Unilateral Biportal Endoscopic Management of Cement Leakage After Cement-Augmented Pedicle Screw Fixation: A Technical Report
Article information
Abstract
With the growth of the population of older adults, cement-augmented pedicle screws (CAPS) have become more commonly employed. Although CAPS are considered safe, cement leakage can occur, leading to complications. Neurological symptoms resulting from bone cement leakage pose significant challenges in both diagnosis and treatment. Unilateral biportal endoscopy (UBE) offers a minimally invasive solution for these issues. UBE enables a thorough exploration of potential compression sites, allowing precise visualization of the entire nerve roots without necessitating removal of the instrument or compromising spinal stability. Additionally, it facilitates the removal of cement fragments under direct vision. Herein, we present the case of an 84-year-old female patient who underwent endoscopic interbody fusion of L4–5. After surgery, she presented with radiating pain in the right lower extremity. Postoperative magnetic resonance imaging indicated indirect evidence of cement leakage under the right L5 pedicle screw. The patient underwent UBE exploration under spinal anesthesia. During the procedure, the cement fragment was detected and removed without complication. UBE can also be performed under local or regional anesthesia, significantly reducing the anesthetic risk for medically fragile individuals. Using UBE, it is also possible to monitor neurological function while manipulating the neural tissue. UBE is a viable option for both the diagnosis and treatment of cement leakage following CAPS placement.
INTRODUCTION
With increasing longevity, reconstructive surgeries on osteoporotic spine have become more common. Among the many available methods, the pedicle screw fixation remains the most frequently employed technique for internal fixation in cases of osteoporosis [1]. To enhance the fixation power of the screws, the cement-augmented pedicle screw (CAPS) has been proposed [2]. CAPS may employ nonfenestrated screws, using a vertebral body augmentation technique similar to that of a vertebroplasty for osteoporotic fractures, or fenestrated screws that can be augmented by injecting cement into the screws [3,4].
There are various complications associated with CAPS, a substantial portion of which are related to cement leakage, occurring in 21.8% (6%–43.1%) of cases. Although the leakage is asymptomatic in most patients, there is a pooled neurovascular complication rate of 1.6%, including 0.8% of symptomatic pulmonary embolism [5]. The diagnosis of cement leakage is often made intraoperatively, as most of the cement augmentations are carried out under fluoroscopy. When cement leakage occurs, cement injection is stopped immediately, and cement removal is performed if necessary.
However, postoperative detection of cement leakage is not a simple problem. Plain radiographs are often inadequate due to the presence of implants and superimposed cement masses. Therefore, postoperative diagnosis usually requires the use of computed tomography (CT) or magnetic resonance imaging (MRI), along with selective nerve block to confirm the involved nerve root. Despite these measures, the exact diagnosis of cement leakage causing neurological symptoms remains difficult [6]. Even after a diagnosis is made, treating cement leakage is challenging and may necessitate revision surgery, increasing postoperative morbidities. This remains unchanged even in the development of endoscopic surgical techniques in various spine pathologies. Several studies have introduced cement removal using endoscopic methods. However, most of them focus on cement leakage after percutaneous vertebroplasty. To our knowledge, one previous case report introduced an endoscopic method for removing leaked cement in CAPS [7]. In that case, cement leakage was initially detected on postoperative CT, and the conventional translaminar approach was used to address the leaked cement. However, in situations where the diagnosis is unclear, it is necessary to explore the entire nerve root using endoscopy. Therefore, the single-portal translaminar approach has its limitations.
Unilateral biportal endoscopy (UBE) is a good option for both diagnosing and treating neurological symptoms following a CAPS procedure. It is a relatively recent development in minimally invasive spine surgery with expanding indications. UBE provides better visualization and facilitated access to bony and neural structures through 2 independent portals [8]. These independent portals allow for visualization of the entire length of the nerve root. Given its capability for adequate visualization of the spinal canal and intervertebral foramen, we speculated that it could be effectively employed for diagnosis and treatment of neurological symptoms following a CAPS procedure.
In this technical report, we present a biportal endoscopic technique employed for the diagnosis and treatment of postoperative neurologic symptoms in a patient who underwent endoscopic transforaminal lumbar interbody fusion at L4–5 with cement-augmented fenestrated screws.
MATERIALS AND METHODS
Written informed consent was obtained from the patient for the publication of this case.
1. Patient Description
An 84-year-old female presented with severe low back pain and stooping. Her symptoms began 15 years ago and gradually progressed, with a recent aggravation over the past few months. She had no radiating pain. Despite diligently receiving osteoporosis treatments, she sustained multiple vertebral compression fractures and underwent percutaneous vertebroplasties for T11, T12, L1, L2, L3, and L5. Consequently, she developed a kyphoscoliosis deformity with severe sagittal imbalance (Figure 1A and B).
Preoperative L-spine plain radiographs. Anterior-posterior (A) and lateral (B) views.
The patient underwent endoscopic transforaminal lumbar interbody fusion at L4–5 with cement augmentation of the pedicle screws using fenestrated screws (Figure 2A and B). Postoperatively, she reported radiating pain with paresthesia in the right L5 dermatome. The right L5 pedicle screw seemed slightly low and medial on postoperative x-ray and MRI (Figure 3A and B). Because there was no motor weakness, the radiating pain was initially treated with a selective L5 root block. However, the effect of the injection was only transient, suggesting potential mechanical irritation of the nerve root. Considering it caused by the malpositioned screw, the right L5 pedicle screw was repositioned percutaneously without additional cement augmentation 5 days after the fusion surgery. Despite appropriate repositioning, the radiating pain persisted. A postoperative magnetic resonance suggested the presence of a cement fragment at right L5–S1 foramen. However, this was only indirect evidence due to metal artifacts and limited resolution (Figure 4A–C).
Postoperative L-spine plain radiographs. Anterior-posterior (A) and lateral (B) views.
Postoperative magnetic resonance T2 image. (A) Right L5 pedicle screw was positioned slightly low on sagittal view (arrow). (B) Low signal intensity suspected of cement leakage, when reviewed retrospectively (arrow).
Post-screw-repositioning L-spine radiographs. Anterior-posterior (A) and lateral (B) views. (C) Post-screw-repositioning magnetic resonance T2 axial image. Retrospectively, low signal intensity indicated by the arrow may be suspected to be leaked cement.
2. Surgical Procedure
The patient was placed in a prone position under the spinal anesthesia. The surgeon stood on the left side of the patient throughout the entire procedure.
1) Step 1. Medial side exploration
Two 1-cm vertical incisions were made medially at the level of the pedicles at L4 and L5, adjacent to the spinous process on the right side (Figure 5). Through these incisions, the right L5 nerve root was explored from its origin at the dura mater, down the lateral recess, and into the intervertebral foramen using a 30° scope. A 70° scope was used for a deeper exploration into the foramen. From this medial side approach, a thorough exploration of the right L5 nerve root from its origin to the medial aspect of the intervertebral foramen was performed, along with adequate decompression of the spinal canal.
Incisions of the procedure. Red line: two 1-cm incisions were made medially, adjacent to the spinous processes, for decompression of the spinal canal and exploration of the intervertebral foramen from the medial side. Blue line: two 1-cm incisions were made at the lateral margin of the pedicles at L5 and S1 for the exploration of the L5 root from the outside to the lateral part of the foramen.
2) Step 2. Lateral side exploration
Two additional 1-cm vertical incisions were made at the lateral margin of the pedicles at L5 and S1, with the L5 incision reusing the entry site for the pedicle screw insertion (Figure 5). Through this lateral approach, the most lateral and extraforaminal part of the the L5 root to the lateral aspect of the foramen was explored. As with the medial approach, a 30° scope was used initially, followed by a 70° scope for deeper exploration into the foramen.
Due to the risk of creating an isthmic defect by simultaneous medial and lateral approaches, utmost care was taken not to disturb the isthmus and L5 lamina during the lateral approach.
3) Step 3. Cement removal
Leaked cement was discovered in the L5–S1 foramen abutting the L5 nerve root. The cement fragment was identified while approaching from the medial side, making way towards the entry zone of the foramen. The fragment was located proximally, just below the pedicle.
The cement fragment was not fixed to the bone and showed some mobility, but it was adherent to the root. The fragment was carefully ground to a wafer-thin layer using a diamond burr and then gently removed with a small punch (Figure 6A–C).
Endoscopic pictures of the procedure. All the pictures were taken from the medial side of the foramen. (A) Cement fragments were removed by a diamond burr. (B) Further removal of cement fragments abutting the nerve root using a small punch. (C) After the removal of cement fragments, clear vision of the nerve root was obtained.
The total surgical time was 1 hour and 20 minutes. The perioperative blood loss was minimal.
RESULTS
Following the exploration and cement removal, the radiating pain was relieved. Postoperative MRI showed removal of cement fragments (Figure 7). Some numbness persisted at discharge but improved after 2 months.
After unilateral biportal endoscopic exploration and cement removal, previous low signal intensity mass was removed (arrow).
DISCUSSION
Obtaining an adequate fixation is an important determinant for favorable outcomes in reconstructive surgery for the osteoporotic spine. Among the various methods available, pedicle screw fixation remains the most commonly used modality. However, pedicle screws are often less effective in osteoporotic spine, prompting the development of methods to enhance their holding power. CAPS are the most commonly employed technique to improve fixation in osteoporotic spines, either alone or in conjunction with other methods [1]. Numerous biomechanical studies have reported improved holding power of pedicle screws augmented with bone cement [4].
However, complications related to CAPS are notable, with a significant portion involving cement leakage [5]. Leaked cement can cause thermal injury to adjacent neurovascular tissues and physically compress the nerves, leading to neurologic symptoms [9]. The presence or development of neurological symptoms in patients undergoing CAPS necessitates thorough evaluation for potential cement leakage.
Detecting cement leakage in postoperative patients is challenging. In MRI, bone cement cannot be detected directly. Instead, it is indirectly visualized as a lack of signal [10]. Plain radiographs fail to detect cement leakage in areas overlapping with the screws due to lack of 3-dimensional visualization. Although metal artifacts often complicate detection of leaked cement, CT can be a useful modality [6]. However, it was not performed solely because there was no CT in our clinic.
An endoscopic approach can be an effective modality for detecting and treating cement leakage. Several technical articles have introduced cement removal using endoscopic methods, though most focus on cement leakage after percutaneous vertebroplasty. To our knowledge, only one previous article has introduced an endoscopic method for removing leaked cement in CAPS [7]. However, it adopted a conventional translaminar approach with single-portal. In that study, cement leakage was initially diagnosed on postoperative CT, and the endoscopic maneuver was only used to address the leaked cement. While it is possible to follow the nerve root with single-portal endoscopy, it would necessitate creating multiple portals to visualize the entire length of the root when the diagnosis is unclear. Furthermore, given that cement fragments are often adherent to the involved root, biportal endoscopy, which allows for decoupling of the scope and the instrument, is more advantageous for dissecting the nerve root.
Visualization of the entire length of the nerve root is even more critical when CAPS is performed with fenestrated screws. Malpositioning of these screws can result in cement leakage through the radial holes, spreading to the spinal canal, foramen, or paravertebral tissues [11]. This risk is increased in patients with a history of spine fusion or vertebroplasty, as proper screw positioning is often obscured by hardware and preexisting cement mass. In this case, the cement leakage must have occurred during the initial insertion of the screw, as there was no additional cement augmentation during the repositioning procedure. It may have leaked through either the fenestrations of the pedicle screw due to breaching of the pedicle cortex or holes inadvertently made during the attempted insertion of the screw into the vertebral body with a previous vetebroplasty.
UBE is a safe and effective alternative for both diagnosing and treating potential cement leakage. It is a minimally invasive technique that reduces the risks of further complications or potential revision surgery. In UBE, a surgeon can explore neural tissue under direct vision and remove cement fragments with appropriate instruments. Also, a thorough exploration from a single side is capable in UBE, once the surgeon has gained adequate experience with this technique. Additionally, UBE can be performed under regional or local anesthesia, which reduces complications related to general anesthesia in elderly patients with comorbidities [12]. It also allows for monitoring motor or sensory changes during surgery, confirming the effect of cement removal, and reducing potential neural tissue damage. Although this technical report describes only 1 patient, the case described is not a unique case. Cement leakage is a potential complication for any patient following CAPS. This report is based on the experience of several similar cases. Therefore, the technique can be generally employed in patients with postoperative neurological symptoms following CAPS. It is especially effective when the diagnosis is unclear with imaging modalities due to prior spine surgeries such as fusion or vertebroplasty.
CONCLUSION
UBE is an effective minimally invasive method for both diagnosing and treating potential cement leakage in patients with postoperative neurological symptoms following CAPS. It could be especially helpful when the diagnosis is not absolutely certain with suboptimal imaging study results.
Notes
Conflict of Interest
The authors have nothing to disclose.
Funding/Support
This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Author Contribution
Conceptualization: KM, JSK, WJK; Data curation: KM, JSK, WJK; Formal Analysis: KM, JSK, WJK; Funding acquisition: KM, JSK, WJK; Methodology: KM, JSK, WJK; Project administration: KM, JSK, WJK; Visualization: KM, JSK, WJK; Writing – original draft: KM, JSK, WJK; Writing – review & editing: KM, JSK, WJK