OrthoLoad

New Publication about the influence of patient expectation and patient age to the in vivo joint loads

Bender A., Damm P., Hommel H., Duda G.N.
Overstretching Expectations May Endanger the Success of the “Millennium Surgery”
Frontiers in Bioengineering and Biotechnology, 2022, https://doi.org/10.3389/fbioe.2022.789629 

New Publication about the influence of the joint line orientation onto the tibio femoral load distribution

Trepczynski A., Moewis P., Damm P., Schütz P., Dymke J., Hommel H., Taylor WR., Duda GN.
Dynamic knee joint line orientation is not predictive of tibio-femoral load distribution during walking
Frontiers in Bioengineering and Biotechnology, 2021;
https://doi.org/10.3389/fbioe.2021.754715 

Themistocles-Gluck-Preis für Endoprothetik 2021

The German Society for Orthopedics and Orthopedic Surgery (DGOOC) awarded our publication about the
“In vivo loading on the hip joint in patients with total hip replacement performing gymnastic and aerobic excercises”
H. Haffer, S. Popovic, F. Martin, S. Hardt, T. Winkler & P. Damm
with the Themistocles-Gluck-Preis 2021.

New Publication: In vivo Analysis of Hip Joint Loading on Nordic Walking Novices

Palmowski Y., Popovic S., Schuster S., Damm P.
In vivo analysis of hip joint loading on Nordic Walking Novices
Journal of Orthopaedic Surgery and Research, 2021
https://doi.org/10.1186/s13018-021-02741-7

Vertebral body replacement

Instrumented implant

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

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.

 

 

WP1	WP2	WP3	WP4	WP5

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

Knee joint

Instrumented implant

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

The coordinate system of the instrumented knee implant is a

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

K1L	K2L	K3R	K4R	K5R
K6L	K7L	K8L	K9L

Table with basic information about the knee joint patients:

Shoulder joint

Instrumented implant

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

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

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

S1R	S2R	S3L	S4R
S5R	S6R	S7R	S8R

Table with basic information about the shoulder joint patients:

Ground reactions forces

Ground reaction forces were measured using two 6 degrees of freedom force plates (AMTI, Watertown, MA). The coordinate system is a right-handed system.

Raw data:

For the calculation of the center of pressure the following offsets were used. The true origins of the coordinate systems are located below the top surfaces, with a distance (zo).

Processed data

(see Comprehensive Data Sample (http://orthoload.com/comprehensive-data-sample/)):

grf2f.eof data:

(Downsampled Ground Reaction Forces)

Bending Moment

The resultant bending moment Mbend , acts in the middle of the femoral neck and perpendicular to the neck axis, and is calculated with the following formula:

with

The forces (F_x’, F_y’, F_z’) and moments (M_x’, M_y’, M_z’) are measured in the “implant coordinate system” x’, y’, z’ centered in the middle of the implant head. The force component F_x’ acts laterally, F_y’ anteriorly, and –F_z’ distally along the femur axis. The measured moment components M_x’, M_y’, and M_z’ turn right around the x’, y’, and z’ axes. N is the distance between the head center and the middle of the femoral neck and is equal to ½ L.

M_tne acts around the neck axis of the femur and represents the torsional loading of the neck. It is calculated by α = -45° rotation of the “bone coordinate system” around the y-axis.

Instrumented Crutches

F_cont – Contralateral Crutch Force

F_ipsi – Ipsilateral Crutch Force

2kN Force Transducer (KM 30z)