A brief discussion of interspinous devices and decompression of lumbar stenosis is warranted given the popularity of these devices. Gazzeri et al. [9] discussed the controversies related to these devices and their ability to provide relief of degenerative lumbar disease. Although not an entirely minimally invasive procedure, the insertion of an interspinous device follows the principle of minimal anatomical disruption. These devices are used to treat a range of lumbar pathologies including canal stenosis, segmental instability, facet pain syndrome, and discogenic low back pain. Reported benefits to use of an interspinous device include local anesthetic, preservation of bone and soft tissue, reduced risk of epidural scarring, reduced risk of CSF leak, and even reversibility of the procedure [9]. Looking more closely at the use of the interspinous devices simply for lumbar decompression, the selection criteria are specific to those patients who have relief of their stenotic pain with flexion of the lumbar spine. The mechanism of flexion of the lumbar spine is believed to stretch the redundant ligamentum flavum, which causes posterior compression and stenosis. Once the ligamentum is stretched by the continuous flexion of the interspinous device, there is increased canal diameter and enlargement of the neural foramina, relieving lower extremity symptoms. As reviewed by Gazzeri et al., mean expansion of the spinal canal with insertion of a device is reported between 18 % and 22 % and neural foramina area increased by approximately 25 %. The interspinous devices can be inserted through small, tissue-sparing midline incisions, or even percutaneously. There are a multitude of different devices on the market. The only device with level 1 data is the X-Stop (Medtronic, Tolochenaz, Switzerland; Formerly St. Francis Medical Technologies, Alameda, CA). Looking at published literature the short-term results with the use of the X-Stop device had a significant benefit over nonoperative therapy. Compared to open decompression, the X-Stop showed no significant difference in symptoms or function at 24 months; however, there was a significant increase in reoperation rates for those in the X-Stop group (26 % vs 6 %) [9]. Overall the current evidence does not support a benefit to an interspinous device over surgical decompression, either open or minimally invasive.

A major consideration in the use of MISS is the learning curve encountered when beginning the use of the technique [3, 10–12]. All surgical techniques have a learning curve, and in advanced neurosurgical fields such as complex spine and skull base surgery, there are often a higher incidence of complications encountered during the initial phase of a surgeon’s application of a new technology. Depending on the similarity of a technique to one already in use or familiar to the surgeon, it can be understood that some techniques have steeper curves than others. Generally it is believed that familiarity of a surgical technique occurs after approximately 30 cases, while mastery of a technique may continue for some number of cases after. Complications encountered early in the learning process include unintentional durotomy, nerve root injury, inferior facet fracture, wrong level surgery, infections, and new neurologic deficits. Looking at Ikuta et al.’s [12] retrospective review of 114 patients, they found that the incidence of neurologic complications in the first 34 patients was 18 %, whereas it was down to 6.3 % in the last 80 patients.

Minimally invasive spine surgery can be done for lumbar spinal stenosis. The literature confirms that MISS is equivalent or better than open procedures in clinical patient outcome measures [3, 7, 10, 12, 13]. It allows for less blood loss, shorter overall operative time, shorter hospital stay, decreased postoperative narcotic use, decreased rate of infection, decreased incidence of symptomatic CSF leak, and a decrease in the time required for the patient to return to work [3]. As well, as was illustrated in Smith et al.’s biomechanical study [4], MISS has the advantage of less tissue disruption allowing for decreased rates of spinal instability and subsequent requirement for future procedures. One may thus conclude that MISS decompression is a superior technique to a traditional open approach, once the technique has been mastered.

Minimally invasive TLIF is covered extensively in another chapter, and it is a TLIF that has emerged as the current gold standard treatment for spondylolisthesis. We provide a brief summary of the literature outlining the efficacy and feasibility of MISS TLIF (Fig. 37.4).

MISS TLIF is being increasingly performed and has shown reduction in perioperative complications with comparable clinical and radiological outcomes. Compared to an open technique, the benefits of MISS TLIF are decreased postoperative pain, decreased intraoperative blood loss, shorter postoperative hospital stay, faster return to normal activity, and reduced reoperation rates for adjacent segment disease [6, 14]. In example, Parker et al. [15] demonstrated a significant benefit to MISS TLIF with only 2.6 weeks of postoperative narcotic use compared to 6.5 weeks in open cases and a return to work at 8.3 weeks compared to 16.3 weeks. Lee et al. [16] showed a mean operating time of 166 min for MISS TLIF compared to 181 min with open. The mean blood loss was 50.6 mL compared to 447.4 mL and mean hospital stay 3.2 days compared to 6.8 days.

Quality of life in MISS TLIF was studied prospectively by Perez-Cruet et al. [14] with mean 47 months of follow-up in 304 patients. It was found that MISS TLIF provided statistically significant improvement in clinical outcome for patients with symptomatic spondylolisthesis and degenerative disk disease with or without stenosis. There was a high rate of fusion (>95 % majority achieved by 6.8 months) with the technique and very low rate of interbody device failure (1 %) and very low rate of adjacent segment disease requiring reoperation (2 %). Looking at quality-of-life scores: visual analog scale (VAS) improved by 35.7 % in the immediate short-term and this benefit was maintained long term; the Oswestry Disability Index (ODI) also demonstrated immediate and long-term significant improvement as did the SF-36 physical and mental component scores.

Concern about obtaining bilateral decompression with a unilateral approach was discussed by Kim et al. [17] via magnetic resonance imaging (MRI) analysis. Sagittal T1 MRI was used to calculate the foraminal stenosis at the level of the mid pedicle both quantitatively and qualitatively and central canal stenosis examined both qualitatively and quantitatively on axial T2 MRI. They found significant improvement in all measurements following unilateral TLIF. Contralateral decompression is achieved during the procedure by angling of the retractor medially providing access to the contralateral lateral recess and indirect decompression of the neural foramen by placement of a distracting intervertebral cage. By restoring disk height with an interbody cage, it is believed the disk bulge is reduced and unfolding of the ligamentum flavum occurs which provides central stenosis decompression.

In refinement of technique, the idea of using unilateral versus bilateral percutaneous instrumentation was examined by Dahdaleh et al. [18]. This study was done as a single-center randomized controlled trial with follow-up out to approximately 1 year. Results demonstrated no significant difference between the groups in terms of clinical outcome (measured on validated outcome scores) lordosis correction or in fusion rate. Biomechanical studies have demonstrated superiority of bilateral pedicle screws in both open and MISS constructs, but unilateral fusion may be sufficient for measurement of clinical and radiographic improvement and outcome. Unilateral fusion after TLIF is an option, however, only for single level disease.

The cost benefit of MISS TLIF compared to open was examined by Perez-Cruet et al. and Parker et al. [14, 15]. Parker et al. calculated a 2 year treatment mean cost difference of $8,731 in favor of MISS TLIF compared to open. Wang et al. [19] showed that hospital stay cost was $2,106 less per patient with two-level MISS versus an open approach, but no significant difference with one level approaches. Surgical site infections were examined by McGirt et al. [20] and with 6.1 % for open compared to 4.5 % in MISS procedures there was a direct cost difference for investigation and treatment of infections at $3,593,862 for open and $1,024,950 for MISS.