Use of a Hybrid Dynamic Stabilization and Fusion System in the Lumbar Spine
Abstract and Introduction
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. However, while many patients have benefited from fusion procedures, successful (that is, solid) fusion has not always been accompanied by clinical improvement. 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. 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. 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. 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. 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.
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.