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Manual

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Introduction

What is OrthoLoad?


OrthoLoad is a public database containing the loads acting in orthopaedic implants. They were measured in vivo using instrumented implants with telemetric data transmission. Currently load data are available for the

Hip joint, shoulder joint, knee joint, vertebral body replacement and internal spinal fixator.

Data is presented as videos, containing the time-dependent forces and moments, force vectors, video images of the patients activity and numerical data. Many results involving the 'Hip Joint' are already available in the database. More data are continuously added from the actual 'Hip Joint III' where also the three moments were measured.  From hip and knee implants, only selected examples are available because access to this data must be detained until it has been published in scientific journals.

From the OrthoLoad database you can select an implant, an activity with parameters, a patient and one or several trials. The time course of the loads is shown in videos (encoded in the wmv- or mp4-format) and can be analyzed in more detail by displaying single video frames. Numerical data files (text files, suffix .akf) can additionally be downloaded and the forces and moments then be used in finite element studies or joint simulators, for example.

It's recomended to run OrthoLoad on a Windows PCs with Media Player Classic, VLC Player or FairPlay Lite player or on Linux/Mac OS X with VLC Player!

How to use OrthoLoad?


Enter DATABASE and in the top left frame 'Joint Loads' you can choose an 'Implant' type, an 'Activity', possibly an additional 'Parameter', a 'Patient' and a trial by 'File Name'. Then an OrthoLoad video will be shown on the right frame 'Now Selected'.

Alternatively you may select a trial directly by typing its basic trial number into the upper right frame 'Select Video by File Name'. The basic trial number is the first part of the file name e.g. 's1r_211005_1_80' of the file 's1r_211005_1_80_screen.mp4'  

(s1r = shoulder patient #1 with implant at the right side,  _211005 = date: October 21st 2005,  _1_80 = internal trial number  _screen = video file,  _fmax = png-image)

Use the buttons in the top left frame 'Joint Loads' to play, show or download videos, data or pictures. You may just play the video in your browser with Flash Plug-in. Or you download and play the video on your computer with your standard video player. We clearly favour the 'Media Player Classic' or 'VLC Player' for MS Windows and 'VLC Player' for Mac OS X and Linux. Videos are encoded in the wmv or mp4(H.264) format.

Structure of an ORTHOLOAD video
Structure of an ORTHOLOAD video

The vertical marker line inside the force diagram shows the actual measuring time. All other data is displayed synchronously to this time (patient video, vectors, tables ...).

The 'Hip Joint' was instrumented with a 4-channel telemetry transmitter and only the forces were measured,  no moment diagram is shown. All other implants measure forces and moments with measuring units %BW and %BW*m. Using the patients' body weight (BW), the values in N and Nm can be recalculated.

To show or download a data file *.akf belonging to the video *.wmv or *.mp4 use the buttons 'Show' or 'Download' in the top left frame 'Joint Loads'.

'Additional Data'  *.eof, *.cof etc. synchronized to the video file is available for some trials

Measurements


Measurements

A coil for the inductive power supply is arranged around the implant and the antenna is placed close to it. The data received is at first controlled in regard to transmission errors and then led to a notebook where the forces and moments are calculated and displayed in real time. The images of the patients' exercises and the synchronous data stream are both recorded on the same video tape. On a monitor or using a video beamer, the forces and moments can be controlled immediately. This allows one to detect unexpected loading situations and immediately modify the way an exercise is performed.

OrthoLoad Videos

Video format

The older OrthoLoad videos have a frame rate of 25 fps (time resolution = 0.04 s). Newer videos run at a speed of 50 fps (time resolution = 0.02 s).

Video size

All OrthoLoad videos have a size of 1024x768 pixels. In order to see them in best quality in a media player, choose Zoom = 100%. On a notebook with a resolution of 1024x768 pixels you should play the videos in the 'Full Screen' modus.

Video codec

We encode all files using the Windows Media Encoder 9 which produces files in the wmv-format (Windows Media Video). The quality and file size are at least as good as those of avi-files using the DivX or Xvid codec. The wmv-codec is supplied with each Windows installation from Windows XP onwards. In nearly all cases the OrthoLoad videos therefore run on Windows computers without any difficulties. This is an advantage as no additional codec must be installed on your PC, and the videos almost always run in PowerPoint presentations. If the wmv-codec is not installed on your PC, you can download it. Or you can download the newest version of the Windows Media Player which includes the wmv codec (see comments on the Windows Media Player).

Furthermore, we convert all OrthoLoad videos in the mp4-video format(H.264) using ffmpeg codec library. You can play mp4-videos on Windows, Mac OS X and Linux computers with VLC player. We suggest VLC Player 2.0 or higher.

Conversion of wmv video format

If you want to convert an OrthoLoad video to another format, for example to an avi-file with the Xvid-codec, we suggest that you use the free conversion program 'Super'.

Media player

These are some popular free video players:

Media Player Classic

This simple player must not be installed. It plays 25 fps and 50 fps videos at a correct speed and you can study movements in detail frame by frame by using the arrow key button (forwards only !). The time counter has a resolution of only 1s, but the precise time is shown in the small table 'Video' & 'Time Now' in the OrthoLoad videos. You can open several instances of the program at the same time, for example if you would like to compare different exercises.

FairPlay Lite

This player is very small, easy to handle and for free. Installation is not required. 50 fps videos are shown at correct speed and you can proceed with the arrow keys. The time counter has a resolution of 0.02s (50 fps). Several instances of the player can be opened.

Windows Media Player

This player is installed together with Windows. It does play 50 fps videos, but it is overloaded with features, and it is difficult to select a single video frame using the mouse. Proceeding frame-by-frame is not possible. The time counter has a resolution of only 1s.

VLC media player

VLC player is a powerfull open source media player für Windows, Mac OS X and Linux. It plays 25 fps and 50 fps videos at a correct speed and you can study movements in detail frame by frame by using the hotkey 'e' (see 'Tools/Options/Hotkeys').

Other Video Players

Kinovea can be used to play 2 videos synchronously. It doesn't work properly with wmv-videos, however.

We suggest

Use of the Media Player Classic or FairPlay Lite as the Standard Video Player for the wmv-video format (Windows). Use of the VLC media player as the Standard Video Player for the mp4-video format (Windows, Mac OS X, Linux).

Additional Load Data

Numerical data files

Beispiel AKF

For each OrthoLoad video *.wmv, an additional numerical data file *.akf exists. The data in k2l_140607_1_9.akf, for example, belongs to the video k2l_140607_1_9_screen.wmv. The video frame rate is only 25 or 50 Hz and thus the load values seen in the bottom left table of the OrthoLoad video are available at this rate, too. The loads from the instrumented implants were measured at the much higher sampling rate of typically 120 Hz. They are stored in the akf files, which can be opened with any text editor. Small time shifts between the videos and the numerical data can exist. They were compensated for during production of the OrthoLoad videos.

The data in the akf-files are self-explanatory. 'Marker' is a signal used to synchronize the telemetric data with external measurements and is of no use to you. The time is given in seconds. Forces or moments are not listed in %BW or %BW*m, as in the OrthoLoad videos (more info). Instead, they are given in measuring units N or Nm in the akf-files. Because the body weight on the measuring day is also stated in the akf-files, you can easily transform the units to %BW or %BW*m. Just divide them by one percent of the body weight [N]. A force of 1000N in a patient with a body weight of 870N (88.7kg), for example, equals the force of 114.9 %BW.10 Nm then corresponds to a moment of 1.15 %BW*m.

If you want, you can directly apply the numerical data, i.e. the time-dependent forces and/or moments in finite element studies or in joint simulators.

You can access each file separately (button 'Download' in the frame 'Additional Data File').

Data collection 'HIP98'

Hip98 Screen

The data collection HIP98 contains the forces acting in the hip joint during the most common activities of daily living. Measurements were taken in 1998 in 4 subjects. In addition to the implant loads and the synchronous videos of the subjects (as in OrthoLoad), this database provides gait analysis data, calculated muscle forces, EMG signals and numbers for the frequencies of the different activities (show abstract of Bergmann et al., 2001).

The forces acting at the acetabulum, i. e. the pelvic side of the hip joint, were additionally determined, using the forces acting relative to the femur plus the belonging gait analysis data. From the results of the individuals, the loads acting in a 'typical' or representative subject are also provided (download HIP98).

Measuring units [%BW, %BW*m or N, Nm]

Measuring Units

Forces from the spine have the measuring unit N, moments have the unit Nm. Data from all other implants are given in %BW (percent of body weight) for the forces and %BW*m for the moments. This is done because the results are then more uniform between the subjects. If you replace %BW by one percent of the patient's body weight, you will then obtain the forces or moments in N or Nm.

Example: If a patient has a body weight of 850 N (86.4kg) you have to multiply the forces or moments, given in %BW or %BW*m, with the factor 8.5 to obtain them in N or Nm. The body weight and multiplication factor of each individual subject is stated in the window 'Info Patient' of the OrthoLoad videos, for example 8.5*{%BW, %BWm} --> {N, Nm}.

Your Computer

Computer requirements

We suggest

  • A PC with Microsoft Windows XP / Vista / Win7 / Mac OS X / Linux
  • A display having XGA resolution 1024x768 pixel or higher
  • Mozilla Firefox 2.0 or Microsoft Internet Explorer 7.0 (or higher)
  • Microsoft Media Player Classic as standard player for the wmv-video format and / or VLC Player 2.0 (or higher) as the standard video player for mp4-video format)
  • The installation of Windows Media Player if the wmv video codec is not installed.

Internet Browser

OrthoLoad was tested using Microsoft Internet Explorer 7.0 , Mozilla Firefox 4.0, Google Chroma 1ß.0 and Safari 5.0 and higher. For playing the OrthoLoad videos in your browser you need the Flash Plug-in.

Hip joint

Two different hip implants (Hip I and Hip II) monitor the three force components acting on the ceramic head of the hip joint.


Instrumented implant

Hip I with one 4-channel transmitter

Implant Hip I
Implant Hip I

The implant is made of a titanium stem and a ceramic head. A compartment, 32 mm deep and 9.5 mm wide, houses the electronic instrumentation inside the neck of the prosthesis. Three semiconductor strain gauges were applied at the lower end of the inner wall and connected to the 4-channel transmitter. Two electrical feed-throughs, welded in the top plate by electron beam, form the transmitter antenna inside the ceramic ball. After the instrumentation, the top plate is welded by laser onto the prosthetic neck, thus sealing the inner space in such a manner that it is absolutely safe against the body.

Since 1988 four instrumented hip joints (Hip I) were implanted in three patients (EBL/EBR, JBR, IBL).

Hip II with two 8-channel transmitters

Implant Hip II
Implant Hip II

To get more information about a potential temperature increase of hip implant after longer walking distances, an implant with a hollow shaft was instrumented with two 8-channel telemetry transmitters. A common coil in the middle of the shaft supplies power to both telemetry circuits. Inside, eight temperature sensors are arranged along the whole neck and shaft. Three strain gauges placed inside the prosthetic neck monitor the three force components which act at the centre of the ceramic ball. A fourth strain gauge measures the strain of the stem. One telemetry transmitter is placed inside the prosthetic neck; the second device is fixed inside the hollow shaft of the implant. A 4-lead feed through is welded by laser in the top plate of the neck and forms two single loop antennas for the signal transmission.

Since 1997 five instrumented hollow shaft hip joints (Hip II) were implanted in four patients (KWL/KWR, HSR, PFL, RHR).


Coordinate system

Femur system

Coordinate system at left Femur

All forces are reported in a right-handed coordinate system of the left femur (different from hip joint type: Hip III). The load components are reported as -Fy, -Fy, -Fz with negative signs. Positive values therefore indicate components acting toward the femoral head.

Femur Sytem Loads

In many previously produced >OrthoLoad videos from the hip joint the minus signs are lacking!

The femur system is fixed at the centre of the femoral head. The femoral midline (dotted black/white) intersects with the axis of the neck in point P1. This midline leaves the femur distally at point P2. Point P2 is defined as the deepest point of the fossa intercondylaris at the distal end of the femur. The straight connection between P1 and P2 defines the z axis (marked in red). Perpendicular to z and parallel to a plane through the most dorsal parts of the condyles, the x axis is defined (green) and points medially. The y axis (blue) is perpendicular to x and z and points ventrally.

Implant system

In order to test fatigue or strength of the implant itself, it may sometimes be required to know the force components in an implant-based coordinate system. Axis zi of this system coincides with the shaft axis of the implant. The xi axis lies in the neck-shaft-plane. For the transformation of forces from the femur to the implant system, two angles are required: angle S between the z axis of the bone and the shaft axis of the implant, and the anteversion angle AV of the implant. This data is provided in a table.

Because the angle S is always small, transformation of the force components can be performed with sufficient accuracy by


  • Turning the system by +AV around the +z axis
  • Turning the system by +S around the +x axis


More details about this transformation are given here and in Bergmann et al. (2001).

Patients

Pat EBL big.png Pat IBL big.png Pat JBR big.png  
EBL / EBR  (Hip I) IBL  (Hip I) JBR  (Hip I)  
Pat HSR big.png Pat KWR big.png Pat PFL big.png Pat RHR big.png
HSR  (Hip II) KWL / KWR  (Hip II) PFL  (Hip II) RHR  (Hip II)

Table with basic information about the patients with Hip I and Hip II implants:

Patient Implant Side Gender Weight
[kg]
Height
[cm]
Age at
Implantation
[years]
Indication
EBL Hip I left m 62 168 83 Osteoarthritis
EBR Hip I right m 62 168 83 Osteoarthritis
IBL Hip I left f 84 170 76 Osteoarthritis
JBR Hip I right f 47 160 69 Femoral head necrosis
HSR Hip II right m 82 174 55 Osteoarthritis
KWR Hip II right m 72 165 61 Osteoarthritis
KWL Hip II left m 72 165 61 Osteoarthritis
PFL Hip II left m 98 175 49 Osteoarthritis
RHR Hip II right f 60 N/A 63 Osteoarthritis

For the hip joint, the forces and moments in an implant-based coordinate system are of special interest. The torque around the shaft axis, for example, is one of the most important parameters for the stability of implant fixation. To transform the forces measured relative to the bone, as delivered by OrthoLoad, to the loads acting in the implant system, the anteversion angle AV of the implant, the CCD angle and the neck length L are required. This data are listed in the following table:

Patient Anteversion
Angle AV
[degree]
CCD Angle
[degree]
Neck Length L
[mm]
Shaft Angle S
[degree]
EBL 5 135 60 10
EBR 5 135 60 10
IBL 14 135 60 9
JBR 10 135 60 10
HSR 4 135 62 10
KWR -2 135 62 9
KWL 17 135 62 8
PFL 23 135 62 7
RHR 34 135 62 6


Hip joint III

The actual hip implant (Hip III) monitor the three force components and the three moment components acting on the ceramic head of the hip joint.


Instrumented implant

Hip III with one 9-channel transmitter

Implant Hip III
Implant Hip III

This new design of a instrumented hip implant was developed to measure contact forces and the friction at the joint in vivo. A clinical proven hip implant ('Spotorno' design) was modified in the neck area. The stem is build by TiAl6V4 and Al2O3-Ceramic was choosen for the implant head material. The neck was widened and enhanced with a 6.2 and 10mm hole. In the hollow neck are housed six semiconductor strain gauges, an internal induction coil and the telemetry. The six strain gauges are applied at the lower part on the inner wall (10mm hole) and connected to the 9-channel transmitter. The antenna, placed under the implant head, is connected by electronically feed-through to the internal telemetry. The feed-through is welded by a laser beam into the top plate. The hollowed neck is closed by the top plate and welded with an electron beam. Therefore the internal space is hermetically closed against the body fluids.

With this implant three contact forces acting onto the implant head center and three friction moments acting between the gliding partners can be measured in vivo.

Since April 2010 ten instrumented hip joints (Hip III)  were implanted in ten patients (H1L, H2R, H3L, H4L, H5L, H6R, H7R, H8L, H9L and H10R) to monitor forces and moments. No further implantations are planned.

Coordinate system

Femur system

Coordinate System at right Femur

All forces are reported in a right-handed coordinate system of the right femur (different from hip joint type I and II). The load components are reported as Fx, Fy, Fz. The femur system is fixed at the centre of the femoral head. The femoral midline (dotted black) intersects the axis of the neck in point P1. Point P2 is defined as the deepest point of the fossa intercondylaris at the distal end of the femur. The straight connection between P1 and P2 defines the z axis of the femur. The z axis of the coordinate system is parallel to the z axis of the femur. The x axis of the coordinate system is defined perpendicular to z and parallel to a plane through the most dorsal parts of the condyles and points laterally. The y axis of the coordinate system is perpendicular to x and z and points ventrally.


Implant system

Implant System Patient

In order to test fatigue or strength of the implant itself, it may sometimes be required to know the force components in an implant-based coordinate system. Axis zi of this system coincides with the shaft axis of the implant. The xi axis lies in the neck-shaft-plane. For the transformation of forces from the femur- to the implant system, three angles are required: angle Sx between the z axis of the bone and the shaft axis of the implant, angle Sy between the z axis of the bone and the shaft axis of the implant and furthermore the anteversion angle AV of the implant. These data are provided by the table in the video ("Info Patient").

  1. Turning the system by + Sx around the - x axis
  2. Turning the system by + Sy around the - y axis
  3. Turning the system by - AV around the + z axis

More details about this transformation are given here and in Bergmann et al. (2001).

Patients

Pat-H1L big.png Pat-H2R big.png Pat-H3L big.png Pat-H4L big.png Pat-H5L big.png
H1L H2R H3L H4L H5L
Pat-H6R big.png Pat-H7R big.png Pat-H8L big.png Pat-H9L big.png Pat-H10R big.png
H6R H7R H8L H9L H10R

Table with basic information about the patients with Hip III implants:

Patient Side Gender Weight
[kg]
Height
[cm]
Age at
Implantation
[years]
Indication
H1L left m 73 178 55 Coxarthrosis
H2R right m 75 172 61 Coxarthrosis
H3L left m 92 168 59 Coxarthrosis
H4L left m 85 178 50 Coxarthrosis
H5L left f 87 168 62 Coxarthrosis
H6R right m 84 176 68 Coxarthrosis
H7R right m 95 179 52 Coxarthrosis
H8L left m 80 178 55 Coxarthrosis
H9L left m 118 181 54 Coxarthrosis
H10R right f 98 162 53 Coxarthrosis

For the hip joint III, the forces and moments in an implant-based coordinate system are of especial interest. The torque around the shaft axis, for example, is one of the most important parameters for the stability of implant fixation. To transform the forces measured relative to the bone, as delivered by OrthoLoad, to the loads acting in the implant system, the anteversion angle AV of the implant, the CCD angle and the neck length L are required. This data is listed in the following table:

Patient Anteversion
Angle AV
[degree]
CCD Angle
[degree]
Neck Length
L
[mm]
Shaft Angle
Sx
[degree]
Shaft Angle
Sy
[degree]
H1L -15.0 135 55.6 2.3 -2.3
H2R -13.8 135 59.3 4.1 0.6
H3L -13.8 135 55.6 4.0 -3.0
H4L -18.9 135 63.3 7.5 -1.7
H5L -2.3 135 55.6 4.0 -2.3
H6R -31.0 135 55.6 5.8 -1.7
H7R -2.4 135 63.3 6.3 -1.7
H8L -15.5 135 59.3 4.6 -1.7
H9L -2,3 135 59.3 4.6 0.6
H10R -9,7 135 59.6 1.7 -1.2


Shoulder joint

Instrumented implant

Implant: Shoulder joint
Implant: Shoulder joint

The picture shows an instrumented shoulder implant capable of measuring forces, moments and, in addition, the temperature acting in the glenohumeral joint. It was developed in the Biomechanics Lab of the Charité and contains a measuring unit with 6 semiconductor strain gauges and a 9-channel telemetry transmitter. Each strain gauge requires one channel of the telemetry while the remaining three channels are used for transmitting the temperature, the current supply voltage and a synchronising signal. At the lower end, an inductive coil ensures the power supply. The measuring signals are led with a pacemaker feed-through to the antenna (protected by a cap of PEEK) which transmits the signals to the external measuring unit.

Coordinate system

Humerus system

Coordinate System Shoulder Joint

All loads are displayed as acting at the humerus. They are based on the ISB-recommended coordinate system (Wu et al., 2005) for the right shoulder joint. In this bone-based shoulder coordinate system, the positive x-Axis points in the anterior, the y-axis in the superior and the z-axis in the lateral direction. The moments Mx, My and Mz turn clockwise around the +x, +y and +z axes.

This system is right-handed for a right shoulder joint. For patient S3L, who obtained her implant on the left side, all values are mirrored to the right side to make it comparable to the other patients.

Implant system

Implant System Shoulder Joint
Implant System Shoulder Joint
Implant System Shoulder Joint

In the implant-based coordinate system of the shoulder joint, the positive z-axis coincides with the neck of the implant and points in the medial-cranial direction. x- and y-axes are in the plane perpendicular to the implant neck. Axis x points laterally and y is oriented anteriorly. Load components relative to this implant-base system may be used to test fatigue or wear of implants, for example.

To obtain the forces and moments relative to the implant, the retroversion of the humeral head has to be known, indicated as α in the picture below. It can be measured relative to the anatomical landmarks of the epicondyles at the elbow or related to the orientation of the forearm in 90° elbow flexion as it is chosen during surgery (Hernigou et al., 2002). For some patients in OrthoLoad exact values for the retroversion to the epicondyles are available from a postoperative CT, taken for medical reasons. For the other patients a retroversion angle of 30° relative to the forearm in 90° elbow flexion was assumed as chosen by the surgeon during implantation.

The retroversion value for each patient can be found in the "Info Patient" window in OrthoLoad as the third rotation angle (picture below, right). In this example the given rotation angle of 63° corresponds to a retroversion angle of 27° (90°-63°). The other two angles are determined by the geometry of the implant and are therefore the same for all patients. The vector plot pictures (below, left) are simplified representations for better visualisation. The shown angle α is always the same and differs from the true angle in the patients.

General advice for the transformation of loads from a bone-based to an implant-based system is described here.

Scapula system

To obtain the loads relative to the scapula, a coordinate transformation would be required, taking into account the relative movement between humerus and scapula. This requires an accurate movement analysis. Such transformations are already planned but are not yet available.

Patients

Pat S1R big.png Pat S2R big.png Pat S3L big.png Pat S4R big.png
S1R S2R S3L S4R
Pat S5R big.png Pat S6R big.png Pat S7R big.png Pat S8R big.png
S5R S6R S7R S8R

Table with basic information about the shoulder joint patients:

Patient Side Gender Weight
[kg]
Height
[cm cm]
Age at
Implantation
[years]
Indication
S1R right m 101 186 69 Osteoarthritis
S2R right m 85 161 61 Osteoarthritis
S3L left f 72 168 70 Osteoarthritis
S4R right f 50 154 80 Osteoarthritis
S5R right f 103 163 66 Osteoarthritis
S6R right m 135 186 50 Osteoarthritis and Necrosis
S7R right m 89 172 68 Osteoarthritis
S8R right m 83 173 72 Osteoarthritis

Literature:

Hernigou, P., Duparc, F., Hernigou, A., 2002. Determining humeral retroversion with computed tomography. J Bone Joint Surg Am 84-A, 1753-1762. Wu, G., van der Helm, F.C., Veeger, H.E., Makhsous, M., Van Roy, P., Anglin, C., Nagels, J., Karduna, A.R., McQuade, K., Wang, X., Werner, F.W., Buchholz, B., 2005. ISB recommendation on definitions of joint coordinate systems of various joints for the reporting of human joint motion--Part II: shoulder, elbow, wrist and hand. J Biomech 38, 981-992.

Knee joint

Instrumented implant

Implant: knee joint
Implant: knee joint

In order to obtain realistic loading data, a knee implant with a 9-channel telemetry transmitter was developed which enables six-component load measurements in a primary total knee replacement. Both forces in axial, medio-lateral and anterio-posterior direction and flexion-extension, varus-valgus and internal-external moments can be measured.The instrumented knee joint is a modification of the INNEXTM System, Type FIXUC (Zimmer GmbH, Winterthur, Switzerland). The standard femur component and tibial insert are used. Only the tibial component was modified to enable the integration of the electronic devices. During modification of the tibial component, the patients' safety was deemed to be especially important.

Coordinate system

Coordinate system Knee Joint
Coordinate system knee joint

The coordinate system of the instrumented knee implant is a right-handed coordinate system fixed at the right tibial implant (not at the bone!). If forces and moments are measured in a left knee, they are transformed to the right side. The coordinate system is located at the height of the lowest part of the polyethylene insert. The z-axis is aligned with the stem axis of the implant.

The force components +Fx, +Fy and +Fz act in lateral, anterior and superior direction on the tibial tray. The moment Mx acts in the sagittal plane of the tibial component and turns clockwise around the +x-axis. The moment My acts in the frontal plane and turns clockwise around the +y-axis and the moment Mz turns clockwise around +z-axis in the transverse plane. A positive moment Mz acts if the tibial implant component (or the femur) rotates inwards and/or if the tibia bone rotates outwards. The OrthoLoad videos show the load components relative to the tibial tray. The stem axis z of the tibial implant component is rotated backwards in the sagittal plane by about 7 degree relative to the long axis of the tibia bone. This slope of the implant varies inter-individually.

Patients

Pat K1L big.png Pat K2L big.png Pat K3R big.png Pat K4R big.png Pat K5R big.png
K1L K2L K3R K4R K5R
Pat K6L big.png Pat K7L big.png Pat K8L big.png Pat K9L big.png
K6L K7L K8L K9L

Table with basic information about the knee joint patients:

Patient Side Gender Weight
[kg]
Height
[cm]
Age at
Implantation
[years]
Indication
K1L left m 100 177 63 Osteoarthritis
K2L left m 93 171 71 Osteoarthritis
K3R right m 95 175 70 Osteoarthritis
K4R right f 92 170 63 Osteoarthritis
K5R right m 94 175 60 Osteoarthritis
K6L left f 76 174 65 Osteoarthritis
K7L left f 70 166 74 Osteoarthritis
K8L left m 77 174 70 Osteoarthritis
K9L left m 100 166 75 Osteoarthritis


Vertebral body replacement

Instrumented implant

Implant: vertebral body replacement
Implant: vertebral body replacement

Severe compression fractures of a vertebral body or a tumour in the region of the spine sometimes require the replacement of a vertebral body by an implant. The loads on such an implant are not well known. In order to measure these loads, the commercially available vertebral body replacement 'SYNEX' was modified. It allows the in vivo measurement of three force components and three moments acting on the implant. The 9-channel telemetry transmitter developed in our biomechanics laboratory was placed into the cylinder of the implant together with 6 load sensors and a coil for the inductive power supply. Usually, the spine is in addition stabilized dorsally by an internal spinal fixation device implanted from the back side.

Coordinate system

Coordinate system Vertebral body replacement

The bone-based coordinate system was chosen according to ISO 2631. The x- axis in the median plane points anteriorly, the y-axis in the frontal plane to the left side, and the z-axis cranially.

The forces and moments are presented in the measuring units N and Nm.


Patients

Pat WP1 big.png Pat WP2 big.png Pat WP3 big.png Pat WP4 big.png Pat WP5 big.png
WP1 WP2 WP3 WP4 WP5

Table with basic information about those patients who had vertebral body replacements:

Patient Gender Weight
[kg]
Age at
Implantation
[years]
Indication
WP1 m 66 62 Fracture L1
WP2 m 72 71 Fracture L1
WP3 f 64 69 Fracture L1
WP4 m 60 64 Fracture L1
WP5 m 63 67 Fracture L3


Internal Spinal Fixator

Instrumented implant

Implant: internal spinal fixator
Implant: internal spinal fixator

Little was known about the loads acting on internal spinal fixators. In order to measure the loads, a commercially available implant was modified. A measuring cartridge was integrated into the longitudinal rod containing six load sensors, an 8-channel telemetry transmitter, and the secondary coil for the inductive power supply.

Both telemeterized fixators transmit their load values as a radio frequency pulse train outside the body. For the measurements, a flat power coil, fixed to the patient's back, supplies the energy needed by both fixators. The power coil has an integrated antenna which delivers the signals to the external components of the telemetry system.

Coordinate system

Coordinate system Internal Spinal Fixator
Coordinate system Internal Spinal Fixator

The internal fixators were implanted pairwise. All reported data came from the left implant and are reported in a right-handed coordinate system. The measured load components act at the centre of the cylindrical part of the implant. The z-axis is the long axis of the fixator and points upwards. The y-axis is parallel to the axis of the Schanz screw and points ventrally. The x-axis is perpendicular to both others and is directed to the right side. All force components Fx, Fy, Fz act in axis directions while the moment components Mx, My, Mz turn clockwise around the axes.

Due to the anatomical conditions at the implantation site this coordinate system does not coincide exactly with the sagittal and frontal plane of the upper body. The forces and moments are presented in the measuring units N and Nm.

Patients

Pat WFI MS big.png Pat WFI NF big.png Pat WFI HS big.png Pat WFI FJ big.png Pat WFI JT big.png
MS NF HS FJ JT
Pat WFI BB big.png Pat WFI JW big.png Pat WFI HB big.png Pat WFI LG big.png Pat WFI AG big.png
BB JW HB LG AG

Table with basic information about those patients who had instrumented spinal fixators:

Patient Gender Weight
[kg]
Age at
Implantation
[years]
Indication
MS f 75 59 Degenerative instability L3
NF m 90 34 Compression fracture (old) L4
HS f 66 54 Compression fracture L3
FJ m 80 72 Degenerative instability L4
JT m 75 36 Compression fracture T11
BB m 81 42 Degenerative instability L4
JW f 53 46 Compression fracture (old) T12
HB f 85 62 Compression fracture (old) L1
LG f 48 47 Compression fracture L1
AG f 68 54 Compression fracture T12