Clinical Significance of the Radiolucent Zone Around the Pedicle Screws in the Lumbar Degenerative Disease

Jong Ill Kwak; Kyu Yeol Lee; Hyeon Jun Kim; Sang Kyu Sun

doi:10.4184/jkss.2009.16.3.202

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Kwak, Lee, Kim, and Sun: Clinical Significance of the Radiolucent Zone Around the Pedicle Screws in the Lumbar Degenerative Disease

Original Article

Journal of Korean Spine Surg 2009;16(3):202-209.

Published online: 21 February 2009

DOI: https://doi.org/10.4184/jkss.2009.16.3.202

Clinical Significance of the Radiolucent Zone Around the Pedicle Screws in the Lumbar Degenerative Disease

Jong Ill Kwak, M.D., Kyu Yeol Lee, M.D., Hyeon Jun Kim, M.D., Sang Kyu Sun, M.D.

Department of Orthopedic Surgery, College of Medicine, Dong-A University, Busan, Korea

Address reprint requests to Kyu-Yeol Lee, M.D. Department of Orthopedic Surgery, College of Medicine, Dong-A University, 1, Dongdaesin-dong 3-ga, Seo-gu, Busan 602-715, Korea Tel: 82-51-240-2867, Fax: 82-51-243-9764 E-mail: gylee@dau.ac.kr

Received 8 December 2008 Accepted 8 September 2009

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Study design

A retrospective study.

Objective

To analyze the clinical significance of the radiolucent zones surrounding pedicle screws.

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.

Conclusion

The presence of clear zones does not always mean pseudoarthrosis but clear zones persisting for more than 2 years after surgery have a higher rate of pseudoarthrosis.

Keywords: Degenerative lumbar disease, Pedicle screw, Radiolucent zone, Pseudoarthrosis

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
Clear zone	<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
Clear zone	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
Bone union	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
Clear zone	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

^∗ PLF: Posterolateral fusion

^† PLIF: Posterior lumbar interbody fusion

Table 5.

Relationship between clear zone and reoperation

Reoperation	Clear zone - 6 months		Clear zone - 3 years
Reoperation	Positive	Negative	Positive	Negative
Positive	13	10	8	15
Negative	111	265	33	343
Total	124	275	41	358
p-value	p = 0.07		p < 0.001

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