Pelvic axial rotation in hindlimb lame horses changes after diagnostic analgesia.

BACKGROUND: Visual assessment of mild to moderate hindlimb lameness has low sensitivity and specificity, potentially leading to flawed diagnostic procedures. Pelvic axial rotation (roll) makes the assessment more complex but is also a potential source of information. OBJECTIVES: To describe pelvic roll patterns in horses with unilateral hindlimb lameness before and after diagnostic analgesia. STUDY DESIGN: Retrospective study. METHODS: Optical motion capture data from 20 horses with unilateral hindlimb lameness before and after successful local analgesia (assessed visually and objectively) were retrospectively retrieved. Pelvic rotation discrete variables (e.g., range of motion, angular velocities) were calculated. Measurements before and after diagnostic analgesia were compared using mixed models with horse as random effect or Wilcoxon signed rank test for non-normally distributed variables. RESULTS: Pelvic roll range of motion from time of pelvic vertical minimum to time of vertical maximum differed between lame and sound diagonals at baseline by 0.8° ± 0.17° (least square mean ± SE). This was reduced to 0.3° ± 0.17° after diagnostic analgesia (p = 0.004). Additionally, maximum roll angular velocity during push-off of the lame limb increased from 51° ± 12°/s (median ± median absolute deviation) to 61° ± 12°/s (+13%, p < 0.001). The pelvic rotation parameters showing the clearest difference before and after diagnostic analgesia varied between horses. MAIN LIMITATIONS: A small sample of clinical cases with varying diagnoses and of diverse breeds. CONCLUSIONS: Pelvic roll may change due to hindlimb lameness and return towards symmetry in response to diagnostic analgesia. Roll differences can contribute to changes in hip hike symmetry. The findings suggest that future studies should investigate if pelvic roll may provide additional information useful for lameness assessment.