C-arm-Free Simultaneous OLIF51 and Percutaneous Pedicle Screw Fixation in a Single Lateral Position

Summary

C-arm-free oblique lumbar interbody fusion at the L5-S1 level (OLIF51) and simultaneous pedicle screw fixation are performed in a lateral position under navigation guidance. This technique does not expose the surgeon or operating staff to radiation hazards.

Abstract

Oblique lumbar interbody fusion (OLIF) is an established technique for the indirect decompression of lumbar canal stenosis. However, OLIF at the L5-S1 level (OLIF51) is technically difficult because of the anatomical structures. We present a novel simultaneous technique of OLIF51 with percutaneous pedicle screw fixation without fluoroscopy. The patient is placed in a right lateral decubitus position. A percutaneous reference pin is inserted into the right sacroiliac joint. An O-arm scan is performed, and 3D reconstructed images are transmitted to the spinal navigation system. A 4 cm oblique skin incision is made under navigation guidance along the pelvis. The internal/external and transverse abdominal muscles are divided along the muscle fibers, protecting the iliohypogastric and ilioinguinal nerves. Using a retroperitoneal approach, the left common iliac vessels are identified. Special muscle retractors with illumination are used to expose the L5-S1 intervertebral disc. After disc preparation with navigated instruments, the disc space is distracted with navigated trials. Autogenous bone and demineralized bone material are then inserted into the cage hole. The OLIF51 cage is inserted into the disc space with the help of a mallet. Simultaneously, percutaneous pedicle screws are inserted by another surgeon without changing the lateral decubitus position of the patient.

In conclusion, C-arm-free OLIF51 and simultaneous percutaneous pedicle screw fixation are performed in a lateral position under navigation guidance. This novel technique reduces surgical time and radiation hazards.

Introduction

Spondylosis is regarded as a stress fracture¹ and occurs in about 5% of the young adult population². The most common level of occurrence is at the L5 level due to the unique shearing force applied at the L5-S1 area. The main symptoms of spondylosis and spondylolisthesis are low back pain, leg pain, and numbness. If conservative treatment proves ineffective, surgical treatment is recommended³. Transforaminal lumbar interbody fusion (TLIF) is an effective and established technique⁴, but the nonunion rate of this procedure is relatively higher at the L5-S1 level⁵. Furthermore, with TLIF, it is difficult to create adequate lordosis compared to oblique lumbar interbody fusion (OLIF) or anterior lumbar interbody fusion (ALIF)⁶.

Indirect decompressions such as ALIF or OLIF are currently common methods for treating lumbar stenosis⁷. However, the conventional ALIF technique causes a large amount of muscle damage. Oblique lateral interbody fusion at the L5-S1 level (OLIF51) was first reported in 2017⁸. Posterior instrument augmentation is usually necessary to ensure solid fusion, but the conventional OLIF technique uses a C-arm, and the patient position is changed from lateral to prone. To overcome these problems, we report herein a novel technique of C-arm-free simultaneous OLIF51 and percutaneous pedicle screws (PPSs) in a single lateral position.

We introduce the case of a 75-year-old woman with symptomatic L5 spondylolisthesis (grade 2).

Protocol

This study was approved by the ethics committee at Okayama Rosai Hospital (No. 201-3).

1. Patient examination

1. History taking
   1. Evaluate a patient with a suspected herniated disc or stenosis by taking their history. Usually, the patient presents with a history of prodromal low back pain. The patient may correlate their symptoms with an episode of trauma.
   2. Ask the patient to describe the radiating leg pain, its location, and aggravating and relieving activities.
2. Physical examination
   1. To determine the level of the affected nerve, look for signs of motor weakness or loss of sensation in the leg. Check the lumbar range of motion, the straight leg raise (SLR) test, deep tendon reflexes, and muscle weakness.
   2. Perform the Kemp test to check the location of the herniated discs. If the Kemp test yields a positive result, local pain suggests a facet pathology, while radiating pain into the leg is more suggestive of nerve root irritation, which frequently accompanies foraminal disc herniation or stenosis.
      NOTE: Usually, the SLR test is negative for patients with lumbar canal stenosis and positive for patients with lumbar disc herniation.

2. Evaluation of images

1. Magnetic resonance imaging (MRI)
   1. Perform an MRI. This is the most accurate diagnostic modality for assessing lumbar disc herniation, showing the site of herniation and the nerve roots affected. The L5 nerve root can be compressed by fibrocartilage at the pars interarticularis of L5.
2. Computed tomography (CT)
   1. Use CT to check whether the herniated disc is calcified and to rule out nerve compression by any osteophyte.
3. CT-MRI fusion imaging
   1. Use the fusion image to evaluate the feasibility of performing OLIF51. The vascular window, made by the common iliac vessels at the L5-S1 disc level, is clearly visualized. A vascular window of less than 20 mm makes OLIF technically difficult (Figure 1).

Figure 1: Preoperative image. (A) Midsagittal reconstruction CT, (B) T2 weighted midsagittal image, (C) CT MRI fusion image. CT and MRI show grade 2 isthmic spondylolisthesis. The vascular window is 37 mm. Please click here to view a larger version of this figure.

3. Patient positioning and neuromonitoring

1. Patient positioning
   1. Place the patient in a right lateral decubitus position on a carbon table. Use an O-arm to obtain 3D images of the lumbar spine of the patient (Figure 2).
   2. To protect the neurovascular structures, place an axillary roll underneath the patient's right axilla.
   3. Flex the hip and knee to 20° to relax the psoas muscle and the lumbar nerve. Secure the patient to the table with tape.
   4. Insert a percutaneous reference pin into the left sacroiliac joint.
   5. Obtain 3D images of the O-arm and transmit them to the navigation system.
2. Neuromonitoring
   1. Whenever possible, neuromonitor the patient to prevent neurological complications (Figure 3).

Figure 2: Patient positioning. Right lateral decubitus position secured with tape. Please click here to view a larger version of this figure.

Figure 3: Neuromonitoring. Neuromonitoring is preferable for this technique. Please click here to view a larger version of this figure.

4. Intraoperative CT and spinal navigation

1. Intraoperative CT
   1. Place a navigation reference frame (RF) percutaneously into the contralateral sacroiliac joint or L5 spinous process, and obtain intraoperative CT images (Figure 4).
2. Navigation
   1. The navigation system is necessary for this technique. Transmit the CT 3D reconstructed images to the navigation system (Figure 5).

Figure 4: O-arm. One O-arm scan is just 23 s. Please click here to view a larger version of this figure.

Figure 5: Navigation system. Every instrument is navigated with this system. Please click here to view a larger version of this figure.

5. Navigated instrument registration

1. Register every navigated instrument and perform an accuracy check.

6. Incision and muscle dissection

1. Skin incision
   1. Mark the skin incision using a navigated pointer. Direct the entry point to the center and parallel to the L5-S1 disc space.
   2. Make a 4 cm long oblique incision on the skin, 4 cm medial to the anterior superior iliac spine and parallel to the pelvis (Figure 6).
2. Muscle dissection
   1. Divide the abdominal muscles and dissect along the line of the skin incision. A monopolar cautery is contraindicated due to the risk of injury to the iliohypogastric and ilioinguinal nerves.
   2. With a retroperitoneal approach, use both index fingers to dissect the retroperitoneal space, following the internal abdominal wall posteriorly down to the psoas muscle, which can then be visualized (Figure 7).
      CAUTION: If the iliohypogastric nerve is injured, abdominal herniation may occur.

Figure 6: Skin incision. The skin is marked using a navigated pointer, which is directed to the center and parallel to the L5-S1 Please click here to view a larger version of this figure.

Figure 7: Navigated pointer. The white arrow indicates a navigated pointer. Please click here to view a larger version of this figure.

7. Disc preparation and trialing

1. Disc preparation
   1. After exposing the promontorium, identify the left common iliac vessels and retract laterally (upward) using a special self-retaining retractor under illumination. Take great care to preserve the left ureter. The L5/S1 intervertebral disc is exposed (Figure 8).
   2. Retract both common iliac vessels and the bifurcation with three self-retaining retractors. A blunt dissection of the adventitial layers on the L5/S1 disc is necessary to not injure the sympathetic chain. Retrograde ejaculation may occur in male patients if the sympathetic chain is injured.
   3. After the center of the disc is marked with a navigated pointer, incise the annulus with a knife, and perform a discectomy using Kerrison rongeurs, pituitary forceps, a navigated Cobb elevator, a navigated shaver (Figure 10), a navigated combo tool (periosteum elevator), and a navigated curved curette (Figure 11).
   4. Use the navigated curved curette to remove the posterior part of the disc.
      NOTE: Since all the instruments are navigated, the use of an intraoperative C-arm is not required.
2. Trialing
   1. After disc preparation, sequentially distract the disc space using navigated trials. Determine the size of the cage on a preoperative lateral radiogram. For Asian patients, a disc height of 10-14 mm and an angulation of 12°-18° is advisable.
   2. At this step, perform intraoperative radiography to check the implant position and the size of the cage. If the cage protrudes beyond the disc space, choose another adequately sized cage (Figure 12).
      CAUTION: The surgeon should check the accuracy of the navigation system before using the navigation instruments, as the reference frame may sometimes be accidentally altered. Unlike the C-arm, the disc space in the navigation image does not open on insertion of a trial with an adequate height.

Figure 8: Approach to the promontorium. (A) Navigated pedicle probe, (B) navigation monitor. A navigated pedicle probe (white arrow) is used to check the L5-S1 disc level. Please click here to view a larger version of this figure.

Figure 9: Self-retaining retractors. These three retractors retract both common iliac vessels and the bifurcation. Please click here to view a larger version of this figure.

Figure 10: Navigated shaving. (A) Navigated shaver, (B) navigation monitor. Navigated shavers are from 6 mm to 12 mm. Please click here to view a larger version of this figure.

Figure 11: Navigated curved curette. (A) Navigated curved curette, (B) navigation monitor. A navigated curved curette is very useful to completely remove the posterior part of the disc. Please click here to view a larger version of this figure.

Figure 12: Trialing. After disc preparation, the disc space is sequentially distracted with navigated trials (white arrow). Please click here to view a larger version of this figure.

8. Cage placement and screwing

1. Cage placement
   1. Insert a mixture of autogenous bone and demineralized bone material into the cage hole. Confirm the angle of insertion for the cage with a navigation pointer to insert the OLIF51 cage accurately.
   2. Use a mallet to gently insert the OLIF51 cage. After the implant is positioned, take anteroposterior and lateral radiographs to confirm the position of the cage (Figure 13A).
2. Screwing
   1. After cage insertion, insert one or two supplemental screws to prevent cage back-out (Figure 13B).

Figure 13: Cage placement and screwing. (A) OLIF51 cage at the L5-S1 disc, (B) cage with screw. A mixture of autogenous bone and demineralized bone material is inserted into the cage hole. Please click here to view a larger version of this figure.

9. Simultaneous percutaneous pedicle screw (PPS) fixation

1. Have another surgeon insert the PPSs in the same lateral decubitus position of the patient under navigation guidance.
2. Make the screw hole with a navigated high-speed burr, navigated pedicle probe, and navigated tap. Measure the length and diameter of the screws by navigation.
3. Insert the S1 PPS in a transdiscal manner to enhance the screw pullout strength.
4. Take radiograms after the insertion of the screws (Figure 14).

Figure 14: Simultaneous PPS fixation. PPSs are inserted in the same single lateral position by another surgeon under navigation guidance. Please click here to view a larger version of this figure.

10. Postoperative procedure

1. Ambulate the patient 1 day after the surgery. The use of a soft brace is recommended for 3 months. Follow-up at 3 months, 6 months, and 12 months after the surgery to assess for solid bony fusion.

Representative Results

Fourteen cases (average age: 71.5 years) were treated using this new technique. They were compared to 40 cases (average age: 74.0 years) of L5-S1 TLIF. L5-S1 lordosis angle and disc height were measured in both groups. The OLIF51 group obtained a better L5-S1 lordosis than the TLIF 51 group (Figure 15).

Figure 15: Radiological measurement. (A) Antero-inferior corner, (B): postero-inferior of the upper vertebra, (C) antero-superior corner, (D) postero-superior corner of the lower vertebra. Disc height = EF, segmental lordosis = angle AGC. Please click here to view a larger version of this figure.

	Preoperative L5/S1 angle	Postoperative L5/S1 angle	Preoperative L5/S1 disc height	Postoperative L5/S1 disc height
OLIF 51 (N=14)	11.4+-4.1°	21.3+-3.3°	7.2 +-2.1mm	10.9+-1.8 mm
TLIF 51  (N=40)	10.1+-4.4°	12.1+-4.7°	8.6+-2.7 mm	9.4+-1.8 mm
	not significant	p<0.05	not significant	p<0.05

Table 1: L5-S1 disc angle and height for OLIF51 versus TLIF51.

Discussion

Recently, the lateral lumbar approach for interbody fusion has been gaining popularity due to its minimal invasiveness⁹. Among these approaches, the direct lateral psoas splitting approach has several disadvantages, such as lumbar nerve plexus injury and psoas muscle weakness¹⁰. To reduce these complications, prepsoas or OLIF was introduced by Davis et al. in 2014¹¹. However, it is difficult to operate at the L5-S1 disc due to its anatomical features. In 2017, a novel technique was devised to approach the L5-S1 disc in a lateral position (OLIF51), enabling interbody fusion from the lower thoracic spine to L5-S1 ⁸. The advantages of OLIF51 are good anterior release, a greater bone graft, greater stability that is suitable for osteoporosis, and a high fusion rate¹². The applicability of OILF51, however, is restricted due to the location of the blood vessels, which may restrict the access.

Strict criteria for patient selection and careful preoperative planning are necessary for this technique. This procedure is carried out with the patient in a lateral decubitus position, offering the advantage of inserting the PPSs in the same position, thus reducing both operating time and blood loss¹³. The conventional OLIF51 technique with PPS insertion entails radiation exposure. Occupational radiation exposure is one of the main issues of concern for minimally invasive spinal surgeons¹⁴. Repeated multiplanar images are necessary for accurate screw and cage insertion, increasing both radiation exposure and operating time. With O-arm guided navigation, the radiation exposure to the patient is reduced due to the use of low-resolution mode and the small FOV of the O-arm. The time required for an O-arm scan is less than 24 s, which is an equivalent dose to that of 90 s of fluoroscopy. This has been shown to eliminate the need for cumbersome lead protective gear, clear the surgical field of the C-arm, and reduce radiation exposure without compromising the accuracy¹⁵.

Another advantage of this technique is achieving OLIF from L1 to L5. Especially for adult spinal deformity, this technique is very useful because five level OLIF cages from the L1 to S1 level in a single lateral position can be inserted. Compared with the conventional technique, changing the patient position is not required for this technique, decreasing the surgical time and the total cost of the surgery. For future applications, robotic surgery can be combined with this novel technique.

The critical steps of our new technique are as follows. First, a preoperative evaluation of the location of common iliac vessels is done, and a vascular window less than 20 mm is a contraindication for OLIF51. CT-MRI fusion image is recommended for this purpose¹⁶. Second, the reference frame pin is firmly inserted into the left sacroiliac joint percutaneously¹⁷. If the reference frame is moved, the accuracy of this procedure decreases, risking screw or cage malpositioning. If any doubt exists regarding the navigation accuracy, an O-arm scan should be performed. Third, navigated instruments including a pointer, pedicle probe, shaver, Cobb elevator, curette, and trial should be used effectively. In particular, navigated curved curettes are useful for this C-arm-free procedure¹⁸. As an alternative, a C-arm technique is also available for this simultaneous method.

Certain limitations to this technique must be considered. Relatively expensive equipment (the O-arm and navigation system) is necessary, and there is a steep learning curve for this technique. A vascular window less than 20 mm poses a contraindication for this procedure. Further studies in the form of case series are required to further corroborate the effectiveness of this technique in managing isthmic spondylolisthesis.

C-arm-free OLIF51 and simultaneous percutaneous pedicle screw fixation are performed in a lateral position under navigation guidance. This novel technique reduces surgical time and radiation hazards to surgeons and operating staff.

Materials

Name	Company	Catalog Number	Comments
Adjustable hinged operating carbon table	Mizuho OSI	6988A-PV-ACP	OSI Axis Jackson table
CD Horizon Solera Voyager	Medtronic	6.4317E+11	Percutaneous pedicle screw system
Navigated Cobb elevator	Medtronic	NAV2066
Navigated combo tool	Medtronic	NAV2068
Navigated curette	Medtronic	NAV2069
Navigated high speed bur	Medtronic	EM200N	Stelth
Navigated passive pointer	Medtronic	960-559
Navigated pedicle probe	Medtronic	9734680
Navigated shaver	Medtronic	NAV2071
NIM Eclipse system	Medtronic	ECLC	Neuromonitouring
O-arm	Medtronic	224ABBZX00042000	Intraoperative CT
Radiolucent open spine cramp	Medtronic	9731780
Self-retaining retractor	Medtronic	29B2X10008MDT151
Sovereign Spinal System	Medtronic	6.4317E+11	OLIF51 cage
Spine small passive frame	Medtronic	9730605
Stealth station navigation system Spine 7R	Medtronic	9733990	Navigation
U-NavLock Gray	Medtronic	9734590
U-NavLock Green	Medtronic	9734734
U-NavLock Orange	Medtronic	9734683
U-NavLock Violet	Medtronic	9734682