Table 3. The effect of laminectomy and instrumentation on the stiffness of spinal segments in FE, LB, and AR.

					Untreated versus laminectomy		Laminectomy versus instrumentation
Stiffness	Segments	Untreated (degrees)	After laminectomy(degrees)	After instrumentation (degrees)	%	p value	%	p value
FE
Laminectomy	5 × L2–L3 and 6 × L4–L5	0.81 (± 0.44) (E = 9)	0.70 (± 0.35) (E = 9)	X	−14.4	0.129 (E = 9)	X	X
Adjacent	6 × L1–L2 and 6 × L3–L4	1.56 (± 1.20) (E = 12)	1.33 (± 1.10) (E = 12)	1.24 (± 0.68) (E = 11)	−14.7	0.080 (E = 12)	−9.7	0.320 (E = 11)
Control	6 × L2–L3 and 6 × L4–L5	1.14 (± 0.58) (E = 12)	1.10 (± 0.56) (E = 12)	1.14 (± 0.56) (E = 11)	−4.3	0.417 (E = 12)	−0.5	0.358 (E = 11)
LB
Laminectomy	5 × L2–L3 and 6 × L4–L5	1.49 (± 1.91) (E = 9)	1.29 (± 1.24) (E = 9)	X	−13.4	0.604 (E = 9)	X	X
Adjacent	6 × L1–L2 and 6 × L3–L4	1.73 (± 1.32) (E = 12)	1.50 (± 0.91) (E = 12)	1.87 (± 1.52) (E = 11)	−13.6	0.231 (E = 12)	+22.5	0.369 (E = 11)
Control	6 × L2–L3 and 6 × L4–L5	1.90 (± 1.57) (E = 12)	1.67 (± 1.43) (E = 12)	1.63 (± 1.00) (E = 11)	−12.2	0.006 (E = 12)	+20.5	0.730 (E = 11)
AR
Laminectomy	5 × L2–L3 and 6 × L4–L5	2.63 (± 1.58) (E = 11)	2.16 (± 1.33) (E = 11)	X	−18.0	0.005 (E = 11)	X	X
Adjacent	6 × L1–L2 and 6 × L3–L4	2.43 (± 1.34) (E = 9)	2.16 (± 1.21) (E = 9)	2.35 (± 1.44) (E = 8)	−10.8	0.533 (E = 9)	+19.3	0.386 (E = 8)
Control	6 × L2–L3 and 6 × L4–L5	2.42 (± 1.13) (E = 11)	2.25 (± 1.16) (E = 11)	2.40 (± 1.08) (E = 11)	−6.8	0.177 (E = 11)	+6.4	0.302 (E = 11)

Abbreviations: ANOVA, analysis of variance; AR, axial rotation; E, number of excluded measurements (see Note below and text); FE, flexion and extension; LB, lateral bending; X, not analyzed.

Note: Effects of laminectomy and instrumentation on treated, adjacent, and control segments were analyzed with ANOVA. If a measurement was excluded, the ANOVA also excludes its corresponding value, noted with an E.