Table 1 Patients’ demographics

Age (years, \(\overline{\mathrm{x} }\) ± s)

59.9 ± 9.1

62.0 ± 8.0

59.0 ± 9.0

T = 2.495

Gender

χ² = 3.541

Male

144 (72.0%)

44 (63.8%)

100 (76.3%)

Female

56 (28.0%)

25 (36.2%)

31 (23.7%)

BMI (kg/m², \(\overline{\mathrm{x} }\) ± s)

25.5 ± 3.7

25.1 ± 3.5

25.6 ± 3.9

T = − 0.906

OPLL type

χ² = 50.332

Continuous

71 (35.5%)

46 (66.7%)

25 (19.1%)

Mixed

67 (33.5%)

18 (26.1%)

49 (37.4%)

Segmental

51 (25.5%)

3 (4.3%)

48 (36.6%)

Unclassified

11 (5.5%)

2 (2.9%)

9 (6.9%)

K-line

χ² = 0.295

Positive

155 (77.5%)

55 (79.7%)

100 (76.3%)

Negative

45 (22.5%)

14 (20.3%)

31 (23.7%)

F/U duration (month)

42 (36–54)

38 (36–42)

48 (35–70)

U = 6118.5

Operative time (min)

110 (90–150)

97 (90–120)

129 (92–166)

U = 6231.5

Blood loss (ml)

200 (100–400)

300 (200–400)

200 (25–400)

U = 3225.5

Pre-JOA score

11.3 (9.0,14.0)

9.0 (8.0,12.5)

12.0 (10.0,15.0)

U = 5915.5

Post-JOA score

15.0 (13.0–16.0)

15.0 (14.0–16.0)

15.0 (12.0–16.7)

U = 4521.5

JOA score’s RR

0.60 (0.05–0.82)

0.67 (0.50–0.75)

0.47 (0–0.89)

U = 4003.0