Table 1.

Moduli measured at 10%–50% ramp strain for lumbar facet joint capsules tested parallel (n= 25) and perpendicular (n= 10) to the primary collagen orientation. The tangent modulus (tangent) was computed as the slope of the most linear portion of the engineering stress-first principal strain relationship. The viscous and elastic moduli were calculated as secant moduli from (0,0) to the peak of the ramp when the load was a maximum and to the load 300 s after peak displacement, respectively. Parallel to the collagen fibers, the elastic modulus was significantly smaller than the viscous modulus at all ramp strains (p<0.001, for all comparisons, Wilcoxon signed rank test). Perpendicular to the collagen fibers, the elastic modulus was not significantly different than the viscous modulus at all ramp strains (p>0.125 for all comparisons, Wilcoxon signed rank test.

		Ramp strain
Modulus (MPa)		10%	20%	30%	40%	50%
Parallel	Tangent	0.13±.08	0.40±0.33	1.06±0.73	2.92±1.91	8.08±5.75
	Viscous	0.10±0.09	0.18±0.13	0.33±0.17	0.92±0.49	1.61±0.36
	Elastic	0.10±0.10	0.14±0.11	0.24±0.15	0.73±0.44	1.33±0.49
Perpendicular	Tangent	0.39±0.32	2.51±2.14	3.97±3.66	2.26±1.32	2.76±1.32
	Viscous	0.23±0.20	1.04±0.86	2.57±1.93	2.33±1.19	1.81±0.29
	Elastic	0.12±0.08	0.66±0.57	1.21±0.79	1.23±0.10	1.00±0.27