Back pain at a symptomatic motion segment may originate from vertebral endplates, disc annulus, vertebral periosteum, facet joints, and/or surrounding soft tissue structures [7
]. These structures also contribute to the biomechanical stability of the spinal column. The pathology of discogenic pain and degenerative instability has been described by Kirkaldy-Willis and Farfan [8
]. Pain is reported to be the simplest description as well as the major symptom of instability. If a patient's limited instability is the result of glacial instability and dysfunctional segmental motion, he or she will experience pain but will be able to lead a life without neurologic deficit [9
]. Recent studies have suggested that the chronic instability related to the disc or vertebral body degenerative changes associated with abnormal motion results in the potential for pain.
The management of painful, unstable spinal segments due to degenerative disorders is much more difficult than spinal trauma or tumor surgery. During spinal surgery, instability must be taken into account when relieving pain with adequate neural tissue decompression. Whenever possible, bone, joint, ligament, and muscle tissues must be preserved, and suitable fixation methods must be chosen for the damaged ones; otherwise, decompressive procedures may induce or increase instability [10
The concept of spinal segment arthrodesis as a treatment for unstable degenerate spinal segments evolved almost 100 years ago. Spinal fusion was first described by Albee [3
], for the treatment of Pott disease, and Hibbs [14
], who performed spinal fusion as a treatment for spinal deformity. Since that time, fusion has been the conventional surgical treatment for chronic low-back pain attributed to degenerative disorders. For a long time, fusion was thought to be a necessity for a successful outcome, but the results of many recent studies have challenged this concept by showing that patients had limited improvements in pain relief and increased mobility after surgery [15
]. Posterior spinal instrumentation and fusion led to deteriorated biomechanical properties of the ligamentum flavum, posterior longitudinal ligament, and interspinous and supraspinous ligaments [19
]. Adequate preservation of the partial lamina, spinous process, and supraspinous and interspinous ligaments during laminectomy was helpful for alleviating the stress on the adjacent segment. Furthermore, biomechanical studies showed that posterolateral fusion with hemilaminectomy had less stress concentrated on the adjacent disc than posterolateral fusion with total laminectomy had on flexion [20
]. Moreover, fusion eliminates the motion of the functional spinal segment and may overload the adjacent segments. Indeed, adjacent segment degeneration is a known consequence of spinal fusion [3
]. Lehmann et al. reported accelerated degenerative changes of the adjacent segment and segmental instability above the fusion in 45% of their patients [26
]. Major drawbacks of spinal fusion are stiffness, pseudoarthrosis, mechanical failure, and/or adjacent degenerative disease [27
]. Because of these problems, less rigid stabilization systems have recently become more popular in spine surgery. Mobile stabilization systems have been shown to neutralize injurious forces and restore normal functions of the spine segments while also protecting the adjacent segments [32
]. One of the motion preservation technologies is the dynamic pedicular screw-rod system. It is a nonfusion dynamic implant system that controls displacement in rotation and translation as well as providing stabilization. This system allows potential sagittal mobility at the hinge site between the screw head and the shank of the screw. Mobility occurs mechanically between the longitudinally oriented rod and the sagittally placed screw shank. This articulated connection between the rod and the screw caused a reduction in flexion strain and resulted in a lower rate of implant failure [33
]. In these systems, the stress load was transferred from the implant to the spine, which decreased the tension on the bone [34
]. Although it tends to restrict mobility in flexion, extension, lateral bending, and axial rotation, a sharing of the motion and stress load still permits movement, prevents deterioration of the neighboring superior disc level, and slows the process of degenerative progression at the adjacent levels [35
]. Further, this controlled distribution of load between the implant and the spine may reduce postoperative damage to joint segments.
Microdiscectomy using Yasargil's microscope has been the standard surgical treatment for symptomatic disc herniation. However, treatment of disc herniations with degenerative changes is still a matter of debate. A simple discectomy cannot stop the continuing segmental degeneration and in some instances can even cause an acceleration of this process [6
]. In addition, the segmental fusion leads to an irreversible loss of function of the treated segment and a resulting risk of adjacent segmental degeneration and pseudoarthrosis [6
]. Disappointing surgical outcomes observed in the literature were generally due to increasing instability after surgery [40
]. Additional dynamic stabilization, applied by Putzier et al., showed significantly fewer signs of progressive degeneration and stabilized the motion segment after nucleotomy to prevent further disc degeneration [35
]. Kaner et al. showed the importance of the annular defect. They concluded that to apply a posterior dynamic stabilization is reasonable to the patients with disc herniation and an annular defect larger than 6
In spinal stenosis with degenerative spondylolisthesis, decompression and fusion are widely recommended. Clinical improvements observed in patients with spinal stenosis and degenerative spondylolisthesis generally depend on the effectiveness of the neural decompression; however, the value of instrumentation is still a matter of debate. Some surgeons recommend fusion with instrumentation because it prevents further sliding and applies more decompression without the risk of destabilization. Studies show that the decompression combined with arthrodesis (posterolateral or interbody) significantly improved patient outcome compared to decompression alone [43
]. However, some studies revealed that the additive instrumentation leads to higher fusion rates and less progression of spondylolisthesis; however, it is unlikely to improve clinical outcome [17
Surgeons advocating fusion without instrumentation indicate that this process gives a little chance to adjacent segment degeneration, and this concept is supported by various studies. Fischgrund et al. reported a randomized study comparing decompressive laminectomy and arthrodesis with or without spinal instrumentation. After a 2-year followup period, the authors concluded that successful fusion did not influence the patients' outcomes [17
]. Considering the older age of patients, major lengthy procedures like a fusion operation, especially posterolateral and interbody fusion with autogenous iliac crest graft, are associated with wound problems in the donor site, neurovascular damage, infections, pelvic fracture, and bleeding, all of which increase morbidity and mortality [53
]. Because the degenerative spondylolisthesis is a dynamic process, the purpose of fusion should be to prevent listhesis rather than cure the mechanical pain. Recent studies suggest that the dynamic stabilization system may maintain enough stability to prevent further translation of vertebra without fusion [55
Lumbar arthrodesis for the management of an unstable spine has dramatically increased over the last few decades. The purpose of spinal instrumentation is to increase fusion, but it is obvious that fusion with very long segment instrumentation is being tried, especially for different segment degenerative disorders.
In our study, we adopted a surgical approach that only targeted unstable degenerated and pain-producing segments. Using this approach, we applied neural decompression by a minimally invasive approach that resulted in very little disruption of tissue integrity, discectomy by sparing ligamentum flavum, and decompression by hemilaminectomy in stenosis [58
]. We provided stabilization of pain-producing degenerated unstable segments by posterior dynamic transpedicular instrumentation while skipping stable segments. Postoperative VAS and Oswestry scores of a limited series of patients treated with this preservative surgical approach were satisfactory.