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Assessment of in vivo human cartilage loading generally requires computer modeling, since loads usually cannot be directly measured. The utility of these models for assessing knee behavior during complex activities has been limited by the relatively poor quality of experimental data on in vivo knee function. We have developed a method combining high-accuracy knee kinematics (from high-speed stereo-radiography) with subject-specific finite-element models to estimate in vivo cartilage contact pressures during stressful tasks. When applied to ACL reconstruction, significantly higher contact pressures were found in reconstructed knees as compared to the contralateral (uninjured) knees of the same individuals.Copyright © 2003 by ASME

The effectiveness of ACL reconstruction for restoring normal joint mechanics is poorly understood, especially during physically demanding tasks. For this study, 3D kinematics of ACL-reconstructed and contralateral (uninjured) knees were assessed during down-hill running, using a unique high frame rate stereo-radiography system. Though anterior/posterior tibial translation was restored to normal levels, significant rotational abnormalities were identified in the ACL-reconstructed knees in both the coronal and transverse planes.Copyright © 2003 by ASME

This paper presents a method to calculate functional joint space during dynamic movement. This method combines high-speed biplane radiographic image data and three-dimensional (3D) bone surface data obtained from computed tomography (CT). Subjects were patients undergoing anterior cruciate ligament (ACL) reconstructive surgery. Three tantalum beads were implanted bilaterally into both the femur and tibia during surgery. CT scans were performed after bead implantation, and the CT slices were reconstructed into 3D solid figures, with the implanted beads identifiable within the stack of CT slices. Subjects were tested 6,12 and 24 months post surgery. Testing activities included downhill running on a treadmill and one-legged hopping onto a force plate. During testing, the stereo-radiographic imaging system collected images at 250 frames per second. Later, the implanted beads were identified in the x-ray images and tracked in 3D with an accuracy of 0.10 mm. The 3D bead location data were used to position the reconstructed solid bone figures in 3D space. In this way, the location of each bone surface was determined each instant. This method can be used to identify the regions of close contact between bones during dynamic motion, to calculate the surface area of subchondral bone within close contact, and to determine the changing position of the close contact area during dynamic activities. Using these techniques, comparisons can be made between subchondral bone motion in healthy and reconstructed joints and changes in dynamic joint space can be measured over time.Copyright © 2003 by ASME