Simultaneous Single-Position Oblique Lumbar Interbody Fusion and Percutaneous Pedicle Screw Fixation under O-Arm Navigation for Modified MISDEF Type II Adult Degenerative Scoliosis: Case Series and Surgical Technique

Data Collection

Intraoperative observations were recorded for blood loss and duration of operation. Adverse events or surgical complications related to this technique, such as nerve or dural sac injury, endplate fracture, hematoma, vascular injury, incisional infection, transient hip flexion weakness and transient thigh pain or numbness, ureteral injury, symptomatic adjacent segment degeneration, and instrument failure or pseudoarthrosis, were also recorded during the operation and at final follow-up.

Immediate postoperative X-ray and CT scans were performed to observe the accuracy of percutaneous screws, which was recorded in accordance with the modified Gertzbein–Robbins classification¹² (grade A, no breach or deviation; B, breach <2 mm; C, 2 mm < breach ≤ 4 mm; D, breach >4 mm). Screw grade A and B were considered clinically acceptable, and screw grade C and D were defined as in malposition. Immediate postoperative MRI was performed and Schizas classification¹³ was used to evaluate the indirect decompressive effect. CT was performed at the final follow-up to assess the fusion status. The Japanese Orthopedic Association (JOA) score for low back pain¹⁴ was used to evaluate surgical outcomes preoperatively and postoperatively at 1 month and at the final follow-up (average at postoperative 17.4 months and range 12–24 months) to evaluate the clinical outcome.

Surgical Technique of Navigated OLIF 360 in adult degenerative scoliosis

Positioning of the Patient

After endotracheal intubation for general anesthesia, the patient was positioned in a right lateral decubitus position in the carbon fiber bed. The dorsal side of the patient was close to the edge of the bed, and enough space was reserved for the screw placement on the right side. The right lower limb was bent to increase stability. Non-elastic tapes were used to fix the upper thoracic vertebra below the shoulder and below the iliac crest (across the level of the greater trochanter of the femur, avoiding the posterior superior iliac crest and the range of the OLIF procedure) and to fix a pillow between the lower legs. The angle of the operating bed was adjusted to ensure a true lateral position (Figure 1A, B).

Navigation-Assisted Oblique Lumbar Interbody Fusion and Percutaneous Pedicle Screw Fixation

First, a navigation probe was used to locate the disc space on the body surface. The OLIF procedure started from the cephalic disc furthest away from the reference frame, and PPSF under navigation was performed simultaneously (Figure 1C). After the blunt separation of abdominal muscles and entering the retroperitoneal space, the retroperitoneal fat tissue was swiped away from the posterior abdominal wall and psoas by a blunt finger. The navigated dilator was docked to the disc surface between the psoas and abdominal major blood vessels (Figure 1D). Sequentially dilatation was performed, and the retractor was placed. The lateral discectomy was performed, and the cartilage endplate was scraped (Figure 1E). With the help of navigation, the reamer was used to penetrate and release the contralateral annulus fibrosus or osteophyte bridge with an orthogonal maneuver (Figures 1F and 2A). Following disc preparation, the navigated templates were used sequentially to distract disc space until adequate disc height and foraminal size were achieved (Figure 2B). Allogeneic bone was placed in the central cavity of cage and the implant was attached to the navigated inserter. The cage was inserted using an orthogonal maneuver under navigational assistance (Figure 2C). The important point was that the OLIF and PPSF procedures started from the cephalic segment, and the OLIF cage was inserted after completing the trajectory of the cephalic pedicle screws because navigational accuracy will decrease if the caudal cage is placed first.

At the same time as the front OLIF operation, the PPSF under navigation was also performed at the cephalic vertebra furthest away from the reference frame. The navigated pedicle access kit (PAK) needle was used to identify the entry point and mark the skin where the screws would be placed. A virtual guide wire was created for the tip of the PAK needle to help with accurate screw placement. After the PAK needle was placed, the guide wire placement and taps were performed in turn. Before the screws are placed, it is necessary to determine the accuracy of the guide wire position by fluoroscopy (Figure 2D,E) or use the non-guide wire screw placement technology to directly place the screw after self-drilling tap placement. After the placement of the OLIF interbody cages and screws, a 3D image was generated in the software of navigation system and fluoroscopy was performed to evaluate the final position of internal fixation (Figure 2F–I). Anterior closure and the posterior final rod locking were performed simultaneously.

Illustrative Cases

Case 1

A 75-year-old man presented with low back pain and pain in both hips and lateral thighs for 2 years. He had intermittent claudication for 100 m, with his body leaned forward and normal posture difficult to maintain, which was completely relieved after bed rest. Whole spine X-ray showed lumbar scoliosis with coronal and sagittal imbalance. CT showed lumbar degenerative spondylolisthesis (L4), with an osteophyte bridge at the right lateral intervertebral space of L_3/4 and L_4/5. MRI showed severe spinal stenosis at L_3/4 and L_4/5 with Schizas grade C and D, respectively (Figure 3).

The patient underwent an OLIF 360 operation with the operative level at L_2/3, L_3/4, and L_4/5. During the operation, 8 mm, 10 mm, and 12 mm reamers were used to fully release the contralateral bone bridge of the L_3/4 and L_4/5 before trailing and implant placement. Posterior L₂ to L₅ PPSF was performed simultaneously. The coronal and sagittal imbalance of the lumbar spine were significantly improved on the postoperative X-ray. Postoperative CT showed that pedicle screws were all grade A according to the Gertzbein–Robbins classification, and the degree of lumbar spondylolisthesis was improved significantly. The osteophyte bridge at the contralateral disc space of L_3/4 and L_4/5 was also released sufficiency. Postoperative MRI showed that the degree of lumbar spinal stenosis was significantly improved, and the Schizas grades of L_3/4 and L_4/5 segments were A3 and A4, respectively (Figure 4).

Case 2

A 65-year-old man with lumbar disc herniation underwent fenestration discectomy at L_1/2 and L_4/5. Twenty years after the first surgery, he had low back pain with numbness of both lower limbs, difficulty with ambulation, and an inability to maintain a forward gaze after walking 50 m, but these symptoms were relieved after bed rest. A whole spine X-ray showed significant lateral slip of the L2 vertebral body, reduced lumbar lordosis, and sagittal imbalance. CT showed spontaneous fusion of L_1/2 and L_4/5 interbody spaces, and intradiscal vacuum changes at L_2/3 and L_3/4. MRI showed severe spinal stenosis at L_2/3 and L_3/4, and Schizas grade was C and D, respectively (Figure 5A–G).

The patient underwent an OLIF 360 operation, with L_2/3 and L_3/4 OLIF and PPSF simultaneously. Postoperative X-rays showed that the lateral slip of L₂ and L₃ vertebra was significantly improved. CT showed that the height of disc space had increased without end plate injury. MRI showed that the central spinal canal stenosis was significantly improved, and the Schizas grades of L_2/3 and L_3/4 segments were both improved to grade B (Figure 5H–N).

Case 3

An elderly female aged 64, presented with mechanical low back pain and intermittent claudication for 6 months, which was completely relieved after bed rest. X-rays showed mild scoliosis of the lumbar spine, lateral slip of the L3 vertebral body, and formation of a lateral bone bridge at L_2/3 level. CT showed L3 spondylolisthesis and significant stenosis at L_3/4. MRI showed extremely severe stenosis at the L_3/4 segment with Schizas grade D and obvious cauda equina redundancy at L_2/3 (Figure 6A–G).

The patient underwent an OLIF 360 operation at L_2/3 and L_3/4. The postoperative X-ray showed that the lumbar scoliosis was improved. CT showed that the lumbar spondylolisthesis was improved, and the height of the intervertebral space was restored satisfactorily. MRI showed that the cauda equina redundancy was significantly improved at L_2/3, and the spinal canal stenosis at the L_3/4 segment was improved to Schizas grade B (Figure 6H–N).

Main Findings of this Study

Oblique lumbar interbody fusion is part of the stepped minimally invasive surgical strategies in the treatment of ADS, suitable for ADS patients who have the potential for interbody distraction and indirect decompression.⁴ Nonetheless, traditional OLIF technology often needs repositioning for one stage or staged posterior fixation for ADS, and the surgical steps are relatively complicated. OLIF 360 under navigation can perform OLIF and PPSF in a single lateral decubitus position simultaneously, and showed encouraging surgical outcomes and good spinal imbalance correction in treating modified MISDEF type II ADS patients in this study. However, care should be taken regarding patient selection and the surgical details of the OLIF procedure and PPSF under navigation.

Indication for OLIF 360 in adult degenerative scoliosis

According to the MISDEF algorithm, patients classified as type 3 have fused or rigid spines, and the curve correction or lumbar lordosis remodeling effect of OLIF is limited. In these patients, a second-stage posterior surgery and osteotomy are required.¹¹ In ADS patients with modified MISDEF type 2, the OLIF procedure of multi-level decompression and fusion with fixation might satisfy surgical demand, without the need for posterior osteotomy.¹¹ In these patients, OLIF 360 technology simplifies surgical procedures, with OLIF and PPSF performed simultaneously in a single lateral decubitus position without repositioning.

Adult degenerative scoliosis is often complicated by moderate-to-severe spinal canal stenosis. Strict inclusion criteria are the key to achieve a good indirect decompression effect, and the disc distraction potential needs to be fully evaluated before the OLIF 360 procedure. Liu reported that OLIF with PPSF could achieve satisfactory clinical and radiographic effects in severe lumbar stenosis patients, but patients with bone fusion of the facet joint or severely calcified intervertebral discs were excluded.¹⁵ Shimizu excluded patients with extra-ligamentous disc herniation, locked facets, and stenosis due to bony compression in an OLIF group, and the surgical and radiographic outcomes were better in an OLIF group than a conventional posterior fusion group.⁵ In this study, in the preoperative imaging evaluation, there were no signs of fusion of the facet joint and no bony narrowing of spinal canal. If disc spaces were rigid with lateral and anterior osteophyte bridges in patients with ADS, the osteophyte bridges should be released intraoperatively for sagittal and coronal imbalance correction. According to the preoperative symptom assessment, the patients’ symptoms were mainly caused by lumbar stenosis or mechanical low back pain, and the symptoms of lower limb were relieved completely after rest in bed. Although the patients’ situations were complicated by severe spinal stenosis in this study, all the patients achieved good indirect decompression with OLIF technology. The degree of spinal canal stenosis, mismatched lumbosacral pelvic parameters, and the sagittal and coronal imbalance were all significantly improved.

Navigated OLIF 360 in adult degenerative scoliosis

The traditional OLIF technology requires one stage or staged posterior fixation in the treatment of ADS. Two operations need to be completed under two positions, and the surgical steps are relatively complicated. In OLIF 360, the two operations can be carried out simultaneously in decubitus position without mutual interference.^7-10 The operation steps are changed from series to parallel, greatly improving the efficiency of the operation. Meanwhile, in OLIF 360 single-position workflow with navigation and O-arm imaging, the instruments and implants are fully navigated, allowing for continuous visibility and precise placement with a real-time image guidance mode, in which the accuracy and efficiency of PPSF and OLIF procedure are further improved.^8-10

The concept of OLIF 360 is not novel and has been used in treating degenerative spinal instability. Sardhara reported that navigational-assisted OLIF decreased the duration of surgery and showed encouraging early surgical outcomes, once the surgeon gains sufficient experience and becomes well-versed at the procedure.⁸ Tan¹⁶ and Cheng¹⁷ found that single-position OLIF combined with PPSF is safe and effective, and it has the advantages of a shorter operation time and less intraoperative blood loss. This study is the first to describe this technique for treating ADS. Different from OLIF 360 performed at one level, the PPSF and OLIF procedures were both performed from cephalic to caudal segments in ADS because navigational accuracy will decrease if the cage is placed in the caudal segment first.

There are many advantages of navigated OLIF in treating ADS. All procedures from the localization of intervertebral space to the placement of the cage are navigated, and repeated fluoroscopies are avoided.^{8, 18} The procedure of penetrating the contralateral annulus fibrosus and the cage placement are more accurate, especially in ADS patients with osteophytes or bone bridges on the lateral or contralateral side of the intervertebral space. Moreover, using navigation-assisted OLIF, it is easier to determine the direction of the intervertebral space for further disc preparation in ADS, reducing the incidence of intraoperative complications such as poor positioning of the cage, end plate injury, or fracture. In this situation, we believe navigation-assisted endplate preparation and accurate cage placement might prevent long-term cage sinking and pseudarthrosis in ADS. Meanwhile, effectively releasing the osteophytes and fibrous anulus under navigation is important for the restoration of disc height, the recovery of lumbar lordosis, and the correction of coronal and sagittal imbalance.

Percutaneous freehand screw placement using C-arm assistance is challenging in an unfamiliar position of OLIF 360.¹⁷ Robotic and navigation assistance have been used to improve the accuracy of PPSF. Budu¹⁹ reported that navigation can play an important role in patient safety during the surgeon's learning curve, which improves the accuracy of screw placement and reduces complications, especially in the hands of less experienced surgeons. Diaz-Aguilar⁷ found that PPSF with robotic guidance resulted in greater accuracy (95%) in the decubitus position. In this study, all screw placements were clinically acceptable, and we believe that navigated percutaneous screw placement provides high screw insertion accuracy in the lateral decubitus position. Furthermore, OLIF 360 avoided the repeated fluoroscopic adjustment due to a different intervertebral space tilt in ADS during the operation, which significantly decreased the radiation exposure for the surgeon and operating room staff. The more complex the lumbar alignment restoration and PPSF procedure in ADS was, the better the operators’ experience was in the navigation-assisted OLIF 360 technique.

In this study, no patient suffered from surgical site infection. It is crucial to ensure strict sterile manipulation during surgery, especially placing the pedicle screw in the lateral decubitus position. Moreover, PPSF on the lower side might be difficult and is influenced by the curve of lumbar scoliosis and the rotation of the vertebra in ADS. In this situation, the operating table can be rotated by an appropriate angle to neutralize the rotation and provide enough space for PPSF, and navigational accuracy is unaffected.

Limitations and Clinical Prospects

The limitations of this study include its retrospective, single-center design, the small sample size, and the absence of a control group, which restrict the generalizability and statistical power of the findings. Regarding fusion level, OLIF 51 is more difficult than OLIF 25 due to the vascular anatomy, and OLIF 51 is not included in this study. The OLIF technique involves a slight learning curve problem for surgeons. Furthermore, fused or rigid ADS with posterior osteotomy is required, and patients with radicular pain not relieved by bed rest are not suitable for OLIF 360. Further prospective research and increased sample sizes are needed to confirm the values of navigated OLIF 360 in ADS.