In vivo measurement of stress-strain distribution in the ligament using arthroscopic images

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We have developed a method of measurement that might be applied to in-vivo measurement of strain distribution in the ACL using arthroscopy. The method reconstructs the 3D shape and deformation of a moving object from its image streams. We call it the modified motion capturing method. It eliminates the need for camera calibration processes. In a pilot study, we applied the method to perform in-vitro measurement of the ACL. A cadaver knee was modified to expose its ACL for observation, and small black paper markers were affixed to the ACL along the macroscopically observed fiber bundles. The knee locked in a special knee motion simulator jig and was moved. The ACL's shape was recorded simultaneously by multiple video cameras at different angles. From individual video frames, 3D animation of the deformations of the ACL and some fiber bundles were made with computer software. The method made it possible to see in what state the fiber bundles bear tension. It also gave insight into the problems that must be solved before in-vivo measurement can be done. We think it possible to use this technique in conjunction with arthroscopy.