Table 6 

Z joint analyses

Parameter Cnull n = 11 mean (SD) Csau (n = 12) mean (SD) Difference: Cnull versus Csau Ff n = 21 mean (SD) Fn n = 17 mean (SD) Fr n = 19 mean (SD) Difference: Ff, Fn, Fr
Osteophytes/animal** Number of Z joints with osteophytes/animal (degeneration occurrence parameter). 2.3 (1.3) 1.3 (1.5) t=1.72, P = .10 ‡ 2.8 (1.4) 2.8 (1.2) 3.4 (0.8) KW = 2.25, P = .32 #
Severity of osteophytes/animal 0.8 (0.7) 0.4 (0.5) U = 38.50, P = .10 § 1.3 (0.9) 1.0 (0.8) 1.4 (0.7) KW = 221, P = .33
ASD/animal †† Number of articular surfaces with ASD/animal (degeneration occurrence parameter). 2.0 (2.5) 1.8 (1.6) t = 0.19, P = .85 6.9 (1.9) 6.5 (2.2) 6.3 (2.2) F = 0.35, P = .71 @
Severity of ASD/animal 0.3 (0.5) 0.3 (0.2) U = 60.50, P = .76 1.7 (0.8) 1.4 (0.7) 1.5 (0.7) KW = 2.20, P = .33

Z, Zygapophysial; Cnull, control group-surgery only (no spinal attachment units placed); Csau, control group-spinal attachment units placed during surgery; Ff, fixed in flexion; Fn, fixed in neutral; Fr, fixed in rotation; ASD, articular surface degeneration; ANOVA, analysis of variance; KW, Kruskal-Wallis statistic.

‡ t value of 2-tailed, unpaired t test.
#KW statistic of Kruskal-Wallis test (nonparametric ANOVA), osteophytes/animal was non-Gaussian in distribution. Therefore, the Kruskal-Wallis test was performed. Because the severity of osteophytes and severity of ASD/animal were ordinal in nature, the Kruskal-Wallis test was the appropriate test for these parameters as well.
§U-statistic of Mann-Whitney test (2-tailed).
@F value of ANOVA, data were Gaussian in distribution.