The use of a hybrid dynamic stabilization and fusion system in the lumbar spine: preliminary experience

Full access

Object

The authors report the use and preliminary results of a novel hybrid dynamic stabilization and fusion construct for the surgical treatment of degenerative lumbar spine pathology.

Methods

The authors performed a retrospective chart review of all patients who underwent posterior lumbar instrumentation with the Dynesys-to-Optima (DTO) hybrid dynamic stabilization and fusion system. Preoperative symptoms, visual analog scale (VAS) pain scores, perioperative complications, and the need for subsequent revision surgery were recorded. Each patient was then contacted via telephone to determine current symptoms and VAS score. Follow-up was available for 22 of 24 patients, and the follow-up period ranged from 1 to 22 months. Clinical outcome was gauged by comparing VAS scores prior to surgery and at the time of telephone interview.

Results

A total of 24 consecutive patients underwent lumbar arthrodesis surgery in which the hybrid system was used for adjacent-level dynamic stabilization. The mean preoperative VAS score was 8.8, whereas the mean postoperative VAS score was 5.3. There were five perioperative complications that included 2 durotomies and 2 wound infections. In addition, 1 patient had a symptomatic medially placed pedicle screw that required revision. These complications were not thought to be specific to the DTO system itself. In 3 patients treatment failed, with treatment failure being defined as persistent preoperative symptoms requiring reoperation.

Conclusions

The DTO system represents a novel hybrid dynamic stabilization and fusion construct. The technique holds promise as an alternative to multilevel lumbar arthrodesis while potentially decreasing the risk of adjacent-segment disease following lumbar arthrodesis. The technology is still in its infancy and therefore follow-up, when available, remains short. The authors report their preliminary experience using a hybrid system in 24 patients, along with short-interval clinical and radiographic follow-up.

Abbreviations used in this paper: DTO = Dynesys-to-Optima; VAS = visual analog scale.

Abstract

Object

The authors report the use and preliminary results of a novel hybrid dynamic stabilization and fusion construct for the surgical treatment of degenerative lumbar spine pathology.

Methods

The authors performed a retrospective chart review of all patients who underwent posterior lumbar instrumentation with the Dynesys-to-Optima (DTO) hybrid dynamic stabilization and fusion system. Preoperative symptoms, visual analog scale (VAS) pain scores, perioperative complications, and the need for subsequent revision surgery were recorded. Each patient was then contacted via telephone to determine current symptoms and VAS score. Follow-up was available for 22 of 24 patients, and the follow-up period ranged from 1 to 22 months. Clinical outcome was gauged by comparing VAS scores prior to surgery and at the time of telephone interview.

Results

A total of 24 consecutive patients underwent lumbar arthrodesis surgery in which the hybrid system was used for adjacent-level dynamic stabilization. The mean preoperative VAS score was 8.8, whereas the mean postoperative VAS score was 5.3. There were five perioperative complications that included 2 durotomies and 2 wound infections. In addition, 1 patient had a symptomatic medially placed pedicle screw that required revision. These complications were not thought to be specific to the DTO system itself. In 3 patients treatment failed, with treatment failure being defined as persistent preoperative symptoms requiring reoperation.

Conclusions

The DTO system represents a novel hybrid dynamic stabilization and fusion construct. The technique holds promise as an alternative to multilevel lumbar arthrodesis while potentially decreasing the risk of adjacent-segment disease following lumbar arthrodesis. The technology is still in its infancy and therefore follow-up, when available, remains short. The authors report their preliminary experience using a hybrid system in 24 patients, along with short-interval clinical and radiographic follow-up.

Over the past decade, spinal arthrodesis with or without instrumentation has become a common technique in the surgical treatment of symptomatic degenerative disease of the lumbar spine. Technological advances such as transpedicular instrumentation have resulted in increased fusion rates, while decreasing the need for postoperative immobilization and brace therapy, and have fueled a seemingly inexorable (recently estimated as 4-fold) increase in the number of spinal fusions performed each year.9 However, while many patients have benefited from fusion procedures, successful (that is, solid) fusion has not always been accompanied by clinical improvement.2 This apparent disconnect between surgical and clinical outcomes raises important questions. Does this subset of patients represent a failure of patient selection and should these patients have been offered a different surgery more likely to address their particular pathology? Might spinal fusion lead in some cases to secondary, delayed effects that negatively affect the final clinical outcome?

Evidence is growing that fusion may in fact have undesirable long-term effects on the remainder of the spine, particularly on the immediately adjacent motion segments.3,4 This adjacent-level degeneration is typically seen rostral to a fused segment but may also occur caudal to a fusion, especially when the fusion occurs at the L4–5 level. The phenomenon is thought to be due to the altered biomechanics of the fused spine, wherein abnormal forces acting upon the intervertebral discs and facet joints adjacent to the fused segment precipitate the accelerated failure of these stabilizing elements.5 From this evidence for adjacent-segment degeneration emerged the concept of “dynamic” or nonfusion stabilization of the lumbar spine.

Posterior dynamic stabilization, in which pedicle screw fixation is coupled with a flexible longitudinal connecting system, presumably allows for the normalization of intersegmental motion.6–8 This stands in contrast to traditional fusion surgery, in which the goal is complete and immediate elimination of motion and, ultimately, arthrodesis. While both strategies seek to address the underlying pathology of microinstability, the dynamic stabilization approach promises to do so in a more physiological manner. By “restoring” normal motion, mobility is theoretically preserved rather than eliminated, and the forces acting above and below the construct are altered to a lesser extent, reducing the potential undesirable effects of fusion.

Nearly a dozen such systems are currently available, and all employ a variety of motion-preserving technologies ranging from semirigid rods to ball-and-socket joints.1 Of note, due in large part to the exigencies of the medical device approval process, FDA approval of these systems has thus far been for their use as an adjunct to fusion in the lumbar spine, a decision based on the demonstration of noninferiority of the approved systems compared with traditional pedicle screw/rod–based fusion. Nevertheless, “off-label” use for motion-preservation surgery is widespread, and several investigational device exemption studies for nonfusion applications are ongoing.

At our institution, we have been using one of these systems—the Dynesys Dynamic Stabilization System (Zimmer Spine)—for motion-preservation surgery for nearly 5 years. Recently available is a hybrid system (DTO, Zimmer Spine; Fig. 1) in which dynamic stabilization may be performed immediately above (or less commonly, below) a fusion. The system is intended for use in patients in whom fusion is desired—whether to treat gross instability or severe, advanced degeneration—at one or more levels, and in whom one or more adjacent segments exhibit degenerative changes that are thought to be contributing to the patient's symptoms but are not of a severe-enough degree to warrant arthrodesis. This study was performed to evaluate the preliminary experience with the DTO hybrid construct.

Fig. 1.
Fig. 1.

Photograph of the DTO implant, which is a hybrid construct with dynamically stabilized segment (at left) and rigidly fixated segment (at right). Image used with permission from Zimmer Spine.

Methods

We performed a retrospective review of all DTO posterior lumbar hybrid dynamic stabilization and fusion procedures at the University of Pittsburgh Medical Center, Presbyterian Hospital. Patients with degenerative lumbar disc disease were chosen to undergo the procedure if they were candidates for fusion and had symptomatic adjacent-level pathology in which dynamic stabilization was thought to be more appropriate than arthrodesis. The DTO procedure involves placement of standard transpedicular instrumentation and fusion utilizing the Zimmer Optima system at segments deemed to require rigid fixation and fusion. A unique Dynesys screw is then placed in the superior pedicle of the segment believed to be at risk for subsequent degeneration adjacent to the fusion. A transitional screw is placed in the intervening pedicle that allows the 2 systems to be connected. An intertransverse process fusion is then performed at the levels to be fused and is typically supplemented with interbody fusion via a transforaminal approach. Autograft bone, obtained from the same incision in the course of the bony decompression, is supplemented with demineralized bone matrix and laid down between the decorticated transverse processes.

Medical records were reviewed to determine preoperative VAS pain scores (with 1 being very little pain and 10 being very severe pain) obtained at the time of surgical consent, to assess clinical outcomes at follow-up (including the need for reoperation), and to record complications. Postoperative imaging studies, including radiographs, CT scans, and MR images, were reviewed when available. Patients were contacted via telephone at the time of chart review to assess their current level of back and leg pain. In all cases, patient permission was obtained for this review.

Results

A total of 24 patients underwent the DTO procedure between March 2008 and December 2009. The mean patient age was 49 years (range 29–66 years). There were 12 men and 12 women. Fifteen patients had undergone previous lumbar surgery at one or more of the surgically treated levels. Patient demographics are summarized in Table 1. Figure 2 shows a representative case, including a preoperative provocative discogram and postoperative lateral radiograph.

TABLE 1:

Summary of demographics

VariableValue
sex
 male12
 female12
age (yrs)
 range29–66
 mean49
prior lumbar op
 yes15
 no9
Fig. 2.
Fig. 2.

Radiographs obtained in a 43-year-old man with a 5-year history of disabling low-back pain and in whom nonsurgical therapy had failed. A: A preoperative blinded provocative discographic study was performed and demonstrated severe disc degeneration with contrast extravasation and concordant pain replication at L5–S1. Less severe disc degeneration with an anular tear but nonconcordant pain replication was demonstrated at the L4–5 level. The L3–4 level was found to be completely normal on CT scanning. B: A postoperative lateral radiograph demonstrating the hybrid construct with a dynamically stabilized segment (L4–5) above a rigid fused segment (L5–S1).

Clinical Outcomes

Postoperative VAS scores were available for 22 (92%) of the 24 patients. The mean follow-up duration was 8 months (range 1–22 months). For the entire group, the mean preoperative VAS score was 8.8, and the mean postoperative VAS score was 5.3. Pain in 3 patients improved by 7 points, in 2 patients by 6 points, in 3 patients by 5 points, in 3 patients by 4 points, in 3 patients by 3 points, in 4 patients by 2 points, and 4 patients rated their pain unchanged. Of the 4 patients who experienced no improvement in pain, one case was notable for the patient having a complicated postoperative course requiring reoperation after 8 months for a disc herniation at the stabilized level, which was further complicated by a wound infection requiring irrigation and debridement and long-term antibiotics. The other 3 patients had an uneventful postoperative course.

Complications

There were 5 perioperative complications. These included 2 dural tears for which primary repair was performed. In 1 of the patients with a dural tear, a persistent CSF leak developed and required wound revision. One patient awoke with new radicular pain that was attributable to a medially placed L-4 pedicle screw. This patient was taken back to the operating room and underwent revision of the screw. In 2 patients a postoperative wound infection developed, in both of whom the incisions healed following irrigation and debridement of the wound. All of these cases were believed to be unrelated to the DTO system itself and were thought to be rather typical for lumbar arthrodesis surgery with instrumentation. There were no cases of hardware failure.

Treatment Failures

Treatment failure was defined as persistent pain or the need for further surgery at either the surgically treated or adjacent levels. Three patients (12%) underwent extension of their fusion for adjacent-level disease during this follow-up period. In one patient, persistent pain attributed to the dynamically stabilized level prompted revision with interbody fusion at that level. In 2 other patients adjacent-level disease developed immediately rostral to the dynamically stabilized segment. Results are summarized in Table 2.

TABLE 2:

Summary of pain scores, complications, and treatment failures*

FactorValue
mean VAS score
 preop8.8
 postop5.3
no. of complications
 dural tear2
 symptomatic screw misplacement1
 wound infection2
no. of treatment failures
 symptomatic degeneration at the DSS‡1
 symptomatic degeneration above the DSS‡2

* DSS = dynamically stabilized segment.

† One of the 2 patients required operative wound revision for a persistent CSF leak.

Discussion

The phenomenon of adjacent-segment disease, referring to accelerated degenerative changes occurring at the ends of the fused spine, has received increasing attention as ever more spinal fusions are performed and long-term follow-up data become available.3,7 While the time course and prevalence of adjacent-segment disease are not fully known, there is increasing evidence in the spine literature that its effects may be seen soon after fusion surgery and in as many as 30% of patients.3,4 In a recently published large retrospective analysis Cheh et al.3 reported a rate of clinical adjacent-segment disease of 30.3% and showed that patients in whom adjacent-level disease developed had significantly worse Oswestry Disability Index scores than those without adjacent-level disease. They further identified age > 50 years at time of surgery, increasing length of fusion, and extension of the fusion to L1–3 as significant risk factors for the development of adjacent-level disease. No significant difference was identified between posterior and circumferential fusion.

Over the past 20 years, an array of posterior pedicle fixation–based motion preservation systems have been introduced as many in the spine community have sought to decrease the incidence of adjacent-level disease.1 One of these systems—the Dynesys Dynamic Stabilization System—has been in use at our institution for the past 5 years. More recently, we have begun to use a hybrid system in which Dynesys dynamic stabilization is performed above (or less commonly, below) a traditional pedicle screw–augmented fusion. The DTO hybrid construct has proven useful in the treatment of the patient in whom decompression and fusion are required at one or more levels, but in whom there is also the potential for symptomatic degenerative changes at one or more adjacent levels. In our series, clinical improvement, as measured by changes in VAS pain scores, was seen in 18 (82%) of 22 patients. Three (12%) of the original 24 patients developed symptomatic degenerative changes at or above the dynamically stabilized levels and subsequently underwent revision with fusion—a not insignificant rate of adjacent-segment degeneration whose cause is the subject of an ongoing investigation. Finally, 5 (21%) of 24 patients experienced a complication, including 2 dural tears, 2 wound infections, and a single screw misplacement requiring revision. However, these complications were not believed to have been related to the actual DTO system itself.

Conclusions

The DTO hybrid system represents a unique new technology that allows for the coupling of arthrodesis with dynamic stabilization at adjacent levels in the lumbar spine. Application of the technique is in the early stages, and long-term follow-up data are therefore scarce. However, based on preliminary results in 24 patients, the technique merits further investigation as an alternative to multilevel lumbar arthrodesis.

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: PC Gerszten, MB Maserati, MJ Tormenti. Acquisition of data: MB Maserati, MJ Tormenti, CM Bonfield, DM Panczykowski. Analysis and interpretation of data: PC Gerszten, MB Maserati, MJ Tormenti. Drafting the article: MB Maserati, MJ Tormenti. Critically revising the article: PC Gerszten. Reviewed final version of the manuscript and approved it for submission: PC Gerszten. Statistical analysis: MB Maserati, MJ Tormenti, DM Panczykowski. Administrative/technical/material support: PC Gerszten. Study supervision: PC Gerszten.

References

  • 1

    Bono CMKadaba MVaccaro AR: Posterior pedicle fixation-based dynamic stabilization devices for the treatment of degenerative diseases of the lumbar spine. J Spinal Disord Tech 22:3763832009

  • 2

    Bono CMLee CK: Critical analysis of trends in fusion for degenerative disc disease over the past 20 years: influence of technique on fusion rate and clinical outcome. Spine 29:4554632004

  • 3

    Cheh GBridwell KHLenke LGBuchowski JMDaubs MDKim Y: Adjacent segment disease following lumbar/thoracolumbar fusion with pedicle screw instrumentation: a minimum 5-year follow-up. Spine 32:225322572007

  • 4

    Chou WYHsu CJChang WNWong CY: Adjacent segment degeneration after lumbar spinal posterolateral fusion with instrumentation in elderly patients. Arch Orthop Trauma Surg 122:39432002

  • 5

    Lee CKLangrana NA: Lumbosacral spinal fusion. A biomechanical study. Spine 9:5745811984

  • 6

    Nockels RP: Dynamic stabilization in the surgical management of painful lumbar spinal disorders. Spine 30:16 SupplS68S722005

  • 7

    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

  • 8

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

  • 9

    Weinstein JNLurie JDOlson PRBronner KKFisher ES: United States' trends and regional variations in lumbar spine surgery: 1992–2003. Spine 31:270727142006

If the inline PDF is not rendering correctly, you can download the PDF file here.

Article Information

Address correspondence to: Peter C. Gerszten, M.D., Department of Neurological Surgery, 200 Lothrop Street, Suite B-400, Pittsburgh, Pennsylvania 15213. email: gersztenpc@upmc.edu.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Photograph of the DTO implant, which is a hybrid construct with dynamically stabilized segment (at left) and rigidly fixated segment (at right). Image used with permission from Zimmer Spine.

  • View in gallery

    Radiographs obtained in a 43-year-old man with a 5-year history of disabling low-back pain and in whom nonsurgical therapy had failed. A: A preoperative blinded provocative discographic study was performed and demonstrated severe disc degeneration with contrast extravasation and concordant pain replication at L5–S1. Less severe disc degeneration with an anular tear but nonconcordant pain replication was demonstrated at the L4–5 level. The L3–4 level was found to be completely normal on CT scanning. B: A postoperative lateral radiograph demonstrating the hybrid construct with a dynamically stabilized segment (L4–5) above a rigid fused segment (L5–S1).

References

1

Bono CMKadaba MVaccaro AR: Posterior pedicle fixation-based dynamic stabilization devices for the treatment of degenerative diseases of the lumbar spine. J Spinal Disord Tech 22:3763832009

2

Bono CMLee CK: Critical analysis of trends in fusion for degenerative disc disease over the past 20 years: influence of technique on fusion rate and clinical outcome. Spine 29:4554632004

3

Cheh GBridwell KHLenke LGBuchowski JMDaubs MDKim Y: Adjacent segment disease following lumbar/thoracolumbar fusion with pedicle screw instrumentation: a minimum 5-year follow-up. Spine 32:225322572007

4

Chou WYHsu CJChang WNWong CY: Adjacent segment degeneration after lumbar spinal posterolateral fusion with instrumentation in elderly patients. Arch Orthop Trauma Surg 122:39432002

5

Lee CKLangrana NA: Lumbosacral spinal fusion. A biomechanical study. Spine 9:5745811984

6

Nockels RP: Dynamic stabilization in the surgical management of painful lumbar spinal disorders. Spine 30:16 SupplS68S722005

7

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

8

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

9

Weinstein JNLurie JDOlson PRBronner KKFisher ES: United States' trends and regional variations in lumbar spine surgery: 1992–2003. Spine 31:270727142006

TrendMD

Metrics

Metrics

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 73 73 42
PDF Downloads 58 58 9
EPUB Downloads 0 0 0

PubMed

Google Scholar