Early clinical outcome and learning curve following unilateral primary total knee arthroplasty after introduction of a novel total knee arthroplasty system

Table 3 Indicators of inter- and early postoperative outcome for patients

	Control group	Introduction group	P value (Control vs Introduction)	Follow-up group	P value (Control vs Follow-up)	Test
Length of operation, mean (95%CI)	50 min (48-52)	64 min (62-67)	< 0.0001	59 min (57-61)	< 0.0001	Unpaired T test
Length of stay, median (range)	2 d (0-5)	1 d (0-3)	0.24	1 d (0-9)	0.032	Mann-Whitney U test
Intra-operative blood loss, median (range)	200 mL (0-500)	250 mL (20-1200)	0.002	200 mL (50-1150)	0.84	Mann-Whitney U test
Intra-operative complications, n (%)	0 (0)	1 (1.3)	1.0	0 (0)	1.0	Fisher’s exact t-test
Readmissions within 90 d, n (%)	9 (12)	12 (16)	0.56	7 (11.3)	0.83	χ2
Deaths within 90 d, n (%)	0 (0)	0 (0)	1.0	0 (0)	1.0	Fisher’s exact t-test

For normally distributed data, in accordance with Shapiro Wilk-test, kurtosis, skewness and histogram inspection mean values are presented and P value calculated using the unpaired T-test. Otherwise Mann-Whitney U test was applied. P values for categorical data is calculated using Pearsons Chi-squared (χ²) test or Fisher’s exact t-test. Fischer’s exact test is applied when chi-squared (χ²) conditions may be violated due to expected cell number count below 5 and/or total cell count below 40. 95%CI: 95% Confidence interval.