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IV.

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Summary Reasons for performing study Studies examining the effect of stifle joint angle on tibial rotation, adduction-abduction angle, and articular contact area are lacking. Objectives To test the hypothesis that tibial rotation, adduction-abduction angle, and articular contact area change with stifle joint angle. Study Design Descriptive study of normal kinematics and articular contact patterns of the equine stifle through the functional range of motion using 3D radiosteriometric analysis (RSA) and equine cadaver stifles. Methods Multiple, radiopaque markers were embedded in the distal femur and proximal tibia and sequential, bi-planar x-rays captured as the stifle was passively extended from 110° to full extension. Computer-programmed RSA was used to determine changes in abduction-adduction and internal-external rotation angles of the tibia during stifle extension as well as articular contact patterns (total area and areas of high contact) through the range of motion. Results The tibia rotated externally (p<0.001) as the stifle was extended. Tibial abduction occurred from 110–135° of extension (p<0.001) and tibial adduction occurred from 135° through full extension (p = 0.009). The centre of joint contact moved cranially on both tibial condyles during extension with the lateral moving a greater distance than the medial (p = 0.003). Articular contact area decreased (p = 0.001) in the medial compartment but not in the lateral compartment (p = 0.285) as the stifle was extended. The area of highest joint contact increased on the lateral tibial condyle (p<0.001) with extension but decreased (p = 0.001) on the medial tibial condyle. Conclusions Significant changes occur in tibial rotation, adduction-abduction angle, and articular contact area of the equine stifle through the functional range of motion. Understanding the normal kinematics of the equine stifle and the relationship between joint positions and articular contact areas may provide important insight into the etiology and location of common stifle joint pathologies (articular cartilage and meniscal lesions).

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