The impact of body position on measurement of equine lumbar and hindquarter volume using 3- dimensional scans

Well-developed musculature is important for performance yet difficult to quantify. Recently, we validated infrared 3-dimensional (3-D) photonic scanning as an accurate measure of body volume and proxy for regional muscle mass in horses. Our current objective was to determine the impact of body position on measures of lumbar (LV) and hindquarter (HQV) volume. Anatomic markers were placed on 8 horses, positioned at: (1) four hooves square, (2) neck turned similar to 25 degrees, (3) head raised mean 17 cm, (4) one hind hoof (HH) forward 14 +/- 5 cm, (5) a front and contralateral HH similar to 15 cm all offset, (6) one HH resting. A handheld Occipital Structure Sensor photonic scanner, iPad, Skanect and Materialise 3-Matic programs captured LV and HQV. Measured LV and HQV for whole, same and opposite-side with altered head positions and whole LV and HQV with altered HH positions were compared to volume standing square using repeated measures ANOVA. The volumes of the opposite-side or same-side with altered HH positions were compared to the corresponding side when square using a paired t test with multiple test correction (P<0.017). Head elevated negatively impacted measured left LV (-10% difference, P=0.1) compared to square, however, differences were not significant. Head turned did not impact measured LV. Resting HH significantly increased measured whole (18%, P=0.04) and same-side LV (49%, P=0.001) versus square but not the opposite-side LV. One HH forward (whole 16%, P=0.02; same-side 19%, P=0.01) or all offset (whole 14%, P=0.002; same-side 27%, P=0.0001) significantly increased measured whole or same-side LV versus square. Measured HQV was not impacted by head elevated or limb position but was 2% higher on the opposite-side of the turned head (P=0.01). We conclude that alterations in body position have minimal impact on measured HQV, whereas accurate assessment of LV requires horses stand squarely.