Julius Wolff Institut (JWI) - Center for Musculoskeletal Biomechanics and Regeneration 

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Joint Loading & Musculoskeletal Analysis

The loads acting in joint prostheses and other orthopaedic implants is still partially unknown. The acting loads are required for different purposes.

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Knee Joint

Modell Knie-Implantat (Zimmer)

The knee joint is the biggest joint in the human body. Since it has to carry the entire weight of the body, it is heavily loaded. In case of degenerative arthritis or rheumatoid arthritis, after fractures and other diseases the joint can be replaced by an endoprosthesis. More than 150.000 knee replacements are implanted in Germany every year (Source: Statistisches Bundesamt, data from 2011). With this routine operation the function and resilience of the joint can be reconstructed for the next 15 years or longer.

In exceptional cases complications can occur at an earlier time. One reason for these complications can be a high loading of the knee joint. So far only few realistic data about the loading of the knee joint is available. Better knowledge will allow testing the stability of new implants under realistic conditions and to improve them before their use in patients. It will furthermore help to improve the physiotherapeutic treatment to optimize the healing process and to give patient advices for a right behaviour after implantation. In general the knowledge of the loading helps to understand the biomechanics of the knee joint.

Publications

Schnittmodell einer instrumentierten Knieendoprothese
Instrumented Knee Joint

In order to obtain realistic load data, a knee endoprosthesis with an integrated 9-channel telemetry transmitter for load measurement and data transmission was developed in several years of research. With the prosthesis, all six load components occurring in the knee joint of the patient can be measured: the medio-lateral, antero-posterior and axial-compressive forces, as well as the flexion-extension, varus-valgus and rotational moments. The instrumented knee endoprosthesis is a modification of the INNEXTM system, type FIXUC (Zimmer GmbH, Winterthur, Switzerland). The femoral component and the polyethylene inlay were taken over. Only the tibial component was slightly modified to allow the installation of the measurement electronics.

Patients

At the time of the operation the patients were between 60 and 75 years old and suffered from gonarthrosis. During the first weeks after the operation the patients are accompanied to the physiotherapy to measure the loading in the knee joint during the physiotherapeutic treatment. In the following months mainly activities of daily living like walking, stair climbing, standing up and sitting down are subject of the measurement.

The instrumented knee prosthesis were implanted at nine patients at the  Klinik für Endoprothetik (Head: PD Dr. med. Andreas M. Halder) of the  Sana Kliniken Sommerfeld where also the first measurements during physiotherapy have been performed.

The following pictures show the patients with instrumented knee implants during load measurements.

First Results

The first results show that the knee joint is heavily loaded. During walking the resultant force is typically about 250 %BW (Video 717KB). Going downstairs the knee joint is even loaded with up to 350 %BW (Video 463KB). Some acting moments are higher than expected. This knowledge will have a high influence on the preclinical testing of new implants.

Further data are available from the database OrthoLoad.