Table 1.

Patient characteristics.

	All Patients	Without microscope	With microscope	p †
Overall	23670 (100%)	21444 (90.6%)	2226 (9.4%)
Age				0.002
15-39	14.8%	14.5%	17.2%
40-49	20.8%	20.6%	21.9%
50-59	25.7%	25.9%	23.9%
60-69	21.2%	21.4%	19.8%
≥70	17.5%	17.5%	17.2%
Male sex	51.6%	51.6%	51.4%	0.828
Body mass index				0.033
18-25	21.1%	10.9%	22.7%
25-30	34.7%	34.6%	35.9%
30-35	25.3%	25.3%	24.1%
≥35	19.0%	19.2%	17.4%
ASA 3-4	36.8%	35.1%	37.0%	0.078
Modified CCI				0.001
0-1	33.4%	33.1%	37.0%
2	23.0%	23.2%	21.5%
≥3	43.5%	43.7%	41.5%
Number of levels				<0.001
1	80.4%	79.5%	88.9%
2	15.0%	15.7%	8.0%
≥3	4.6%	4.8%	3.1%

ASA = American Society of Anesthesiologists; CCI = Charlson comorbidity index.

^†Bolding indicates statistical significance (p < 0.05).