# The common and specific osteoarthritis gait characteristics: A quantitative grading system for OA associated gait changes in mice

## TL;DR

This study introduces a new system to measure gait changes in mice with osteoarthritis, helping detect early signs of the disease.

## Contribution

A novel quantitative OA Gait grading system for mice that captures both common and specific gait changes.

## Key findings

- Common gait changes include reduced stride time and length, and increased stride frequency in both aging-OA and PTOA mice.
- Aging-OA affects gait symmetry, while PTOA affects limb ataxia, indicating distinct pathogenic mechanisms.
- The OA Gait system detected functional changes before histopathological signs in some aging-OA cases.

## Abstract

Osteoarthritis (OA) severity in animal models has been quantified primarily through grading systems reflecting the changes of joint morphology. There is a lack of a uniform grading system to quantify the changes in motion. Here, we develop a quantitative, easy-to-use grading system for OA-associated gait changes in mice.

We characterized the mouse gait changes in a surgery induced post-traumatic OA (PTOA) model and aging-associated OA (aging-OA) models using DigiGait. This treadmill system captured running motions for video analysis. We developed and validated the OA Gait grading system with a quantitative formula indicating the extent of OA-related movement changes.

We found gait changes in both aging-OA and PTOA mouse models, consistent with OA cartilage degeneration and increasing OARSI (Osteoarthritis Research Society International) scores. The female aging-OA and male PTOA mice share common gait alterations including a significant decrease in stride time and stride length and a significant increase in stride frequency. These three gait changes compose the “Common OA Gait” in mice. In addition, aging-OA alters gait symmetry between forelimbs and hindlimbs while PTOA alters ataxia coefficient between left and right limbs. These “Specific OA Gait” may indicate the involvement of aging and/or injury in OA pathogenesis.

The OA Gait grading system correlated with OA pathogenesis. In some instances of aging-OA, it preceded the histopathological changes indicated by the OARSI grading system. Thus, the OA Gait grading system may be widely used for detecting alteration of functional movement outcomes in a sensitive, quantitative, and mechanistic manner.