Knee Alignment Device
Motion Lab Systems developed the Knee Alignment Device (KAD) originally used by the Vicon Clinical Manager (VCM) software from Oxford Metrics Ltd.
The first Knee Alignment Device was developed at Newington Children's Hospital in Connecticut by the Gait Lab engineers and made from various materials found around the lab - principally delrin, glue and rubber bands. Software support for the KAD was written into the Vicon Clinical Manager software and this created a demand for the KAD which, at this point, only existed in the Newington lab. Motion Lab Systems then worked with the engineers to create a version of the KAD that would be easy to manufacture, reliable and lightweight. These devices were then sold by Vicon with their VCM software - the MLS units are the original, red, anodized, aluminum devices that are illustrated here.
After a few years Vicon started supplying their customers with a different black plastic KAD design that they manufactured. Motion Lab Systems has continued to manufacture and repair the original MLS designed KADs up to the present day.
The KAD is used during static trials to independently define the alignment of the knee flexion/extension axis of the subjects knee prior to a series of walking trials. The use of the KAD based knee model enables the subject marker set to eliminate the medial knee markers which are prone to being knocked off during testing when the subject knees cross or pass closely during swing. This is primarily a problem during clinical gait trials.
The KAD is a spring-loaded metal jig that fits gently over the subjects knee while a static calibration data collection is performed. The design of the KAD is such that the absolute distance between all three of the markers on the device is identical (5.66 inches). The design of the Motion Lab Systems KAD enables the software to establish a virtual knee marker at the central joint of the Knee Alignment Device and this, combined with the KAD wand marker, enables the knee flexion axis to be measured.
When a supported software application finds marker labels for a Knee Alignment Device defined in the C3D file, it uses the orientation of the three markers on the Knee Alignment Device to establish the knee flexion axis. After the knee flexion axis has been established, the software calculates the relative transverse alignment of this axis, to the transverse plane orientation of the thigh and shank, as calculated using the mid-thigh and mid-shank stick markers. These relative alignments are stored in the subject’s Session form as Thigh and Shank Rotations and are applied to all dynamic data within the session. Thus the correct alignment of the thigh and shank wands becomes less critical as any minor alignment errors are measured during the static trial and can be automatically removed during the processing of the dynamic trials. Please refer directly to the software User Guide or contact the application manufacturer for information on the kinematic calculations that use the KAD data.
The Knee Alignment Device is fully supported by the VICON Clinical Manager and the Vicon Plug in Gait biomechanical modeling software as well as selected packages by other 3D Motion Capture System manufacturers.
Spare parts for the Motion Lab Systems KAD are available on request.