Analysis of three-dimensional joint space of the tibiofemoral joint

The purpose of this study was to quantify in vivo the differences in knee joint space volume between upright, weightbearing and supine, non-weightbearing conditions using C-arm computed tomography (CT) with sub-millimeter voxel size. Three volunteers were scanned while lying supine and while standing using a C-arm CT scanner. Using tantalum fiducial markers, patients´ involuntary motion-induced artifacts were corrected in 3D. Point clouds of the femur and tibia in standing and supine reconstructions were automatically segmented. The tibia in standing reconstruction was registered to that in supine reconstruction using a rigid body transformation. Joint space width (JSW) was then compared under weightbearing and non-weightbearing. A pixel-wise JSW was measured as the shortest Euclidean distance between each pixel on the tibial plateau and the femoral condyles. A comparison of joint space parameters (minimum (JSWmin), mean (JSWmean), and volume (JSV)) under weightbearing to non-weightbearing conditions was made. Our results demonstrate that the relative joint space of the medial and lateral compartments between weightbearing and non-weightbearing were different in the three subjects. In general, JSWmin, JSWmean, and JSV decreased as loads were applied. Given an applied load, JSWmin decreased by up to 1.44 mm and 1.34 mm in the medial and lateral compartments, respectively, and specific regions with most narrow JSW were concentrated more locally. The maximum decrease in JSV due to weightbearing was 21.4 % and 14.9 % for the medial and lateral compartments, respectively. In conclusion, a C-arm CT system can be used to provide measurements of 3D joint space under loaded conditions. 2D scanning might lead to inaccurate diagnosis about knee cartilage health.