Over the past 20 years, the field of spine surgery has changed dramatically, mostly because of the development and adoption of revolutionary technologies such as spine arthroplasty, direct lateral interbody fusion via transpsoas and antepsoas approaches, minimally invasive transforaminal interbody fusion techniques, expandable cage technology, and computer-assisted navigation with or without robotic assistance. The adoption of these techniques has enabled surgeons to correct degenerative and deformity disorders with the inclusion of fewer levels fused, less muscle damage, and shorter recovery times with improved short- and long-term outcomes.

Transforaminal lumbar interbody fusion (TLIF) is a long-established and well-accepted surgical approach to lumbar spinal fusion. Since its inception in 1982, the TLIF procedure has evolved greatly,¹ overcoming several limitations posed by other posterior fusion techniques including risk of dural tears, nerve root injury, and epidural fibrosis.¹ Still, open TLIF procedures are highly invasive, and although fusion is achieved in most cases, complication risk, blood loss, and muscle injury remain subjects of concern.²,³,⁴,⁵ The advent of minimally invasive spinal surgery techniques brought about a new wave of TLIF approaches, leading to the introduction of the minimally invasive surgery (MIS) TLIF procedure in 2003.⁶ MIS TLIF, similar to open TLIF, aims to provide anterior column support, restoring sagittal alignment and increasing disk space height through decompression and fusion.

Indications for MIS TLIF match those for open TLIF. Grade I or II spondylolisthesis (with or without radiculopathy), and mechanical back pain caused by these
presentations, are indications for the procedure. Degenerative disk disease with diskogenic low back pain, postlaminectomy instability, recurrent disk herniation, lumbar spinal stenosis, spine trauma, and pseudoarthrosis may be additional indications depending on other clinical factors.⁷,⁸ Contraindications are less precise and are highly dependent on the individual patient and the surgeon’s experience. High-grade spondylolisthesis (>grade II), more than two-level fusion, severe osteoporosis, and presence of conjoined roots may contraindicate the use of MIS TLIF.⁷,⁸

Traditional open TLIF can result in unnecessary damage to the paraspinal musculature and other muscular structures during dissection.⁹,¹⁰ MIS TLIF emerged as a way to achieve the goals of traditional open TLIF while avoiding damage to local musculature. The MIS procedure is less invasive and has comparable outcomes relative to open TLIF. According to numerous comparative studies, MIS TLIF results in shorter length of hospital stay, fewer complications postsurgery, and decreased blood loss.¹¹,¹²,¹³

A primary goal in fusion surgery is the achievement of acceptable sagittal alignment. The difficulty of achieving this aim is well documented with traditional TLIF. The restoration of lordosis is particularly difficult with MIS TLIF given the reduced surgical window, which decreases the ease of insertion of interbody devices. Novel technologic developments, such as expandable interbody cages, have emerged in recent years in an effort to improve lordosis-associated outcomes postsurgery.

A significant learning curve exists for surgeons inexperienced in MIS. Because MIS lacks the three-dimensional spatial orientation and tactile environment of open surgery, MIS can be especially challenging for new surgeons. Increased familiarity with the anatomy is necessary given the reduced visualization and narrow surgical field of MIS. This is especially true for the MIS TLIF procedure given the vast heterogeneity that exists between approaches. For MIS TLIF specifically, it has been found that surgeon experience is directly correlated with length of postoperative stay and increased probability of fusion.¹⁴ It is therefore critical for new surgeons to be aware of this learning curve.

Patients undergoing a TLIF procedure are typically positioned prone on a Jackson table and are usually placed under general anesthesia. Intraoperative imaging can be used to localize the incision; at minimum, one facet should be exposed at the level of interest. Incisions should be placed approximately 5 cm from the patient’s midline to allow for easy placement of pedicle screws. A tubular retractor can be inserted as the soft tissue is bluntly dissected; this, along with intraoperative microscopy, provides sufficient visualization. At this point, a partial or total facetectomy is performed, as well as an ipsilateral laminotomy. When visualization of the disk is achieved, a diskectomy can be performed. The posterior longitudinal ligament and the anterior longitudinal ligament are preserved. A bony fusion can be facilitated by rasping the cartilaginous end plates of the superior and inferior vertebrae. Bone graft and structural implants should be inserted into the diskectomy space. Further decompression and removal of the lamina can be performed as necessary before closure. These steps are largely consistent among MIS TLIF procedures; yet, there exists significant diversity in the specific technique.

There exist a wide variety of navigation techniques for surgeons performing MIS TLIF. Broadly, these can be categorized into robot-assisted and fluoroscopy-based techniques. Traditional fluoroscopy and fluoroscopy-based instrumentation are generally preferred given that they pose lower risk of complications and a less significant learning curve relative to robot-assisted techniques.¹⁵ Robotic navigation is growing in popularity as technology advances.

As already mentioned, achieving desired lumbar lordosis is difficult using MIS TLIF. Lengthening the anterior column or shortening the posterior column can help to restore lordosis. In MIS TLIF procedures, this may be accomplished through the use of expandable intervertebral cages. These fit within the narrow access corridor exposed in MIS TLIF and expand in situ. When positioned asymmetrically, these can correct coronal alignment. Despite the increasing popularity of expandable cages, their utility in improving lordosis is disputed—a meta-analysis of several studies monitoring clinical and radiographic outcomes conducted in 2019
suggests that although expandable cages can result in a larger change in segmental lordosis than standard nonexpandable cages, they are not associated with higher fusion rate or lumbar lordosis.¹⁶ Some direct comparison studies included in this meta-analysis, however, associate the use of expandable cages with improved fusion rate and lordosis correction. This contributes to the notion that there indeed exists vast individuality in the MIS TLIF approach. Variation in outcomes could be attributed to the use of expandable or nonexpandable cages or to cage placement and other surgeon-specific parameters.

Adult spinal deformity (ASD) is a complex condition characterized by vast heterogeneity in clinical presentation; it is estimated that more than 60% of elderly patients are affected by ASD. Conditions that can be defined under the category of ASD include degenerative de novo scoliosis, adult idiopathic scoliosis, and iatrogenic scoliosis. As a result, there are a variety of strategies for surgical correction of ASD. It is generally characterized by a coronal Cobb angle greater than 20°, a sagittal vertebral axis greater than 5 cm, or a pelvic tilt greater than 20°. Primary goals of spinal deformity surgery include neural element decompression, promotion of sagittal and coronal balance, and achievement of an arthrodesis. MIS has become increasingly popular in recent years as an avenue by which these goals can be accomplished. There exist several MIS techniques for ASD surgery; the choice of technique, as well as the larger choice of whether to opt for MIS, is largely dependent on patient and surgeon.

Over the past 2 decades, MIS has evolved rapidly. Although during its inception MIS was mostly used for simple cases, as its advantages become clear and techniques improve, MIS is increasingly used in the management of complex cases. One emerging field is MIS correction of ASD. Multiple MIS approaches are used in ASD correction; these will be described further. Among Scoliosis Research Society members, 43.1% of surgeons use MIS as part of their surgical management of ASD.¹⁷ However, 43.5% of this cohort uses MIS in less than 20% of their cases, and only 7.2% exclusively use MIS.¹⁷ These discrepancies can be attributed to the steep learning curve associated with MIS and the perceived need for increased comparative studies between MIS and traditional open techniques in ASD correction to ascertain the advantages of MIS.

Three primary categories of MIS approaches for ASD surgery exist: MIS decompression, circumferential MIS (cMIS), and MIS + open (hybrid) surgery.¹⁸ All of these techniques have demonstrated comparable efficacy in terms of primary surgical goals relative to traditional open techniques.¹⁹,²⁰ In addition, all have demonstrated advantages over open techniques, including shorter length of postoperative hospital stay, reduced complications, and lower blood loss.²⁰,²¹,²² However, as with MIS in general, technical difficulty poses a limitation—limited surgical access and reduced visualization are disincentives for the use of MIS approaches in ASD correction.