Minimally invasive procedures on the lumbar spine

Abstract

Degenerative disease of the lumbar spine is a common and increasingly prevalent condition that is often implicated as the primary reason for chronic low back pain and the leading cause of disability in the western world. Surgical management of lumbar degenerative disease has historically been approached by way of open surgical procedures aimed at decompressing and/or stabilizing the lumbar spine. Advances in technology and surgical instrumentation have led to minimally invasive surgical techniques being developed and increasingly used in the treatment of lumbar degenerative disease. Compared to the traditional open spine surgery, minimally invasive techniques require smaller incisions and decrease approach-related morbidity by avoiding muscle crush injury by self-retaining retractors, preventing the disruption of tendon attachment sites of important muscles at the spinous processes, using known anatomic neurovascular and muscle planes, and minimizing collateral soft-tissue injury by limiting the width of the surgical corridor. The theoretical benefits of minimally invasive surgery over traditional open surgery include reduced blood loss, decreased postoperative pain and narcotics use, shorter hospital length of stay, faster recover and quicker return to work and normal activity. This paper describes the different minimally invasive techniques that are currently available for the treatment of degenerative disease of the lumbar spine.

Key Words: Minimally invasive surgery; Spine surgery; Lumbar spine; Degenerative disease; Interbody fusion; Posterolateral fusion; Decompression; Indirect decompression techniques

Core tip: Degenerative disease of the lumbar spine is a common and increasingly prevalent condition that is often implicated as the primary reason for chronic low back pain and the leading cause of disability in the western world. Compared to the traditional open spine surgery, minimally invasive techniques require smaller incisions and decrease approach-related morbidity. The benefits of minimally invasive surgery over traditional open surgery include reduced blood loss, decreased postoperative pain and narcotics use, shorter hospital length of stay, faster recovery and quicker return to work and normal activity.

INTRODUCTION

Modern minimally invasive spine surgery (MIS) was introduced in the 1990s with the description of tubular retractors for access to the lumbar spine and the report of the first lumbar microendoscopic discectomy[1,2]. Since that time, advances in technology and surgical instrumentation have led to MIS developing into an important and rapidly growing filed of spine surgery. Today, MIS techniques and approaches are used in the treatment of a wide variety of spinal pathologies including degenerative disc disease, disc herniation, instability, deformity, fracture, infection and tumors[3]. Compared to the traditional open spine surgery, MIS was pursued as a means to reduce iatrogenic tissue trauma during surgery. The theoretical benefits of MIS over traditional open surgery include smaller incisions, less soft tissue damage, reduced estimated blood loss (EBL), decreased postoperative pain and narcotics use, shorter hospital length of stay (LOS), faster recover and quicker return to work and normal activity[4,5]. Traditional open spine surgery approaches often require extensive muscular and ligamentous disruption during the surgical approach to the spine resulting in decreased spinal stability and subsequent associated morbidities[6]. MIS minimizes approach-related morbidity by avoiding muscle crush injury by self-retaining retractors, preventing the disruption of tendon attachment sites of important muscles at the spinous processes, using known anatomic neurovascular and muscle planes, and minimizing collateral soft-tissue injury by limiting the width of the surgical corridor[7]. The decrease in the approach-related morbidity and indirect iatrogenic destabilization of the spine are important advantages of MIS over open spine surgery.

MIS approaches have been increasingly used in the treatment of degenerative diseases of the lumbar spine. As microsurgery, endoscopy and various percutaneous techniques advance and our rapidly aging population drives greater demand for spinal care, MIS will likely play an increasingly important role in the treatment of lumbar degenerative disease. This paper describes the different MIS techniques that are currently available for the treatment of degenerative disease of the lumbar spine.

MINIMALLY INVASIVE NON-FUSION PROCEDURES

MIS microdiscectomy

Lumbosacral nerve root compression or irritation secondary to an intervertebral disc herniation is a major cause of sciatica and low back pain. Patients with disc-related sciatica may be managed conservatively or via surgery when conservative treatment fails or symptoms worsen over time. It is estimated that over 250000 elective lumbar spine surgeries are performed in the United States each year for persistent symptoms of sciatica[8]. Of those, lumbar discectomy remains one of the most commonly performed procedures[9]. The goal of surgery is most commonly to remove intervertebral disc material and decompress the nerve root. Traditionally, the standard surgical treatment of lumbosacral disc herniation has been open microdiscectomy, however, with the rapid advances in surgical techniques and technology, there has been a growing trend towards MIS microdiscectomy.

An MIS microdiscectomy involves the use of serial tubular retractors to dilate the paraspinous musculature without stripping it off the spinous processes, and an endoscope or surgical microscope to visual the surgical field[10]. While the benefits of minimal soft tissue disruption appear to favor MIS microdiscectomy over open microdiscectomy, there is a significant learning curve associated with performing the procedure safely. Although many innovative techniques in the treatment of lumbar disc herniation have been developed, open microdiscectomy remains the standard of care at the current time[11].

A recent meta-analysis of controlled trials that compared outcomes of MIS and open microdiscectomy in patients with sciatica evaluated 29 studies (16 randomized controlled trials and 13 non-randomized studies) with a total of 4472 patients[11] (Table 1). Regarding clinical outcomes, the study found a moderate to low quality evidence of no differences between MIS and open microdiscectomy. Regarding perioperative outcomes, there was low to moderate evidence of no difference between MIS and open microdiscectomy; this was particularly notable for complications and reoperation rates. The study also found no significant difference in quality-adjusted life years (QALYs) or total costs from a societal perspective during the first year following treatment. The authors found low quality evidence that MIS took 10-15 min longer, resulted in a 52 cc reduction in EBL and reduced mean LOS by 1.5 d. The increased surgical time with MIS may be explained by the learning curve associated with MIS, variability in the techniques used and differences in how operative times were defined[11].

Table 1 Differences between outcomes of minimally invasive vs open surgical techniques.

MIS techniques	Ref.	Differences in outcome compared to open techniques
Non-fusion techniques
MIS microdiscectomy	Kamper et al[11]	Moderate to low evidence of no differences between MIS and open microdiscectomy No significant differences in QUALYs or total costs MIS took 10-15 min longer, resulted in 52 cc reduction in EBL and reduced mean LOS by 1.5 d
MIS direct decompression (Laminectomy/laminotomy)	Rahman et al[16]	Decreased EBL compared to open technique MIS procedures were 37-47 min shorter Decreased LOS by 2.52 d in patients undergoing decompression at ≤ 2 levels MIS had fewer complications (7.9% vs 16.1%)
	Anderson et al[17]	No significant differences in terms of ODI, Short-Form-12, and VAS
	Khoo et al[18]	Longer operative times in MIS group (109 min vs 88 min) Decreased EBL and postoperative stay in MIS group
	O’Toole et al[21]	0.10% surgical site infection rate Authors concluded that MIS technique may reduce SSI rate by 10-fold
MIS indirect decompression (Interspinous process devices)	Kuchta et al[26]	Statistically significant improvement in symptom severity and physical functioning throughout 2-yr follow-up period
	Bowers et al[27]	85% failure rate and 38% complication rate
	Brussee et al[28]	Poor outcome in 68.9% of patients
	Kim et al[29]	Cost analysis study found devices to be extremely costly and questioned cost-effectiveness
Fusion techniques
Intertransverse onlay fusion	-	No literature available comparing MIS versus open posterolateral onlay fusion
Percutaneous pedicle screw fixation	Lehmann et al[34]1	EBL and muscle damage markers significantly lower in MIS group Compartment pressure, blood flow and EMG readings similar between both groups Radiation exposure greater in MIS group
MIS transforaminal lumbar interbody fusion	Seng et al[51]	Statistically increased fluoroscopic times (55.2 s vs 16.4 s) and operative times (185 min vs 166 min) in MIS group MIS had less EBL than open (127 cc vs 405 cc) Postoperative morphine use less in MIS group (8.5 mg vs 24.2 mg) Shorter LOS in MIS group (3.5 d vs 5.9 d)
	Parker et al[55]	MIS associated with reduction in mean hospital cost of $1758, indirect cost of $8474, total 2-yr social cost of $9295 Similar 2-yr direct health care cost and QALYs gained
MIS direct lateral interbody fusion	Villavicencio et al[73]	Lower complication rate in MIS versus open (8.2% vs 16.7%)
	Rodgers et al[74]	Significantly lower complication rate in MIS cohort (7.5% vs 60%) Decreased EBL, lower transfusion rate and shorter LOS
	Deluzio et al[75]	Average LOS in MIS group 49% shorter Average cost savings for MIS group at 45 d of $2536/patient

¹Animal study. MIS: Minimally invasive surgery; LOS: Length of stay; EBL: Estimated blood loss; ODI: Oswestry Disability Index; VAS: Visual analog scale; SSI: Surgical site infection; EMG: Electromyography; cc: Centimeter cubed; QALY: Quality adjusted life year.

Currently, there is evidence from several comparative studies of MIS and open microdiscectomy suggesting that clinical outcomes between the two groups are similar. As surgeons become more proficient with MIS techniques and investigators conduct well-powered, randomized controlled trials, the indications favoring MIS microdiscectomy will be better defined.

MIS direct decompression

Lumbar spinal stenosis is the most common indication for spine surgery in patients older than 65, and its prevalence in the United States is expected to rise 59% by the year 2025[12]. Age-related degenerative changes in the lumbar spine such as hypertrophy of the facet joints with or without synovial cyst formation, foraminal stenosis due to decrease in the intervertebral disc height or osteophyte formation, ligamentum flavum thickening causing central and lateral recess compression and bulging or herniation of the intervertebral disc are all potential contributors to lumbar spinal stenosis. Surgery has been shown to decrease pain and improve functional status in patients with lumbar spinal stenosis[13]. Traditionally, an open midline approach involving a wide, bilateral laminectomy with medial facetectomy with or without foraminotomy has been the standard technique for surgical treatment of lumbar spinal stenosis. However, lumbar decompression surgery is increasingly being performed using tubular decompression, a MIS technique. This procedure utilizes a small paramedian incision and through the use of serial tubular dilators to reduce multifidus muscle injury while providing sufficient exposure of the surgical decompression site and allowing for bilateral decompression through a single incision[14]. Decompressing the contralateral side through a single unilateral paramedian incision allows the surgeon to spare the spinous process, rostral and caudal supraspinous and interspinous ligaments as well as the contralateral lamina and facet joint, thereby minimizing iatrogenic destabilization of the spine while achieving sufficient decompression for symptomatic relief. Furthermore, the use of an intraoperative endoscope or microscope for magnification and lighting allows for adequate visualization of the spinal anatomy[15].

Multiple studies have described shorter operating room times, decreased EBL, shorter LOS, lower surgical site infection rates, fewer complications and faster recovery times in MIS compared to the open lumbar decompression for spinal stenosis[16-20].

Rahman et al[16] retrospectively reviewed the medical records and relevant imaging of 126 patients (38 MIS vs 88 standard open technique) who underwent bilateral surgical decompression for lumbar stenosis to determine intraoperative EBL, length of operation, LOS, and number and nature of complications. On average, patients undergoing open procedures had 194 cc more EBL than patients undergoing MIS procedures, with the greatest difference in patients undergoing procedures involving ≥ 3 levels. MIS procedures were 37-47 min shorter than open procedures. Looking at the hospital LOS, the authors found that patients undergoing decompression at ≤ 2 levels had a LOS that was 2.52 d shorter in the MIS group. In terms of overall complications, the MIS group had fewer complications than the open group (7.9% vs 16.1%). However, one limitation of this study was that it did not evaluate long-term outcomes of the two procedures.

Anderson et al[17] performed a retrospective analysis of 110 patients in two matched cohorts to compare the tubular retractor approach and traditional midline approach to decompressive surgery for unilateral lumbar radiculopathy. The two approaches were evaluated based on patient reported outcomes using the Oswestry Disability Index (ODI), Short Form-12, and visual analog scale. The authors found no significant differences between the surgical approaches with respect to patient reported outcomes.

Khoo et al[18] compared 25 patients undergoing mic-roendoscopic decompressive laminotomy to 25 patients undergoing open decompression for lumbar spinal stenosis. The authors found that effective circumferential decompression was achieved in the majority of patients in both groups. Surgery was longer for the MIS procedure group compared to the open group (109 min per single level vs 88 min per single level). EBL was reduced by 125 cc in the MIS group and postoperative stay was decreased 48 h, from 94 h in the open group to 42 h in the MIS group.

O’Toole et al[21] performed a retrospective review of prospectively collected data in 1274 patients undergoing MIS decompression and found a 0.10% rate of surgical site infection. The authors concluded that MIS techniques may reduce postoperative wound infections as much as 10-fold compared to open techniques.

At the current time, favorable complication profiles and patient outcome studies with MIS tubular decompression makes this technique an acceptable treatment option in the surgical management of lumbar spinal stenosis (Table 1). Studies assessing long-term outcomes and cost-utility of MIS vs open lumbar decompression are needed to further establish the value of MIS decompression.

MIS indirect decompression

Lumbar interspinous process devices (IPDs) are a MIS technology intended to unload the facet joints, restore foraminal height, lower intradiscal pressure, restricts overextension and provide motion-preserving stabilization[22]. IPDs are used in the treatment of degenerative lumbar spinal stenosis and intermittent neurogenic claudication where they provide indirect decompression to the neural structures[23]. They have also been used in the treatment of discogenic low back pain, facet syndrome, disc herniation and lumbar spinal instability[24]. In 2005, the United States Food and Drug Administration (FDA) approved the first ever IPD (X-STOP, Medtronic, Memphis, TN, United States) for the treatment of patients aged 50 or older suffering from neurogenic intermittent claudication secondary to a confirmed diagnosis of lumbar spinal stenosis. The device was indicated for those patients with moderately impaired physical function who experience relief in flexion from their symptoms of leg/buttock/groin pain, with or without back pain, and have undergone a regimen of at least 6 mo of non-operative treatment. The device may be implanted at one or two lumbar levels in patients in whom operative treatment is indicated at no more than two levels[25]. Since the FDA approval of the first IPD, a growing number of devices have been introduced to the spine implant market and used for a wide range of lumbar spinal pathologies, many of them outside of the intended indications.

Outcomes with the use of IPDs have thus far been inconsistent. Kuchta et al[26] reported on a single-center clinical outcomes of 175 patients with symptomatic lumbar spinal stenosis treated with X-STOP implantation and reported statistically significant (P < 0.001) impro-vements in symptom severity and physical functioning throughout the 2-year follow-up period. Bowers et al[27] reviewed complications associated with the use of X-STOP in 13 patients and found a 85% ultimate failure rate with patients requiring additional surgery for symptomatic relief. The authors also reported a 38% complications rate, including 3 spinous process fractures and 2 instances of new onset radiculopathy. Brussee et al[28] review 65 patients with neurogenic claudication who underwent placement of X-STOP device and found poor outcomes in 68.9% of patients.

Multiple studies have also reported high complication and reoperation rates following implantation of IPDs. Complication rates published in the literature range from 11.6% to 38% while reported reoperation rates range from 4.6% to 85%[26-31]. Epstein et al[23] reported on the cost of the treatment of 16 patients with a total of 31 X-STOP devices and found a total cost of $576407 charge for the devices alone plus an added $80944 charge for the operating/recovery room. The authors concluded that IPDs appear to be extremely costly and questioned the cost-effectiveness of these devices.

At the current time, there is evidence of poor long-term outcomes as well as high complication and reoperation rates following the use of IPDs for the treatment of degenerative lumbar conditions (Table 1). Studies on the cost-effectiveness and value of IPDs are currently lacking and are needed to determine the future faith of these devices.

MIS LUMBAR FUSION PROCEDURES

MIS posterolateral intertransverse onlay fusion without instrumentation

In the traditional posterior midline approach to the lumbar spine, access to the intertransverse region requires extensive stripping of the paraspinal musculature to the tips of the transverse processes. This process results in significant destruction, postoperative atrophy and scarring of the multifidus muscles which has been associated with significant postoperative morbidity[32]. For this reason, a MIS paraspinal muscle-splitting technique (modified Wiltse approach) using an expandable tubular dilator has become an increasingly popular technique used for exposure of the transverse processes and intertransverse space. The use of an expandable tubular retractor allows for both of the transverse processes and the fusion bed to be simultaneously exposed.

The theoretical advantages of this MIS technique are decreased paraspinal muscle destruction, decreased surgical incision size, decreased EBL, decreased postoperative narcotic use and shorter LOS. However, there are no studies in the literature comparing outcomes or cost-effectiveness of lumbar intertransverse onlay fusion utilizing the MIS muscle-splitting approach compared to the traditional open approach (Table 1).

MIS percutaneous pedicle screw fixation

Pedicle screw fixation allows for the creation of a solid and biomechanically rigid construct that allows for fusion to occur at the intended levels. Traditionally, open midline incisions were utilized for exposure of the spine in preparation for pedicle screw placement. Open procedures require extensive tissue dissection to expose the entry points and provide adequate lateral-to-medial orientation for optimal screw trajectory. This dissection in turn may result in muscular denervation, facet capsule disruption, damage to the proximal facet joints and weakening of other ligamentous structures, resulting in prolonged post-operative pain and morbidity[33]. Open lumbar fusion procedures are associated with increased operative times, increased EBL and risk of postoperative surgical site infection[34]. LOS and cost of treatment are also adversely affected by open pedicle screw fixation and spinal fusion techniques[35]. Recently, MIS percutaneous pedicle screw fixation has become an increasingly popular MIS technique for lumbar spine fixation[36-38]. Percutaneous pedicle screw placement offers several distinct advantages over the traditional open approach. It eliminates the need for a midline incision and extensive paraspinal muscle dissection. Kim et al[38] revealed that percutaneous vs open instrumentation was associated with decreased multifidus muscle atrophy, a superior postoperative trunk muscle strength, lower blood loss and less postoperative narcotic use. However, the authors did not find an improved clinical outcome in terms of patient satisfaction and pain scores. Muscle damage is also related to direct compression by muscle retractors, which result in ischemia of the compressed muscle groups and can lead to postoperative muscle necrosis. Percutaneous pedicle screw placement allows the surgeon to more easily achieve an ideal lateral-to-medial trajectory, especially advantageous in obese patients. The advantage of a minimally traumatic access to the lumbar spine carries the disadvantages of longer operative times and increased radiation exposure, both dependent on surgeon experience and comfort level.

Several authors have demonstrated reduced intrao-perative EBL, perioperative risk of transfusion, improved cosmesis, decreased post-operative pain and narcotic use, decreased LOS, faster return to activity and reduced overall costs[39-43]. To date, however, there exists no high-quality literature to support the notion that MIS pedicle screw instrumentation is superior to the traditional open technique. Most of the studies evaluating open vs percutaneous pedicle techniques do so in context of interbody fusion techniques with no study directly evaluating the two instrumentation techniques alone. Lehmann et al[34] compared open vs percutaneous pedicle screw insertion in a sheep model and found that EBL and muscle damage markers were significantly lower in the percutaneous group while radiation time was significantly longer in the percutaneous group. In terms of compartment pressure, blood flow and electromyography measurements at different time points during the operative procedure, no significant differences were revealed.

Many technical challenges unique to the percutaneous pedicle screw placement technique and a steep learning curve exists, requiring different technical, psychomotor and cognitive skills. Mobbs et al[44] noted several challenges in percutaneous screw placement including changing direction of screw placement following initial pedicle cannulation, L5/S1 screw head proximity, cannulation of small pedicles, skin incision selection and insertion of rod for multi-segmental fixation, and difficult Jamshidi placement in hard pedicles. Surgeon experience plays a key role in perioperative outcomes of MIS techniques. It is recommended that surgeons have adequate experience with open techniques before attempting MIS fixation techniques and that they begin with simple MIS procedures[44].

Despite all the encouraging clinical data (Table 1), prospective outcomes studies with long-term follow up comparing percutaneous instrumented fusion to conventional open instrumented fusion are required to determine the safety, effectiveness and clinical benefit of MIS spinal fixation.

MIS transforaminal lumbar interbody fusion

The TLIF is a versatile surgical procedure modified from the posterior lumbar interbody fusion (PLIF) and pioneered by Harms and Rolinger in 1982[45]. Transforaminal lumbar interbody fusion (TLIF) utilizes the principles of load sharing to provide a circumferential fusion consisting of an anterior column support and a posterior tension band. It is designed to restore lumbar lordosis, widen neural foramina, restore disc height and indirectly relieve spinal stenosis. TLIF has been effective in the treatment of lumbar spondylosis with or without spondylolisthesis and has also been used successfully in the treatment of lumbar degenerative disc disease, recurrent lumbar disc herniation and complex lumbar stenosis. One of the main disadvantages to TLIF is the significant postoperative morbidity due to the extensive paraspinal muscle and soft tissue dissection and retraction required in order to provide access to the vertebral column. This approach-related morbidity can potentially affect short- and long-term patient outcomes due to increased postoperative pain, delayed rehabilitation and impaired spinal function.

MIS TLIF was first described by Foley et al[46] in 2003 and has since become an increasingly popular MIS method to achieve lumbar arthrodesis[47-50]. MIS TLIF has been shown to have short- and long-term clinical outcomes comparable to open TLIF with the additional benefits of decreased postoperative pain, decreased EBL, faster recovery times, reduced postoperative narcotic use, faster postoperative ambulation and shorter LOS[51-54] (Table 1).

Seng et al[51] retrospectively analyzed 40 cases of MIS TLIF compared to 40 open TLIFs and compared fluoroscopic times, operative times, EBL, LOS, postoperative narcotic use, complication rates and patient outcomes. The authors found a statistically significant increase in fluoroscopic times in the MIS TLIF group (MIS: 55.2 s, open 16.4 s, P < 0.001) as well as a statistically insignificant increase in operative times for the MIS TLIF group (MIS: 185 min, open: 166 min, P = 0.085). MIS had less EBL than open (127 cc vs 405 cc, P < 0.001). Postoperative morphine use for the MIS group was significantly less than the open group (8.5 mg vs 24.2 mg, P = 0.006). The authors also found that patient in the MIS TLIF group ambulated on average 1.5 d earlier (P < 0.001) and had an overall shorter LOS (MIS: 3.6 d, open: 5.9 d, P < 0.001). The overall complication rate was 15% for the MIS group and 20% for the open group, however this did not reach statistical significance (P = 0.774). Fusion rates, assessed by the Bridwell classification, showed that grade 1 fusion was achieved in 97.5% of both groups at 5 years. Both groups showed significant improvement in ODI, neurogenic symptom score, back and leg pain and SF-36 scores at follow-ups of 6 mo up to 5 years with no significant differences between them.

Parker et al[55] prospectively evaluated 100 patients undergoing TLIF (50 MIS vs 50 open) for back-related medical resource use, missed work, and QALY. The authors found that LOS and time to return to work were less for MIS compared to open TLIF (P = 0.006 and P = 0.03, respectively). MIS and open TLIF patients demonstrated similar improvements in patient-reported outcomes assessed. MIS was associated with a reduction in mean hospital cost of $1758, indirect cost of $8474, and total 2-year social cost of $9295 (P = 0.03), but similar 2-year direct health care cost and QALYs gained. The authors concluded that while both MIS and open TLIF are effective treatments for degenerative spondylolisthesis, MIS TLIF may represent a valuable and cost-saving advancement from a societal and hospital perspective.

Disadvantages of the MIS TLIF are related to the decreased visualization of the surgical field and a steep learning curve for the procedure resulting in increased fluoroscopic times and operative times which may be more significant in less experienced surgeons.

MIS direct lateral approaches

The lateral transpsoas, retroperitoneal approach, also known as extreme lateral interbody fusion (XLIF) or direct lateral interbody fusion (DLIF) is a minimally invasive technique that has become an increasingly common method to achieve fusion in the lumbar spine. This MIS approach was intially described in by Pimenta[56] (DLIF) in 2001, and later by Ozgur et al[57] (XLIF) in 2006. The MIS direct lateral approach differs from the traditional anterior lumbar interbody fusion (ALIF) and open posterior interbody fusion techniques in several important ways. In addition to being an MIS technique, the direct lateral approach requires the patient to be in the lateral decubitus position. The technique utilizes specialized retractors allowing for direct visualization of the surgical approach corridor. Continual neurophysiologic monitoring and fluoroscopic guidance during the approach phase of the procedure is necessary as the psoas splitting technique exposes the lumbar plexus and predisposes it to injury, which can result in psoas muscle weakness and thigh numbness[58,59].

Initial studies evaluating the safety and postoperative results of the MIS transpsoas approach concluded that the MIS technique was safe and allowed for exposure of the lumbar spine without mobilization of the great vessels or sympathetic plexus[60,61].

Smith et al[62] compared the long term outcome of XLIF compared to ALIF in a group of 202 patients (115 XLIF vs 87 ALIF) and found that the overall general surgical complication rate was significantly lower for XLIF compared to ALIF (8.2% vs 16.7%). Rodgers et al[63] described the complications in a large prospective series of 600 patients who underwent XLIF. The authors found the overall incidence of perioperative complications was 6.2% (1.5% in-hospital surgery-related, 2.8% in-hospital medical events, 1.0% out-of-hospital surgery-related, and 0.8% out-of-hospital medical events). There were no wound infections, no vascular injuries, no intraperitoneal visceral injuries and a 0.7% transient postoperative neurologic deficit rate. These complication rates compared favorably to the ALIF risk of vascular injury (1.9%-3%)[64-66]. Another major risk of open ALIF approach is retrograde ejaculation, occurring in 0.6%-4.5% of men[67]. There are currently no reports of retrograde ejaculation following %g MIS lateral interbody fusion which can be attributed to the fact that the sympathetic plexus is not mobilized during the transpsoas approach. Motor deficits after MIS lateral interbody fusion have been reported to range from 0.3%-2.9% with the majority of cases resolving spontaneously within three months[63,68,69]. These rates are comparable to the reported motor deficit rates after PLIF (1.0%-6.1%) and MIS TLIF (4.1%) procedures[70-73].

Rodgers et al[74] retrospectively compared lumbar fusion outcomes in geriatric patients over 80 years of age who underwent XLIF or open PLIF. The authors observed a significantly lower complication rate in the XLIF group compared to the open TLIF group (7.5% vs 60%) we well as less blood loss (hemoglobin change, 1.4 g vs 2.7 g), a lower transfusion rate (0% vs 70%) and shorter LOS (1.3 d vs 5.3 d). The authors also described a lower overall mortality rate in the lateral interbody group compared to the open PLIF group (2.5% vs 30%).

Deluzio et al[75] retrospectively reviewed 210 patients (109 MIS vs 101 open) who underwent 2-level lumbar spine fusion from L1-2 to L4-5. They found the average LOS in the MIS group to be 49% shorter than in the open group (1.2 d vs 3.2 d). The authors noted that the average cost for the entire perioperative period, including both surgical and post-surgical costs out to 45 d, showed an average savings of 9.6% or $2563/patient in the MIS group.

The MIS lateral interbody fusion appears to present a safe and effective technique for treating degenerative lumbar disorders (Table 1). Long-term outcome studies and cost-analysis and value studies are needed to further clarify the benefits of this MIS approach.

CONCLUSION

In the recent years, there has been a growing trend in MIS approaches for the treatment of degenerative diseases of the lumbar spine. Although traditional open approaches are still performed by the majority of spine surgeons, the body of evidence supporting the safety and efficacy of MIS approaches in appropriately selected patients is growing. MIS approaches for lumbar microdiscectomy, laminectomy, and lumbar interbody fusion by way of the transforaminal or direct lateral approach have shown favorable complication profiles and clinical outcomes compared to traditional open approaches. MIS interspinous process devices have shown poor long-term outcomes as well as high complication and reoperation rates.

While the disadvantages of MIS techniques are the steep learning curve, narrow operative corridor and diminished visual field, these are outweighed by the benefits of MIS techniques in many instances. Going forward, long-term outcome studies and cost-effectiveness studies will be needed to fully assess the benefits of MIS techniques for treating degenerative disease of the lumbar spine.