Table 6.

Bone mechanical properties of the L₄ vertebral body determined by compression testing

	ZDF Comparison			ZDSD vs. Parent Strain
	ZDFfa/+ (n = 11)	ZDFfa/fa (n = 8)	P	Controls* (n = 11)	ZDSD (n = 17)	P
Vertebral body dimensions
Height, mm	6.49±0.25	5.64±0.14	<0.050	6.11±0.19	6.05±0.25	0.106
CSA, cm2	0.30±0.01	0.25±0.02	<0.050	0.32±0.01	0.30±0.01	0.073
Structural properties
Yield force, N	254±32	145±23	<0.050	270±18	175±16	<0.001
Stiffness, N/mm	2,401±595	937±225	<0.001	3,574±557	1,657±378	<0.005
Ultimate load, N	412±37	195±15	<0.001	439±32	270±21	<0.001
Postyield displacement, mm	0.14±0.04	0.08±0.02	0.206	0.07±0.02	0.07±0.01	0.886
Energy to ultimate load, mJ	70.6±8.4	31.2±2.5	<0.050	52±7.2	33.2±1.7	<0.010
Preyield energy, mJ	34±5	21±3	0.067	26±4	17±2	0.066
Postyield energy, mJ	41±7	14±4	<0.010	41±10	16±2	<0.010
Material properties
Ultimate stress/(BV/TV), N/mm2	56.8±3.9	43.6±2.7	<0.050	62.9±4.3	46.5±3.9	<0.050
Modulus/(BV/TV), N/mm2	1,880±304	1,083±149	<0.051	3,036±439	1,679±256	<0.050
Toughness/(BV/TV), mJ/mm3	1.63±0.29	1.30±0.018	0.657	1.22±0.14	0.91±0.08	<0.051
Preyield toughness/(BV/TV), mJ/mm3	0.74±0.13	0.84±0.16	0.717	0.64±0.11	0.44±0.08	0.147
Postyield toughness/(BV/TV), mJ/mm3	0.98±0.22	0.60±0.18	0.224	0.90±0.20	0.48±0.08	0.101
Postyield strain	0.105±0.033	0.085±0.024	0.793	0.057±0.008	0.049±0.009	0.566

Values are means ±SE. CSA, cross-sectional area. Some of the vertebral samples were inadvertently compromised as a result of movement in the fixture used for end plate removal. Because specimens that were not cut planoparallel were eliminated from this test, n was reduced for some groups of biomechanically tested vertebral specimens.

^*Charles River Laboratory:CD rats were used as one of the parent strains to develop the ZDSD rats.