The iO-Flex system is a minimally invasive, facet-sparing approach that allows for direct decompression of impinging tissue via a ventral-to-dorsal action of the MicroBlade Shaver. In contrast, traditional decompression procedures utilize an invasive medial-to-lateral approach that removes a significant portion of the posterior elements at the treated level. Another advantage of the iO-Flex system is that, unlike open laminectomy that utilizes fixed-angle tools with a limited ability to address lateral recess and foraminal stenosis, the iO-Flex System uses low-profile flexible instrumentation that targets impinging tissue in the spinal canal, lateral recess, and foramen (). This cadaver study demonstrated that the iO-Flex system allows for decompression of the spinal canal with limited resection of structural posterior elements and with selective resection of compressing structures in the lateral recess and foraminal regions.
Figure 7 Reconstructed axial computed tomography scans illustrating the ability of the iO-Flex® system to decompress the lateral recess and foramen effectively while maintaining facet joint integrity. Images are provided for nondiseased preoperative ( (more ...)
Although the clinical relevance of these study findings is unknown, the iO-Flex system has been utilized in two clinical studies with data published prior to this current study.13
A postmarket pilot study of nine patients with one-year follow-up demonstrated a median 73% reduction in pain, a 50% improvement in back function, 72% and 31% improvements in Zurich Claudication Questionnaire physical function and symptom severity, respectively, and a 36% improvement in health-related quality of life. A retrospective study of 67 patients treated with the iO-Flex system for LSS reported no reoperations or cases of neurologic impairment through approximately one year post-treatment. Thus far, the cumulative data on the iO-Flex system support safety and clinical utility, although additional study is required.
Although laminectomy is the traditional treatment of choice for patients with recalcitrant LSS, long-term outcomes are mixed.14
Laminectomy is often associated with postoperative pain, disability, and dysfunction, due to extensive resection of muscle, ligament, and bone. Resection of excessive bone from the posterior elements may contribute to subsequent lumbar instability and increased intradiscal pressure by establishing an alternate path of axial loading, transferring forces to the adjacent annulus and anterior longitudinal ligament.16
Consequently, disc degeneration may be accelerated following this procedure. Johnsson et al reported that 44% of patients presented with subsequent degenerative spondylolisthesis after decompressive lumbar laminectomy.17
Furthermore, Sanderson and Getty reported an average loss of 1.3 mm of disc height after partial undercutting facetectomy.18
Progression of stenotic symptoms following laminectomy is quite common19
and is due, in part, to inadequate decompression,20
local tissue trauma, and subsequent adhesion formation.22
Inadequate decompression of lateral recess stenosis has been shown to be responsible for 25%–56% of failed back surgery syndrome cases.24
Ultimately, 11%–23% of laminectomy patients undergo reoperation within 10 years.27
Results from this cadaver study confirmed that traditional decompression has a limited effect in improving lateral recess and foraminal area, especially in stenotic specimens. Decompression surgery using the iO-Flex system may reduce muscle trauma by allowing bilateral decompression through a single access point and, in theory, may result in a lower degree of destabilization, as seen in traditional decompression surgery.
Microdecompression procedures have recently been advocated due to a perceived lower risk of iatrogenic insult. However, these procedures require great technical skill and surgical experience, and evidence for these treatments is limited. In addition, while these procedures can be done via a less invasive exposure, fixed-angle tools still limit the ability to perform facet-sparing bilateral decompression of the lateral recess and foramen. Interspinous spacers have recently been advocated as an indirect method for relieving symptomatic LSS. Lumbar extension narrows the spinal canal and lateral recess by approximately 15% compared with a neutral posture,29
and therefore exacerbates LSS symptoms. Interspinous spacers limit back extension at the affected level by distracting the spinous processes of the degenerated segment, thereby unloading the posterior annulus fibrosus and facet joints. Despite promising mid-term outcomes, loss of radiographic correction after only 1.5 years is a well established phenomenon with these devices,30
and high clinical failure rates have been reported.31
Furthermore, interspinous spacers are only appropriate for patients with mild-to-moderate intermittent neurogenic claudication that is relieved by lumbar flexion and they do not directly address the underlying anatomical cause of pain, such as bony neuroforaminal encroachment and buckled ligamentum flavum. Because LSS is a progressive condition, interspinous spacers likely represent only a temporary solution to this disease. Overall, decompression using the iO-Flex system may have potential advantages over micro-decompression and interspinous spacers, including use of a simple minimally invasive approach and procedure, and the ability to treat patients with severe LSS symptoms.
This cadaver study had limitations. First, surgeons were not blinded to the procedures being performed in this study and, therefore, the possibility of intervention bias exists. However, all surgeons were well experienced and used a similar surgical technique, thus minimizing potential bias. Second, despite the noted advantages of the iO-Flex system in this cadaver study, the results do not necessarily translate into superior clinical outcomes compared with HL, especially given the variable relationship of LSS severity and clinical symptoms.32
Additional prospective human clinical studies are required to elucidate further the safety and effectiveness of this procedure. Two prospective studies measuring multiple clinical outcomes are currently underway. The first study is evaluating the clinical performance of the iO-Flex system in patients with one or two levels of LSS (NCT01067014), and the second study (STRiDE) is evaluating the iO-Flex system in patients with LSS and stable grade 1 spondylolisthesis (NCT01338766).