Table 2 Subgroup analysis of the effect of different devices on cervical alignment
| Â | Subgroup title | No. of studies | No. of participants (ZP) | No. of participants (CP) | Subgroup outcome | Test for subgroup differences: I2 (%) | ||
|---|---|---|---|---|---|---|---|---|
Subtotal (95%CI) | P | I2 (%) | ||||||
Cobb (preoperative) | No. of levels | Â | Â | Â | Â | Â | Â | Â |
|  |  1 | 5 | 214 | 258 | − 0.36 [− 1.08, 0.36] | 0.32 | 0 | 0 |
|  |  ≥ 2 | 8 | 299 | 327 | − 0.23 [− 0.78, 0.33] | 0.43 | 0 |  |
Cobb (postoperative) | No. of levels | Â | Â | Â | Â | Â | Â | Â |
|  |  1 | 5 | 214 | 258 | − 0.72 [− 2.24, 0.81] | 0.36 | 76 | 0 |
|  |  ≥ 2 | 8 | 299 | 327 | − 0.91 [− 1.76, − 0.07] | 0.03* | 38 |  |
Cobb (last follow-up) | No. of levels | Â | Â | Â | Â | Â | Â | Â |
|  |  1 | 4 | 197 | 234 | − 1.70 [− 2.42, − 0.99] | < 0.00001* | 23 | 67.9 |
|  |  ≥ 2 | 7 | 233 | 243 | − 0.83 [− 1.48, − 0.18] | 0.01* | 49 |  |
| Â | Years of the last follow-up | Â | Â | Â | Â | Â | Â | Â |
|  |  < 3 | 7 | 265 | 265 | − 1.07 [− 2.21, 0.06] | 0.06 | 46 | 0 |
|  |  ≥ 3 | 4 | 165 | 212 | − 1.62 [− 2.56, − 0.67] | 0.0008* | 36 |  |
IDH (preoperative) | No. of levels | Â | Â | Â | Â | Â | Â | Â |
|  |  1 | 2 | 101 | 146 | 0.03 [− 0.25, 0.30] | 0.83 | 0 | 0 |
|  |  ≥ 2 | 5 | 163 | 173 | 0.02 [− 0.06, 0.11] | 0.6 | 0 |  |
IDH (postoperative) | No. of levels | Â | Â | Â | Â | Â | Â | Â |
|  |  1 | 2 | 101 | 146 | − 0.00 [− 0.20, 0.20] | 0.98 | 0 | 0 |
|  |  ≥ 2 | 5 | 163 | 173 | 0.10 [− 0.02, 0.22] | 0.11 | 34 |  |
IDH (last follow-up) | No. of levels | Â | Â | Â | Â | Â | Â | Â |
|  |  1 | 2 | 101 | 146 | − 0.09 [− 0.29, 0.12] | 0.42 | 0 | 0 |
|  |  ≥ 2 | 5 | 163 | 173 | − 0.02 [− 0.31, 0.27] | 0.89 | 76 |  |
| Â | Years of the last follow-up | Â | Â | Â | Â | Â | Â | Â |
|  |  < 3 | 4 | 136 | 139 | 0.09 [− 0.17, 0.36] | 0.49 | 55 | 60.1 |
|  |  ≥ 3 | 3 | 128 | 180 | − 0.18 [− 0.40, 0.03] | 0.1 | 39 |  |
ASD | No. of levels | Â | Â | Â | Â | Â | Â | Â |
| Â | Â 1 | 3 | 170 | 218 | 0.54 [0.33, 0.88] | 0.01* | 0 | 0 |
|  |  ≥ 2 | 7 | 286 | 311 | 0.37 [0.20, 0.70] | 0.002* | 0 |  |
| Â | Years of the last follow-up | Â | Â | Â | Â | Â | Â | Â |
|  |  < 3 | 6 | 258 | 275 | 0.39 [0.18, 0.83] | 0.01* | 0 | 0 |
|  |  ≥ 3 | 4 | 198 | 254 | 0.41 [0.23, 0.70] | 0.001* | 0 |  |
Dysphagia (postoperative) | No. of levels | Â | Â | Â | Â | Â | Â | Â |
| Â | Â 1 | 2 | 62 | 63 | 0.68 [0.27, 1.71] | 0.41 | 0 | 0 |
|  |  ≥ 2 | 3 | 97 | 104 | 0.74 [0.41, 1.34] | 0.32 | 0 |  |
Dysphagia (2 or 3Â months) | No. of levels | Â | Â | Â | Â | Â | Â | Â |
| Â | Â 1 | 3 | 84 | 88 | 0.21 [0.06, 0.80] | 0.02* | 0 | 0 |
|  |  ≥ 2 | 5 | 147 | 160 | 0.15 [0.07, 0.33] | < 0.00001* | 0 |  |
Dysphagia (6Â months) | No. of levels | Â | Â | Â | Â | Â | Â | Â |
| Â | Â 1 | 2 | 57 | 58 | 0.13 [0.02, 1.07] | 0.06 | 0 | 0 |
|  |  ≥ 2 | 4 | 149 | 156 | 0.10 [0.03, 0.37] | 0.0006* | 0 |  |
Dysphagia (last follow-up) | No. of levels | Â | Â | Â | Â | Â | Â | Â |
|  |  1 | 1 | 27 | 30 | 0.36 [0.01, 9.15] | 0.53 | – | 0 |
|  |  ≥ 2 | 4 | 118 | 125 | 0.48 [0.20, 1.15] | 0.1 | 0 |  |