Treatment of L5‐S1 Floating Calcified Lumbar Disc Herniation with Percutaneous Endoscopic Interlaminar Discectomy

Abstract

Objective

The floating calcified tissue in floating calcified lumbar disc herniation (FCLDH) is hard and often adheres to the dura mater, which can easily cause nerve root damage during surgery, making the operation challenging. We proposed the classification of FCLDH and a new technique for removing floating calcified tissue and reported the clinical efficacy and safety of this new technique in clinical practice.

Methods

From January 2019 to October 2021, 24 patients (13 males and 11 females, 46.4 ± 7.72 years) with L5‐S1 floating calcified lumbar disc herniation were treated with percutaneous endoscopic interlaminar discectomy (PEID). According to FCLDH classification, a total of Type Ia: nine cases, Type Ib: five cases, Type IIa: four cases, and Type IIa: six cases were included. The visual analogue scale (VAS) and Oswestry disability index (ODI) were recorded pre‐operatively and 3 days postoperatively, 6 months postoperatively, and at the last follow‐up. The postoperative curative effect was evaluated according to the modified MacNab criteria. Computed tomography (CT) and magnetic resonance imaging (MRI) of the lumbar spine were performed 3 days after surgery to evaluate the efficacy of the surgery.

Results

All patients successfully underwent PEID. The VAS and ODI scores at 3 days postoperatively, 6 months postoperatively, and at the last follow‐up were significantly improved and statistically significant compared to those of the preoperative period (p < 0.05). All the patients were followed up for 12–24 months (mean, 16.6 ± 4.6 months). At the last follow‐up, according to the modified MacNab criteria, 15 cases were excellent, eight were good, and one was fair. The combined excellent and good rate was 95.83% (23/24). Postoperative review revealed that all floating calcified tissues were effectively removed and the nerve roots were adequately decompressed without complications such as cerebrospinal fluid leakage and lumbar spine infection.

Conclusion

The classification of FCLDH we proposed can well guide the selection of surgical plans. PEID combined with floating calcified tissue removal technology has good efficacy in the treatment of L5‐S1 FCLDH, ensuring accurate removal of calcified tissue, reducing complications and improving the quality of life of affected individuals.

We proposed the concept and staging of floating calcified lumbar disc herniation (FCLDH) and adequately removed the floating calcified tissue by perfecting the surgical technique. By performing this surgical technique under percutaneous endoscopic interlaminar discectomy (PEID), 24 patients with L5/S1 FCLDH could successfully remove the floating calcified tissues, and the VAS and ODI were significantly improved compared with the preoperative period, with an excellent rate of 95.8%.

Introduction

Calcified lumbar disc herniation (CLDH) ¹ is a complex type of disc herniation that is complicated by disc calcification or osteophyte formation on the basis of lumbar disc herniation. Because calcified tissue often adheres to nerve roots or the dura mater, the difficulty of surgery increases and can easily lead to complications such as nerve damage, dural damage, and cerebrospinal fluid leakage. Clinically, some patients with CLDH have bony connections between the calcified tissue and the vertebral body, and the position of this calcified tissue is relatively fixed. However, there are also patients whose calcified tissue is floating and has no bony connection with the surrounding tissue. This calcified tissue is often mobile and we name it floating calcified lumbar disc herniation (FCLDH). ² , ³ There are few studies on FCLDH in the existing literature. ³ , ⁴ Therefore, this study will further clarify FCLDH and discuss its surgical effects and surgical strategies.

FCLDH represents a distinctive variant of calcified lumbar disc herniation. It is characterized by the presence of posterior free calcification or bony encumbrances where the calcified tissue lacks osseous connections with the surrounding bone tissues and can be displaced into the vertebral canal, exerting pressure on and irritating the dural membrane or nerve roots. ² , ³ Clinically, FCLDH typically presents with lumbar pain accompanied by radiating pain in the lower extremities, numbness, intermittent claudication, and other symptoms. ⁴ , ⁵

While the prevalence of CLDH has been reported to range from 4.7% to 15.9% in the existing literature, ⁵ our study findings demonstrate that the incidence of FCLDH accounted for 30.7% of CLDH. The exact mechanisms underlying the development of floating calcified tissue remain unclear. However, some theories suggest its formation may be linked to factors such as inflammation, trauma, or chronic strain injuries. ⁵ , ⁶

Due to the distinct properties of hardiness and mobility in the floating calcified tissue, the clinical symptoms associated with FCLDH tend to be more severe than those of simple lumbar disc herniation. Consequently, patients who do not respond favorably to conservative treatment frequently require surgical intervention. ⁷ Traditionally, the removal of calcified tissue was achieved through open surgery, a procedure associated with invasiveness and the potential to disrupt spinal stability. ⁸ , ⁹

In recent years, with the development of spinal endoscopic techniques, spine surgeons have begun to treat CLDH endoscopically. Currently, many researchers are exploring the use of percutaneous endoscopic interlaminar discectomy (PEID) to treat L5/S1 CLDH. ⁸ , ¹⁰ However, the management of calcified tissue, especially floating calcified tissue, under microscopic visualization raises questions about the necessity of complete removal and the optimal surgical techniques. The objectives of this study were to: (i) define the concept of FCLDH, propose a staging system and discuss the surgical techniques pertinent to its management; and (ii) provide an analysis of the clinical and radiological outcomes resulting from these surgical interventions.

Methods

Inclusion and Exclusion Criteria and Patient Selection

The inclusion criteria for this retrospective study were as follows: (i) confirmation of FCLDH characteristics through imaging; (ii) ineffectiveness of conservative treatment lasting more than 3 months; and (iii) a single segment of L5/S1 involvement with signs and symptoms consistent with the clinical presentation of the prominent segment.

The exclusion criteria were as follows: (i) multisegmental calcification; (ii) concomitant lumbar spine infection, lumbar spine slippage, lumbar spine tumor, or lumbar spine fracture; (iii) floating calcified tissue located in the intervertebral foramina; (iv) history of lumbar disc surgery; and (v) inability to tolerate surgery.

Patient Characteristics

The study included 24 patients with L5‐S1 FCLDH (13 males and 11 females), with ages ranging from 20 to 78 years (mean age 46 years), who underwent PEID from January 2019 to October 2021. According to FCLDH classification (Figure 1), a total of Type Ia: nine cases, Type Ib: five cases, Type IIa: four cases, and Type IIa: six cases were included. Written informed consent was obtained from all participants.

FIGURE 1.

Imaging of the two types of FCLDH. (A)–(B): Type Ia: floating calcified tissue confined to the central canal and is <4 mm in size. (C) –(D): Type Ib: floating calcified tissue located in the lateral recess and is <4 mm in size. (E) – (F): Type IIa: floating calcified tissue confined to the central canal and is >4 mm in size. (G) –(H): Type IIb: floating calcified tissue located in the lateral recess and is >4 mm in size. (I) –(J): Type C: floating calcified tissue located in the intervertebral foramina.

Classification of the FCLDH

There are different surgical strategies for different classifications of FCLDH. ⁴ , ¹¹ , ¹² , ¹³ Based on the information that was obtained using computed tomography, we classified FCLDH into three types (Figure 1).

Type I

Floating calcified tissue <4 mm, further divided into two subtypes based on its location:

• Type Ia: floating calcified tissue located in the central canal; and

• Type Ib: floating calcified tissue located in the lateral recess.

Type II

Floating calcified tissue >4 mm, further divided into two subtypes based on its location:

• Type IIa: Floating calcified tissue located in the central canal; and

• Type IIb: Floating calcified tissue located in the lateral recess.

Type III

Floating calcified tissue located in the intervertebral foramina.

Surgical Procedures

The patient was placed in a prone position, and the operation was performed under general anesthesia. The L5‐S1 intervertebral space was localized under fluoroscopy and marked on the body surface, followed by sterilization of the drapes. A skin protection film was applied over the surgical field of view. An approximately 8 mm incision was made on the body's surface projection. The dilating tube was placed above the ligamentum flavum in the L5‐S1 intervertebral space, and after confirming the position under fluoroscopy, the working sleeve was placed along the dilating tube, and the endoscope was placed after confirming the position. The endoscope was introduced once the position was confirmed to be unchanged. Under endoscopic guidance, the ligamentum flavum was incised layer‐by‐layer, partially occluding the lamina to expose the dura mater and nerve roots fully. The working sleeve was carefully advanced into the spinal canal, protecting the S1 nerve root until the protruding nucleus pulposus and floating calcified tissue were visible microscopically. The nucleus pulposus tissue was removed using medullary forceps, and the fibrous tissue surrounding the floating calcified tissue was dissected with blue forceps. Individual removals of calcified tissue were performed using medullary forceps. Upon the completion of decompression, the working cannula was retracted, and the incision was sutured (Figure 2).

FIGURE 2.

Treatment of floating calcified lumbar disc herniation via percutaneous endoscopic interlaminar discectomy (PEID). A male aged 34 years complained of low back pain for 6 months, which worsened with numbness and pain in the left lower extremity for more than 2 months. (A) –(B): preoperative lumbar spine frontal and lateral x‐rays. (C) –(D): preoperative CT revealed L5‐S1 Type II FCLDH. (E) –(F): Preoperative MRI revealed L5‐S1 disc herniation. (G) –(H): intraoperative X‐ray localization fluoroscopy. (I): intraoperative removal of protruding nucleus pulposus tissue and floating calcified tissue. (J): endoscopy showed that the nerve roots and dural sac were fully decompressed. (K) –(L): postoperative CT revealed complete removal of floating calcified tissue. (M): postoperative four‐dimensional CT reconstruction of lumbar spine.

Clinical Assessment

We analyzed the outcomes using the visual analogue scale (VAS) and the Oswestry disability index (ODI). Clinical efficacy was assessed at the last follow‐up using the modified Macnab criteria. The safety of the surgical technique was assessed by recording the operative time, intraoperative blood loss, and complications. Lumbar computed tomography (CT) and magnetic resonance imaging (MRI) were performed 3 days postoperatively to assess the removal of calcified tissue and adequate decompression of the nerve roots.

Statistical Analysis

Data were expressed as means ± standard deviation. Student's t‐tests were used to compare continuous variables, such as VAS and ODI scores, between different time points. Measurement data that do not conform to the normal distribution are represented by the median (upper quartile, lower quartile) [M (P25, P75)], and a multi‐sample rank sum test is performed. Statistical significance was set at p < 0.05. SPSS software (version 25.0, IBM, Armonk, NY, USA) was used to analyze all the data.

Results

Surgical Information

The operation was successfully completed for all patients. The operative time was 60–100 min, mean (72.5 ± 13.8) min; intraoperative bleeding was 10–20 mL; mean (12.3 ± 3.0) mL, and postoperative hospitalization ranged from 3 to 5 days, mean (3.8 ± 0.7) days.

Clinical Outcomes

Postoperative follow‐up was done at 12–24 months, with a mean of 16.6 ± 4.6 months. The preoperative VAS score of low back pain was 7.59 ± 0.79; the score on postoperative day 3 was 3.00 ± 0.8; the score on postoperative month 6 was 1.50 ± 0.83; and the last follow‐up score was 0.63 ± 0.49. The preoperative ODI was 59.57 ± 8.29; the score on postoperative day 3 was 23.06 ± 3.26; the score on postoperative month 6 was 12.80 ± 2.09; and the last follow‐up score was 10.72 ± 1.75. The VAS and ODI scores at 3 days postoperatively, 6 months postoperatively, and at the last follow‐up were significantly improved and statistically significant compared to those of the preoperative period (p < 0.05) (Table 1). At the last follow‐up, according to the modified MacNab criteria, 15 cases were excellent, eight were good, and one was fair. The combined excellent and good rate was 95.83% (23/24).

TABLE 1.

The preoperative and postoperative VAS and ODI score (n = 24, mean ± SD).

Indexes	Pre‐operative	Post‐operative (3 days)	Post‐operative (6 months)	Last follow‐up	Statistic value
VAS score	7.59 ± 0.79	3.00 ± 0.8*	1.50 ± 0.83*	0.63 ± 0.49*	F = 472.466 p = 0.000
ODI score	59.57 ± 8.29	23.06 ± 3.26	12.80 ± 2.09*	10.72 ± 1.75*	F = 162.148 p = 0.000

^* p < 0.05 versus preoperative value.

Postoperative follow‐up lumbar CT and MRI showed that the floating calcified tissue was effectively removed and the nerve roots were adequately decompressed.

Subgroup Analysis

By comparing the efficacy of PEID in treating different subtypes of FCLDH, we found that the four subtypes had no statistical significance in intraoperative blood loss, preoperative and postoperative VAS scores, and preoperative and postoperative ODI scores (p > 0.05). In terms of operation time, the operation time of Type Ia is longer than that of Type IIa, the operation time of Type IIa is longer than that of Type Ib, and the operation time of Type II is longer than that of Type Ib. The difference is statistically significant (p < 0.05, Table 2).

TABLE 2.

Data comparison of various classifications in FCLDH [M(P25, P75)]

Parameters	Type Ia	Type Ib	Type IIa	Type IIb	p value
Number	9	5	4	6
Operative time (min)	65.0 (62.5, 70.0)a	65.0 (60.0, 65.0)bc	82.5 (72.5, 92.5)ab	75.0 (63.8, 100.0)c	0.430
Intraoperative blood loss (mL)	12.0 (10.0, 13.5)	10.0 (10.0, 13.5)	12.5 (10.0, 15.0)	11.0 (10.0, 14.0)	0.874
VAS scores
Pre‐operative	7.0 (7.0, 8.0)	7.0 (7.0, 8.0)	7.5 (7.0, 8.0)	8.0 (7.0, 9.0)	0.713
Post‐operative (3 days)	3.0 (2.0, 3.5)	3.0 (3.0, 3.5)	3.5 (3.0, 4.0)	3.0 (2.0, 4.0)	0.416
Post‐operative (6 months)	1.0 (1.0, 2.0)	2.0 (1.5, 2.0)	1.5 (0.3, 2.8)	2.0 (0.8, 2.3)	0.506
Last follow‐up	0.0 (0.0, 1.0)	1.0 (0.5, 1.0)	1.0 (0.3, 1.0)	1.0 (0.8, 1.0)	0.166
ODI scores
Pre‐operative	18.0 (12.0, 18.0)	12.0 (12.0, 16.5)	18.0 (12.0, 24.0)	16.5 (14.3, 24.0)	0.475
Post‐operative (3 days)	57.6 (55.8, 69.0)	59.2 (51.2, 65.4)	60.0 (53.2, 66.2)	54.4 (50.4, 67.5)	0.775
Post‐operative (6 months)	20.8 (18.0, 27.0)	24.0 (23.2, 24.0)	24.0 (24.0, 28.5)	22.0 (20.6, 24.5)	0.264
Last follow‐up	10.8 (10.4, 12.4)	14.4 (12.6, 14.4)	14.4 (11.1, 14.4)	12.8 (12.0, 16.2)	0.110

Note: Operative time comparison: comparison of Type Ia and Type IIa, ^a p <0.05; comparison of Type Ib and Type IIa, ^b p <0.05; comparison of Type Ib and Type IIb, ^c p <0.05.

Complications

During follow‐up, two patients developed numbness in the lower limbs; however, both recovered after 1 week of nutritional nerve therapy. No postoperative complications, such as infection or cerebrospinal fluid leakage, were observed in any patient.

Discussion

FCLDH is not uncommon in clinical practice, however, to date, it has not been studied thoroughly. Takata et al. ³ classified fractures of the posterior margin of the vertebral body according to morphology as follows: Type I is a partially dissected cortical bone with no bone defects; Type II is a fracture of the posterior margin of the vertebral body containing cancellous bone; and Type III is a localized fracture of the posterior margin of the vertebral body, including the cartilage overlying the annulus fibrosus. In Types II and III, the dissected fracture fragments are floating without bony connections with the surrounding bone tissues. However, Takata et al. did not further investigate the size and location of the floating calcified tissues, which had some limitations in guiding the selection of treatment modalities. Although the subsequent Epstein et al. ¹¹ and Chang et al. classifications ⁴ improved the Takata et al. classification, they did not further explore the floating calcified tissue. Therefore, to fill this gap in knowledge, we aimed to clarify the concept of FCLDH, its typing based on clinical symptoms and imaging, and discuss its surgical techniques.

Surgery is required for FCLDH when it fails to respond to conservative treatment. ⁷ However, there is controversy regarding the surgical options for FCLDH, ¹² , ¹⁴ , ¹⁵ , ¹⁶ such as whether complete removal of calcified tissue is required. Researchers ⁴ believe that the residual calcified tissue can cause spinal stenosis and increase the risk of long‐term low back pain. Others have argued that the removal of calcified tissue is not necessary. Shirado et al. ¹² suggest that the need for complete intraoperative removal of calcified tissue is determined by whether the calcified tissue is active or not. According to Akhaddar et al., ¹³ the location of the protruding nucleus pulposus in relation to the calcified tissue should be analyzed by imaging data to assess whether the neurological symptoms are caused by the calcified tissue; if the nucleus pulposus protrudes beyond the calcified tissue, then the patient's neurological symptoms are caused by the protruding nucleus pulposus, and complete removal of the calcified tissue can be avoided; conversely, complete removal of the calcified tissue is required to alleviate the neurological symptoms. Both views have their advocates, causing a lack of consensus.

The surgical protocols for the removal of calcified tissue are also not uniform. Previous studies have demonstrated the removal of calcified tissues using open surgery, and although good results have been achieved, open surgery has the disadvantages of high trauma rates, high bleeding rates, and slow postoperative recovery. With the development of minimally invasive spinal techniques, PEID has begun to replace open surgery in the management of L5‐S1 CLDH and has achieved good results. ² , ⁸ , ¹⁰ , ¹⁷

However, previous studies have shown that it is more technically difficult to remove calcified tissue intraoperatively for patients with CLDH, and they are prone to injury to the dura mater or nerve roots. Cheng et al. ¹⁷ used PEID to treat 28 patients with L5‐S1 CLDH, and although good efficacy was achieved, two patients developed nerve root injuries and sensory deficits after surgery. Dabo et al. ¹⁰ mentioned that the use of a ring drill to remove calcified tissue in PEID increases the risk of postoperative sensory deficits due to the intraoperative pulling of the nerve root. Therefore, to reduce intraoperative damage to the nerve root in PEID, Kim et al. ² proposed the concept of the calcified floating technique, in which an endoscopic punch is used to separate the calcified tissue from the vertebral body edge, and the working channel is rotated to remove the floating calcified tissue, completing the decompression of the nerve root. However, we have identified that the method of removing the floating calcified tissue is time‐consuming and has a low success rate. Relying on the rotational working channel alone makes it difficult to separate the floating calcified tissue from the surrounding fibrous tissue, and large movements around the nerve root increase the risk of nerve root injury. In this study, 24 patients with L5/S1 FCLDH were treated using the PEID surgical technique, which allowed adequate intraoperative removal of floating calcified tissue, and there were no postoperative complications such as infection or dural injury.

Using the results of previous reports, we analyzed and summarized the surgical protocols and precautions: the imaging was carefully observed beforehand to clarify the staging of FCLDH before drawing up a surgical plan. We classified FCLDH into three types based on the size and location of the floating calcified tissue and used this as a basis for selecting a surgical plan.

The need for the removal of calcified tissue; Type Ia does not clinically compress the nerve root, but because of its mobility and the small size of the calcified tissue, the floating calcified tissue can be completely removed intraoperatively to reduce the risk of long‐term postoperative low back pain; Type Ib often compresses the nerve root and needs to be completely removed intraoperatively; Type II FCLDH cannot be visualized in its entirety microscopically and requires the floating calcified tissue to be divided into smaller pieces before removal; Type III is difficult to remove using PEID, and other surgical options are recommended because the floating calcified tissues located in the intervertebral foramina.

Surgical Techniques (Figure 3): for Type I FCLDH, the fibrous tissue surrounding the floating calcified tissue was first cut with a blue forceps intraoperatively and then removed in one piece with a medullary forceps; Type II FCLDH was removed intraoperatively by first protecting the nerve root using the beveled surface of the working trocar, then dividing the calcified tissue with anosteotome, and rotating the tube after cutting the fibrous tissue surrounding the calcified tissue with a blue forceps.

FIGURE 3.

Schematic diagram of removal of floating calcified tissue. (A): exposure of prominent nucleus pulposus and floating calcified tissue. (B) –(C): cut the fibrous tissue around the floating calcified tissue with blue forceps. (D): remove the floating calcified tissue with medullray forceps.

In Type IIa FCLDH, the surgical exposure would be more difficult, and the surgeon would need to adjust the working channel more dramatically in order to obtain a larger surgical field of view, and the intraoperative operation time is often longer and the operation is more difficult; therefore, it is recommended that it be carried out by a surgeon who is skilled in microscopic operation in order to minimize complications; in Type IIb FCLDH, the position of the needle insertion point should be reasonably biased to the side according to the movable range of the edge of the calcified tissue and the working channel.

There is no significant difference in clinical efficacy between different subtypes of FCLDH treated with PEID, but the operation time of Type II is longer due to the size and location of floating calcified tissue, and this difference is statistically significant (p < 0.05, Table 2). Therefore, surgeons need to be demonstrate stamina and patience when treating Type II FCLDH.

PEID combined with osteotomes significantly reduces intraoperative traction on the nerve root during the division of large calcifications, greatly reducing the risk of the procedure and the incidence of postoperative complications. ¹⁴

Limitations and Strengths

The classification of FCLDH we proposed can well guide the selection of surgical plans. The technique presented in this article to remove floating calcified tissue can ensure precise removal of calcified tissue, reduce complications and improve the quality of life of the affected individual.

The present study had some limitations. First, this study had a small number of cases and was a single‐center retrospective study. Second, the classifying of FCLDH was based on what we have observed in our clinic, and its richness and feasibility require further investigation. Finally, due to the small number of cases, we did not conducted a comparative study on the efficacy of PEID in the treatment of L5‐S1 FCLD and L4/5 FCLDH, and did not set up a control group to compare the efficacy of different surgical methods in the treatment of FCLDH. We will conduct controlled studies in the future when conditions are sufficient.

Conclusion

On the basis of previous research, we further clearly proposed the concept and staging of FCLDH, and adequately removed the floating calcified tissue by perfecting the surgical technique. Good clinical outcomes were achieved in all 24 cases of L5/S1 FCLDH treated with PEID. We believe that this technique is promising and deserves further clinical practice and long‐term follow‐up.

Ethics Statement

This study has been reviewed and approved by the appropriate ethics committee of The First Affiliated Hospital of Guangzhou University of Chinese Medicine (Ethics number: NO. K‐2023‐180).

Conflict of Interest Statement

The authors declare no competing interests.

Author Contributions

Conceptualization, methodology and writing—original draft, GNG and TL, Investigation, GNG. Validation, HZG and KY. Writing—review and editing, HZG and ZDY, Visualization, YXL; Project Administration, YCT and SCZ. All authors read and approved the final manuscript.

Authorship Declaration

All authors meet the authorship criteria according to the latest guidelines of the International Committee of Medical Journal Editors and agree with the content of the manuscript. Conceptualization, GuoNing Gu and Teng Liu; Methodology, GuoNing Gu and Teng Liu; Investigation, GuoNing Gu; Validation, HuiZhi Guo and Kai Yuan; Writing—Original Draft, GuoNing Gu and Teng Liu; Writing—Review & Editing, HuiZhi Guo and ZhiDong Yang; Visualization, YongXian Li; Project Administration, YongChao Tang and ShunCong Zhang; Funding Acquisition, YongChao Tang and ShunCong Zhang.