The single-position, prone, lateral approach allows for both lateral lumbar interbody placement and direct posterior decompression with pedicle screw placement in one position.
Lateral interbody fusion provides a significant biomechanical advantage over the traditional transforaminal lumbar interbody fusion due to the large implant size and optimal implant position. However, current methods for lateral interbody cage placement require either a two-staged procedure or a single lateral decubitus position that precludes surgeons from having either full access to the posterior spine for direct decompression or comfortable pedicle screw placement.
Herein is one institution’s experience with 10 cases of a prone single-position approach for simultaneous access to the anterior and posterior lumbar spine. This allows both lateral lumbar interbody cage placement, direct posterior decompression, and pedicle screw placement, all in one position. Three-dimensional (3D) navigation is utilized for increased precision in both approaching the lateral spine and interbody cage placement. The traditional blind psoas muscle tubular dilation was also modified. Tubular retractors and lateral vertebral body retractor pins were used to minimize the risks to the lumbar plexus.
First described as extreme lateral interbody fusion (XLIF) in 2006, the lateral lumbar interbody fusion approach (LLIF) utilizes a transpsoas approach to the vertebral body1. The LLIF presents several operative advantages over other traditional approaches. First, the LLIF is one of the least invasive interbody fusion approaches, minimizing perioperative tissue damage and blood loss, as well as postoperative pain and length of hospital stay2,3. The LLIF allows for the placement of larger interbody spacers, which confers a greater likelihood of fusion and greater disc height distraction4,5.
Several LLIF protocols are currently employed, each of which presents limitations. The two-stage approach requires two patient positions for cage placement and posterior screw fixation, respectively. This protocol may increase intraoperative time and anesthetic exposure as the surgeon must wait for patient repositioning between the first and second stages of the procedure. Single-position LLIF variants have also been developed to improve the two-position process. Using a stand-alone LLIF technique forgoes the posterior component of the LLIF surgery and thus negates the need for patient repositioning. However, this technique precludes direct posterior decompression and the added stability of pedicle screw placement. Performing the entire surgery in the lateral position has also been described, but this introduces additional ergonomic challenges for the surgeon6,7.
A prone single-position approach effectively decreases operative time, thus speeding patients’ recovery. Below, the protocol for performing a prone single-position approach for simultaneous access to the anterior and posterior lumbar spine is outlined. Unlike a previously described variation of this approach, 3D navigation is employed to guide both the lateral approach and the interbody cage placement8. Finally, this article includes a case series of the first 10 patients who underwent this prone, lateral lumbar interbody fusion (Pro-LLIF) procedure at the authors’ institution.
NOTE: The protocol follows the guidelines of and was approved by the Brigham human research ethics committee.
1. Equipment and positioning
2. Initial posterior approach and posterolateral instrumentation
3. Lateral approach and interbody cage placement
4. Completion of the posterior portion
Cohort demographics
Ten consecutive patients underwent the Pro-LLIF procedure from August 2020 to February 2021. The eligibility criteria for this procedure were ages 18 and older and symptomatic degenerative spondylosis with spinal instability (spondylolisthesis or degenerative scoliosis) from L2 to L5, requiring interbody fusion. Per the institution's standard of care, all patients had trialed and failed a course of conservative management. The exclusion criteria were patients excluded from operative intervention based on their medical inability to tolerate surgery. In addition, in patients with unfavorable anatomies, especially if the L4-5 disc level is caudal to the top of the iliac crest, it would be difficult to use the Pro-LLIF approach. All operations were performed by the same neurosurgeon (Y.L.).
The initial Pro-LLIF cohort comprised eight female and two male patients. The mean age at the time of surgery was 66 years, with individual ages ranging from 41 to 77 years. Eight patients were current or former smokers, and five patients met the Center for Disease Control's definition of obesity (BMI > 30).
Spondylolisthesis was the most common spinal disease amongst this cohort (five patients). The most common indication for surgery was radiculopathy with low back pain (six patients), followed by radiculopathy alone (three patients). Four patients had undergone prior fusion procedures.
Operative characteristics
The majority of the patients in this cohort (60%) underwent one level of Pro-LLIF (Table 1). The mean total operative time for the Pro-LLIF procedure was 4.5 h (median 4.1 h, range 3.2-6.9 h). The total time under anesthesia averaged 6.5 h (median 5.9 h, range 4.2-9.7 h). The average estimated blood loss during the Pro-LLIF procedure was 240 mL (range 50-650 mL).
Preoperative and postoperative magnetic resonance images (MRIs) of the lumbar spine were used to evaluate the changes in foraminal height, segmental lordosis, lumbar lordosis, and disc height after undergoing Pro-LLIF (Table 2). For some patients, the foraminal height or lumbar lordosis improvement is limited, which might be due to the significant disc space and facet joint stiffness in those patients.
Hospital course, length of stay, and dispensation
Pro-LLIF patients experienced an average length of stay of 3.5 days. One patient required early reoperation to recover a retained surgical drain in the posterior incision. No neurological injury or subsidence was reported for any patient in the immediate postoperative period. Six of the ten patients were discharged to home; the remaining four patients were discharged to rehabilitation facilities.
Follow-up and postoperative clinical evaluation
One-month follow-up data were available for all ten patients. The Odom Criteria's 4-point rating scale was adapted to assess Pro-LLIF surgical outcomes (Table 3). At one month, three patients met the criteria for an "Excellent" rating, and six patients reported symptoms consistent with a "Good" rating. One patient reported similar symptoms post-ProLLIF, earning the patient an Odom rating of "Poor." That patient was a complex lumbar deformity patient who has failed multiple surgeries in the past with the development of severe left leg pain following a previous lumbar fusion surgery at another hospital.
Comparison with a propensity score-matched cohort analysis
Retrospective data were also collected on patients who had undergone oblique lateral interbody fusion (OLIF) procedures at the same institution by the same senior neurosurgeon. Using propensity-score matching, 10 OLIF patients were identified who had undergone comparable levels of lateral interbody fusion and decompression as the Pro-LLIF patients. Student's two-sided, unpaired t-tests with Bonferroni multiple-comparison correction were used to compare the quantitative outcome measures between the Pro-LLIF and OLIF groups. No significant differences in total operative time, total anesthesia time, lengths of stay, and estimated blood loss were identified between the Pro-LLIF and OLIF patients (Figure 5).
Figure 1: Intraoperative view of single-position pro-LLIF procedure, showing the setup, air-planing of the operative table, and intra-operative navigation and two surgeons performing the lateral and the posterior portions of the surgery simultaneously. Abbreviation: pro-LLIF = prone lateral lumbar interbody fusion. Please click here to view a larger version of this figure.
Figure 2: Intra-operative close-up view showing the placement of the expandable retractor system superficial to the psoas muscle in the retroperitoneal space, providing a clear view for direct psoas dissection. Please click here to view a larger version of this figure.
Figure 3: Following direct psoas muscle dissection, separate retractor pins (in red oval) placed in the cranial and caudal vertebral bodies kept the psoas muscle (in blue oval) out of the surgical corridor, allowing easy disc preparation and interbody cage placement. Please click here to view a larger version of this figure.
Figure 4: After the disc preparation, the lateral Conduit titanium interbody cage is inserted into the disc space. Please click here to view a larger version of this figure.
Figure 5: Comparison of operative outcomes between Pro-LLIF and OLIF patients. Student's two-sided, unpaired t-tests were used to compare (A) total anesthesia time (h), (B) estimated blood loss (mL), (C) lengths of stay (days), and (D) total operative time (h). Bonferroni correction was used to adjust for multiple comparisons. No significant difference between the Pro-LLIF and OLIF cohorts was identified for any of the evaluated outcome measures. Abbreviations: pro-LLIF = prone lateral lumbar interbody fusion; OLIF = oblique lateral interbody fusion. Please click here to view a larger version of this figure.
case | age | sex | BMI | diabetes | smoking | chronic steroids | obesity | asa | Prior fusion | disease | indication | Operated levels | ||||||||||
1 | 64 | 0 | 19.92 | 0 | 0 | 0 | 0 | 2 | 1 | spondylolisthesis | radiculopathy/LBP | L2-L3 | ||||||||||
2 | 65 | 0 | 40.24 | 0 | 0 | 0 | 1 | 3 | 0 | spondylolisthesis | radiculopathy | L4-L5 | ||||||||||
3 | 77 | 0 | 34.72 | 1 | 1 | 1 | 1 | 3 | 1 | Sagittal deformity | radiculopathy.LBP | L2-L4 | ||||||||||
4 | 62 | 1 | 35.25 | 0 | 1 | 0 | 1 | 2 | 0 | spondylolisthesis | radiculopathy.LBP | L3-L4 | ||||||||||
5 | 68 | 1 | 33.75 | 0 | 1 | 0 | 1 | 2 | 0 | spondylolisthesis | radiculopathy | L3-L5 | ||||||||||
6 | 77 | 0 | 23.44 | 1 | 1 | 1 | 0 | 3 | 1 | scoliosis | radiculopathy.LBP | L3-L4 | ||||||||||
7 | 41 | 0 | 19.5 | 0 | 1 | 1 | 0 | 2 | 0 | degenerative | radiculopathy | L2-L3 | ||||||||||
8 | 72 | 0 | 35.15 | 0 | 1 | 0 | 1 | 3 | 0 | scoliosis | radiculopathy.LBP | L2-L5 | ||||||||||
9 | 65 | 0 | 21 | 0 | 0 | 0 | 0 | 2 | 0 | Spondylolisthesis, scoliosis | radiculopathy.LBP | L3-L4 | ||||||||||
10 | 74 | 0 | 22 | 0 | 1 | 0 | 0 | 2 | 1 | pseudoarthrosis | LBP | L2-L4 |
Table 1: Pro-LLIF cohort demographics. Basic patient demographics, surgical indications, and operative data for all 10 Pro-LLIF cases of this series. Key: 0 = no, 1 = yes. "ASA" refers to the American Society of Anesthesiologists Physical Status Classification System, which scores patients' health status and the likelihood of surgical and anesthetic comorbidities. ASA score was determined preoperatively by anesthesiology teams at this institution. Abbreviations: pro-LLIF = prone lateral lumbar interbody fusion; ASA = American Society of Anesthesiologists; BMI = body mass index.
case | Pre-operative foraminal height | Post-operative foraminal height | Pre-operative segmental lordosis | Post-operative segmental lordosis | Pre-operative lumbar lordosis | Post-operative lumbar lordosis | Pre-operative disc height | Post-operative disc height |
1 | 18 | 18 | 5 | 16 | 50 | 61 | 8 | 11 |
2 | 14 | 20 | 15 | 18 | 30 | 39 | 7 | 15 |
3 | 11 | 13 | 5 | 34 | 30 | 45 | 3 | 11 |
4 | 21 | 21 | 6 | 20 | 80 | 109 | 12 | 16 |
5 | 18 | 23 | 17 | 23 | 28 | 33 | 9 | 10 |
6 | 14 | 15 | 4 | 13 | 35 | 50 | 2 | 8 |
7 | 13 | 15 | 5 | 10 | 59 | 55 | 2 | 7 |
8 | 16 | 15 | 16 | 25 | 40 | 70 | 3 | 10 |
9 | 19 | 19 | 4 | 7 | 37 | 39 | 5 | 9 |
10 | 19 | 19 | 33 | 23 | 60 | 60 | 12 | 15 |
Table 2: Radiographic evaluation of Pro-LLIF outcomes. Comparison of pre- and postoperative MRIs was used to assess Pro-LLIF's impact on foraminal height, segmental lordosis, lumbar lordosis, and disc height for each patient. Abbreviations: pro-LLIF = prone lateral lumbar interbody fusion; MRIs = magnetic resonance images.
Outcome | Definition |
Excellent | All preoperative symptoms relieved; no postoperative symptoms |
Good | Minimal persistence of preoperative symptoms with minor postoperative symptoms |
Fair | Relief of some preoperative symptoms with persistence or worsening of others; minor to major postoperative symptoms |
Poor | Persistence or worsening of all preoperative symptoms; minor to major postoperative symptoms |
Table 3: Odom's criteria (adapted). A 4-point rating scale for assessing clinical outcomes post-PLLIF, adapted from Odom's criteria for cervical spine surgery outcomes. Abbreviation: pro-LLIF = prone lateral lumbar interbody fusion.
This study provides a detailed protocol for a prone, single-position, 3D-navigation-guided lateral lumbar interbody fusion (Pro-LLIF). Pro-LLIF permits concurrent access to the anterior and posterior spine and does not require patient repositioning, unlike the two-stage OLIF or XLIF approach9. This single-position approach has been associated with decreased operative time, anesthesia time, and surgical staffing requirements, presenting physical and financial benefits8,9,10.
Critical steps in the pro-LLIF procedure include the following: 1) as this technique is reliant upon stereotactic navigation, obtaining a high-quality interoperative CT and making sure the registration continues to be accurate throughout the case is of the utmost importance. 2) Blunt dissection and separation of the retroperitoneal cavity from the lateral lumbar surface needs to be done thoroughly to make sure no peritoneal membrane is still adherent to the spine surface at the surgical area to avoid inadvertent injury to the peritoneal content. 3) As with all transpsoas approaches, care needs to be taken when traversing the psoas muscle to avoid damage to the lumbosacral plexus. Splitting the psoas muscle carefully under direct vision, in the anterior portion of the muscle, with the aid of intraoperative neuromonitoring, and using pins holding the muscle away from the surgical corridor during disc preparation and cage insertion are keys to avoiding nerve damage. 3) During the lateral disc preparation portion of the procedure, performing not only an ipsilateral annulotomy to enter the disc space, but also a contralateral annulotomy to further release the anterior column is important to maximize the amount of lordosis and correction of scoliosis at each level.
As mentioned in the protocol, this technique can be modified to insert multiple interbody cages through a single incision. Doing so often involves separate retractor positions in the lateral approach as described in the protocol. To limit any inaccuracies in the intraoperative navigation that are caused by the insertion of interbody spacers, we recommend that surgeons place the pedicle screws immediately after obtaining the registration CT scan.
Obtaining an optimal lateral trajectory in the prone position requires several adjustments. First, the incision may be too close to where the patient's body meets the operating room table, specifically around where the supporting hip pad typically sits. This can be avoided by translating the hip pads caudally slightly upon initial positioning. Second, the natural tendency for the surgeon is to operate in a downward trajectory, and sometimes it is difficult to have an accurate perception of an operative trajectory that is parallel to the ground. This can be alleviated with the use of a sitting stool, rolling the patient ("airplaning") away from the surgeon, raising the table height, and most importantly, using intra-operative stereotactic navigation for the optimal surgical trajectory.
As with all lateral approaches, the cranial and caudal limits of this technique are bounded by the ribcage and iliac crest, respectively. Therefore, L5-S1 will not be feasible for this approach. This approach will not be easy for certain patients with potential L4-5-accessing trajectory blocked by the top of the iliac crest. Careful examination of the preoperative AP X-ray is important in determining the feasibility of this surgical approach for the L4-5 level.
Several factors limit the comparison between Pro-LLIF and other established methods of lateral interbody fusion. First, no significant differences in operative timing or outcomes were identified in this study. It is likely that a ten-patient cohort is underpowered for comparative statistics; repeating the presented analyses on an expanded cohort will ameliorate this issue. Another potential confound is the learning curve associated with optimizing, training in, and teaching the new Pro-LLIF procedure. These are the very first 10 Pro-LLIF cases performed in this institute, and surgical nuances are being worked up and optimized over time. For example, we have modified the psoas retraction technique compared to the regular minimally invasive lateral access method.
We added the direct psoas muscle dissection and distraction pin placement above and below the operated disc under direct vision to create the surgical corridor rather than inserting the expandable tube into the psoas muscle. This allows surgeons to be more confident that the lumbar plexus is not being compressed by the expandable tube, and to avoid the issues of "muscle creeping" that is frequently associated with using the expandable tubes. In addition, while all ten Pro-LLIF procedures were performed by the same neurosurgeon, the second operator, anesthesiologists, and surgical staff varied between cases. Increased team experience with Pro-LLIF will likely result in decreased operative time, lengths of stay, and postoperative complication rates. Despite these limitations, the data support the utility and efficacy of the Pro-LLIF approach for patients requiring lumbar interbody fusions from L2 to L5. The single-position, prone, lateral approach provides safe and simultaneous access for lateral interbody cage placement and direct posterior neural decompression and segmental fixation. Efficiency will improve with increased experience with this promising technique.
The authors have nothing to disclose.
We thank the dedicated work from our nurses and surgical technicians in making the advance of this technique a possibility.
CONDUIT Lateral Lumbar Implants | DePuy Synthes | EIT Cellular Titanium Interbody | |
COUGAR LS Lateral Spreaders | DePuy Synthes | Lateral Spreaders: 6, 8, 10, 12, 16 mm | |
COUGAR LS Lateral Trials | DePuy Synthes | Parallel Trial, 18 x 6 mm | |
COUGAR LS Lateral Trials | DePuy Synthes | Lordotic Trials, 18 x 8 mm 18 x 10 mm 18 x 12 mm 18 x 14 mm | |
DePuy Synthes ATP/Lateral Discetomy Instruments | Avalign Technologies LLC | ||
Dual Lead Awl Tip Taps 4.35 mm – 10 mm | DePuy Synthes | Navigation Enabled Instruments used with Medtronic StealthStation Navigation System | |
EXPEDIUM 5.5 System | DePuy Synthes | with VIPER Cortical Fix Screws | |
EXPEDIUM Driver Shaft T20 5.5 | DePuy Synthes | Navigation Enabled Instruments used with Medtronic StealthStation Navigation System | |
EXPEDIUM Drive Sleeve 5.5 | DePuy Synthes | Navigation Enabled Instruments used with Medtronic StealthStation Navigation System | |
Phantom XL3 Lateral Access System | TeDan Surgical Innovations, LLC | Lateral Access retractor (includes dilators and LED Lightsource) | |
PIPELINE LS LATERAL Fixation Pins | DePuy Synthes | ||
The R Project, R package version 4.0, MatchIt package | propensity-score matching | ||
SENTIO MMG Lateral Probe | DePuy Synthes | Lateral Access Probe | |
SENTIO MMG Stim Clip | DePuy Synthes | attaches to insilated dilators, conducting triggered EMG while rotating 360 degrees | |
VIPER 2 1.45 mm Guidewire, Sharp | DePuy Synthes |