The clinical effect of floating island laminectomy technique for severe thoracic spinal stenosis and myelopathy caused by ossification of the ligamentum flavum: a retrospective study

doi:10.21203/rs.3.rs-4663488/v1

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The clinical effect of floating island laminectomy technique for severe thoracic spinal stenosis and myelopathy caused by ossification of the ligamentum flavum: a retrospective study

https://doi.org/10.21203/rs.3.rs-4663488/v1

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Background

Severe thoracic ossification of the ligamentum flavum often leads to thoracic spinal canal stenosis and spinal cord injury, which generates severe symptoms. Generally, patients required surgery and aggravated spinal cord function impairment is a common complication. We propose a novel surgical technique to remove the ossified ligamentum flavum with the adhesive dura as a floating island. The purpose of this study was to evaluate the clinical efficacy and safety of floating island in the treatment of severe ossification of ligamentum flavum.

Methods

A total of 31 patients with thoracic spinal stenosis and myelopathy caused by thoracic ossification of the ligamentum flavum from January 2019 to April 2022 were included in the study and were followed up at 1, 3, 6, and 12 months, respectively. All patients were treated with floating island laminectomy technique. Neurological function was assessed by the modified Japanese Orthopaedic Association (mJOA) scoring system before and after operation and the rate of improvement was calculated. Perioperative complications were also recorded in this study.

Results

All 31 patients were successfully completed by the same professional surgery team. The average operative time was 207.74 ± 58.54 minutes, and the average intra-operative blood loss was 406.45 ± 217.85 ml. The mJOA score at 1 month, 3 months, 6 months and 12 months after surgery increased from 4.68 ± 0.60 to 6.71 ± 0.73, 7.35 ± 0.76, 8.45 ± 0.85 and 9.06 ± 0.81, respectively. The mJOA score after surgery was significantly higher than before (P < 0.001). The recovery rate was (32.41 ± 8.55)%, (42.57 ± 9.00)%, (60.12 ± 11.07)% and (69.76 ± 11.38)% for 1 month, 3 months, 6 months and 12 months after surgery, respectively. Postoperative complications included dural tear in 13 cases (41.9%), defect in 10 cases (32.2%) and cerebrospinal fluid leakage in 10 cases (32.2%). There was no recurrence of ossification or postoperative thoracic vertebra deformity in patients with aggravated neurological injury.

Conclusion

The results of this study indicate that although the incidence of cerebrospinal fluid leakage is a little high after operation, the floating island laminectomy method for the treatment of thoracic ossification of the ligamentum flavum is still safe and effective, which can effectively avoid the aggravation of neurological symptoms and enable patients to obtain satisfactory neurological function improvement and functional recovery.

Floating island laminectomy

Ossification of ligamentum flavum

Thoracic spinal stenosis

Thoracic myelopathy

Compression of spinal cord

Since thoracic ossification of the ligamentum flavum(TOLF) was first proposed by Polgar in 1920, TOLF has been increasingly recognized as a major cause of slowly progressive thoracic myelopathy in the world⁽¹⁾.TOLF is a degenerative disease, as we all know, which has occurred in more than half of the patients with thoracic myelopathy⁽²⁾.More frequently, lower thoracic levels were involved in TOLF, especially in T9-T12 and it’s characterized by the substitution of hypertrophied fibrous tissue within the ligaments by pathological ossification.(3)It was reported that TOLF mostly occurred in East Asian countries, such as Japan(36%), South Korea(16.9%) and southern China(3.8%)^(3–5).Recently, other countries and areas except Asian countries have also reported the TOLF, including North America, Middle East and Caribbean^{(6, 7)}.

The ossified lesion usually progresses insidiously for severe thoracic spinal stenosis caused by ossification of the ligamentum flavum. Even if the patients have only mild symptoms, the compression of the spinal cord by ossified blockage is often very serious⁽⁸⁾. The symptoms of the patient's lower limb weakness are not quite obvious and serious, while the main manifestations of the patient are ataxia, increased muscle tone, walking instability, etc⁽⁹⁾. Occasionally, the patient will occur paraplegia caused by sudden weakness of the lower limb due to minor trauma⁽¹⁰⁾.Takenaka et al. have illustrated symptoms specific to anatomical pathology or compressed segments in thoracic myelopathy. Relationships between the manifestations and anatomical pathology can be helpful in the initial investigation of pre-operation patients, although auxiliary examination such as computed tomography (CT) or magnetic resonance imaging (MRI) are necessary for definitive diagnosis⁽¹¹⁾.

Surgery is the best solution for who has severe spinal cord compression, which is aimed at the resection of the calcified ligamentum flavum and the decompression of spinal cord, including conventional surgical procedures, such as en bloc laminectomy, fenestration, and laminoplasty^(12–15).However, due to severe compression with calcification of the ligamentum flavum adherent to the dura mater or even dura calcification, the surgical resection of the calcified ligamentum flavum carries a high risk of iatrogenic spinal cord injury in the process of pulling the spinal cord which is already on the verge of paralysis. The risk of iatrogenic spinal cord injury and paralysis have been reported in the literature as high as 30%⁽¹⁶⁾.Therefore, how to reduce spinal cord injury caused by operative manipulation is a main challenge that needs us to resolve in the treatment of TOLF⁽¹⁷⁾.

In this study, we present a novel technique, floating island laminectomy, which uses specific surgical procedures to reduce the risk of spinal cord injury during surgery and improves clinical outcomes in the treatment of TOLF.

Study Design and Patient Population

This study was a retrospective, single-center clinical study and was approved by the Ethics Committee of our hospital (No.2023241). There were 31 patients who presented with thoracic stenosis and myelopathy caused by severe TOLF from January 2019 to April 2022 in this study (Fig. 1). Informed consents were obtained from all patients in this study. Those patients were admitted to the Department of Spine Surgery at the West China Hospital of Sichuan University. The inclusion criteria were as follows: (1) Typical symptoms of thoracic stenosis and spinal cord compression caused by TOLF (mainly including ataxia, increased muscle tone, walking instability, lower limb weakness); (2) Presenting with spinal stenosis and myelopathy by computed tomography (CT) scan and magnetic resonance imaging (MRI) scan; (3) Patients with a poor conservative treatment and with a general condition allowing and requiring surgical interventions. The exclusion criteria were as follows: (1) Other thoracic diseases, such as thoracic fractures, thoracic tumors, thoracic tuberculosis, etc; (2) Unable to undergo surgery with poor systematic conditions, such as severe hepatic and renal dysfunction, severe coagulation dysfunction, severe infectious diseases; (3) Previous thoracic surgery for various reasons such as trauma or infections; (4) Incomplete information or the follow-up was lost.

Preoperative Planning

It is very important to accurately locate the compression segments and sites caused by ossification of the ligamentum flavum(OLF), including the following aspects: (1) Thoracic stenosis often involves multiple segments, which is also combined with ossification of the posterior longitudinal ligament of thoracic spine. Meanwhile, the pathogenic factors are often limited to ascertain the exact segment, so in order to avoid damage to adjacent segment, we identify the most stenosed and symptomatic segments in combination with physical examination and imaging examination. (2) The segment with the most compressed symptoms identified on sagittal CT and MRI before surgery was corresponding to the segment on plain film in the operating room, so as to facilitate the design of surgical incisions during intra-operative positioning and prevent the opening of wrong segments. (3) The location of the pedicle infusion and the fenestration were determined on sagittal CT and MRI before surgery.

Surgical Technique

After endotracheal anesthesia, the patient was placed in prone position, and the accurate thoracic segment was located under X-ray. The incision was marked, and then routine disinfection and towel were performed after accurate positioning. Bilateral lamina, spinous process and transverse process were exposed by using the standard posterior approach. The lamina adjacent to the upper and lower segments of the ossified ligamentum flavum were partially resected and fenestrated. The depth and boundary of the dural membrane above and below the segments of the ossified ligamentum flavum were exposed by subperiosteal dissection. Appropriate pedicle screws were placed on both sides of the lamina above and below the affected segment. The longitudinal osteotomy incisions were made to the lateral of the lamina involved in ossification of the ligamentum flavum with reference to the depth and boundary of the visible dura. A floating island of the OLF was made at the end of longitudinally excising the lamina of the OLF. Gently lift and shake the lamina from side to side to free the lamina completely. Then, nerve stripper and sharp knife were used to separate the OLF from the dura. The lamina and the OLF complex were completely separated. The screws were then affixed with 2 longitudinal rods for further stabilization (Fig. 2). Intraoperative improvements in pulsation of the lamina and ossified ligamentum flavum complex as well as dura pulsation were observed, indicating that decompression of the spinal cord had been achieved. Posterior bone graft fusion was performed between the longitudinal osteotomy incisions of the bilateral of the lamina. Finally, the incision was closed layer by layer with a drainage tube preserved. No significant changes in somatosensory evoked potentials (SSEPs), motor evoked potentials (MEPs) and other neuroelectrophysiological monitoring indicators, were observed between pre-operation and postoperation in the operating room.

Assessment Indicators

Demographic data (sex, age, symptom duration and TOLF level), operative time, intra-operative blood loss and clinical complications were recorded for all patients who were followed-up at least 12 months after surgery. X-ray, CT scan of the thoracic spine are used for all patients to estimate the stability of the internal fixation and the effect of bone fusion before and after operation. MRI scan of the thoracic spine was used to assess the degree of the spinal cord compression and decompression. Pre- and post-operative neurological function of all patients were evaluated by the modified Japanese Orthopaedic Association (mJOA) score system. The mJOA score of 1 month, 3 months, 6 months and 12 months after operation were recorded in comparison with pre-operation mJOA score to calculate recovery rate, which was calculated as follows: (final mJOA score - preoperative mJOA score)/(11- preoperative mJOA score) x100% according to the Hirabayashi recovery rate. The recovery rate was defined as follows: excellent (75%-100%), good (50%-74%), fair (25%-49%), and poor (0%-24%). Peri-operative complications, including dural tears, dural defect, cerebrospinal fluid (CSF) leakage, neurological impairment (NI) surgical site infection (SSI) and thoracic deformity were recorded and analyzed.

Statistical Analysis

Statistical analysis was performed using SPSS version 26.0 (IBM Armonls, NY, USA). The variable data was defined as mean ± standard deviation (SD). Paired Sample T-test was used to evaluate the mJOA scores of different follow-up periods relative to the previous period and differences of variables were considered statistically significant at P < 0.05.

Demographic Data Outcomes

There were 17 males and 14 females with TOLF who accepted floating island laminectomy in our hospital from January 2019 to April 2022 were analyzed in this study. All patients were followed up for an average of 12.52 months (range 12–13). The mean operative time was 207.74 min (range 122–425); the mean intra-operative blood loss was 406.45 ml (range 150–1000) and the mean symptom duration time was 29.45months (range 1-120). Demographic data of all patients in this study was performed in Table 1.

Table 1

Demographic data outcomes of patients
Item		Value
Sex: male/female		17/14
Age(years)		55.94 ± 9.95
Follow-up (months)		12.52 ± 0.51
Symptom duration (months)		29.45 ± 31.93
Intra-operative blood loss (ml)		406.45 ± 217.85
Operative time (minutes) TOLF level T1-T6 T7-T12		207.74 ± 58.54 4 27

Clinical Outcomes

Clinical manifestations, such as weakness, gait disturbances and pain, of patients who have achieved the 12 months of follow-up were remarkably improved. The mJOA score respectively increased to 6.71 ± 0.73 (range 5–8), 7.35 ± 0.76 (range 5–8), 8.45 ± 0.85 (range 6–10) and 9.06 ± 0.81 (range 7–10) in 1 month, 3 months, 6 months and 12 months after operation, which were significantly higher than preoperative mJOA score of 4.68 ± 0.60 (range 3–5). The postoperative mJOA scores compared with the preoperative mJOA score were noticeably improved (P<0.01) (Table 2). The postoperative 1 month mJOA score versus the preoperative mJOA score, the postoperative 3 months mJOA score versus the postoperative 1 month mJOA score, the postoperative 6 months mJOA score versus the postoperative 3 months mJOA score and the postoperative 12 months mJOA score versus the postoperative 6 months mJOA score were also improved observably (P < 0.01) (Table 2). The Hirabayashi's recovery rate was (32.41 ± 8.55)%, (42.57 ± 9.00)%, (60.12 ± 11.07)% and (69.76 ± 11.38)% for 1 month, 3 months, 6 months and 12 months after surgery, respectively (Table 3). Ten patients were defined as excellent, twenty-one as good, and no one as fair and poor. The neurological function of all post-operative patients was significantly improved.

Table 2

Clinical outcomes of patients
Time		mJOA score
Preoperative		4.68 ± 0.60
Postoperative 1 month		6.71 ± 0.73^a
Postoperative 3 months		7.35 ± 0.76^ab
Postoperative 6 months		8.45 ± 0.85^ac
Postoperative 12 months		9.06 ± 0.81^ad
P-value		<0.01
a: P < 0.01, versus preoperative value; b: P < 0.01, versus Post 1 month value; c: P < 0.01,

versus Post 3 months value; d: P < 0.01, versus Post 6 months value.

Table 3

Recovery rate after surgery
Follow-up		Recovery rate (%)
Postoperative 1 month		32.41 ± 8.55
Postoperative 3 months		42.57 ± 9.00
Postoperative 6 months		60.12 ± 11.07
Postoperative 12 months		69.76 ± 11.38

Postoperative complications included dural tears in 13 cases (41.9%), defects in 10 cases (32.2%) and cerebrospinal fluid (CSF) leakage in 10 cases (32.2%) (Table 4). All patients with dural tears or defects underwent appropriate procedures, such as suture and repair, etc. All patients with CSF leakage were successfully pulled out the drainage tube 5–7 days after surgery, and wound healed 10–14 days without wound infection, fluid leakage and other complications. There was no recurrence of ossification or postoperative thoracic vertebra deformity in patients with aggravated neurological injury.

Table 4

Surgical outcomes of patients
Complications			Value
Dural tears (%)			13/31(41.94%)
Dural deficit (%)			10/31(32.26%)
Cerebrospinal fluid leakage (%)			10/31(32.26%)
Neurological deterioration (%)			0
Infection (%)			0
Deformity (%)			0

TOLF is usually rare, insidious and progressive that may cause severe spinal cord compression in spite of mild symptoms⁽¹⁸⁾.Patients with TOLF have various symptoms, which can result in muscle weakness, numbness and sensory disturbance in the lower limbs and different degrees of walking dysfunction, even in severe cases, complete paraplegia⁽¹²⁾.Other symptoms also occur in disease, including back pain, gait disturbance, neurogenic bladder and bowel dysfunction, etc⁽¹⁹⁾.Once the TOLF is symptomatic, it is generally refractory to conservative treatment and necessary to surgical decompression⁽²⁰⁾.The most common surgery of spinal cord decompression is laminectomy. Other techniques have also been reported, such as fenestration, laminoplasty, and hemilaminectomy⁽²¹⁾.

Based on the characteristics of spinal stenosis and the continuity of ossification, Onishi et al.⁽²²⁾ proposed 5 types for TOLF: lateral type, extended type, enlarged type, fused type and tuberous type. French door laminectomy and fenestration are recommended for the first 3 types of TOLF, which are almost impossible not to damage the dura mater or spinal cord, as both require a longitudinal incision. An en bloc laminectomy is required for the latter two types of TOLF, which are the common cause of severe thoracic spinal cord compression. However, en bloc laminectomy is technically demanding and usually has a high incidence of early complications⁽²³⁾.In addition, direct manipulation of spinal canal can result in postoperative complications, such as dural tears or cerebrospinal fluid leakage, leading to unsatisfactory treatment outcomes⁽²⁴⁾.Simultaneously, manipulation of the posterior appendages of the spine may damage the stability of spine⁽²⁵⁾.

The idea of the floating island technique is to remove the lamina of ossified ligamentum flavum under the direct vision of the depth and boundary of the dural mater, reducing disturbance with the spinal cord during spinal canal manipulation. Decompressing the spinal canal can be controlled, because we separate the ossified ligamentum flavum and the dural mater from the surrounding area to form a floating island, which allows us to visualize the intraspinal situation during surgical resection. The key factors to ensure the effect of operation are to determine the location of the compression of OLF and the location of the fenestration. Our experience is that preoperative thoracic CT and thoracic MRI are accurately positioned, and X-ray is positioned again after anesthesia, so as to reduce the incidence of excessive laminectomy and dural tear caused by positioning errors. Complete decompression is marked by pulsation of the dura mater.

The outcome of surgery is closely related to postoperative complications and postoperative recovery is also closely related to the occurrence of complications. Sun et al.⁽²⁴⁾ have reported that the most common complications of spinal surgery are dural tears an CSF leakage because of adhesion or ossification of the dural mater, which can lead to CSF pseudocyst, respiratory obstruction, wound dehiscence, and meningitis. Dural adhesion makes it difficult to directly remove the ossified mass by traditional surgical methods, which results in a high incidence of postoperative cerebrospinal fluid leakage⁽²⁶⁾.The incidence of dural tear or CSF leakage was 32% and the incidence of patients who had dural ossification with CSF leakage was highly to 78.8%⁽²⁴⁾.Early neurological deterioration is not uncommon in traditional surgery⁽²⁶⁾.Hou et al.⁽¹⁴⁾ have reported that the complication of thoracic spine surgery for ossification of ligamentum flavum are as follows: CSF leakage (32%)(78.8% had ossified dura), neurological deterioration (21%), infection (5%), dehiscence (3%), deep venous thrombosis (1%) and death (1%). Takahata et al.⁽²⁷⁾ have revealed that decompression and posterior instrumented fusion surgery is a reliable surgical procedure with stable long-term clinical outcomes. They found 15(60%) patients experienced late neurological deterioration, and 10 patients had a relapse of myelopathy due to OLF in the region outside the primary operative lesion. The causes of early neurological impairment were postoperative epidural hematoma and direct intraoperative spinal cord injury⁽²⁸⁾.The causes of late neurological deterioration or paralysis may include ischemia-reperfusion injury, microthrombi and changed perfusion due to internal recoil of the spinal cord structure after decompression, which were four patients among the results of the Li's study.(20) Kanno et al.⁽²⁹⁾ have reported that two extremely rare cases successfully treated by revision surgery for a recurrent of ossification of ligamentum flavum at the same intervertebral level in the thoracic spine after the primary surgery. In our study, postoperative complications included dural tear in 13 cases (41.9%), defect in 10 cases (32.2%) and cerebrospinal fluid leakage in 10 cases (32.2%). All dural complications are due to the removal of the dural ossification along with the adhesion of the ossified ligamentum flavum. All patients with cerebrospinal fluid leakage were successfully pulled out the drainage tube 5 to 7 days after surgery, and wound healed 10 to 14 days without wound infection, etc. There was no recurrence of ossification or postoperative thoracic vertebra deformity in patients with aggravated neurological injury.

The advantages of our new technique are as follows: 1. Before longitudinal cutting of the lamina where ossification of the ligamentum flavum is located, partial excision of the upper and lower lamina, fenestration, and exposure of the dura mater were performed. Since the operation was performed in the normal space, the ossified mass was not dissociated, so the fenestration process would not cause shock to the ossified mass, which was very safe; 2. The spinal cord can be partly decompressed after the exposure of the upper and lower dural mater, which increases the space of retrodisplacement for the spinal cord at the compression site and makes subsequent operation safer; 3. The depth and boundary of the dural mater can be seen after laminectomy at the upper and lower margins, which can provide reference for the location and depth of the incision when making longitudinal osteotomy incision of the lamina with ossified ligamentum flavum. 4. When the lamina of the calcified ligamentum flavum is longitudinally incised, which can be gently lifted and shaken left and right to check whether the lamina is completely free, the ossification of the ligamentum flavum becomes a floating island. Although the ossification mass of the ligamentum flavum is adherent and fused with the dural mater, which is isolated from the subarachnoid space and the spinal cord, the dural mater is gently pulled upward without pulling the spinal cord. Only when the dural mater tension is too large, it will interfere with the spinal cord. The surgery under direct vision can’t cause severe compression or strain on the spinal cord; 5. There is only one incision in the traditional floating method. It is often found that there is still residual bone that has not been cut off or there is attachment of the joint capsule of the ligamentum flavum in operation, which requires further operations which can increase the surgery time and the risk of injury of spinal cord because the ossified mass of the ligamentum flavum has become loose. Compared with the traditional uncovering method, the new floating island technique can more accurately detach the lamina and completely free the lamina to form an island, which is more conducive to the traditional floating operation and reduce the uncovering time. 6. The dural mater is exposed directly above the ossified mass, allowing a better view of dural tension during uncovering. If the dural mater is not heavily adhesive to the ossified mass of the ligamentum flavum, it can be carefully separated from the ventral side with a nerve stripper during uncovering. On the contrary, if it is difficult to separate, the adherent dural mater on the surface of the ossified mass of the ligamentum flavum should be incised sharply in time to reduce the pull on the spinal cord and safely remove the ossified mass of the ligamentum flavum and the lamina.

However, the limitation of our new technique in this study is that a small number of patients for a relatively short period, resulting in a lack of judgment on the further clinical efficacy and safety of floating island laminectomy technology, limiting the generalization of the procedure and potentially undermining the validity of the long-term results of this technique. Therefore, further study with a larger sample size and longer follow-up period is entailed to approve our new technique.

This study emphasizes a safer and more effective technique, the floating island laminectomy technique, for the treatment of severe thoracic spinal stenosis and myelopathy caused by ossification of the ligamentum flavum, which can decrease the risk of spinal cord and nerve injury. Most patients with symptomatic TOLF have more satisfactory clinical improvements after surgery. Further generalization of our new technique could need the study with larger sample size and longer follow-up time.

mJOA: modified Japanese Orthopaedic Association

TOLF: thoracic ossification of the ligamentum flavum

OLF: ossification of the ligamentum flavum

SSEPs: somatosensory evoked potentials

MEPs: motor evoked potentials

CSF: cerebrospinal fluid

NI: neurological impairment

SSI: surgical site infection

Acknowledgements

None.

Funding

None.

Authors and Affiliation

Cheng Zhong, Peng Xiu, Hua Chen, Yueming Song, Jiancheng Zeng, Tao Li

Department of Orthopedic Surgery and Orthopedic Research Institute, West China Hospital, Sichuan University, No. 37 Guo Xue Xiang, Chengdu 610041, China

Contributions

Cheng Zhong and Peng Xiu were the major contributors in writing the manuscript. Hua Chen and Tao Li helped collected and analyzed the patient clinical data. Yueming Song, Jiancheng Zeng and Tao Li provided supervision and direction in the revision of the manuscript, including the figures and tables. All authors reviewed and approved the manuscript.

Ethics declarations

Ethics approval and consent to participate

This study was approved by the Ethics Committee of West China Hospital of Sichuan University. Informed consents were obtained from all patients in this study.

Consent for publication

Not applicable.

Competing interests

There are no competing interests.

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No competing interests reported.

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05 Jul, 2024
Submission checks completed at journal
05 Jul, 2024
First submitted to journal
30 Jun, 2024

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The clinical effect of floating island laminectomy technique for severe thoracic spinal stenosis and myelopathy caused by ossification of the ligamentum flavum: a retrospective study

Status:

Version 1

Abstract

Background

Methods

Results

Conclusion

Figures

Introduction

Materials and Methods

Study Design and Patient Population

Preoperative Planning

Surgical Technique

Assessment Indicators

Statistical Analysis

Results

Demographic Data Outcomes

Clinical Outcomes

Discussion

Conclusion

Abbreviations

Declarations

References

Additional Declarations

Status:

Version 1