Long-Term Clinical Outcomes
Glassman et al 13 outlined VAS, ODI, and SF-36 outcome improvement thresholds for substantial clinical benefit from 357 patients at 12 months after lumbar spine fusion.13 Three response parameters for each of the aforementioned clinical outcome measures were examined: net change (from baseline), percent change (from baseline), and final raw score. Substantial clinical benefit thresholds for the SF-PCS were a 6.2-point net improvement, a 19.4% improvement, or a final raw score of 35.1 or more points. Substantial clinical benefit thresholds for the ODI were an 18.8-point net improvement, a 36.8% improvement, or a final raw score of less than 31.3 points. Substantial clinical benefit thresholds for the VAS back pain numeric rating scale were a 2.5-point net improvement, a 41.4% improvement, or a final raw score of less than 3.5 points. The 12-month, 24-month, and 47-month VAS, ODI, and SF-PCS results in this study (Table 4) were statistically significant and all met 1 or more of Glassman criterion thresholds for substantial clinical benefit, therefore endorsing the long-term clinical efficacy of the MITLIF procedure.
In addition, Glassman et al 14 reported ODI improvements of 22.9% and 22.8% at 1-year and 2-year follow-up, respectively, from a group of 152 patients who underwent open TLIF and/or open PLIF,14 which were significantly lower than the respective 12-month and 24-month ODI improvements (31.3% and 29.9%) from this study. This may support the superiority of the MITLIF approach compared with the open procedure, at least with regards to patient-reported improvements in ODI scores. Nevertheless, since the study by Glassman et al 14 is being used as a historical control for purposes of outcome comparison, no definitive conclusion regarding the long-term superiority of the MITLIF technique over the traditional, open technique, can be drawn. Multicenter long-term prospective randomized trials directly comparing the 2 approaches to lumbar fusion are needed to confirm this finding.
Reoperation and ALP
In this analysis, a total of 12 (3.9%) patients underwent reoperation. Six (2%) of those underwent surgery at the level where MITLIF was performed, either as a result of failed interbody device (either broken or retropulsion) or pedicle screw failure. No patients required re-exploration and arthrodesis of the MITLIF level for failed fusion. This study showed an extremely high fusion rate (>95%). We feel this high fusion rate was largely due to use of patient's own bone, preservation of the paraspinal muscular and bony anatomy, and instrumentation with bilateral percutaneous pedicle screws, making the final fusion construct extremely conducive to arthrodesis.
ALP was only seen in 6 (2%) patients during the study period. Four of these patients had symptomatic lumbar stenosis requiring minimally invasive laminectomy. Three of these patients required minimally invasive laminectomy alone. The remaining patient had a prior open laminectomy, which had removed the spinous processes and taken down the midline muscular anatomy, requiring adjacent level MITLIF with extension of percutaneous pedicle screw hardware. This low rate of ALP is thought to be due to preservation of the paraspinal muscular and bony anatomy afforded by the MITLIF approach. Open approaches strip these muscles off the midline bone and often remove the spinous process to visualize the thecal sac and its bony confines adequately to perform neural decompression. These anatomical structures are preserved in the MITLIF approach.12 Additionally, postoperative magnetic resonance imaging performed on some of the patients in this series showed significantly less scar formation and normal anatomical distribution of nerve roots within the thecal sac in patients who underwent MITLIF when compared with patients who underwent open lumbar fusion.
There is a growing body of evidence supporting the short-term advantages of MITLIF compared with open TLIF. Lee et al 15 compared the outcomes of 144 patients who underwent MITLIF or an open TLIF (72 patients in each group). Mean operative time for the MIS group was 166.4 minutes, versus 181.8 minutes for the open group; mean blood loss was 50.6 mL, versus 447.4 mL for the open group; and mean hospital stay was 3.2 days, versus 6.8 days for the open group.9 Peng et al 16 reported less blood loss with MITLIF (150 mL; open, 681 mL), a shorter hospital stay (MIS, 4 d; open, 6.7 d), less total morphine used (MIS, 17.4 mg; open, 35.7 mg), and similar fusion rates (MIS, 80%; open, 86%) between a 29-patient MIS TLIF group and 29-patient open TLIF group. Schizas et al 17 also reported less intraoperative blood loss with MITLIF (456 mL; open, 961 mL) and a shorter hospital stay (MIS, 6.1 d; open, 8.2 d) between an 18-patient MIS TLIF group and an 18-patient open TLIF group. Similar secondary outcomes were demonstrated in our present series as mean intraoperative blood loss was 128.4 mL, mean hospital stay was 4.4 days, and mean operative time was 185.4 minutes.
The annual cost of treating spinal disorders has been estimated at more than $100 billion.18 Although comparable long-term clinical outcomes between MITLIF and open TLIF have been demonstrated in small comparative studies,16 , 17 the MITLIF commands cost-saving advantages compared with open TLIF secondary to decreased blood loss, shorter hospital stay, and lower infection rates.
Parker et al 19 examined the cost savings associated with open TLIF versus MITLIF among 30 patients (15 patients in each group). Total mean 2-year cost to treat the open-TLIF patient group after surgery was $44,727 compared with $35,996 to treat the MIS TLIF patient group, representing a total cost difference of $8731 between the 2 groups. In addition, duration of narcotic use for the MIS group was 2.6 weeks (vs. 6.5 wk, open) and return to work was 8.3 weeks (vs. 16.3 wk, open) (P = 0.02).19 A large study by Wang et al 20 provides a powerful look at the cost savings associated with the minimally invasive surgical approach. This multicenter study examined 6106 patients who underwent either MITLIF (1667 patients) or open TLIF (4439 patients).20 Although there was no significant cost-saving difference between 1-level open and MIS TLIF groups, total inflation-adjusted acute hospitalization cost averaged $2106 less (P = 0.0023) for patients who underwent 2-level MIS TLIF compared with those who underwent 2-level open TLIF.20 Similarly, McGirt et al 21 conducted a meta-analysis of 5170 patients who underwent MIS—versus open—TLIF by examining the cost savings associated with lower surgical site infection (SSI) rates. The incidence of SSI was 65 (4.5%) for the MIS group versus 227 (6.1%) for the open group (P = 0.037), and the direct costs associated with the diagnosis and management of the SSIs identified in the study was $1,024,950 for MIS versus $3,593,862 for the open technique. In the current series an expected average direct cost per MITLIF case at our institution was $26,736. However, we observed an average direct cost of $16,505/case, based on acuity level, approach, operating room efficiency, techniques, instrumentation, and product use. This has resulted in significant cost savings.
Limitations to This Study and Future Directions
The findings in this study are limited to patients undergoing MITLIF because it was not controlled, randomized, or compared with patients undergoing open TLIF. Large, long-term, prospective, comparison studies need to be performed to solidify the short-term and long-term benefits and outcomes of MIS versus open spine surgery. Glassman et al 13 demonstrated that younger patients treated with open TLIF might have better clinical outcomes than older patients. Although MIS is thought to be better tolerated by older and obese patients, exploring this relationship was beyond the scope of this study and would be a useful area of future investigation.
The MITLIF approach seems to provide both short- and long-term statistically significant outcome improvements in patients experiencing debilitating low back pain. In addition, long-term benefits observed in this study include a reduced rate of adjacent segment disease requiring reoperation while providing high rates of fusion and a low rate of complications. From a clinical prospective these patients show an extremely high rate of satisfaction in the treatment of their chronic back pain disorders. In fact, the majority of these patients are completely pain free and have returned to work or activities of daily living full time. The MITLIF procedure is a highly cost-effective approach for addressing a costly and debilitating medical condition.
- Long-term clinical outcomes after MITLIF are not well studied and this examines whether patients undergoing this surgery demonstrate appropriate spinal fusion over an average follow-up of 47 months.
- Patients with MITLIF demonstrate a high rate of spinal fusion and a very low rate of interbody fusion failure and/or adjacent segment disease requiring reoperation while reducing postoperative complications.
- This suggests MITLIF provides a cost-effective approach for addressing chronic lower back pain.
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Keywords:© 2014 by Lippincott Williams & Wilkins
lumbar fusion; minimally invasive spine surgery; minimally invasive transforaminal; lumbar interbody fusion, percutaneous pedicle screws; patient outcomes