Screw loosening in the Dynesys stabilization system: radiographic evidence and effect on outcomes

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Object

Dynamic stabilization systems are used to stabilize degenerative lumbar spondylosis. Loosening of the pedicle screws in such nonfusion implants is predictable. This retrospective study evaluated the incidence of screw loosening and its effect on clinical outcomes.

Methods

Charts, radiographic films, and medical records of 71 consecutive patients who underwent decompression using Dynesys dynamic stabilization for 1- or 2-level lumbar spondylosis were reviewed. Radiographic films were evaluated and compared to detect screw loosening. A visual analog scale (VAS) for back pain and the Oswestry Disability Index (ODI) were used for measuring clinical outcome. Statistical analysis was conducted using the chisquare test and Student t-test.

Results

The 71 patients in the study sample had a mean age of 59.2 ± 11.65 years (range 23–80 years), with slight female predominance (39 women, 32 men). The mean follow-up duration was 16.6 months (range 8–29 months). There were loose screws in 14 of 71 patients (19.7%), for a rate of 4.6% per screw (17 of 368 screws). Most screw loosening occurred in patients ≥ 55 years old (13 of 14 patients) although age and sex had no effect on screw loosening (p = 0.233 and 0.109, respectively). Both the loose screw and solid screw groups experienced significant improvement after the surgery in VAS and ODI scores. On the VAS, scores improved from 5.9 ± 2.99 to 2.1 ± 2.14 in the loose screw group (p = 0.003), and from 5.7 ± 3.45 to 2.9 ± 2.68 in the solid screw group (p < 0.001). For the ODI scale, scores improved from 43.5 ± 16.78% to 28.0 ± 18.18% (p = 0.006) in the loose screw group, and from 52.1 ± 20.92% to 24.6 ± 19.78% (p < 0.001) in the solid screw group. There were no significant differences between the 2 groups (p = 0.334 for VAS, p = 0.567 for ODI).

Conclusions

The preliminary study of this pedicle-based dynamic stabilization device for 1- and 2-level lumbar spondylosis shows radiographic evidence of screw loosening in 19.7% of patients and 4.6% of screws. Nonetheless, the loosening of screws has no adverse effect on clinical improvement.

Abbreviations used in this paper: ODI = Oswestry Disability Index; VAS = visual analog scale.

Abstract

Object

Dynamic stabilization systems are used to stabilize degenerative lumbar spondylosis. Loosening of the pedicle screws in such nonfusion implants is predictable. This retrospective study evaluated the incidence of screw loosening and its effect on clinical outcomes.

Methods

Charts, radiographic films, and medical records of 71 consecutive patients who underwent decompression using Dynesys dynamic stabilization for 1- or 2-level lumbar spondylosis were reviewed. Radiographic films were evaluated and compared to detect screw loosening. A visual analog scale (VAS) for back pain and the Oswestry Disability Index (ODI) were used for measuring clinical outcome. Statistical analysis was conducted using the chisquare test and Student t-test.

Results

The 71 patients in the study sample had a mean age of 59.2 ± 11.65 years (range 23–80 years), with slight female predominance (39 women, 32 men). The mean follow-up duration was 16.6 months (range 8–29 months). There were loose screws in 14 of 71 patients (19.7%), for a rate of 4.6% per screw (17 of 368 screws). Most screw loosening occurred in patients ≥ 55 years old (13 of 14 patients) although age and sex had no effect on screw loosening (p = 0.233 and 0.109, respectively). Both the loose screw and solid screw groups experienced significant improvement after the surgery in VAS and ODI scores. On the VAS, scores improved from 5.9 ± 2.99 to 2.1 ± 2.14 in the loose screw group (p = 0.003), and from 5.7 ± 3.45 to 2.9 ± 2.68 in the solid screw group (p < 0.001). For the ODI scale, scores improved from 43.5 ± 16.78% to 28.0 ± 18.18% (p = 0.006) in the loose screw group, and from 52.1 ± 20.92% to 24.6 ± 19.78% (p < 0.001) in the solid screw group. There were no significant differences between the 2 groups (p = 0.334 for VAS, p = 0.567 for ODI).

Conclusions

The preliminary study of this pedicle-based dynamic stabilization device for 1- and 2-level lumbar spondylosis shows radiographic evidence of screw loosening in 19.7% of patients and 4.6% of screws. Nonetheless, the loosening of screws has no adverse effect on clinical improvement.

Lumbar spine degeneration has been described by Kirkaldy-Willis and Farfan in 198210 using the concept of 3 phases: 1) temporal dysfunction, 2) unstable phase, and 3) restabilization. Phase 1 patients may respond to conservative treatment, while late Phase 2 and Phase 3 cases require surgery for stabilization, decompression, and correction of deformity. To stabilize the lumbar spine, internal fixation with bone graft fusion is acceptable, and various rigid fixation systems have been developed, including screws and rods.

Over the years, spinal fusion facilitated by instrumentation has been regarded as the standard treatment for severe degenerative lumbar spondylosis. However, a considerable amount of associated morbidity and complications have been reported,3,8 and adjacent segment degeneration is one that has drawn the most attention. The transition syndrome theoretically occurs from an overloading of adjacent segments,1,15 thereby challenging the long-accepted choice of fusion as standard surgical treatment. Numerous devices have since been developed to overcome the shortcomings of spinal fusion.

Dubois and colleagues first used the Dynesys system (Zimmer Spine) in 1994. Although several studies report that this system is a safe and promising alternative to fusion in treating unstable lumbar spondylosis,2,14,21 there has been no randomized controlled study addressing long-term outcome. To date, there is still a lack of strong evidence corroborating the concept of “dynamic stabilization.”

The use of pedicle-based lumbar stabilization devices spares the need for graft incorporation and spinal fusion. However, demands for durability and mechanical strength of the implant are higher than those required for fusion. Few reports address the problem of screw loosening in the literature. The true incidence of screw loosening and its effect on clinical outcomes remain uncertain.

This retrospective study evaluated the rate of screw loosening in the Dynesys system and correlated image findings to clinical outcomes. This study cohort was the largest from a single center with a reasonable follow-up duration, although this duration was shorter than in studies for spinal fusion because no graft incorporation was involved.

Methods

Patient Enrollment

Eighty-two consecutive patients were enrolled based on operative indications of symptomatic lumbar spinal stenosis and/or Grade 1 degenerative spondylolisthesis presenting as low-back pain, radiculopathy, or neurogenic claudication that failed conservative treatment longer than 12 weeks. Surgical procedures included lumbar total laminectomy in addition to dynamic posterior stabilization using the Dynesys system. All patients were treated and followed-up at the Taipei Veterans General Hospital in Taipei, Taiwan. The patients provided informed consent for the retrospective analysis of their clinical data.

Seventy-one patients completed the clinical and radiological follow-up evaluations. Eleven patients were excluded from the study due to inadequate neurological or radiological evaluations, or were lost to follow-up. The mean patient age was 59.2 ± 11.65 years (range 23–80 years) and the mean follow-up duration was 16.6 months (range 8–29 months). There was slight female predominance (39 patients, 55%). The Dynesys system was implanted for 1 level in 29 patients and for 2 levels in 42 patients, with 368 total screws inserted (Table 1).

TABLE 1:

Patient characteristics

VariableValue (%)
no. of patients71 (100)
M/F32:39 (45:55)
mean age ± SD (yrs)59.2 ± 11.65
op
 1 level29 (41)
 2 level42 (59)
total no. of screws368 (100)
 L-22 (0.5)
 L-364 (17.4)
 L-4134 (36.4)
 L-5130 (35.3)
 S-138 (10.3)

Surgical Procedures

Patients were placed prone in natural lumbar lordosis with adequate cushions, and fluoroscopy was used routinely for confirmation of this positioning. Standard lumbar total laminectomies with foraminotomies were performed via midline incision for direct posterior decompression at indicated levels. The exiting and traversing nerve roots were probed to confirm the adequacy of decompression. Generous subdermal dissection through the same incision provided access to another 2 fascial incisions, one on each side, allowing a bilateral approach through the Wiltse plane. The Dynesys pedicle screws were then inserted and connected in the relatively avascular intermuscular plane.24

All pedicle screws used in the series were standard titanium alloy, closed-head (side-loading) screws, without hydroxylapatite coating. The trajectory, length, and diameter of the screws used were previously determined based on preoperative CT scans and correlated with intraoperative measurements and fluoroscopic images. The polycarbonate-urethane spacer was inserted following the standard insertion techniques, with independent measurement using the pedicle distance gauge to tailor the length for every spacer. We attempted to hold the spinal segment in a more neutral anatomical position, avoiding excessive distraction on the facets; pre- and intraoperative fluoroscopic images were compared for confirmation. The tension cord was then assembled accordingly. In the setting of 2-level constructs, the lower level was always assembled first. A drainage catheter was placed before wound closure. Three fascial incisions (1 midline and 1 on each side for the Wiltse plane) and the midline skin excision were closed by interrupted sutures.

Clinical Evaluations

Charts, radiological imaging, and medical records were reviewed. Neurological examination and functional assessment were recorded preoperatively, at 3 weeks, and at 3, 6, 12, and 24 months postoperatively. Two independent nurse specialists under supervision of the attending physicians conducted the evaluations. Short questionnaires were completed, including the VAS for back pain and the ODI for functional disability.6

Radiographic Evaluations

In every patient, the following preoperative images were obtained: standing anteroposterior and lateral radiographs, dynamic lateral radiographs (flexion-extension views), lumbar spine CT scans, and lumbar spine MR imaging. All patients underwent anteroposterior plain radiography and lumbar spine CT scans within 1 week postoperatively, or as soon as the drains were removed. The follow-up protocol included anteroposterior and dynamic (flexion-extension) radiographs at 3, 6, 12, and 24 months postoperatively. Lumbar CT scans confirmed questionable screw loosening.

Definition of Radiographic Loosening of Screws

On digital anteroposterior radiographs, a wide (> 1 mm) radiolucent zone surrounding the screws, regardless of length of lucency, was described as a “halo zone sign,” and was defined as radiographic loosening (Figs. 1A and 2A).4,16 Sometimes the films were difficult to read because of bowel gas, body mass, or osteoporotic changes. The “double halo” sign was used to confirm the diagnosis if later radiographs were available (Figs. 1C and 2C). The “double halo” was described as a radiolucent rim surrounding the screw that is framed by the rim of radiopaque dense bone trabiculae.4 The radiologists and neurosurgeons resolved all ambiguities by consensus. The radiographic signs used for determination of screw loosening were usually better appreciated on anteroposterior than on lateral radiographs. (Figs. 1B, 1D, 2B, and 2D).

Fig. 1.
Fig. 1.

Anteroposterior (A and C) and lateral (B and D) postoperative radiographs obtained in a 64-year-old man who underwent L4–5 laminectomy for decompression and L4–5 Dynesys stabilization. A and B: At 6 months after the operation, a halo zone sign (arrows) indicated loosening of the left L-5 pedicle screw. C and D: At 12 months after the operation, a double halo sign (arrows) further confirmed the loosening.

Fig. 2.
Fig. 2.

Anteroposterior (A and C) and lateral (B and D) postoperative radiographs obtained in a 77-year-old man who underwent an L3–5 laminectomy for decompression and L4–S1 Dynesys stabilization. A and B: At 4 months after the operation, a halo zone sign (arrows) indicated loosening of the bilateral S-1 pedicle screw. C and D: At 6 months after the operation, a double halo sign (arrows) further confirmed the loosening.

Statistical Analysis

The statistical program SPSS version 17 (SPSS Inc.) was used to perform all statistical analyses. Data were analyzed using the chi-square test and Student t-test, where appropriate. Statistical significance was accepted at a probability value < 0.05.

Results

Radiographic Follow-Up

Dynamic stabilization was applied to 1 disc level in 29 patients and to 2 disc levels in 42 patients. Of the 368 screws inserted and evaluated in this series, 17 screws (4.6%) in 14 patients (19.7%) were loose according to radiographic examinations. The distribution of screw loosening was: 5 screws in 5 patients from the 1-level stabilization group and 12 screws in 9 patients from the 2-level stabilization group (Table 2). Interestingly, none of the loose screws in the patients with 2-level stabilization were found at the middle segment.

TABLE 2:

Loose screws by instrumented segments

Op (no. of patients [%])Level DistributionNo. of Patients (%)No. of Loose ScrewsNo. of Patients w/Loose Screws
1 level (29 [40.8])L3–45 (7)11
L4–520 (28.2)44
L5–S14 (5.6)00
2 level (42 [59.2])L2–41 (1.4)00
L3–525 (35.2)75
L4–S116 (22.5)54
total (71 [100])71 (100)1714

One malpositioned screw was identified on a postoperative CT scan. This malpositioned screw was a breach without compromising the nerve roots. There was no screw breakage or other instrumentation failure in the patient series. There were no wound infections and no secondary surgery was required.

Of the 14 patients (19.7%) with screw loosening, 8 were first found to have screw loosening on radiographs obtained 3 months postoperatively, whereas the other 6 patients were found to have loose screws 3–6 months postoperatively. Regarding confirmation of screw loosening, the interval between the halo zone sign and the double halo sign was 0–3 months in 7 patients, 6–12 months in 6 patients, and 16 months in 1 patient.

The group with loose screws had 14 patients (5 women and 9 men) with a mean age of 62.3 ± 7.25 years (range 47–77 years), whereas the group with solid screws had an average age of 58.3 ± 12.40 years (range 23–80 years; p = 0.223; Table 3). Thus, age was not related to screw loosening. However, if the patients were placed into a subgroup < 55 years old or ≥ 55 years old, almost all loosening (except 1) happened within the group ≥ 55 years old (p = 0.025). Sex also had no significant effect on screw loosening (p = 0.109) (Table 3).

TABLE 3:

Characteristics of the patients in each group

CharacteristicsTotalScrew Loosening*p Value
YesNo
no. of patients7114 (19.7)57 (80.3)
mean age ± SD (yrs)59.2 ± 11.6562.3 ± 7.2558.3 ± 12.400.233
age <55 yrs231 (4.3)22 (95.7)0.025
age ≥55 yrs4813 (27.1)35 (72.9)
M329 (28.1)23 (71.9)0.109
F395 (12.8)34 (87.2)
mean preop ODI score ± SD50.4 ± 20.3443.5 ± 16.7852.1 ± 20.920.160
mean postop ODI score ± SD25.3 ± 19.4028.0 ± 18.1824.6 ± 19.780.567
mean preop VAS score ± SD5.8 ± 3.345.9 ± 2.995.7 ± 3.450.891
mean postop VAS score ± SD2.7 ± 2.592.1 ± 2.142.9 ± 2.680.334
op
 1 level295 (17.2)24 (82.8)0.665
 2 level429 (21.4)33 (78.6)

* Data given as number of patients (%) unless otherwise indicated.

† Statistically significant.

Neurological Evaluations

The overall mean preoperative VAS score was 5.8 ± 3.34 (range 3–10), consisting of 5.7 ± 3.45 (range 3–10) for the solid screw group and 5.9 ± 2.99 (range 3–10) for the loose screw group. The mean preoperative ODI score was 50.4 ± 20.34% (range 22–91%), including 52.1 ± 20.92% (range 22–91%) for the solid screw group and 43.5 ± 16.78% (range 32–91%) for the loose screw group (Tables 4 and 5).

TABLE 4:

Clinical outcome of 14 patients with loose screws*

ScaleMean Preop ScoreMean Latest FU Scorep Value
VAS5.9 ± 2.992.1 ± 2.140.003
ODI43.5 ± 16.7828.0 ± 18.180.006

* FU = follow-up.

† Statistically significant.

TABLE 5:

Clinical outcome of 57 patients with solid screws

ScaleMean Preop ScoreMean Latest FU Scorep Value
VAS5.7 ± 3.452.9 ± 2.68<0.001*
ODI52.1 ± 20.9224.6 ± 19.78<0.001*

* Statistically significant.

The mean postoperative VAS score for low-back pain was 2.7 ± 2.59 (range 0–9), consisting of 2.9 ± 2.68 (range 0–9) for the solid screw group, and 2.1 ± 2.14 (range 0–7) for the loose screw group. The mean postoperative ODI score was 25.3 ± 19.4% (range 0–67%), including 24.6 ± 19.8% (range 0–67%) for the solid screw group and 28.0 ± 18.2% (range 4–51%) for the loose screw group (Table 3).

Comparing the latest VAS score with the preoperative VAS score, low-back pain improved significantly after surgery in both groups (p = 0.003 for the loose screw group and p < 0.001 for the solid screw group). Similarly, there was significant improvement in the ODI (p = 0.006 and p < 0.001, respectively; Tables 4 and 5; Figs. 3 and 4).

Fig. 3.
Fig. 3.

Graph showing significant improvement on the ODI in both the solid screw group and the loosening group.

Fig. 4.
Fig. 4.

Graph showing significant improvement on the VAS in both the solid screw group and the loosening group.

Discussion

Arthrodesis is a well-accepted strategy in the surgical treatment of degenerative lumbar spondylosis, with satisfactory outcomes.7,22 Achieving fusion has therefore been the goal of every spine surgeon for decades. However, there are a few reports in the literature of patients with failed spinal fusion and pseudoarthrosis that have comparable clinical outcomes as solid fusion.7 There is the hypothesis that the reduction, rather than the elimination, of lumbar segmental motion results in alleviated back pain.9 Moreover, the issue of adjacent level disease resulting from spinal arthrodesis has drawn much attention in the past. Despite insufficient data, various dynamic stabilization systems have been developed to neutralize noxious forces as well as to restore the normal movement of the spinal segments.

The Dynesys neutralization system, as a pedicle screw-based system, is compatible with direct decompression procedures without requiring the presence of the posterior element, which interspinous stabilizers rely on.21 The techniques basically decompress the neuroforamen while sparing the need for interbody arthrodesis or posterolateral fusion. Thus, it inherently avoids donor-side morbidity from fusion with autogenous iliac crest graft, decreases intraoperative blood loss, reduces muscle dissection, and shortens operative time. The Dynesys neutralization system reportedly maintains enough stability to prevent further progression of spondylolisthesis with shorter operation time, and less invasiveness.17,19,21 However, scant data in the literature provides little information regarding long-term results of such lumbar dynamic stabilization.

One major argument against the dynamic stabilization system is the possibility of implant failure.19 A broken Dynesys pedicle screw implanted in a multiple sclerosis patient with abnormal gait patterns is reported by Schnake et al.19 and Schaeren et al.17 Di Silvestre et al.5 reported no implant-related complications (screw loosening or breakage) in another series of 29 patients. Despite the limited numbers reported, the Dynesys stabilization system appears to be superior to the rigid pedicle-screw fixation systems in terms of rate of screw breakage.12,13 Such results lead to the assumption that the Dynesys stabilization system offers more biomechanical flexibility than the rigid fixation system, which minimizes the incidence of broken screws.18 On the other hand, more flexibility may translate the shearing force onto the vertebral body, resulting in screw loosening.

The incidence of loosening per screw and percentage of patients with implants reported in the current study is similar to previously presented data. Stoll et al.21 report 10 loose screws (in 7 patients) out of 280 total screws (3.6%). In 1 of the 7 patients, a radiologically suspected screw loosening correlated with clinical symptoms and necessitated a secondary intervention 14.5 months postoperatively. These investigators also noticed that most loose screws appeared in early postoperative radiographs (< 6 months) and none appeared later than 1 year postoperatively. In contrast, in the current report, all cases of screw loosening were discovered within 6 months postoperatively.

Schnake et al.,19 in a series with a minimum 2-year follow-up, reported that 4 (17%) of 24 patients had potential implant failure. They noted 4 pedicle screws with radiolucent lines and 1 broken pedicle screw out of 96 screws. The same patient population was continually followed-up for another 2 years by Schaeren et al.,17 who reported no new cases of screw loosening between the 2-year and the 4-year follow-up evaluations. The loosened screws in 3 patients remained radiologically unchanged, without evidence of progression of instability until the end of observation.

Di Silvestre et al.5 reported a series of 29 elderly patients in which 4 cases (13.8%) had asymptomatic radiolucent lines around the screws of the S-1 level without screw loosening. This finding appeared to be questionable as to whether the screws were solid or moving. Moreover, these investigators claimed no other implant failures. Compared with these data, the percentage of screw loosening in the current study is slightly higher. One explanation is that the patients have been actively followed-up in a prospectively scheduled manner, whereas patients in previous reports have not.

It is interesting to note that radiologically loosened screws have never occurred in the middle segment of vertebral bodies (for the 2-level stabilization). It is an assumption that screws inserted into the marginal segments have greater strength loading than those in the middle segment. As a result, loosening of screws is more likely to occur at the marginal segments. However, current data does not support this hypothesis and further biomechanical studies are warranted.

The present study has been conducted in Taiwan, a region with a high prevalence of osteoporosis. It is reported that in the Taiwanese population, especially among those aged > 50 years, the average prevalence of osteoporosis is 11.4% in women and 1.6% in men.23 Most patients with radiologically loose screws in this study were ≥ 55 years old (13 of 14 patients). Even though none of them had proven osteoporosis using dual-energy x-ray absorptiometry, the possibility of preexisting osteopenia cannot be completely ruled out. According to the experience of Schwarzenbach et al.,20 pedicle-based dynamic stabilization devices such as Dynesys have limitations in elderly patients with osteoporosis. It is crucial to conduct the more demanding techniques during pedicle screw placement to avoid multiple tapping or the backing out and readvance of the screws. Meanwhile, the fact that this system does not require fusion may be considered an advantage over spinal fusion procedures in patients with a high risk of arthrodesis failure, such as cigarette smokers.

Loosening of screws implies more range of motion in the stabilized lumbar spine segments than expected, which can be problematic. In contrast, the data here reveal similar outcomes in patients with or without screw loosening. The clinical results of the VAS for low-back pain and the ODI for functional disability improved significantly, regardless of screw loosening (Figs. 3 and 4; Tables 4 and 5). These data further challenge most spine surgeons' concept that failure of arthrodesis correlates with symptomatic back pain. Schaeren et al.17 also report that neither screw breakage nor loosening causes symptoms or back pain. It is possible that pedicle-based dynamic stabilization devices unload the posterior elements by transmitting the weight loading anteriorly. Thus, the degenerated spinal segment is unloaded with controlled motion, instead of complete immobilization by arthrodesis.11 The hypothesis that the reduction (rather than the elimination) in segmental motion results in the alleviation of back pain is corroborated.9

Regarding the radiographic definition of screw loosening, the radiolucent line, or “halo” sign, noted on plain radiographs can be vague due to overlapping bowel gas, fecal material, body mass, osteoporotic changes, or even digital magnification. Dakhil-Jerew et al.4 report using a “radiolucent zone sign” together with a “double halo sign” based on plain radiographs for detecting screw loosening in dynamic stabilization devices. The experience here of using their method shows that the duration between the occurrence of the halo zone sign and that of the double halo sign is 0–3 months in 7 patients, 6–12 months in 6 patients, and 16 months in 1 patient. Thus, if 1 screw is suspected of being loose, the double halo sign can be used to confirm the diagnosis in the next follow-up, with high concordance.

Conclusions

In this preliminary study of a pedicle-based dynamic stabilization device for 1- and 2-level lumbar spondylosis, radiographic loosening of pedicle screws occurred in 19.7% of patients and 4.6% of screws. Nonetheless, the loosening of screws had no adverse effect on clinical improvement.

Disclosure

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author contributions to the study and manuscript preparation include the following. Conception and design: JC Wu, CC Ko. Acquisition of data: CC Ko. Analysis and interpretation of data: CC Ko, HW Tsai, HC Chen, CL Wu. Drafting the article: JC Wu, CC Ko. Critically revising the article: JC Wu. Reviewed final version of the manuscript and approved it for submission: JC Wu. Statistical analysis: HW Tsai, YC Chen. Administrative/technical/material support: WC Huang, H Cheng. Study supervision: WC Huang, H Cheng, YH Shih.

References

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    Aota YKumano KHirabayashi S: Postfusion instability at the adjacent segments after rigid pedicle screw fixation for degenerative lumbar spinal disorders. J Spinal Disord 8:4644731995

  • 2

    Cakir BUlmar BKoepp HHuch KPuhl WRichter M: [Posterior dynamic stabilization as an alternative for dorsoventral fusion in spinal stenosis with degenerative instability.]. Z Orthop Ihre Grenzgeb 141:4184242003. (Ger)

  • 3

    Christensen FBBünger C: Stabilisation surgery for chronic low back pain: indications, surgical procedures, and outcome. Scand J Rheumatol 33:2102172004

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    Dakhil-Jerew FJadeja HCohen AShepperd JA: Inter-observer reliability of detecting Dynesys pedicle screw using plain X-rays: a study on 50 post-operative patients. Eur Spine J 18:148614932009

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    Di Silvestre MLolli FBakaloudis GParisini P: Dynamic stabilization for degenerative lumbar scoliosis in elderly patients. Spine 35:2272342010

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    Fairbank JCPynsent PB: The Oswestry Disability Index. Spine 25:294029522000

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    France JCYaszemski MJLauerman WCCain JEGlover JMLawson KJ: A randomized prospective study of posterolateral lumbar fusion. Outcomes with and without pedicle screw instrumentation. Spine 24:5535601999

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    Fritzell PHägg ONordwall A: Complications in lumbar fusion surgery for chronic low back pain: comparison of three surgical techniques used in a prospective randomized study. A report from the Swedish Lumbar Spine Study Group. Eur Spine J 12:1781892003

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    Grob DBenini AJunge AMannion AF: Clinical experience with the Dynesys semirigid fixation system for the lumbar spine: surgical and patient-oriented outcome in 50 cases after an average of 2 years. Spine 30:3243312005

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    Lawhorne TW IIIGirardi FPMina CAPappou ICammisa FP Jr: Treatment of degenerative spondylolisthesis: potential impact of dynamic stabilization based on imaging analysis. Eur Spine J 18:8158222009

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    Putzier MSchneider SVFunk JPerka C: [Application of a dynamic pedicle screw system (DYNESYS) for lumbar segmental degenerations - comparison of clinical and radiological results for different indications.]. Z Orthop Ihre Grenzgeb 142:1661732004. (Ger)

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    Rahm MDHall BB: Adjacent-segment degeneration after lumbar fusion with instrumentation: a retrospective study. J Spinal Disord 9:3924001996

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    Sandén BOlerud CPetrén-Mallmin MJohansson CLarsson S: The significance of radiolucent zones surrounding pedicle screws. Definition of screw loosening in spinal instrumentation. J Bone Joint Surg Br 86:4574612004

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    Schaeren SBroger IJeanneret B: Minimum four-year follow-up of spinal stenosis with degenerative spondylolisthesis treated with decompression and dynamic stabilization. Spine 33:E6366422008

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    Schmoelz WHuber JFNydegger TDipl-Ing Claes LWilke HJ: Dynamic stabilization of the lumbar spine and its effects on adjacent segments: an in vitro experiment. J Spinal Disord Tech 16:4184232003

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    Schnake KJSchaeren SJeanneret B: Dynamic stabilization in addition to decompression for lumbar spinal stenosis with degenerative spondylolisthesis. Spine 31:4424492006

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    Schwarzenbach OBerlemann UStoll TMDubois G: Posterior dynamic stabilization systems: DYNESYS. Orthop Clin North Am 36:3633722005

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Article Information

Address correspondence to: Jau-Ching Wu, M.D., Neural Regeneration Center, Department of Neurosurgery, Neurological Institute, Taipei Veterans General Hospital, School of Medicine and Institute of Pharmacology, National Yang-Ming University, Taipei, 201, Section 2, Shih-Pai Road, Taipei 112, Taiwan. email: jauching@gmail.com.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Anteroposterior (A and C) and lateral (B and D) postoperative radiographs obtained in a 64-year-old man who underwent L4–5 laminectomy for decompression and L4–5 Dynesys stabilization. A and B: At 6 months after the operation, a halo zone sign (arrows) indicated loosening of the left L-5 pedicle screw. C and D: At 12 months after the operation, a double halo sign (arrows) further confirmed the loosening.

  • View in gallery

    Anteroposterior (A and C) and lateral (B and D) postoperative radiographs obtained in a 77-year-old man who underwent an L3–5 laminectomy for decompression and L4–S1 Dynesys stabilization. A and B: At 4 months after the operation, a halo zone sign (arrows) indicated loosening of the bilateral S-1 pedicle screw. C and D: At 6 months after the operation, a double halo sign (arrows) further confirmed the loosening.

  • View in gallery

    Graph showing significant improvement on the ODI in both the solid screw group and the loosening group.

  • View in gallery

    Graph showing significant improvement on the VAS in both the solid screw group and the loosening group.

References

1

Aota YKumano KHirabayashi S: Postfusion instability at the adjacent segments after rigid pedicle screw fixation for degenerative lumbar spinal disorders. J Spinal Disord 8:4644731995

2

Cakir BUlmar BKoepp HHuch KPuhl WRichter M: [Posterior dynamic stabilization as an alternative for dorsoventral fusion in spinal stenosis with degenerative instability.]. Z Orthop Ihre Grenzgeb 141:4184242003. (Ger)

3

Christensen FBBünger C: Stabilisation surgery for chronic low back pain: indications, surgical procedures, and outcome. Scand J Rheumatol 33:2102172004

4

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