Clinical Outcomes of Minimally Invasive Versus Open TLIF: A Propensity-Matched Cohort Study

Open TLIF Surgical Technique

In patients undergoing open TLIF, a midline incision was made over the vertebrae of interest, and paraspinal muscles were subperiosteally dissected to the tips of the transverse processes. The appropriate level was confirmed with intraoperative radiograph. Pedicle screws were placed free-hand using anatomic landmarks, and appropriate placement was confirmed with intraoperative radiograph and evoked electromyography stimulation. Laminectomy and facetectomy were performed, and the disc was entered on the side of the facetectomy. After thorough disc-space preparation, bone graft and an interbody cage were placed, rods inserted, and compression carried out. A supplemental posterolateral fusion was also performed after decortication of the transverse processes and cartilaginous surface of the contralateral facet. Layered wound closure was performed over drains.

Analysis

Statistical analysis was carried out using SPSS Statistics version 17.0 (IBM) with significance set at the P < .01 level. A small, conservative P-value threshold was used to minimize type II error that resulted from the multiple comparisons performed. Student t test was used to determine any significant differences between continuous demographic variables, and to compare preoperative and postoperative outcome measure scores within and between study groups. Fisher’s exact test was used to compare categorical variables between the 2 groups.

Results

The MIS TLIF group consisted of 64 patients (average age, 52 years), and included 22 patients with degenerative spondylolisthesis, 33 with disc pathology, 8 with postdecompression, and 1 non-union patient. The open TLIF group consisted of 64 patients (average age, 54 years), and included 39 degenerative spondylolisthesis, 15 disc pathology, 7 postdecompression, and 3 nonunion patients (Table 1). All 64 open and 19 MIS cases were from a spine practice with 6 surgeons, and 45 MIS cases came from a spine practice with 2 surgeons. There was also an unequal distribution of the specific levels fused between the open and MIS groups.

Although the operative time was similar in both groups, the MIS TLIF group had a statistically significantly lower blood loss compared with the open TLIF group (Table 2). Both MIS TLIF and open TLIF lead to significant improvements in pain, ODI, and SF-36 PCS (P < .01) (Table 3). At 1 year, both groups had similar improvements in pain (36.9 vs 30.8, P = .178) and SF-36 PCS (9.9 vs 7.5, P = .231), but the MIS TLIF group had a statistically significantly greater improvement in ODI compared with the open TLIF group (30.4 vs 15.1, P < .000). At 2 years, both groups had similar improvements in SF-36 PCS (12.1 vs 7.5, P = .033), but the MIS TLIF group had a statistically significantly greater improvement in pain (40.2 vs 27.0, P = .005) and ODI (33.1 vs 15.4, P < .000) compared with the open TLIF group (Table 4).

Discussion

The current study compared intermediate-term clinical outcomes of MIS TLIF to open TLIF. We used propensity matching to identify a control group of open TLIFs that were comparable to the MIS TLIF group across a variety of covariates that are known to influence the results of lumbar fusion. This created comparison groups that were as closely matched at baseline as possible. We found that, at 2-year follow-up, MIS TLIF patients had less pain and less low-back pain–related disability as measured by ODI. There was also a trend toward better generic health-related quality of life in the MIS TLIF group.

These data suggest that the decreased soft-tissue trauma of the minimally invasive surgical technique, which leads to improved perioperative parameters in the short term, may also lead to some advantages that translate to improved intermediate-term clinical outcomes. Traditional lumbar fusion procedures have shown excellent clinical results when used for accepted clinical indications.²² However, the procedure requires extensive dissection of the paraspinal muscles, which causes significant muscle damage as evidenced by muscle breakdown products that can be detected in the bloodstream postoperatively.^23,24 The lateral dissection also transects the dorsal ramus of the segmental nerves, which innervate the paraspinal muscles, leading to significant scarring and atrophy on postoperative imaging studies.²³ Some authors have used the term “fusion disease” to describe the constellation of soft-tissue degradation seen after open lumbar fusion.⁵

An MIS version of the TLIF procedure that was described in 2003³ avoids much of this iatrogenic soft-tissue trauma. It involves intramuscular dilation to approach the spine and to carry out neural decompression and interbody fusion, in conjunction with percutaneous pedicle-screw instrumentation. Proponents of this technique point to diminished iatrogenic soft-tissue and muscle damage as an advantage. Multiple studies have, in fact, confirmed improved short-term perioperative parameters, such as less blood loss, lower narcotic requirements, and decreased length-of-hospital stay.²⁵ Economic analyses have also shown lower direct and indirect costs with the MIS technique.²⁶