Biportal Endoscopic Lumbar Ponte Osteotomy for Kyphosis: A Technical Note

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J Minim Invasive Spine Surg Tech. 2024;9(2):131-135

Publication date (electronic) : 2024 October 31

doi : https://doi.org/10.21182/jmisst.2024.01445

Kihyun Moon¹, Seung Deok Sun², Won Joong Kim^,3

¹Department of Orthopedic Surgery, Seoul National University Hospital, Seoul, Korea

²Sun’s Orthopaedic Clinic, Seoul, Korea

³Department of Orthopedic Surgery, Synergy Orthopedic Clinic, Seoul, Korea

Corresponding Author: Won Joong Kim Department of Orthopedic Surgery, Synergy Orthopedic Clinic 308, Hakdong-ro, Gangnam-gu, Seoul 06098, Korea Email: wjkim3865@gmail.com

Received 2024 May 21; Revised 2024 August 23; Accepted 2024 August 23.

Abstract

INTRODUCTION

Restoration of sagittal balance has recently become an important issue in spinal reconstructive surgeries, with some authors arguing that even a single-level fusion is essentially a deformity surgery [1]. Restoring and maintaining a normal sagittal profile is quintessential not only for alleviating back pain and improving postoperative function but also for preventing adjacent segment degeneration and spinal deformity [2]. However, restoring the sagittal profile is often quite complex due to the intricate nature of surgical planning and technique, as well as the typical profile of patients, who are often senile, fragile, and burdened with multiple comorbidities. This remains unchanged even in the development of endoscopic spine surgery, as endoscopic spinal fusion is essentially a posterior approach to interbody fusion. Compared to anterior or lateral interbody fusions, the posterior approach is less effective in restoring of lordosis. This is because the anterior annulus and anterior longitudinal ligament restrict lengthening of the anterior column.

This disadvantage may be overcome by combining the techniques of biportal endoscopy with those of corrective osteotomies to develop an endoscopy-assisted deformity correction technique.

The Ponte osteotomy was originally described for correction of thoracic hyperkyphosis [3]. It involves a wide resection of the facet joints bilaterally, intervening lamina, and removal of the ligamentum flavum while maintaining an intact anterior column. Correction is achieved by applying posterior compression with instruments, and any coronal plane deformity can be corrected by applying asymmetrical compression. The technique can be further modified by adding anterior release or interbody fusion to increase the amount of correction per level [4].

Biportal endoscopic lumbar Ponte osteotomy (BELPO) is an innovative technique that combines the techniques of biportal endoscopy with those of corrective osteotomy to develop an endoscopy-assisted deformity correction technique. The technique is something between and also a combination of a Smith-Peterson osteotomy and an anterior column release. It is performed using a standard biportal endoscopic approach with an additional small incision in the midline over the interspinous gap. The midline incision serves as the viewing and working portal for performing the corrective osteotomy and the release of anterior elements. BELPO allows for a larger correction of kyphosis at a single-level compared to other preexisting minimal invasive deformity surgeries.

The ideal indication for BELPO is in patients with rigid short-level kyphosis, where a single-level correction of less than 25° is needed.

MATERIALS AND METHODS

1. Patient Description

A 71-year-old female patient presented with a low back pain for 3 years. She did not have a radiating pain. The severity of her pain on the visual analogue scale was 8. She exhibited definite signs of sagittal imbalance, including: (1) stooping when walking for distance, (2) inability to maintain an erect posture while performing household chores, and (3) inability to carry heavy objects. She was normal on a neurological examination. Radiographs revealed an old compression fracture of L3 with local kyphosis. She had a rigid deformity with osteophytes at the anterior side of the L2–3. In lateral series, the patient showed fixed deformity of kyphosis angle 21° at L2–3, with little motion on flexion and extension (Figure 1A–D). Whole spine lateral view showed positive sagittal imbalance. Preoperative sagittal profiles were; sagittal vertical axis: +15.9 cm, pelvic incidence: 50 º, pelvic tilt: 36 º, sacral slope: 14 º, lumbar lordosis: 5 º (Figure 1E). Additionally, she had underlying osteopenia at L1–4, with a T-value of -1.84.

Figure 1.

Preoperative standing L-spine radiographs: anterior-posterior (A), lateral (B), extension lateral (C), and flexion lateral (D). (E) Standing whole spine lateral – sagittal profiles; sagittal vertical axis: +15.9 cm, pelvic incidence: 50º, pelvic tilt: 36º, sacral slope: 14º, lumbar lordosis: 5º. LL, lumbar lordosis; SVA, sagittal vertical axis; SS, sacral slope; PT, pelvic tilt; PI, pelvic incidence.

The patient has given written informed consent for the submission of a case report to the journal.

2. Surgical Procedure

The patient was placed in a prone position under the spinal anesthesia with additional regional anesthesia via an erector spinae plane block. After positioning, a C-arm was placed to allow monitoring of intraoperative anterior-posterior (AP) and lateral radiographic views.

Using the AP view, stab incisions for insertion of the pedicle screws were made bilaterally at the L2 and L3 vertebra. An additional 1 cm incision was made at the midline, just over the interspinous space between the osteotomy levels. Through the midline incision, a generous portion of the spinous process and interspinous ligament was removed with a rongeur (Figure 2).

Figure 2.

Incisions of biportal endoscopic lumbar Ponte osteotomy. They consist of lateral incisions for endoscopic resection, discectomy, cage and screw insertion. Midline incision facilitates resection of the facets and the midline structures.

Using the upper lateral incision as the viewing portal and the lower lateral and the midline incision as working portals, complete facetectomy involving a removal of the superior and inferior articular processes and a pedicle-to-pedicle laminectomy were performed (Figure 3A). All the intervening interspinous soft tissue and the ligamentum flavum were then removed.

Figure 3.

Endoscopic photos of biportal endoscopic lumbar Ponte osteotomy procedure: facetectomy (A). discectomy (B), anterior release (C), and cage insertion (D).

After that, an endoscopic interbody fusion was performed. First, a discectomy was performed using an annular cutter, graspers and curettes. A serial curettage of the anterior annulus was carried out under direct endoscopic vision (Figure 3B). The disc space was serially dilated using blunt cage trials. These trials were advanced anteriorly to release the anterior elements and verify segmental mobility under fluoroscopic guidance. The anterior release in this patient included fracturing of the osteophyte using a blunt instrument within the disc space (Figure 3C). Subsequently, a cage was inserted as far anteriorly as possible (Figure 3D). Following cage insertion, bilateral pedicle screws were placed with cement augmentation. Posterior compression was then applied to achieve the desired lordosis.

The total surgical time was 2 hours and 30 minutes. The preoperative hemoglobin was 13.6 g/dL, and the postoperative hemoglobin measured the day after surgery was 11.3 g/dL.

RESULTS

The postoperative kyphosis of L2–3 was 2°, demonstrating a correction of 19° (Table 1). She was discharged on 4th postoperative day. The severity of back pain on the visual analogue scale was reduced from preoperative 8 to 3 at discharge. On the day after surgery, a whole-spine lateral x-ray demonstrated an improved sagittal balance with a sagittal vertical axis of 4.0 cm, a significant improvement from the preoperative measurement of 15.9 cm. Other postoperative sagittal profiles were; pelvic incidence: 50º, pelvic tilt: 31º, sacral slope: 19º, lumbar lordosis: -12º (Figure 4A). At 6th week postsurgery, there were no complications. The patient reported improved functional ability in the activity of daily living. The correction was maintained at 6-week follow-up (Figure 4B and C).

Table 1.

Spinopelvic parameters of the patient

Figure 4.

Postoperative radiographs. There was no postoperative change on 6-week follow-up. (A) Standing whole-spine lateral on the day after surgery. Sagittal profiles: sagittal vertical axis, +4.0 cm; pelvic incidence, 50º; pelvic tilt, 31º; sacral slope, 19º; lumbar lordosis, -12º. (B) Standing L-spine anterior-posterior at 6-week follow-up. (C) Standing L-spine lateral at 6-week follow-up. LL, lumbar lordosis; SVA, sagittal vertical axis; SS, sacral slope; PT, pelvic tilt; PI, pelvic incidence.

DISCUSSION

BELPO is a unique, innovative technique for correcting kyphotic deformity. Through a small incision just over the interspinous space, the surgeon can remove a generous portion of the spinous process and interspinous ligament. As the discectomy and anterior column release are performed under direct endoscopic vision, they can be carried out safely. The anterior release is executed by serial curettage of the anterior annulus and dilation of the disc space with blunt cage trials. The cage is inserted to achieve the correction by lengthening the anterior column. It is essential for interbody fusion and maintenance of the correction. This allows the surgeon to achieve about 20° to 25° of lordosis in a single level with fixed kyphosis, without the need for an anterior approach. Consequently, it shortens surgical time, reduces blood loss, and minimizes the risk of postoperative infection.

In BELPO, anesthesia can be either general or regional, depending on the patient’s condition and the surgeon’s preference. Intraoperative neuro-monitoring may be beneficial but is not absolutely necessary when the angle of correction is not extreme. However, if the surgeon wants to ensure neurologic status during the surgical correction, neuro-monitoring under general anesthesia or modified wake-up test under erector spinae plane block can be chosen [5].

Patients with sagittal imbalance are often senile with osteoporosis [6]. Therefore, cement augmentation for the posterior pedicle instrumentation is often necessary [7]. However, cement leakage in pedicle screw augmentation can occur in many cases. Although asymptomatic in most of those cases, it can cause critical complications [8]. Should such a complication occur during BELPO procedure, the leaked cement may be removed using the endoscopic technique, minimizing the risk of revision.

Though the report describes only one patient, it is based on the experience of multiple failed attempts on correcting lordosis with the biportal endoscopic technique. One of the most critical technical aspects is the generous resection of the adjoining spinous processes and the interspinous soft tissue. The interspinous soft tissue and the spinous processes are often overlooked in endoscopic surgery, as the decompression is more focused on removal of the bony elements. However, when left untouched, these midline elements block extension and thus limit the shortening of the posterior column. Only with the resection of these midline elements, authors were able to achieve the desired lordosis. Another critical aspect is the reinforcement of the pedicle screws. To obtain lordosis, the application of posterior compression is essential. The most effective method is to apply compressive force repeatedly over a short period of rest to allow stress relaxation [9]. For this repeated application of compressive force, reliable fixation with firm holding of the pedicle screws is indispensable. Without cement augmentation, the authors experienced screw loosening, resulting in disappointing outcomes. Even the use of bone cement may increase a little more cost, it is less expensive than having to revise for a mechanical complication.

The demand for spinal deformity surgeries is also rising as the elderly population increases. They not only suffer from deformities but also from various underlying diseases, making conventional, open surgeries risky with potential complications and increased mortality. In older patients, an intended undercorrection should be considered as the full correction of sagittal balance may be detrimental due to their poor general condition and increased risk of complications. If deformities can be treated using minimally invasive endoscopic techniques, it would be a great option for patients who cannot undergo conventional surgeries due to their associated risks.

BELPO has some limitations, such as a long learning curve of endoscopic surgery itself. It is designed to be performed with caution and should only be attempted by surgeons who are highly skilled in other endoscopic spine surgeries. However, it is actually a mere combination of an endoscopic fusion and an anterior column release. When used in proper indications, it offers a significant advantage in correcting kyphosis through a minimally invasive technique. Another limitation of the technique is the lack of long-term result. Follow-up studies should be done to evaluate the long-term outcomes.

Further research would be necessary if multiple level correction were to be attempted by unilateral biportal endoscopy. In this situation an important factor to consider is the surgical time. To save time, incorporation of the endoscopic posterior or posterolateral fusions in some of the levels would save a lot of surgical time as not all levels would need an interbody fusion.

CONCLUSION

Though the role of spinal endoscopy was quite restrictive till now, used for only flexible deformities, the BELPO is a promising novel technique enabling correction of rigid deformity. For now, it is indicated for short-level kyphosis when a single-level correction of less than 25° is needed. It offers distinct advantages by integrating corrective osteotomy and anterior release through an endoscopic posterior approach only.

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