Radiographic assessment of carpal conformation in the horse, part 2: Finding acceptable limits to postural and rotational variations during radiography.

Finding an appropriate location for perpendicular positioning of the X-ray machine to produce zero lateromedial (ZLM) and zero dorsopalmar (ZDP) carpal images (views) and finding an acceptable range of rotational variations for measurement of carpal conformational parameters were two major challenges identified during field radiography of equine forelimbs. 16 cadaver forelimbs transacted at antebrachial midshaft from 10 horses (aged 9.13 ± 4.59 years) were axially mounted into a custom-built frame, and the radiographic machine and plate were perpendicularly aligned with the limb. Each limb was then radiographed at 2.5° interval of vertical rotation of the machine until ZLM and ZDP images were acquired, and at 24 other postural and rotational positions from ZLM and ZDP at 5° interval for comparison of measurements with the standardized ZLM and ZDP images. ZLM radiographs were produced at a mean vertical projection angle (VPA) of 9.84 ± 3.47° palmarolateral-dorsomedial oblique (PaL-DMO), while ZDP was acquired at VPA of 6.41 ± 2.73° dorsolateral-palmaromedial oblique (DL-PaMO). Changes in limbs' postural tilts, vertical plate rotations (VPR) and horizontal beam rotations (HBR) had no effect on the quality of the radiographs and on carpal measurements, while vertical beam rotation (VBR) of X-ray beam produced significant changes on the quality of radiographs and on measurements of carpal parameters. It is recommended that field radiographs of equine forelimbs intended for carpal measurement be obtained within a proposed range of VPA of 2.5° to 12.5° PaL-DMO for ZLM and 2.5° to 10° DL-PaMO for ZDP in order to minimize potential errors attributable to vertical rotational movements.