale, and an opening are made on the bar under the fixing spoke, made at a distance of 30-45 mm from the starting point of the said main scale and being the starting point of the said second auxiliary scale and the point for plotting the value along the said inverted section of the main scale, wherein the frame window is made with the possibility of displaying the values of the said main and first auxiliary scales, wherein each value of the said main scale corresponds to its “own” value of the said first auxiliary scale, all said scales are made on both sides of the bar with the possibility of use for the right and left knee joints.

In particular embodiments of the device, depending on the specific clinical case that determines the choice of the starting point (the medial or lateral epicondyle of the femur), the values of the distance from the epicondyle to the most distal point of the condyle of the femur of the first auxiliary scale for the medial epicondyle and condyle correspond to the values obtained using the formula

MEMFC = 8.92 mm + WF*0.32 mm,

where MEMFC is the distance from the medial epicondyle to the most distal point of the medial condyle of the femur, mm;

WF – femur width, mm.

In another particular embodiment of the device, the values of the distance from the epicondyle to the most distal point of the condyle of the femur of the first auxiliary scale for the lateral epicondyle and condyle correspond to the values obtained by the formula

LELFC = 8.49 mm + WF*0.28 mm,

where LELFC is the distance from the lateral epicondyle to the most distal point of the lateral condyle of the femur, mm;

WF – femur width, mm.

The scales (main and auxiliary) are applied on both sides (surfaces) of the bar.

The installation of the jaws on hinges on axes passing through the bar and frame eliminates the overlap of the measurement zone in the area of surgical intervention. This is ensured by the possibility of their extension to the working position at one stage of measurement by the device and the possibility of their folding (transfer to the non-working position) at another stage of measurement by the device according to the step-by-step algorithm of use described below.

The claimed device is illustrated by drawings:

Fig. 1 - General view of the device, where the values of the first auxiliary scale correspond to the calculated values of the level of the joint line, adjusted from the medial epicondyle;

Fig. 2 - General view of the device, where the values of the first auxiliary scale correspond to the calculated values of the level of the articular line, adjusted from the medial epicondyle;

Fig. 3 - General view of the device, view A (jaws in working position);

Fig. 4 - Measurement of the femur width (first auxiliary scale of MELFC);

Fig. 5 - Positioning of the device on the femur and the femoral component of the endoprosthesis on the medial epicondyle (side view, first auxiliary MELFC scale);

Fig. 6. General view of the device, where the values of the first auxiliary scale correspond to the calculated values of the level of the joint line, adjusted from the lateral epicondyle.

Fig. 7 - General view of the device with folded jaws (top view).

A device for determining the level of the joint line for calculating the thickness of the distal and posterior augments when filling in defects of the femoral condyles during knee arthroplasty includes a bar 1 with a first jaw 2, a frame 3 with a second jaw 4 mounted on the bar 1 with the ability to move along it, and a main scale 5 applied to the bar 1 with the ability to be displayed in the window of the frame 3. The first jaw 2 is pivotally mounted on an axis 6 passing through the bar 1. The second jaw 4 is pivotally mounted on an axis 7 passing through the frame 3 (Fig. 3). Both jaws 2, 4 are mounted on the opposite side of the location of scales 5, 9 of the bar 1. The hinges provide the ability to change the position of the jaws (working and non-working position). Thus, the working position is such that jaws 2 and 4 are oriented perpendicular to the longitudinal axis of the bar 1; wherein the hinges are designed with the possibility of fixing the jaws in such a position as to exclude their deviation when measuring the width WF of the femur. The non-working position is one in which the jaws 2 and 4 are oriented along the longitudinal axis of the bar 1, as shown in Fig. 7.

In the bar 1, an opening 8 is made for the fixing spoke, and the bar 1 is also provided with the first auxiliary scale 9, located with the possibility of displaying in the window of the frame 3, and the second auxiliary scale 10, applied to the bar 1 perpendicular to the main scale 5. The second auxiliary scale can be made on the transverse projection 11. The reference point of the second auxiliary scale 10 coincides with the opening 8 for the fixing spoke. In a particular embodiment of the device, the bar can be made transparent; in this case, the second auxiliary scale 10 is made directly on the bar 1 (there is no transverse projection), while making the bar 1 transparent allows for the necessary measurements to be carried out without hindrance during the operation.

The main scale 5 is made in millimeters with a division value of 1 mm, and is intended for determining the width of the femur (the distance between the most protruding distal points of the lateral and medial epicondyles). Each tenth of the risk is signed with the corresponding number in millimeters. The width of the femur is determined using jaws 2 and 4, which can be equipped with extensions 12 at the end sections (about 2 mm) for precise positioning on the epicondyles of the femur. The result of measuring the width of the femur is visualized in the window of frame 3.

The hole 8 for the fixing pin is made at a distance of 30-45 mm from the start of the main scale 5. In a particular embodiment, the start of the main scale can be made inverted, as shown in Fig. 1, i.e. the specified interval (30-45 mm) is applied in reverse order while maintaining the division value. This is necessary for the convenience of taking measurements by the device at subsequent stages (described below). The specified optimal distance of the hole 8 (30-45 mm) is selected for considerations of the possibility of using the device in male patients, who often have an intercondylar distance (WF) above 65 mm.

In another embodiment of the device, the beginning of the main scale 5 can be made in the usual order, but accompanied by a duplicate scale applied in the reverse order (Fig. 2).

The first auxiliary scale 9 is made in accordance with the calculations according to the formula below based on the main scale 5. The first auxiliary scale is intended to identify the digital value of the optimal distance from the epicondyle to the level of the joint line L in the distal direction (down from the epicondyle to the tibia) and from the epicondyle in the posterior direction. In particular embodiments of the device, depending on the preferences of the operating physician and the clinical situation, the first auxiliary scale 9 can be made in different ways. The choice of one or another particular embodiment of the device is determined by which epicondyle of the femur (medial or lateral) will be chosen as the starting point of measurements:

if the medial epicondyle is chosen as the starting point for further measurements, the values of the first auxiliary scale 9 correspond to those calculated using the formula

MEMFC = 8.92 + WF*0.32,

where MEMFC is the distance from the medial epicondyle to the most distal point of the medial condyle of the femur, mm;

WF – width of the femur, estimated as the intercondylar distance, mm;

if the lateral epicondyle is chosen as the starting point for further measurements, the values of the first auxiliary scale 9 correspond to those calculated using the formula

LELFC = 8.49 + WF*0.28,

where LELFC is the distance from the lateral epicondyle to the most distal point of the lateral condyle of the femur, mm;

WF – width of the femur, estimated as the intercondylar distance, mm.

Thus, each value of the main scale 5 corresponds to “its own” value of the first auxiliary scale 9 (Fig. 1), and the values of both specified scales are displayed in the frame window 3.

The second auxiliary scale 10 and the section of the main scale 5 (the beginning of the scale from 0 to the hole 8) are intended for plotting the value selected according to the first auxiliary scale 9 and thereby determining the optimal distance from the epicondyle to the level of the joint line in the posterior direction and in the distal direction (down from the epicondyle to the tibia), respectively. The second auxiliary scale 10 is made in the same units of measurement as the main scale 5 and the first auxiliary scale 9.

The device is used as follows.

Stage 1

Surgical access is performed at the site of the operation, excision of scar tissue is performed, the upper recess and lateral pockets of the knee joint cavity are formed, and during revision surgery, components of the endoprosthesis or previously installed spacer are removed.

Stage 2

The width WF of the femur is measured (Fig. 4) along the supracondylar line. For this purpose, jaws 2 and 4 are set in a position perpendicular to the longitudinal axis of the bar, then positioned on the epicondyles 13, 14 of the femur by moving the movable frame 3 until tight contact of the extensions 12 with the most protruding points of the medial and lateral epicondyles is achieved. In the window of frame 3, the value of the width WF of the femur and the corresponding value of the optimal distance from the epicondyle to the level of the articular line L along the first auxiliary scale 9 are read on the main scale 5. The selected value is remembered, frame 3 with the movable jaw 4 can then be removed from bar 1 (it is not used further). If a device with the first auxiliary scale calculated as the MEMFC scale is used, then subsequent use of the device is carried out, adjusting from the medial epicondyle. If a device with the first auxiliary scale calculated as the LELFC scale is used, then subsequent use of the device is carried out, adjusting from the lateral epicondyle.

Stage 3

Jaws 2 and 4 are folded by rotating them on axes 6 and 7, respectively (if necessary), in such a way that the device is installed on the most protruding point of the epicondyle (lateral 13 or medial 14), selected as the starting point for further measurements, and fixed with a pin 15 passing through the hole 8. In this case, the bar is oriented longitudinally to the femur, so that the beginning of the main scale is located distally (towards the femur), and the second auxiliary scale is oriented in the posterior direction (Fig. 5). The surgeon determines the location of the installation of the fixing pin 15 empirically, based on the most protruding point. The choice of the epicondyle is determined by a specific clinical situation and/or for reasons of ease of use by the operating physician. As a rule, the starting epicondyle is selected at stage 1. Fig. 5 shows a view of the device installed on the medial epicondyle 14.

Stage 4

The value of the optimal distance L from the epicondyle to the level of the joint line A1-A1 and A2-A2 selected at stage 2. This value corresponds to L=31 mm (Fig. 5). The value is plotted along the inverted section of the main scale 5 and along the second auxiliary scale 10. The value L plotted along the inverted section of the main scale 5 denotes the calculated level of the joint line A1-A1 in the downward direction from the epicondyle to the tibia, as well as the location of the distal surface of the endoprosthesis 16 (Fig. 5). The value L plotted along the second auxiliary scale 10 denotes the calculated level of the joint line A2-A2 from the epicondyle in the posterior direction, as well as the distal surface of the endoprosthesis 16 (Fig. 5). The identified levels of the joint line A1-A1 and A2-A2 in the distal and posterior directions make it possible to determine the thickness of the distal 17 and posterior 18 metal augments necessary to fill (compensate) the bone defect.

Stage 5

The required thickness of the distal 17 augment is calculated. To do this, the value where the bone begins is determined on the main scale 5 of the device. This value corresponds to 23 mm (Fig. 5). After which the thickness T _augm is calculated using the formula

T _augm = L - m - t _end ,

where L is the value of the joint line level selected according to the first auxiliary scale, mm;

m – value on the main scale where the bone begins, mm;

tэ _нд – thickness of the endoprosthesis, mm.

The thickness of the augment is T _augm = 31 - 23 - 5 = 3 mm (Fig. 5).

Stage 6

The required thickness of the posterior 18 augment is calculated. To do this, the value where the bone begins is determined on the second auxiliary scale 10 of the device. This value corresponds to 25 mm (Fig. 5). After which the thickness T _augm is calculated using the formula

T _augm = L - m - t _end ,

where L is the value of the joint line level selected according to the first auxiliary scale, mm;

m – value on the main scale where the bone begins, mm;

tэ _нд – thickness of the endoprosthesis, mm.

The thickness of the augment is T _augm = 31 - 25 - 4 = 2 mm (Fig. 5).

Stage 7

Next, the device is removed, bone defects are compensated, the necessary augments with a thickness calculated according to stages 5 and 6 are installed, an endoprosthesis is installed, and the wound is sutured layer by layer. If necessary, control of the level of the joint line A-A can be performed at all of the above stages.

The device allows for correct performance of knee joint arthroplasty by increasing the accuracy of restoring the level of the joint line and improving the reproducibility of the intervention technique:

the hole for the fixing pin allows the device to be fixed in a precisely specified location and to simultaneously measure the bone defect in two directions (in the distal direction (down from the epicondyle to the tibia) and from the epicondyle in the posterior direction);

the scale lines allow you to select the location of the joint line formation and determine the size of the metal augments needed to compensate for bone defects with an accuracy of up to 1 mm;

improved visualization during sizing of metal augments increases the accuracy and reproducibility of surgical intervention;

the application of scales on both sides of the device allows this device to be used for both the right and left knee joints;

The device allows one to do without specialized expensive computerized navigation systems used in knee joint endoprosthetics.

Example 1

Patient B, 67 years old. Clinical diagnosis: "Right-sided gonarthrosis stage 3. Condition after total endoprosthetics of the right knee joint from 2021. Aseptic instability of the endoprosthesis components." The medial epicondyle of the femur was chosen as the starting point for measurements and calculations. Using the device, the width of the femur (87 mm) was measured with jaws 2 and 4 pre-set in a position perpendicular to the longitudinal axis of the bar. The range of calculated values of the distances from the medial epicondyle to the most distal point of the medial condyle of the femur acceptable for this patient is visualized in the window of frame 3. The operating surgeon chose a value of 37 mm. The physician then places the device, having previously folded jaws 2 and 4, on the medial epicondyle of the femur in such a way that the hole for pin 8 is located exactly on the epicondyle of the femur, the bar is oriented longitudinally to the femur, so that the beginning of the main scale is located distally (towards the femur), and the second auxiliary scale is oriented in the posterior direction. The selected value of 37 mm is laid off from the opening 8 on the inverted section of the main scale 5 and on the auxiliary scale 10. The value L laid off along the inverted section of the main scale 5 denotes the calculated level of the joint line A1-A1 in the downward direction from the epicondyle to the tibia, as well as the location of the distal surface of the endoprosthesis 16. The value L laid off along the second auxiliary scale 10 denotes the calculated level of the joint line A2-A2 from the epicondyle in the posterior direction, as well as the distal surface of the endoprosthesis 16. The identified levels of the joint line A1-A1 and A2-A2 in the distal and posterior directions make it possible to determine the thickness of the distal 17 and posterior 18 metal augments required to fill (compensate) the bone defect (3 mm and 2 mm). During the control examination after 2 months, satisfactory mobility is observed, pain syndrome is absent. The use of a device with folding jaws made it convenient to use for determining the level of the joint line.

Example 2

Patient A, 53 years old. Clinical diagnosis: "Left-sided gonarthrosis stage 3. Condition after implantation of an articulating antimicrobial spacer of the right knee joint from 2023. Deep infection of the surgical site from 2022." The lateral epicondyle of the femur was chosen as the starting point for measurements and calculations. The device was used to measure the width of the femur in a similar manner to the above-described sequence (46 mm), with jaws 2 and 4 pre-set in a position perpendicular to the longitudinal axis of the bar. The operating surgeon selected a value of 21 mm in the window of frame 3. Next, the device was installed on the lateral epicondyle, with jaws 2 and 4 pre-folded, so that hole 8 for the pin was located exactly on the epicondyle of the femur, the bar was oriented longitudinally to the femur, so that the beginning of the main scale was located distally (towards the femur), and the second auxiliary scale was oriented in the posterior direction. The selected value of 21 mm is laid off from the opening 8 on the inverted section of the main scale 5 and on the auxiliary scale 10. The value L laid off along the inverted section of the main scale 5 denotes the calculated level of the joint line A1-A1 in the downward direction from the epicondyle to the tibia, as well as the location of the distal surface of the endoprosthesis 16. The value L laid off along the second auxiliary scale 10 denotes the calculated level of the joint line A2-A2 from the epicondyle in the posterior direction, as well as the distal surface of the endoprosthesis 16. The identified levels of the joint line A1-A1 and A2-A2 in the distal and posterior directions make it possible to determine the thickness of the distal 17 and posterior 18 metal augments required to fill (compensate) the bone defect (1 mm and 2 mm). During the control examination after 2 months, satisfactory mobility is observed, pain syndrome is absent. The use of a device with folding jaws made it convenient to use for determining the level of the joint line.

Example 3

Patient M, 39 years old. Clinical diagnosis: "Post-traumatic deforming arthrosis stage 3, condition after metal osteosynthesis of an intra-articular fracture of the right femur from 2021, removal of the metal structure from 2023. Deep infection of the surgical site, sanitation of the cavity of the right knee joint from 2023." The medial epicondyle of the femur was chosen as the starting point for measurements and calculations. The device was used to measure the width of the femur in a similar manner to the above-described sequence (64 mm), with jaws 2 and 4 pre-set in a position perpendicular to the longitudinal axis of the bar. The operating surgeon selected a value of 29 mm in the window of frame 3. Next, the device was installed on the lateral epicondyle, with jaws 2 and 4 pre-folded, so that hole 8 for the pin was located exactly on the epicondyle of the femur, the bar was oriented longitudinally to the femur, so that the beginning of the main scale was located distally (towards the femur), and the second auxiliary scale was oriented in the posterior direction. The selected value 29 is plotted from the opening 6 on the inverted section of the main scale 5 and on the auxiliary scale 10. The value L plotted along the inverted section of the main scale 5 denotes the calculated level of the joint line A1-A1 in the downward direction from the epicondyle to the tibia, as well as the location of the distal surface of the endoprosthesis 16. The value L plotted along the second auxiliary scale 10 denotes the calculated level of the joint line A2-A2 from the epicondyle in the posterior direction, as well as the distal surface of the endoprosthesis 16. The identified levels of the joint line A1-A1 and A2-A2 in the distal and posterior directions make it possible to determine the thickness of the distal 17 and posterior 18 metal augments required to fill (compensate) the bone defect (1 mm and 2 mm). During the control examination after 2 months, satisfactory mobility is observed, pain syndrome is absent. The use of a device with folding jaws made it convenient to use for determining the level of the joint line.

Example 4

Patient B, 65 years old. Clinical diagnosis: "Right-sided gonarthrosis stage 3. Condition after total endoprosthesis replacement of the right knee joint from 2024. Aseptic instability of the endoprosthesis components." The lateral epicondyle of the femur was chosen as the starting point for measurements and calculations. Using the device, the width of the femur was measured similarly to the sequence described above (70 mm), with jaws 2 and 4 pre-set in a position perpendicular to the longitudinal axis of the bar. The operating surgeon selected a value of 28 mm in the window of frame 3. Next, the device was installed on the lateral epicondyle, with jaws 2 and 4 pre-folded so that hole 8 for the pin was located exactly on the epicondyle of the femur, the bar was oriented longitudinally to the femur, so that the beginning of the main scale was located distally (towards the femur), and the second auxiliary scale was oriented posteriorly. The selected value of 28 mm is laid off from the opening 8 on the inverted section of the main scale 5 and on the auxiliary scale 10. The value L laid off along the inverted section of the main scale 5 denotes the calculated level of the joint line A1-A1 in the downward direction from the epicondyle to the tibia, as well as the location of the distal surface of the endoprosthesis 16. The value L laid off along the second auxiliary scale 10 denotes the calculated level of the joint line A2-A2 from the epicondyle in the posterior direction, as well as the distal surface of the endoprosthesis 16. The identified levels of the joint line A1-A1 and A2-A2 in the distal and posterior directions make it possible to determine the thickness of the distal 17 and posterior 18 metal augments necessary to fill (compensate) the bone defect (2 mm and 3 mm). During the control examination after 2 months, satisfactory mobility is observed, pain syndrome is absent. The use of a device with folding jaws made it convenient to use for determining the level of the joint line.

Thus, the claimed solution provides a simple and effective device for determining the level of the joint line when filling defects of the femoral condyles with significant anatomical abnormalities of the distal epiphysis of the femur by increasing the accuracy of determining the optimal distance from the epicondyle of the femur to the level of the joint line.

References

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Claims (9)

1. A device for determining the level of the joint line for calculating the thickness of the distal and posterior augments when filling defects of the femoral condyles during knee arthroplasty, comprising a bar with a first sponge, a removable frame with a second sponge and a window mounted on the bar with the ability to move along it, the first sponge is pivotally mounted on an axis passing through the bar, the second sponge is pivotally mounted on an axis passing through the removable frame, said sponges can be positioned on the epicondyles of the femur, the bar has a main scale with the values of the femur width measurements and with an inverted section for determining the level of the joint line in the downward direction from the epicondyle to the tibia, a first auxiliary scale with the values of the distance from the epicondyle to the level of the joint line in the distal direction, a second auxiliary scale for determining the level of the joint line from the epicondyle in the posterior direction, located perpendicular to said main scale, and an opening for a fixing a spoke, made at a distance of 30-45 mm from the starting point of the said main scale and being a starting point for the said second auxiliary scale and a point for plotting the value along the said inverted section of the main scale, wherein the frame window is made with the possibility of displaying the values of the said main and first auxiliary scales, wherein each value of the said main scale corresponds to “its own” value of the said first auxiliary scale, all said scales are made on both sides of the bar with the possibility of use for the right and left knee joints. 2. The device according to item 1, characterized in that the values of the distance from the epicondyle to the most distal point of the condyle of the femur of the first auxiliary scale for the medial epicondyle and condyle correspond to the values obtained according to the formula MEMFC = 8.92 mm + WF*0.32 mm, where MEMFC is the distance from the medial epicondyle to the most distal point of the medial condyle of the femur, mm; WF – femur width, mm. 3. The device according to item 1, characterized in that the values of the distance from the epicondyle to the most distal point of the condyle of the femur of the first auxiliary scale for the lateral epicondyle and condyle correspond to the values obtained by the formula LELFC = 8.49 mm + WF*0.28 mm, where LELFC is the distance from the lateral epicondyle to the most distal point of the lateral condyle of the femur, mm; WF – femur width, mm.