Client-specific outcome measure for chronic osteoarthritis pain assessment in horses.

Overview

• This study investigated the use of the Client-Specific Outcome Measure (CSOM), a tool commonly used in small animals, to assess chronic osteoarthritis (OA) pain in horses based on caretaker evaluations.
• The aim was to determine whether CSOM scores correlate with other pain and lameness assessments, supporting its validity as a complementary pain measurement in horses.

Background

• Osteoarthritis (OA) is a common cause of chronic pain and lameness in horses.
• While lameness can be objectively measured (e.g., through gait analysis), directly assessing OA-related pain is challenging in horses.
• The Client-Specific Outcome Measure (CSOM) is a pain assessment tool used in small animals that involves owners/caretakers identifying specific behaviors or activities affected by pain, which are then scored.
• The study explores if CSOM could be adapted for horses by involving caretakers to select and score individual horse-specific pain indicators.

Study Design and Methods

• Seventeen horses with veterinarian-confirmed OA participated in a 20-week randomized, double-blind, placebo-controlled trial.
• For each horse, a veterinarian consulted with the caretaker to identify three individual pain-related indicators (CSOM items) relevant to that animal.
• Caretakers regularly scored these three items on a scale from 0 (no problem) to 4 (severe problem).
• The scores for the three items were summed to create a total CSOM score (CSOM-sum).
• The study compared CSOM-sum scores against other assessments:
  • Caretaker-assigned visual analogue scale (VAS-own) for pain
  • Veterinarian-assigned visual analogue scale (VAS-exp)
  • Subjective lameness scores assigned by veterinarian
  • Objective gait asymmetry index based on movement analysis

Results

• The CSOM-sum demonstrated moderate but statistically significant correlations with all other pain and lameness measures (correlation coefficients rₛ approximately 0.49 to 0.60, p-values less than 0.05).
• CSOM scores correlated specifically with gait asymmetry (rₛ = 0.434, p < 0.0001):
  • Among horses treated for OA, correlation was moderate (r ≈ 0.45, p = 0.0025).
  • In control horses (placebo group), correlation was higher (r ≈ 0.55, p = 0.0006).
• Comparison between caretaker and veterinarian visual analogue scales showed good agreement:
  • Bias was low (-4.76 mm on the scale).
  • Intraclass correlation coefficients (ICC) indicated good consistency (overall ICC = 0.727).
  • However, the limits of agreement were broad, showing some variability.
• The CSOM items had high internal consistency, with Cronbach’s alpha > 0.8 overall (0.81), indicating that the selected indicators reliably measured a common construct (pain severity).

Interpretation and Implications

• The study found that the CSOM approach could effectively capture individual pain-related behaviors in horses with OA when items are carefully selected with the caretaker.
• The moderate correlations with objective measures like gait asymmetry suggest that CSOM scores reflect meaningful changes in pain and function.
• The good internal consistency supports reliability in the measurement process.
• Comparison between caretaker and veterinarian ratings highlighted that while they generally agree, caretaker assessments provide valuable complementary insights particularly in field (non-clinical) conditions.
• CSOM may thus serve as a practical tool for monitoring chronic OA pain in horses over time, especially in real-world settings where constant veterinary assessment is not feasible.
• Using client-specific indicators helps tailor pain evaluation to each horse’s unique presentation of OA-related discomfort.

Limitations and Future Directions

• The relatively small sample size (17 horses) limits broad generalization; future studies with larger populations are needed.
• The necessity of careful item selection by veterinarians and caretakers implies the method requires trained collaboration.
• Further research could explore refinement of the CSOM for horses and investigate responsiveness to treatment changes over longer periods.