J Korean Soc Spine Surg.  2009 Sep;16(3):202-209. 10.4184/jkss.2009.16.3.202.

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

• Kwak JI
• Lee KY
• Kim HJ
• Sun SK

• KMID: 2003115
• DOI: http://doi.org/10.4184/jkss.2009.16.3.202

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 long-term 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 follow-up, 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 multi-levels, 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.

Keyword

Degenerative lumbar disease; Pedicle screw; Radiolucent zone; Pseudoarthrosis

MeSH Terms

Follow-Up Studies
Humans
Pseudarthrosis
Reoperation
Retrospective Studies

Figure

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  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.

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  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.

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  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.

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