TABLE 5.
Association between muscle strength and gray matter area at intervertebral disc level adjusted for potential risk factors
| Model a | Outcome | Factor | Estimate | SE | t‐value | p Value |
|---|---|---|---|---|---|---|
| Model 1 | Muscle strength (N): | Intercept | 267.91 | 194.24 | 1.38 | 0.190 |
| Adj. r 2 = 0.56 p value = 0.002 | Neck flexion (segment C2/C3) | GM area C2/C3 | 12.83 | 4.99 | 2.57 | 0.022 |
| Age | −4.92 | 2.41 | −2.04 | 0.061 | ||
| Sex | 33.84 | 10.49 | 3.23 | 0.006 | ||
| Model 2 | Muscle strength (N): | Intercept | 66.96 | 127.08 | 0.53 | 0.606 |
| Adj. r 2 = 0.32 p value = 0.032 | Wrist extension (segment C7) | GM area C5/C6 | 6.82 | 3.08 | 2.22 | 0.043 |
| Age | −1.01 | 1.87 | −0.54 | 0.599 | ||
| Sex | 23.1 | 8.41 | 2.75 | 0.015 | ||
| Model 3 | Muscle strength (N): | Intercept | 28.47 | 185.78 | 0.15 | 0.882 |
| Adj. r 2 = 0.68 p value = 0.006 | Ankle dorsiflexion (segment L5) | GM area T max | 9.62 | 2.82 | 3.41 | 0.009 |
| Age | −0.72 | 2.80 | −0.26 | 0.804 | ||
| Sex | 15.38 | 17.33 | 0.89 | 0.401 |
Abbreviations: adj, adjusted; GM, gray matter; N, Newton; SE, standard error.
Based on a post‐mortem study [21] and an in vivo magnetic resonance imaging study in healthy persons [10], the intervertebral disc levels C2/C3, C5/C6 and T max project to the spinal cord segments C2/C3, C7 and L5, respectively.
Multivariate models resulting from the backward selection procedures using a starting model with age and sex as fixed predictor variables and the spinal cord gray matter area at the given intervertebral disc level along with all patient‐reported outcome (PRO) variables with a Pearson correlation coefficient of |r| > 0.2 in univariate analysis as predictor variables and muscle strength at the respective corresponding myotome as outcome. The following PRO variables were included in the starting models: for neck flexion strength, fatigue, pain and depression; for wrist extension strength, pain; and for ankle dorsiflexion strength, depression.