Chen mouse scale for early-stage motor assessment in mouse thoracic spinal cord contusion models

The thoracic spinal cord contusion model in mice serves as a critical platform for spinal cord injury (SCI) research, yet identical impact parameters often produce heterogeneous injury severities. Currently, no motor assessment tool can reliably distinguish functional differences between moderate and severe SCI mice during the early post-injury stage, particularly before experimental grouping. Inspired by the Basso Mouse Scale (BMS), we developed a scoring scale composed of three subitems-the Chen Mouse Scale (CMS). Exploratory factor analysis demonstrated a unidimensional structure (cumulative variance explained: 78.7%) with high factor loadings (> 0.87), and internal consistency was strong (Cronbach's α = 0.863). CMS scores at 24 h post-injury (hpi) were strongly negatively correlated with dorsal surface hemorrhagic area and integrated optical density at the lesion site, surrogate markers of acute hemorrhage severity (r = - 0.843 and - 0.821; P < 0.0001), and positively correlated with 28-day BMS scores, spared white matter area, and its percentage of the total cross-sectional area (r = 0.871, 0.870, and 0.825; P < 0.0001). The CMS effectively discriminated functional outcomes across recovery time points (P < 0.0001) and demonstrated greater sensitivity than the BMS throughout the first 4 days after injury, although performance was strain-dependent. Reliability testing showed excellent test-retest (ICC = 0.96) and inter-rater reliability (ICC = 0.97). Nevertheless, 42.4% of mice exhibited score discrepancies between repeated assessments, indicating a tendency toward score attenuation during short-interval retesting. These findings establish the CMS as a valid, sensitive and reliable early-stage motor assessment tool for mice with moderate-to-severe contusion SCI within the 24 ± 2 hpi window.