Predictors of Ultrasound-Derived Muscle Thickness and Echo Intensity After Acute Incomplete Spinal Cord Injury During Inpatient Rehabilitation: An Exploratory Observational Cohort Study

<b>Background/Objectives:</b> Muscle wasting is often observed in the acute phase after spinal cord injury (SCI). We aim to investigate the factors determining rectus femoris muscle thickness and echo intensity on discharge for patients who had acute incomplete spinal cord injury undergoing inpatient rehabilitation. <b>Methods:</b> This is a prospective exploratory observational cohort study, conducted in a standalone inpatient multi-specialty tertiary rehabilitation center in Singapore. Forty-five patients with incomplete SCI, defined as American Spinal Injury Association Impairment Scale (AIS) B-D were recruited from January 2020 to October 2021. Variables including clinico-demographic data, lower limb spasticity, Lower Extremity Muscle Score (LEMS), Functional Independence Measure (FIM) motor score on admission were collected. Muscle ultrasound of the rectus femoris thickness and echo intensity were obtained at 6 weeks after acute SCI via standardized protocols. Stepwise multiple regression analyses were performed to identify the factors that were significant for rectus femoris muscle thickness and echo intensity on discharge. <b>Results:</b> The mean age of participants was 59.6 ± 16.6 years, with patients having AIS of B (11.1%), C (28.9%) or D (60.0%). Rectus femoris muscle thickness on discharge had a significant association with body mass index (B = 4.62; CI = 1.77, 7.47; <i>p</i> = 0.002) and onset of mobilization (B = -4.97; CI = -9.46, -0.484; <i>p</i> = 0.031). The significant variables associated with rectus femoris echo intensity on discharge were age (B = 0.546; CI = 0.126, 0.967; <i>p</i> = 0.012) and onset of mobilization (B = 2.49; CI = 0.439, 4.53; <i>p</i> = 0.019). <b>Conclusions:</b> Our findings suggest that age, body mass index and a delayed onset of mobilization may have significant impact on muscle ultrasound parameters. Patients with incomplete SCI may benefit from early mobilization and nutritional assessment for improved muscle strength and function.