In addition, because measurements are made by human observers even when using an image processing program, both random and systematic errors should be validated. When CT data are processed by image processing programs (i.e., volume or surface rendering programs), systematic errors must be considered. Because 3D-CT scans used for bony reconstruction are currently performed with 0.3 to 0.6 mm voxels, the resolution of 3D-CT scans are close to 0.15 to 0.3 mm this resolution is regarded as negligible in research involving human joint kinematics. The resolution of CT is half the voxel size of CT scan. Recently, there has been a growing interest in 3D-CT as a research tool for the study of bone and joint anatomy and kinematics. Improvements of geometric resolution and computational power for computed tomography (CT) have led to increased utilization of CT images in the development of three-dimensional (3D) models, thus providing a comprehensive outline of shape and 3D coordinate data. For kinematic analysis of the knees, length measurements on 3D-CT using OsiriX program can be used as alternatives to real measurements with less than 0.3-mm accuracy and very high reliability. The intraclass correlation coefficients (ICC) were very high between trials and between replicates (ICC = 0.998 and 0.999, respectively).
There were no significant differences between the replicates and real measurements ( p = 0.544 and 0.622 for replicates 1 and 2, respectively). The mean differences between OsiriX and real measurements were less than 0.1 mm in both replicates, and maximum differences were less than 0.3 mm.
All measurements were recorded by a principal (replicate 1, trial 1) and a secondary observer (replicate 2, trial 1) and were repeated once by each observer (trial 2). The lengths between tunnel orifices were measured using Mitutoyo Digimatic digital calipers to establish the gold standard, and with the OsiriX program in 3D multi-planar reformatting mode for comparison. 3D-CT scans were made of 14 frozen pig knees with five transosseous holes in the metaphyseal portion of femur. We evaluated the accuracy and reliability of length measurement on CT with OsiriX software. However, when CT data are processed and handled manually using image processing programs to yield 3D image and coordinate value, systematic and random errors should be validated. There is a growing interest in three-dimensional computed tomography (3D-CT) as a research tool for the study of bone, joint anatomy, and kinematics.