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Abstract
Summary of Literature Review
Clear zones have been suggested in pseudoarthrosis and a loss of fixation. However, few reports have clearly described the longterm course and clinical significance of clear zones. Materials and Methods:The clear zones were evaluated in 399 patients with pedicle screw fixation after 6 months, 1 year, 2 years and 3 years. The patient was considered to be clear zone positive when 1 mm or greater circumferential lucency was confirmed around a screw on film from 2 or more directions. The time-course of the clear zones was examined with regard to age, number of levels fused, bone union, fusion method and reoperation.
Results
After 6 months, clear zones were observed in 124 patients (31.1%) but the clear zone-positive rate decreased with time. Clear zones were observed in 89 patients(22.3%), 44 patients(11.0%) and 41 patients(10.3%) after 1 year, 2 years and 3 years, respectively. No new clear zones had developed after 6 months. At the final followup, pseudoarthrosis was observed in 12 patients(3.0%). Among them, 11 were clear zone-positive and 1 was clear zone-negative. There was a statistically significant relationship between the clear zone-positive rate and multilevels, older age and nonunion during following up. In addition, there was a relatively lower clear zone-positive rate in posterolateral fusion combined with posterior lumbar interbody fusion than only posterolateral fusion. However, the difference between them was not statistically significant.
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REFERENCES
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Figures and Tables%
 | Fig. 1.Assessment of clear zones around pedicle screws. (A), (B) The presence of a 1 mm or greater radiolucent zone (arrows) around a screw on the radiograph was regarded as clear zone positive. |
 | Fig. 2.Reoperation in case of pseudoarthrosis 70-year-old man with PLF for spinal stenosis L1-2, 2-3, 3-4, 4-5, L5-S1 (A), (B): Dynamic view showing angular motion on L5-S1. (C), (D) Postoperative X-ray showing metal removal and expandable screw fixation & bone graft and PLIF. |
 | Fig. 3.Disappearance of clear zones around pedicle screws: 60-year-old woman with PLF for spinal stenosis L5-S1 with degenerative spondylolisthesis (A), (B): Clear zones (arrows) around pedicle screws were observed at 6 months (C), (D): Clear zones around pedicle screws disappeared at 3 years. |
Table 1.
Relationship between clear zone and age
| Clear zone | 6 months | 3 years | ||
|---|---|---|---|---|
| <60 yrs | ≥60 yrs | <60 yrs | ≥60 yrs | |
| Positive | 34 | 90 | 9 | 32 |
| Negative | 123 | 152 | 148 | 210 |
| Total | 157 | 242 | 157 | 242 |
| p-value | p<0.001 | p=0.018 | ||
Table 2.
Relationship between clear zone and number of levels
| Clear zone | 6 months | 3 years | ||
|---|---|---|---|---|
| 1 level | ≥2 levels | 1 level | ≥2 levels | |
| Positive | 15 | 109 | 4 | 37 |
| Negative | 70 | 205 | 81 | 277 |
| Total | 85 | 314 | 85 | 314 |
| p-value | p<0.001 | p<0.001 | ||
Table 3.
Relationship between clear zone and bone union
| Bone union | Clear zone - 6 months | Clear zone - 3 years | ||
|---|---|---|---|---|
| Positive | Negative | Positive | Negative | |
| Positive | 112 | 275 | 30 | 357 |
| Negative | 12 | 0 | 11 | 1 |
| Total | 124 | 275 | 41 | 358 |
| p-value | p<0.001 | p<0.001 | ||
Table 4.
Relationship between clear zone and procedure of fusion
| Clear zone | 6 months | 3 years | ||
|---|---|---|---|---|
| PLF* | PLF with PLIF† | PLF | PLF with PLIF | |
| Positive | 34 | 90 | 9 | 32 |
| Negative | 123 | 152 | 148 | 210 |
| Total | 157 | 242 | 157 | 242 |
| p-value | p = 0.57 | p = 0.68 | ||
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