Table 3. Bivariate and multivariable regression analyses of muscle-bone associations in participants with chronic SCI (n = 65^a).

	Unadjusted muscle-bone associations			Muscle-bone associations adjusted for confounding variables
	b (95% CI)	P value	R2	b (95% CI)	P value	R2
Trabecular vBMD, mg/cm3
Muscle density	1.94 (1.03, 2.85)	<.001	0.223	0.85 (0.04, 1.66)c	<.040	0.544
Muscle CSAb	3.46 (2.14, 4.78)	<.001	0.304	1.29 (−0.28, 2.86)c	.105	0.532
cLEMS	7.80 (5.67, 9.93)	<.001	0.459	7.69 (4.63, 10.76)d	<.001	0.503
Cortical vBMD, mg/cm3
Muscle density	1.62 (0.72, 2.51)	<.001	0.172	1.70 (0.71, 2.69)c	<.001	0.248
Muscle CSAb	0.79 (-0.70, 2.28)	.294	0.017	0.88 (-1.17, 2.94)c	.394	0.109
cLEMS	2.40 (-0.29, 5.08)	.079	0.048	2.77 (-1.14, 6.68)d	.161	0.104
Cortical thickness, mm
Muscle density	0.03 (0.01, 0.05)	<.001	0.177	0.02 (0.001, 0.034)c	.042	0.370
Muscle CSAb	0.05 (0.03, 0.07)	<.001	0.210	0.02 (-0.01, 0.05)c	.195	0.343
cLEMS	0.10 (0.05, 0.14)	<.001	0.233	0.10 (0.03, 0.16)d	.003	0.313
Cortical CSA, mm2
Muscle density	2.12 (0.77, 3.47)	.003	0.135	0.98 (-0.29, 2.25)c	.127	0.438
Muscle CSAb	4.94 (3.10, 6.78)	<.001	0.313	2.50 (0.12, 4.88)c	.040	0.456
cLEMS	8.12 (4.59, 11.65)	<.001	0.251	5.85 (0.27, 11.43)d	.040	0.456
PMI, mm4
Muscle density	342.6 (1.30, 683.9)	.049	0.060	107.7 (-206.1, 421.47)c	.495	0.414
Muscle CSAb	1205.8 (760.2, 1651.3)	<.001	0.317	731.8 (161.7, 1301.9)c	.013	0.469
cLEMS	1611.6 (709.8, 2513.4)	.001	0.168	1412.0 (311.3, 2512.6)d	.013	0.449

Note: AIS = American Spinal Injury Association Impairment Scale (AIS); cLEMS = calf lower extremity motor score; CSA = cross-sectional area; SCI = spinal cord injury; vBMD = volumetric bone mineral density. Boldface P values indicate statistical significance (P < .05).

^aFive participants did not complete pQCT scans.

^bMuscle CSA (cm²) was multiplied by tibia length (m).

^cAdjusted model for sex, duration of injury, AIS classification (AIS A/B vs AIS C/D), and wheelchair use.

^dAdjusted model for sex, duration of injury, and wheelchair use.