Clinical Outcomes of Minimally Invasive Versus Open TLIF: A Propensity-Matched Cohort Study
In this study, we compare intermediate-term outcomes in minimally invasive surgical transforaminal lumbar interbody fusion (MIS TLIF) to open TLIF. Sixty-four patients who underwent 1- to 2-level MIS TLIF with baseline, 1-, and 2-year outcome measures were identified. These were propensity-matched to a cohort of open TLIF patients based on age, body mass index, sex, smoking status, workers’ compensation status, and preoperative outcome measures. At 1 year, both groups had similar improvements in pain and Short-Form 36 (SF-36) Physical Composite Summary (PCS), but the MIS TLIF group had a statistically significantly greater improvement in Oswestry Disability Index (ODI) compared with the open TLIF group. At 2 years, the MIS TLIF group had a statistically significantly greater improvement in pain and ODI compared with the open TLIF group, but no statistically significant difference in SF-36 PCS. Both MIS TLIF and open TLIF lead to significant improvements in clinical outcomes. At 1 year after surgery, MIS TLIF patients had greater improvements in ODI, and at 2 years after surgery, they had greater improvements in pain and ODI. This study showed that the perioperative advantages of MIS TLIF, such as less muscle dissection and faster recovery, continue to be beneficial 1 to 2 years after surgery.
Several studies have compared patient-reported outcome measures of MIS and open TLIF, and the results have been mixed. Most of these studies have shown similar improvement in clinical outcomes between the 2 procedures, but the MIS technique demonstrated short-term perioperative advantages, such as lower blood loss, less narcotic requirements, and shorter length of stay.7-15 The authors of these studies conclude that the MIS technique can provide similar long-term results with lower short-term morbidity when compared with open TLIF. In contrast, some studies have shown better short- and intermediate-term clinical outcomes with the MIS technique.23,27-29 As a whole, the literature comparing the 2 procedures consists of mostly small retrospective studies with nonrandomized patient samples, heterogeneous surgical indications, and differing surgical techniques, making it difficult to draw conclusions.
The current study suggests that MIS TLIF may lead to improved clinical results at 2-year follow-up, compared with open TLIF. Our study used propensity-score matching to minimize the effects of nonrandom assignment of subjects to MIS TLIF or open TLIF. A limitation of observational studies is that bias in assignment of subjects to treatment groups can lead to overestimation or underestimation of the effect of the treatment itself. Propensity-score matching attempts to reduce this bias by accounting for several covariates that predict whether a subject will receive a certain treatment. These covariates are used in a logistic regression to produce a propensity score, which can be used to match subjects to controls across multiple dimensions, thus ensuring groups are as comparable as possible at baseline.
Our study still has several limitations. Sample size is relatively small, and follow-up is still only intermediate, at 2 years. There was unequal distribution of specific levels of surgery. Because patients were not blinded to the treatment they received, it is possible that patient perception of receiving a newer, less-invasive treatment method may influence their subjective improvement. The study sample was drawn from 2 different centers, with one center providing mostly MIS cases and the other providing mostly open cases. Because of this, undetected differences in how patients were selected for surgery could also affect outcomes. Any latent confounding variables, which are not identified a priori, will not be accounted for in the matching process. Only a prospective, randomized study with large numbers can control for observed and unobserved confounding patient characteristics.
In summary, our study shows that MIS TLIF is associated with improved low back pain and low back–related disability at 2 years compared with open TLIF. Other studies comparing the 2 techniques have come to different conclusions regarding whether the short-term benefits of MIS TLIF translate into long-term differences in clinical outcome. This study adds to this evidence and suggests there may be longer term advantages to the MIS approach, but prospective randomized trials are needed to confirm this finding and determine the true magnitude of these differences.
