# Determining Minimum Trial Numbers for Reliable Lameness Detection in Canine Kinematic Studies

## TL;DR

This study shows that using only five trials is not enough to reliably detect mild lameness in dogs, and the required number of trials depends on the severity and type of gait asymmetry measured.

## Contribution

A statistical framework using the delta method is introduced to determine the minimum number of trials needed for reliable lameness detection in canine kinematic studies.

## Key findings

- Five trials are insufficient for detecting mild lameness in dogs.
- The required number of trials varies from under 20 to over 300 depending on the kinematic variable and lameness severity.
- Subtle asymmetries (≈4%) require up to 347 trials for reliable detection.

## Abstract

Visual gait assessment in dogs is considered subjective and is often associated with inconsistency, especially when lameness is subtle. To address this, biomechanical analysis provides objective measures through the comparison of kinematic variables between limbs. However, the collection of an insufficient number of trials can lead to unreliable conclusions, while the collection of too many is inefficient and may result in the unnecessary use of more animals than required for a specific research objective. In this pilot study, mild forelimb lameness was induced in six dogs, and their gait was filmed with a high-speed camera. A statistical framework based on the delta method was employed to determine the number of trials (i.e., full stride cycles) required to distinguish lameness from normal variability. It was demonstrated that the commonly used five trials are insufficient. Instead, the required number of trials is highly parameter-specific. Depending on the severity of lameness and the kinematic variable measured, reliable detection could require from under 20 to over 300 trials per limb. These findings provide practical guidelines for both clinical and research settings to improve the accuracy of lameness detection.

Visual orthopedic gait assessment in dogs is recognized as subjective and is limited by interobserver variability. Objective detection of lameness is offered by biomechanical analysis, where asymmetry between limbs is quantified through kinematic parameters and symmetry indices. However, the minimum number of trials (full stride cycles) required to reliably discriminate lameness has remained a challenge. In this study, six healthy adult dogs were used. Mild, reversible lameness was induced in one forelimb using a cotton pad. Dogs were walked along a straight runway, and kinematic data were captured with a high-speed video camera. Stride length (SLE), support time (ST), and elbow range of motion (ROM) were measured. Symmetry indices (for linear and temporal parameters) and the symmetry angle (for angular parameters) were computed. The asymptotic distribution of these indices was derived using the delta method, which allowed for the construction of confidence intervals (CIs) and hypothesis tests for an asymmetry threshold of 3%. The number of trials required to achieve reliable detection was estimated through statistical simulations. Results indicated that the required number of trials was highly dependent on both the kinematic parameter and the magnitude of asymmetry. While detecting subtle asymmetries (≈4%) required a high number of trials (up to 347 for stride length), the requirements decreased substantially for more pronounced lameness. For a true asymmetry of 6%, 11–39 trials per limb were sufficient to achieve 80–90% power. It is concluded that the collection of only five trials is insufficient for detecting mild asymmetries. A statistical framework and practical recommendations for kinematic gait studies in dogs are provided.