It is a lumbar arthrodesis that avoids various approach related complications compared to its posterior and anterior counterparts.
Lateral lumbar interbody fusion (LLIF) is a minimally invasive technique first described by Ozgur et al. 1). LLIF allows the surgeon to access the intervertebral space via a minimally invasive direct lateral approach through the psoas muscle. The advantage of LLIF over the traditional anterior approach is the avoidance of exposure of the abdominal viscera, large vessels, and sympathetic plexus. Injury to the nerve roots and dura, and perineural fibrosis, which can occur after PLIF or TLIF, are minimized with this technique 2) 3).
LLIF has been utilized to treat a variety of pathologies including adult degenerative scoliosis, central and foraminal stenosis, spondylolisthesis, and adjacent segment degeneration
They have become an increasingly popular surgical technique due to the benefits of minimal tissue disruption, excellent disc visualization, ability to insert a large intervertebral cage to lessen subsidence, and faster recovery times 4) 5).
The LLIF procedure differs from other lumbar procedures in that the patient is positioned in the lateral decubitus position, often times utilizing bending the bed near the iliac crest region in order to facilitate access to the L4-5 disc space.
In awake volunteers, the pressure at the iliac crest or greater trochanter at the break of the bed increases by increasing the bed angle. Women with a lower BMI had high VAS pain scores when their greater trochanter was at maximal bed break. Men with higher BMI had high VAS pain scores when their iliac crest was at maximal bed break. An awareness of the iliac crest or greater trochanter at the break of the bed should be considered to prevent pain and increased pressure based on the patient's sex and BMI 6).
As with most minimally invasive spine procedures, lateral lumbar interbody fusion (LLIF) requires the use of biplanar fluoroscopy for localization and safe interbody cage placement. Computed tomography (CT)-based intraoperative spinal navigation has been shown to be more effective than fluoroscopic guidance for posterior-based approaches such as pedicle screw instrumentation.
Use of an intraoperative cone-beam CT with an image-guided navigation system is feasible and safe and appears to be accurate, although a larger study is required to confirm these results 7).
One type of minor complication that can be experienced is related to skin abrasion from tape as the patient is secured to the bed. Surgeons typically tape bony prominences by applying foam pads on the skin but not over truncal regions. Since the patient is asleep for the taping procedure, there is no knowledge about how much pressure applied to the skin can cause pain. A second minor complication is the incidence of pain mimicking that of trochanteric bursitis presumably due to direct pressure of the greater trochanter against the table.
A major complication with LLIF is rhabdomyolysis or muscle necrosis due to prolonged soft tissue pressure which can lead to acute renal failure 11). Rhabodmyolsis can be diagnosed by rising creatine phosphokinase levels and must be quickly identified to initiate appropriate medical treatment.
Intervertebral cage settling during bone remodeling after lumbar lateral interbody fusion (LIF) is a common occurrence during the normal healing process.
Malham et al. distinguished between early cage subsidence (ECS) and and delayed cage subsidence (DCS). Radiographic subsidence (DCS) was categorized using descriptors for the location and severity of the subsidence. Neither interbody fusion rates nor clinical outcomes were affected by radiographic subsidence. To protect patients from subsidence after MIS LIF, the surgeon needs to take care with the caudal endplate during cage insertion. If a caudal bilateral (Type 2) endplate breach is detected, supplemental posterior fixation to arrest progression and facilitate fusion is recommended 12).
Over a 5-yr period, 303 patients underwent MIS-LIF at the Department of Neurosurgery, University of South Florida, Tampa, Florida. Sixty-one patients had surgery only at the L4-5 level (20.1%). Twelve of these patients (19.6%) had postoperative neurological deficits including 2 motor deficits (2/61 = 3.2%) and 11/61 (18%) sensory deficits. At 12-mo follow-up, 3 of the deficits persisted for a long-term complication rate of 3/61 (4.9%), motor complication 2/61 (3.2%). Hospital stay and follow-up averaged 2.1 d and 15 mo. Average Oswestry Disability Index improved from 51.1 to 31.1 (P < .00001). Visual Analog Scale (VAS) improved from 7.4 to 3.9 (P < .016). There were no reoperations secondary to hardware failure or pseudoarthrosis. Fusion rate was 89% at 12 mo.
MIS-LIF is a safe and effective approach for interbody fusion at L4-5 with low rate of lumbar plexus injury. Most immediate postoperative deficits will resolve over time 14).
A retrospective review of prospectively collected data was conducted on consecutive patients who underwent stand-alone LLIF between July 2008 and June 2015; 297 patients (623 levels) met inclusion criteria. Imaging studies were examined to grade graft subsidence according to Marchi criteria, and compared between those who required revision surgery and those who did not. Additional variables recorded included levels fused, DEXA (dual-energy x-ray absorptiometry) T-score, body mass index, and routine demographic information. The data were analyzed using the Student t-test, chi-square analysis, and logistic regression analysis to identify potential confounding factors. RESULTS Of 297 patients, 34 (11.4%) had radiographic evidence of subsidence and 18 (6.1%) required revision surgery. The median subsidence grade for patients requiring revision surgery was 2.5, compared with 1 for those who did not. Chi-square analysis revealed a significantly higher incidence of revision surgery in patients with high-grade subsidence compared with those with low-grade subsidence. Seven of 18 patients (38.9%) requiring revision surgery suffered a vertebral body fracture. High-grade subsidence was a significant predictor of the need for revision surgery (p < 0.05; OR 12, 95% CI 1.29-13.6), whereas age, body mass index, T-score, and number of levels fused were not. This relationship remained significant despite adjustment for the other variables (OR 14.4; 95% CI 1.30-15.9). CONCLUSIONS In this series, more than half of the patients who developed graft subsidence following stand-alone LLIF required revision surgery. When evaluating patients for LLIF, supplemental instrumentation should be considered during the index surgery in patients with a significant risk of graft subsidence 15).
Surgical treatment for spinal discitis and osteomyelitis presents challenges because of comorbidities that are common in patients undergoing this procedure. A retrospective review found six patients who met strict operative criteria including instability, intractable pain, neurological deficit, and disease progression. All patients were non-ambulatory before surgery because of intractable back pain. The patients underwent standard lateral minimally invasive surgery using either the extreme lateral interbody fusion (NuVasive, San Diego, CA, USA) or direct lateral interbody fusion (Medtronic Sofamor Danek, Memphis, TN, USA) system. The patients underwent debridement with a discectomy and partial or complete corpectomy, with polyetheretherketone or titanium cage placement. Two patients had additional posterior fixation with percutaneous pedicle screws, and none had immediate perioperative complications. The postoperative CT scans demonstrated satisfactory debridement and hardware placement. All patients experienced significant pain improvement and could ambulate within a few days of surgery. So far, the 1year follow-up data have demonstrated stable hardware with solid fusion and continued pain improvements. One patient demonstrated hardware failure secondary to refractory infection, 2months postoperatively, and required additional posterior decompression and debridement with pedicle screw fixation. The lateral transpsoas approach permits debridement and fixation coupled with percutaneous pedicle screw fixation to further stabilize the spine in a minimally invasive fashion. Due to the significant comorbidities in this patient population, a minimally invasive approach is a suitable surgical technique. A close follow-up period is necessary to detect early hardware failure which may necessitate more extensive treatment 16).
A total of 128 consecutive patients (with 178 treated levels in total) underwent MIS LIF performed by a single surgeon. The subsidence was deemed to be ECS if it was evident on postoperative Day 2 CT images and was therefore the result of an intraoperative vertebral endplate injury and deemed DCS if it was detected on subsequent CT scans (≥ 6 months postoperatively). Endplate breaches were categorized as caudal (superior endplate) and/or cranial (inferior endplate), and as ipsilateral, contralateral, or bilateral with respect to the side of cage insertion. Subsidence seen in CT images (radiographic subsidence) was measured from the vertebral endplate to the caudal or cranial margin of the cage (in millimeters). Patient-reported outcome measures included visual analog scale, Oswestry Disability Index, and 36-Item Short Form Health Survey physical and mental component summary scores.
Four patients had ECS in a total of 4 levels. The radiographic subsidence (DCS) rates were 10% (13 of 128 patients) and 8% (14 of 178 levels), with 3% of patients (4 of 128) exhibiting clinical subsidence. In the DCS levels, 3 types of subsidence were evident on coronal and sagittal CT scans:
Type 1, caudal contralateral, in 14% (2 of 14), Type 2, caudal bilateral with anterior cage tilt, in 64% (9 of 14), and Type 3, both endplates bilaterally, in 21% (3 of 14). The mean subsidence in the DCS levels was 3.2 mm. There was no significant difference between the numbers of patients in the subsidence (DCS) and no-subsidence groups who received clinical benefit from the surgical procedure, based on the minimum clinically important difference (p > 0.05). There was a significant difference between the fusion rates at 6 months (p = 0.0195); however, by 12 months, the difference was not significant (p = 0.2049) 17).
A systematic and critical review of recent literature was conducted in accordance with PRISMA guidelines. The sources of the data were PubMed, MEDLINE, Embase, Cochrane and Scopus. Key search terms were “transpsoas”, “interbody fusion”, “LLIF”, “XLIF” and “spondylolisthesis”. Papers included in the review were original research articles in peer-reviewed journals. The articles were thoroughly examined and compared on the basis of study design, outcomes, and results. Only studies which met the eligibility criteria were included. Eight studies were included in the qualitative and quantitative analysis (three retrospective, four prospective, one randomized controlled trial). A total of 308 patients (227 females) (pooled age 64.5 years) and a total of 353 operated levels were analyzed. Mean follow up time ranged from 6.2 to 24 months. There were no reported cases of durotomies or pseudarthrosis in any study. All neurologic complications were reported to be transient with no permanent deficits. Mean improvement in ODI scores ranged between 19.5 (38.6%) to 36 (54.5%). Mean improvement in slip ranged from 47 to 67.5%. Three studies also reported that patient satisfaction and willingness to undergo the procedure again approached 90%. Minimally invasive transpsoas interbody fusion possibly leads to favorable clinical and radiological outcomes while avoiding the possible complications of its more traditional open and minimally invasive counterparts. Further studies are needed to better establish its role in the management of low grade degenerative lumbar spondylolisthesis 18).