The objective of this research is to synchronously assess in vivo loading data of the knee joint, tibio-femoral 3D kinematics by means of automated video-fluoroscopy, whole leg kinematics by means of skin markers, ground reaction forces, as well as muscle activity patterns in 4 to 6 subjects with instrumented total knee arthroplasty (TKA) during dynamic functional activities of daily life. The comprehensive in vivo dataset will provide unique information to evaluate the relationship between the kinematics, respectively the alignment of the TKA, and the resulting loading of the implant in vivo.

The whole data package will be made available for download on a public database, such that it can be utilized for the testing and improvement of TKA designs as well as for the validation and improvement of musculoskeletal modelling by researchers around the world.

STUDY SUBJECTS:

4-6 subjects with an instrumented TKA, that has been implanted within the study "Kniemessprothese: Belastungsmessung bei Patienten mittels einer instrumentierten Knie-Endoprothese" (EA4/069/06) approved and conducted at the Charité- Universitätsmedizin in Berlin, Germany, will be involved in this project. This instrumented prosthesis was implanted in 9 subjects with osteoarthritis.

DATA ACQUISITION:

The testing will be performed at the Institute for Biomechanics at the ETH Zurich. The kinematic and kinetic measurements include video-fluoroscopic tibio-femoral 3D implant motion; whole leg motion capture based on skin markers as well as ground reaction forces. Simultaneously the joint loading is assessed by means of the instrumented TKA and a telemetry unit for transmitting the strain gage signals. In all subjects, muscle activity is additionally simultaneously assessed using surface electromyography (EMG). The electrodes are placed onto the skin at the sites of eight muscles in the lower limbs. At the beginning of the test session, the maximal voluntary contraction will be assessed by means of the EMG electrodes, performing the following four motion tasks:

• One legged standing and lifting the heel to stand on tiptoe.
• Extension of the knee joint against a load by means of a strap around the lower leg just above the ankle. (Subject is sitting on a bench, lower legs are hanging down).
• Flexion of the knee joint against a load by means of a strap around the lower leg just above the ankle. (Subject is sitting on a bench, lower legs are hanging down).
• Dorsiflexion of the ankle against a manual resistant force of the investigator. (Subject is sitting on a bench, lower legs are hanging down).

To familiarize the subjects with the dynamic data acquisition protocol, six test trials will be conducted that just include the motion capture system (motion capture trials, each performed twice). This is followed by the main test procedure, which will consist of two static (static trials) and three dynamic trials (dynamic trials) assessed simultaneously by the video-fluoroscopy, the motion capture systems the force plates, as well as the instrumented TKA. During the dynamic trials the fluoroscopic measurement unit mounted on an automated trolley will move along the subject and capture the motion of the knee in question.

Motion capture trials:

• Standing trial in an anatomic upright position
• Calibration motion (Standing in upright position, followed by free movement of legs and arms)
• Four basic motion tasks to define functional estimated joint axis, respectively centers: dorsiplantarflexion motion of the ankle, inversion/eversion motion of the ankle, flexion/extension motion of the knee, hip circumduction (List et al., 2012b)

Static trials:

• Standing trial in an anatomic upright position captured from the side.
• Standing trial in an anatomic upright position captured from an angle of 45°.

Dynamic trials:

For each of the following activities the subjects has to perform five valid gait cycles or repetitions respectively. A trial is considered valid, when the knee is in the field of view of the image intensifier during the whole cycle and the force plate got hit for level gait, walking downhill and stair descent.

• Level gait
• Stair descent a two steps staircase
• Downhill walking a 10° inclined slope
• Sit down and stand up from a chair
• Squatting

For documentation, all dynamic trials will additionally be captured by two video cameras. All anonymized data will be made available for download on a public database.

Inclusion Criteria:

• Instrumented TKA
• Participant of the study EA4/069/06, Charité- Universitätsmedizin Berlin, Germany,

Exclusion Criteria:

• Not able to walk freely without walking aid
• Any medical condition that could impact on study results

Patients after total knee replacement surgery from the Charité- Universitätsmedizin in Berlin, Germany