Pseudarthrosis at L5-S1 after Posterolateral Lumbar Fusion

Kyu-Jung Cho; Seung-Rim Park; Jae-Hoon Jung; Man-Hee Won

doi:10.4184/JKSS.2010.17.2.90

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Cho, Park, Jung, and Won: Pseudarthrosis at L5-S1 after Posterolateral Lumbar Fusion

Original Research

J Korean Soc Spine Surg 2010;17(2):90-96.

Published online: 18 June 2010

DOI: https://doi.org/10.4184/JKSS.2010.17.2.90

Pseudarthrosis at L5-S1 after Posterolateral Lumbar Fusion

Kyu-Jung Cho, M.D., Seung-Rim Park, M.D., Jae-Hoon Jung, M.D., Man-Hee Won, M.D.

Department of Orthopaedic Surgery, College of Medicine, Inha University, Incheon, Korea

Corresponding author: Seung-Rim Park, M.D. Department of Orthopedic Surgery, Inha University Hospital 7-206, 3rd Street Shinheung-dong, Jung-gu, Incheon 400-103, Korea TEL: 82-32-890-3043, FAX : 82-32-890-3047 E-mail: srp2002@inha.ac.kr

Received 20 March 200924 March 2010 Accepted 31 May 2010

“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

This is a retrospective study.

Objectives

We wanted to investigate the rate of pseudarthrosis at L5-S1 after posterolateral fusion only for degenerative lumbar spinal disease, and to determine the radiological findings that help diagnose pseudarthrosis.

Summary of the Literature Review

The pseudarthrosis rate at L5-S1 is much higher than that at the other lumbar segments. However, there have been few studies for the rate and risk factors of pseudarthrosis at L5-S1.

Materials and Methods

A total of 88 patients who underwent pedicle screw instrumentation and posterolateral lumbar fusion were evaluated with a minimum of 1-year follow up. Bony union was evaluated by the bony fusion mass, the angulation on the flexion-extension radiographs and the radiolucent zone around the pedicle screws. The patients’ age, bony mineral density, the number of fused segments and lumbar lordosis were evaluated for their association with pseudarthrosis at L5-S1.

Results

Pseudarthrosis developed in 22 patients at L5-S1 and in 8 patients at other levels. The change of angulation on the flexion-extension radiographs at the last follow-up was 5.2° in the pseudarthrosis group and 1.7° in the fusion group (P=0.3). A radiolucent zone of the sacral screws was noted in 10 patients; in 7 of the 22 patients in the pseudarthrosis group and in 3 of the 66 patients in the fusion group. The average age, the mean number of levels fused and the bone mineral density were similar in both groups. Lumbar lordosis was not associated with the development of pseudarthrosis at L5-S1.

Conclusion

The pseudarthrosis rate was significantly higher at L5-S1 than that at the other lumbar segments following instrumented posterolateral fusion. Pseudarthrosis was closely related to hypermobile angulation (≥5°) on the flexion-extension radiographs and a radiolucent zone around the sacral screws.

Keywords: Pseudarthrosis, L5-S1, Posterolateral lumbar fusion, Radiolucent zone, Flexion-extension view

REFERENCES

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Fig.1 (A) A 53 year-old man had postsurgical stenosis L5-S1 after total laminectomy L5. (B) Immediate postoperative radiographs showed insufficient graft bone at the lumbosacral junction. (C) At 3 year after surgery, plain radiographs showed thin, small fusion mass bilaterally and radiolucent zone around S1 screw.

Table 1.

Biological factors related to pseudarthrosis at L5-S1

		Fusion group(n=66)	Pseudarthrosis group(n=22)	P-value
No. of patients		66	22
Age		56	59.5	0.90
	≥55	38(42.4%)	13(59.1%)
	<55	28(57.6%)	9(40.9%)
M:F		14:52	8:14
Smoking		15(22.7%)	6(27.3%)	0.45
BMD		-3.13	-3.46	0.52
No of fused level		2.46	2.64	0.47

Table 2.

Radiographical factors related to pseudarthrosis at L5-S1

	Fusion Group(n=66)	Pseudarthrosis Group(n=22)	P-value
Lumbar Lordosis(˚)	32	33	0.80
Depth of L5 Vertebra(mm)	11.6	12	0.97
Sacral Slope(˚)	32.7	36.8	0.59
Pelvic Tilt(˚)	24.4	25.5	0.51

Table 3.

L5-S1 segmental angle (= Flexion angle-extension angle)

		Fusion Group(n=66)	Pseudarthrosis Group(n=22)	P-value
Preop	≥5˚	38(42.2%)	13(59.1%)	0.13
Preop	< 5˚	28(57.6%)	9(40.9%)	0.13
Postop	≥5˚	0(0%)	4(18.2%)	0.015
Postop	< 5˚	66(100%)	18(91.8%)	0.015

Table 4.

Halo sign of the screws (=Radiolucent zone around screw≥1mm)

	Fusion group(n=66)	Pseudarthrosis group(n=22)	P-value
S1 screw	3(4.5%)	7(31.8%)	0.01
Other screws	5(7.6%)	1(4.5%)	0.15
Total	8(12.1%)	8(36.63%)

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